Imperial HomePage -> Repair -> Wheels & Tires -> Bias Ply vs. Radial
The definitive consensus of the Imperial club:
For touring, get a set of Michelin radials. If you're going to show the car, get an extra set of rims and mount the correct bias-ply tires. Interchange them when you need to. But make the decision based on how and when you drive your car. The differences are there but choose the tire that best fit your driving habits.
Tips from Chris on how to measure tires if you are switching from Bias Ply to Radials:
The measurement of the sidewall height on tires is always done as a function (or percentage) of the section width, and it's called the "aspect ratio."
In the 1950s and early 1960s, the standard aspect ratio was 82-84%, meaning the distance from the top edge of the rim to the top of the tire tread was that percentage of the width of the tire (which is measured about mid-carcass, not at the tread). Tire sizes were usually given as simply the section width and rim size, like 9.15-15 (9.15 inches wide, 15-inch rim).
Around 1970, bias-ply tires moved to a 78% aspect ratio, this the term "H78-15. H was a load rating, 78 was the aspect ratio, 15 the rim size. All tires using the same load rating (for example, G70-15, G60-15, etc.) were the same diameter. Because the diameter was the same and the aspect ratio was lower, a 60-series tire was wider than a 78-series.
As radials became the norm, these designations stayed in use, but an R (for radial, of course) was added: HR78-15. In the 1970s, US tire manufacturers adopted the European system of metric sizing (though the rim diameter is still in inches). Example: 235/75R15. R still stands for Radial, 235mm is the section width, 75 the aspect ratio, 15 the rim diameter. What's different in this system is that the section width is an absolute number, so a 235/75 is just as wide as a 235/60. The 60-series tire is therefore smaller in diameter.
During this time period, the "standard" aspect ratio dropped to 75% (today, 65%, 60% and even down to 35% on some exotic sports cars, are all common).
So, if you wanted to put a set of radial tires on an old car and approximate the original sidewall height, you'd have to go with an enormously wide tire, which is undesirable for many reasons, including more difficult steering and some odd handling response (for these cars, which were not designed to have such a big contact patch between rubber and road).
As such, we compromise with a balance of width and height that comes closest overall... an old 9.15-15 might become a slightly wider but shorter HR78-15, which then becomes an even shorter 235/75R15.
Finding correct-size 14-inch tires today is harder still, because few tire manufacturers make little 14s strong enough and wide enough to manage the load of a 5,000-lb car. Choose carefully, note the load rating (remember, some 65% of your car's weight is on the front wheels) and the temperature grade (B is OK, A is better, C is not good enough), and maintain proper tire pressure (about 4 lbs below max is what I use). We've all seen what happens when under-inflated tires overheat in a heavy vehicle like, oh, I dunno... a Ford Explorer?
Tip from Ron:
If you use the bias type tires and like them, Great ! Just remember to move the car periodically to avoid the annoying flat spot pounding when you go down the road..............Bias belted tires will take a "set" if the weight is kept in one spot for any length of time.
Tip from Kne:
Do not mix and match radials and bias ply on a car. I did this back before I knew any better and I found that if I ran radials on the front, and glass on the back, and if the rear tires were bigger than the front, it would work o.k. What you get is some over-steer and the back end will break loose in a hard turn sort of like being on gravel. Controllable if the rear tires are big, and of course I would never do this again. Young, dumb and poor. Visa-versa, (with radials rear and glass up front) the rear will stay glued down while the FRONT END breaks loose!!! Wow! Do not try this at home! ?!?!?!??!?!?!!!!!!!!!!!!!!!!!!!!!!!!! @#$%#&(#&$(%^!!!! Once I had bias tires on the front of the Blues Mobile just to use a pair up rather than throw them away. Took it in and had a set of snows put on in the fall. The shop just automatically put on bias-snows, to match the fronts. I didn't notice. I did notice when I'd get up to 55+ that the car was handling very weird and felt dangerous. (after I had taken the bias tires off the front and put on radials) Then I looked at the tires and discovered the problem. Those snows were the same size as the front tires/radials, and now I am sure that I WAS very close to losing it when driving down the freeway at 65-75 mph. The car was probably coming close to breaking loose in the rear and spinning me on dry pavement! I'm very thankful that it is a big heavy, wide, low car.
Comments from Mike about Radial Tuned Suspensions:
The '67, '68 and '69 could use the new thing called radial tires because they had RADIAL TUNED SUSPENSIONS. If you use radial tires on a car that did not come with them you need to tune the suspension.
Follow-up from Gregg:
I must disagree on some points as far as when radials were used...
Around 1967 or 1968, We had started to switch to the alpha-numeric system of tire sizes (i.e. H78-15) as opposed to the older system, i.e. 8.5x15. Around that time fiberglass belted tires replaced standard bias plies. Maufacturers were aware of radials but didn't use them. My info indicates that Michelin started pushing radials in the 60's but they didn't catch on in the US till the early 1970's.
My 1970 Owners manual states NOT to use radials, but to use H-78 or H-70 15 fiberglass belted tires. Other Owners manuals around that time stated the same thing.
Fiberglass belted tires, Goodyear Polyglass, Atlas, etc. were standard on cars into the early 70's. On the most expensive cars, Like Caddy's, Linkuns and ...oh yes, our Imps, radials became optional. Then they were phased in completely by the mid 70's. Chrysler phased them in around the time they made disc brakes and electronic ignition standard. GM made radials standard at the same time they made electronis ignition, disc brakes and catalytic converters, slightly before the beginning of the 1975 Model year.
"Radial Tuned Suspension" was a term coined by Pontiac when they introduced the Grand Am for the fall of 1972. I have the motor trend article from December 72. It is said that John Delorean came up with the idea. Radial tuned suspension, which was especially pushed in the GM midsizes, comprised of matching front and rear stabilizer bars, stiffer shocks, 7" wheels, 70-series radials and different alignment specs. Motor Trend matched a new Mercedes with the four GM midsize cars, each four door sedans with floor shifters.
In the early Seventies, owners manuals started saying that even though the car rolled off the line with non-radials, you could out them on if you wanted, so maybe they had already started changing the alignment specs.
And from Dick:
There is a lot of misinformation about putting radials on older cars. As a reformed former tire recap plant worker (inspection and preparation machine operator for tread application, in my teens) and the son of a tire designer (B.F.Goodrich), I have always been interested in tires and their design characteristics. While this doesn't make me an expert, I think it may give me more skepticism about some of the strange stories we all hear.
My experience and opinion, for what it is worth, is that radials work just fine on our cars, with the sole proviso that the toe-in be adjusted to zero, rather than the factory spec for the car if it was originally designed for non-radials. Failing to do this will result in the car wandering and a tendency to nibble at the seams in a cement roadway.
There is a different riding characteristic, and a much changed feel at the steering wheel.
First, the cars without power steering will be VERY hard to park with radials, as they grip the pavement with a much larger contact patch and really hold on!
Second, the low speed ride will be harsher, as you will feel every tiny road imperfection you drive over. This is why the manufacturers put different valving in the shocks, to try to filter out some of this road feel. That was the origin of the term "radial tuned shocks".
The high speed ride will be much better, however, as the tires seem to float over rapid disturbances without transmitting these to the unsprung components.
The handling and steering response will be much improved, as will the traction on slippery road surfaces. The tread-wear is much better also, if that is of any interest.
My new 1958 Peugeot came standard with Michelin radials, as did my very un-new 1968 Mark III (to save an argument, yes it is titled as a 69, but it was built in April 1968).
I have used radials on everything from my 1948 Studebaker with it's "planar" suspension (a sideways spring) to my torsion level Packards, and if it weren't for the odd appearance, I'd probably have them on everything I own.
I believe there is only one brand to buy, and that is Michelin. You get what you pay for. I sure wish they made a wide whitewall!
I would like to add a few comments on the other side of the coin. Radials are great on almost any old car that originally came with non-radial tires. There are many benefits to making this switch - easy availability, handling improvements, longer life, etc.
Nonetheless, that isn't the end of the story. Using my 1960 Chrysler as an example, I can say that installing the correct repro bias ply tire on your old car can yield very favorable results. The benefits of doing so are significant enough for me that I wouldn't even consider putting radials on this car, even if I could. These benefits include:
--Absolutely correct appearance and ride height. These tires are wide-white 9:00x14's, meaning there is 9" of tire between the wheel and the road. No 14" radial is made that comes anywhere near those dimensions. Thus my car sits up off the ground the way it should and the tires fully fill the wheel wells.
--It has been my observation the early Chrysler suspensions were designed around the particular ride qualities of bias ply tires. These soft tires worked with the suspension by absorbing all small road impacts before they got to the suspension. The suspension could therefore be relatively firm, providing the famous Chrysler handling prowess. Installing radial tires may further enhance this handling prowess, but the cost is often significantly diminished ride quality. Radials are hard, lower profile tires that demand more from the suspension in the way of shock absorption. So if you use radials, be sure to specify a soft-compound "touring" tire. I can tell you that my Chrysler on bias plies rides noticeably smoother and softer than either of my Imperials on radials. In fact, a Cadillac collector drove it recently and was shocked to report that none of his Cadillacs rode as well.
-- It is true that radials are much harder to steer. Thus more stress and strain is surely put on our cars' steering mechanisms. Could the wide-spread use of radial tires on '60's Imperials be one of the reasons that worn and leaking steering boxes have become a chronic problem with these cars? You decide. Radials also are great at masking worn steering linkages and suspension components. Therefore. putting them on a car with a worn front end will result in much improved handling feel. My car had a total front end rebuild and I can report that bias tires on a Chrysler with a tight front end steer as straight and true as any of my Imperials on radials. The steering response is noticeably lighter and more responsive, too, a quality I also noticed on my LeBaron for the brief time it was on bias plies. (BTW, 60-66 Imperials and 60-62 New Yorkers share all the same parts numbers for steering and suspension components, so this is all a very direct comparison.)
So, although there are many reasons to use radial tires, one should not feel that significant sacrifices must be made in order to use NOS-style bias ply tires -especially on Imperials with 14" wheels. On these cars in particular, I would say the benefits of using correct original wide white bias plies far outweigh those of incorrect radials.
Follow-up from Dick:
One minor correction: The "9" in the 900X14 designation is for the cross sectional width of the tire, not the distance from the wheel to the road. Tires are built in a particular geometry, which depends on the era and the technology of the manufacturer. Our cars of the 60s were generally shipped with "85" series tires. That number represents the ratio of the section height (read "rim flange to tread distance") to the section width (read "sidewall to sidewall distance"). Thus a 900X14 tire would measure 9 inches from side to side at the fattest part of the tire when properly inflated, and 85% of that from the mounting flange to the tread surface (when the tire is unloaded), or about 7.7". That is still pretty high, when compared to a modern radial.
The radials now in common use range from "45" series (for zippy sports car type tires) up to "75" series, with most of our cars with radials now riding on "65" or "70" series tires. This number is often included in the modern tire size information on the sidewall; thus: 225-70R15 for example.
The 225, by the way represents a conversion in the industry to metric dimensions, and represents millimeters. Roughly, 225 is about 9.4". So a modern radial on a 14 inch wheel rim (size 225-70R14) would measure close to the same as original in section width (9 3/8"), but only 6.6" in height, before placing the load on the tire. With load, the mounting flange of the rim would be about 5.6" from the road, and from the part you can see on the exterior of the wheel, about 4 1/2 inches. This is, as Chris pointed out, a 2 1/2" drop in the car's height, and looks funny, no doubt about it, on an old car.
Older cars, by the way, had even higher section heights. My 40's cars for example, have "88" series tires. These are the ones that look really thin and spindly from the rear (and don't grip the road worth a damn!)
Follow-up from Chris:
Thanks, Dick, for the clarification. Not the first time I've had it backwards! To my eye, 9:00 and similar designations always appeared to correspond with the height of the sidewall. But you know what happens when you assume something....
Follow-up from Norm:
I would like to point out one thing: the ride quality that the cars were originally endowed with was dependent upon several things, among them were properly tensioned, properly resilient body mount cushions-at least in full frame cars. As these cars age, you will notice that some of the original resilient quality in these devices is squeezed out of them over time. This results in a number of possibilities: harsher ride, body misalignment, harmonic chassis vibration at speed in convertible cars, lack of suppleness in ride quality. So, when we talk about experiencing the original quality of ride that the cars were capable of when new, I believe we can get close, but not exactly on point. I do agree that a properly assembled front end with all good components should provide an acceptable result. I would also point out, as one who drove these cars when new, that they were more susceptible to reacting to road grooves and depressions by uncommanded steering moments than the same cars are today when equipped with radials. You do point out that the radials can mask the existence of some poor front end components, but I think that as long as tire technology has improved as greatly as it has, why not have the best of both worlds: a properly assembled front end and great handling radial tires.
Follow-up from Chris:
I agree with your 2 cents. In fact, my low mileage '66 LeBaron has a totally rebuilt front end, modern radials, and KYB shocks. I suspect is tracks, steers, and handles far better than when new. But it is not as smooth and resilient over small road imperfections as the '60 New Yorker with cushier bias ply tires. It's all a trade-off I guess!
I have a '54 New Yorker that came with 8.20X15 originally. I replaced them with P235 75 15XL 721's from firestone. They have a slightly under two inch whitewall, and an extra load sidewall. I like to drive my car a lot, and these tries look great and ride great too. I was concerned of mushiness when I first got them, but the dealer assured me that I would like them, he was right. I would definitely recommend a heavy duty sidewall. Our Imperials are heavy haulers. I have the same tires on my '63 LeBaron. Again, I really like the look and ride. Dad has the same tires on his '65 Crown Coupe and our '68 Crown Coupe. We really like the ride and appearance. The tire is a good tire and it is reasonably priced. I think the last set I bought was about $80 per copy, mounted and balanced. If you are a stickler for originality, then go with the bias ply tires. I will sail past you on the freeway with a smile on my face, while you are frowning and battling the ruts.
This is one each owner will just have to decide for himself. I know what some other folks will say: radials. And probably that is the best choice, overall. But there is nothing wrong with putting bias belted tires on your car, if that's what you want. It just comes down to what you value most: the correct look or the ride. And no one can make that choice for you. But neither choice will be "wrong," as long as you get the right size, etc., and no one should criticize you for your choice. It's YOUR CAR, so do what pleases you!
Well, I finally got the new bias tires on my 57 Imperial...all I can say is, WHAT A DIFFERENCE!!! The car no longer shimmies all over the place, even when you hit cracks and flaws in the road at 60 mph... So much for the "radials are the ONLY choice" rationale. I'm sold on keeping bias tires on originally biased cars.
The main reason many cars were not suitable for radials had more to do with the shape of the rim cross-section profile. Many cars other than Chrysler products did not have a large enough inner lip on the rim. This made it easier for tires to come off in hard cornering. Chrysler had an advantage because they had 'Safety Rim Wheels' starting way back in the late 30's or early 40's. With Chrysler products it took a very large force to get a tire to separate from the inner rim ridge compared to other cars.
On some rims there had been problems with separation of the wheel rim around the center due to metal fatigue using radial tires on rims not designed for them. This was seen mostly on trucks and trailers carrying heavy loads. Even some fairly recent (last 10-12 years) RV trailers came with bias ply trailer special tires. Putting radials on those rims is dangerous and not recommended. Many people put far in excess of the recommended gross weight on their trailer tires.
Of course the usual precautions about observing correct tire pressure at cold condition always apply with any type tire to get the best performance and life as well as safety out of it.
I live in the Dallas area and contrary to popular opinion, we do not all have oil wells, nor do we own ranches and ride horses. It is just like any other metropolitan area in the country. We get so tickled listening to foreign visitors exclaiming about how modern it is and 'Where are the cows and horses?' You can find them if you drive around mostly outside the metroplex (Dallas - Fort Worth Area), but, you do not usually see cowboys out herding the cattle. Just once in a while at the right times of the year you might see some of this.
When radial tires first became available to the mass-market in the late-sixties and early seventies, large car owners were advised not to run radials on their cars. It seems early radials were not up to the weights and forces exerted by cars the size of Imperials.
I think one of the few tire manufacturers to make radials at the time for full-size cars was Pirelli. My mother bought a set for her 1970 Plymouth Sport Fury GT. She remembers that when the radials were installed, the car steered so smoothly it had the sensation of driving on ice. However, her enthusiasm for this first set of radials waned when, cruising at speed just outside of Atlanta on a hot summer day, all four radials suddenly threw their treads.
It was while arguing with Pirelli (I hope I am spelling that correctly) about these tires, that the unhappy early relationship between big cars and radials was discovered. I don't know how or if the issue was ever resolved.
Now, however, I run all-season radials on all my large Chrysler Products, and have had the best experience with Michelin tires.
My worst set of tires was from Sears. While driving home from the Cars & Parts meeting in Springfield, the sidewall of the right front tire failed. Were the car any thing less than an Imperial, I'm sure there would have been an accident. As it was, I wasn't sure anything was wrong until I detected a slight starboard list and a far away sound. Stopping and opening the door, I could hear the scream of escaping air while the tire deflated into a useless mound.
The only thing I don't like about the radials is that I cannot get the original style white-walls Imperial used.
I have owned and driven many cars with both radials and bias ply tires. Radials are definitely superior. But don't forget bias are good tires. I have driven many hours in a '65 Fairlane 289 at 100+ mph with bias/fabric belted tires and always felt safe. (It was a company car, so I didn't care if it blew up.) I had a '69 Town and Country that has seen both coasts and many other road trips. My wife drove it alone, with nine month old twins, from Orlando, FL to Monterey, CA. The tires were "Econo-Brand" L-78 X 15 bias ply rayon. They never gave a problem in 40k miles. The car was one of the best handling large cars I have ever driven. I am sure radials would have been superior but the cheap bias were great.
A lot of the concern for harshness went around when belted tire were introduced. Then again with radials. Tires have continuously improved. I have driven many miles on cotton cord, unbelted tires; synthetic cord, unbelted; bias ply synthetic and steel belted; and most kinds of radials. They just keep getting better. But all were good in their day.
Unless you drive like Juan Fangio, don't be afraid of bias ply tires. Belted are better than unbelted. Use whatever appeals to you, especially if you don't drive the car a lot. If you are "over-driving" bias ply tires you are a menace on the road anyway.
As a kid in the early '70s, I remember hearing this discussion when my grandmother went in to get new tires on her '71 Imperial. The Chrysler dealership guy who sold her the car was pretty convinced that radials would more or less destroy the front end, would be impossible to align correctly, and would just generally be a disaster.
However, my '71 Imperial has about 216,000 miles on it right now, and it had radials on it when I bought the car with 131,000 miles. I've had the front end rebuilt, but only due to twenty some odd years of carrying around a huge cast iron block and all the accessories -- in other words, the normal wear and tear. The car has perfect alignment, and what I consider to be excellent handling.
It is true that radial tires on a car designed for bias-plys puts more wear on it.. I've never noticed anything serious except mildly accelerated wear of suspension components. If it is true they damage the wheels you may want to find something more recent that will fit the car.. but if you're only going to be driving it on sunny Sundays and to shows then I (personally) would try finding original style bias plys.. radials are much better for turning, stopping, and in wet weather, so let these factors influence your decision.
I have driven my 64 Imperial convert from its original 41,000 miles to its current 60,000 miles over the past 10 years on radial tires with no ill effects whatsoever. No rim breaks, no parts breaks. Not even any flats. Just good handling and a glass smooth ride. As for originality, it has been my observation that most people , even so-called knowledgeable ones, do not have any correct idea what whitewall sizes should be to accurately depict the car as it truly was. So, do what you believe will make you happy.
Radials sit lower than bias ply tires (radials roll more so than bias ply which stand taller) and you probably cannot find larger than 215/14's which will not fill the wheel well properly and will also change the circumference of the tire, in turn affecting speedo readings. I have always used bias ply tires on my older luxury cars with 14" rims and wide whites. I just prefer the way they look - they look correct!!! I have never found them to handle poorly. Although I do believe radials are better, I do not believe the difference is that significant as long as the front end is in good condition and you do not plan on racing in Monte Carlo. I do not care for the "on the ground" look of a big Imperial or Lincoln with 215/14 radial tires. I drive my cars regularly and have logged thousands of miles on several late 50s, early 60s Imperials and Lincolns with correct 14" rims and bias ply tires -- absolutely no problems or major ride or handling sacrifices. I firmly believe that much of the bad press given bias ply tires is do to the fact that many people buy a car restored 10 or so years ago and the tires are hard as rocks. At this point a change to anything would be a great improvement, so the credit is given to the new radials they put on. After thousands of miles on new bias ply tires, I believe much of the bad press is hype, and I will continue to use them on any early 60s and earlier cars I drive.
All the advice on DRIVING radials and maybe showing correct bias is good. I wouldn't drive around the block on a set of new bias if I had access to a decent set of used Michelins. Of course, a set of new ones is the best solution and believe me, you'll not be sorry. I first got my father convinced on radials for his 66NY back in about 72..He had to go over the Cascade Mts the next am early, and as it happened there was a fresh dump of snow...he was amazed at the traction as well as quietness...less road noise transmitted thru unibody and unbelievable cornering over what he already thought was great. I agree with whoever it was that said about Michelins 'is there any other tire?' My 67 Crown Coupe doesn't have 'em yet, but she runs decent radials now as is. I just snuck her out a couple weeks ago to blow out the cobwebs (expired tabs & no brake lights...tisk-tisk on me!).
Good radials will be a big improvement in high speed ride, safety and handling. By good, I mean Michelins -accept no substitute! Unfortunately, there ARE NO really "good" wide white tires, including the new radial wide whites sold by Coker and others. All the wide white tires I am aware of are basically very cheaply built tires that are made for show only.
But they are not radials, and they are not "good" tires, just barely acceptable for a show car.
The old wives tale that older cars do not handle properly with radial tires was never true, it was based on the prohibition about mixing radial with bias ply on the same car (which IS important). I have used radials exclusively on my daily drivers since the early 70's, on cars as old as my 48 Land Cruiser (Studebaker, not TOYOTA!). They handle and ride just fine at normal road speed, with a tad more roughness coming through from rough pavement at speeds below about 40 MPH, when compared to Bias ply tires.
I have generally run bias ply www tires on anything I own that had them when new. I tend to be a purist and want my cars to look correct. I have always dealt with Coker and have never had a problem with them. I have always found them to be very helpful and they have all info on what tires are correct for each car. I've heard all the stories about how poorly bias ply tires perform and am not totally convinced that radials are so much better. Granted radials do perform better, but I do not believe it is as significant as long as the bias ply tires are new. Quite often, when hearing bias ply horror stories, it turns out that the tires were put on the car when it was restored 10 years ago and have hardly been used so they are very hard and nearly square from sitting up so long.
Design evolution probably led to softer, better riding radials for luxury cars. A few years back I put a set of Pirelli radials on a 72 Imperial coupe and found them to ride no better than the very old tires they replaced. The Pirelli tires are a higher performance tire, but I found the ride suffered tremendously. I want my Imperial to ride well, so now I stick to Michelins.
Recently I got to drive a '69 Imperial with bias-belted tires, and I have to say, I expected to notice a big difference but I didn't.
The owner of the car kept warning me that the tires didn't feel good, that they were okay when they "warmed up," but you could feel every bump in the road and a car with bias-belt tires will jerk you around with every little change in the road surface, etc.
Then I drove the car and I thought: what is the problem? I could detect none of the problems he had warned me about, and I drove at many different speeds on many different road surfaces.
And I am one of those "Princess & the Pea" types - in case no one has ever heard that story, it's about a lady who sleeps on a stack of mattresses and complains that she can't sleep because there is a single pea at the bottom of the stack.
In other words, I am VERY picky and notice tiny defects in just about anything. But the bias-belted tires were fine with me. You could tell they weren't radials; it seemed they were a bit noisier (?) and had a slight tendency to be more effected by changes in the road surface - but nothing objectionable or impossible to handle.
I suppose one experience at moderate speeds in a car I'm unfamiliar with is not a reliable indicator (I guess the only way to know would be to drive the SAME car with two different sets of tires). But my point is: bias-belted are not as horrible as some would have you believe.
And they do "look" right, which is important to me (but then, you can find radials that have a similar profile, too).
I had radial tires on the 60, I swapped them because the ride was too-soft and if you hit a pot hole the car would rock on its side-walls. Also I curbed and split a radial on the front a couple of years ago.
I know for a fact that today's radial tires give a stiffer ride versus bias ply tires. I once put a set of 9:15 x 15 triple white stripe bias plies on my '66 LeBaron and the ride changed dramatically. A series of speed bumps at a stop sign in my neighborhood will cause your teeth to rattle in this car (and others) with radials. When I went over them with the original-style bias ply tires, you were only barely aware you had hit a rough patch of road. A really dramatic difference. The steering was also lighter and "faster" with bias plies. On the minus side, bias plys do not handle or steer with the precision and tenacity of radials. Or last as long. This comparison made me believe that the suspension hardware our early Imperials was designed to primarily hold up the car and handle the big impacts. The small, jiggly stuff was intended to be smothered by fat, soft, pillowy tires. Put radials on a car that was designed with this philosophy and you get a rather "nervous" and often harsh ride quality. I ultimately struck a happy medium. I installed a set of soft "touring" style radials with a set of KYB shocks. This combination seemed to offer the best of both worlds, good control of low impact harshness while offering all the handling and longevity benefits of radials.
Radials are extremely different in appearance than bias belted tires, though I guess that word "extremely" is a relative term. Some people may not see much difference, but to me they're quite different.
If you were to cut a radial in half and look at it in cross-section, they tend to be more rounded in shape - sort of a big, wide, fat oval shape. They look like skinny donuts, basically (!). Bias ply tires tend to have more of a shoulder on them and a flatter tread. They kind of look like a guy with a crew cut - flat on top, rounded on sides. Plus, they tend to be taller, or more circular in shape, as opposed to a squashed oval shape (I believe this is called the aspect ratio of the tire - radials have a shorter, lower sidewall than bias belted.)
Then there is the matter of logos and typefaces used on the side of the tire. Newer tires tend to have bigger, bolder lettering that is bunched together in groups around the tire. Older tires tended to have smaller lettering with wide spacing and used different typefaces. They also used decorative motifs on tires, like little diamond shapes or chevrons or lines spaced out sort of like the lines around the edges of a clock's face.
This is REALLY getting nitpicky here. If you look, you can find radials that have an old-fashioned, "retro" sort of look. Some folks buy a set of bias plys for shows and use radials for their daily driving. I guess it depends on how picky you want to get. If your concern is accuracy, or "correctness," get bias belted. If your concern is handling, safety, etc., get radials that have a similar shape.
Radial tires can be used on older cars without many problems, but they do cause rim fatigue at an earlier stage. Manufacturers changed to heavier gauge material and sometimes different wheel construction to better suit radial tires. People really like radials on older cars because they mask suspension problems and bad pavement jobs a lot better than cross-ply tires.
Bearing in mind most cars never fatigue a rim anyhow its not a real biggy, but lets say its enough extra strain to cause small problems to grow at an accelerated rate. Maybe like taxi service or trailer hauling. Radials transmit more force into the rims than bias ply tires do, which primarily absorb impacts in the tire carcass.
Typical issues are cracks at the flanges, lug pockets (cones on lug-nuts end up seating on the drum, not the wheel ) and broken welds/loose rivets. Most of these problems will be evident from highway speed vibration from your wobbly wheels. Any post 1975 car shouldn't have any issues with radials, but the older cars would bear a close inspection from time to time if you're doing work nearby. Really, by now all those old steel wheels could stand careful inspection and or replacement! If nothing else many are rusted by now.
Regarding tires, if you plan to use a 235-75R-15 keep in mind these are almost always available in an 'extra load' design, as its a common half ton truck size. Usually the extra $5 a tire for the heavier rating is worthwhile. Carmine made an excellent suggestion re buying cheap generic new wagon wheel type steel wheels of slightly greater width and hiding them under your hubcap. New steel wheels are really inexpensive, and they should correct your bead leaks too!
On my own cars I run whatever they came with from the factory or as close a facsimile as possible, I like that Old Car ride. I have little experience with the reproduction tire guys like Coker, but the repro tires LOOK real good. If the quality is good, that would be great! Avon sells thier old nylon blackwall tires with a speed rating in an Imperialesque size if you need 140 MPH capability also. As I seldom travel over 125, I will have to stick with two ply Rayon, hehehee
Follow-up from Bob:
Yep, early in my ownership of my '66, I cracked 2 rims on different long trips. I figured it's a heavy car and the metal is pretty old. Getting steel wheel replacements is not so easy, as we've discussed here many times before.
Comments from Henry:
The overall diameter of bias ply is more than that of a radial. Just noticed that on my '61. Had bias ply-correct size with HUGE WIDE WHITES that looked new but actually had been on the car for many, many years. So put on Coker WW radials--not as wide as the bias ply, but probably wider than correct. Anyway, immediately noticed the car seemed to sit lower. At first I thought it was a visual thing as there was a wider band of black between the car and the whites. When we measured, sure enough, the radials had a smaller diameter than the bias ply by about an inch. I am not quite as much of a stickler on exactness so I will go with the radials I have. I will say that the improved ride and driving are worth it over putting correct bias ply tires on, having had bias ply on my 62 convert and radials on my '60, or maybe it was the other way around--the mind reels.
Won't the change in diameter affect the speedo and the odometer? Also, what is the correct way to measure wheel size? From rim to rim diameter does not seem to be correct? The 58 hubcaps I bought wont fit the wheels I have now, but 67/68 hubcaps will. Must I go to a tire shop just to find out what rim size I have?
Follow-up from Dick:
I believe the 58's came with 14 inch wheels, so if '67-'68 (15 inch) wheel covers fit, you have the wrong wheels. The easy way to find out what size wheels you have is to look at the last two digits of your tire size label - that is the wheel diameter in inches.
If you want to measure the wheel diameter, measure from the bead seating surface across the diameter to the opposite side. Of course you need to remove the tire to do this, or measure the inside dimension (where the wheel cover grips the wheel) and add 1/4 inch, you'll be close enough to tell the difference between 14 and 15 inch wheels. Wheels come only in even inch sizes on passenger cars in the USA.
Question from Gary (1956):
I'm researching new tires for the '56 C-73 (Babe) that I recently purchased. It has been pointed out by others that the Coker catalog recommends 2 1/2" to 2 11/16" whitewall widths for '54 through '56, and 2 1/4" to 2 1/2" for '57 through '61(2004 catalog).
Last Friday I spoke to Irvin @ Coker and was told that P235/75R15 tires were listed incorrectly as 2 7/8", but were actually 3". More importantly, the 75 and 80 series radials listed under "B F Goodrich Silvertown Radial Wide Whitewalls", in fact carried the Coker logo. The 70 series listed there are the only tires with the BFG logo.He said that the 75 and 80 series tires would be available with the BFG logo in approx. 12/14 weeks. The tires are manufactured in Mexico by Denman.
In a later conversation with one of their dealers from whom I've purchased Coker bias ply tires (Firestone), I learned that they choose not to carry the 75 series tires in inventory because of the yellowing problems they've with them.
So I've decided to wait on the new BFG logo 75 series. Now comes the opinion that one should not buy radials for these older cars. My experience has been the other way around. I removed the Firestones from my '40 Buick Roadmaster and mounted an inexpensive set of radials to see how the car rode and handled. I was amazed at the improvement in ride, reduced squeal in turns, and it tracked beautifully.
Reply from Paul:
You are going to get every opinion on this topic from the IML group that is to be had by anyone. Many advocate that the cars were designed for old style tires, so that is what they should have. Some have claimed that putting radial tires on Imperial wheels from the '60s and earlier causes the rims to crack, or ruined their cars.
I always think safety first, so if one believes that using modern tires on an older car is going to be dangerous, than they should go with what they believe.
I have had excellent luck with radials on '60, '62, '63, '65, and '68 Imperials. I drove my '65 Imperial with several different sets of both new and used radials over the years totaling over 100,000 miles. The current set of radials have been on it for 15 years and seem to be fine. I have never broken a wheel or suffered any road shock, vibration, or handling problems from them. In fact, to the contrary, from the first time that I experienced radial tires on an torsion bar suspension Imperial I have believed that they enhance the superlative handling and cornering characteristics of those cars. My '65 Imperial has had Perrelli, Uniroyal (2 used sets), and finally the current Goodyear Arrivas which are now quite old and out of production.
Not everyone agrees with this so you will have to make your decision once everybody has posted.
On my '48 L.C., and my '55 and '56 Imperials I have had, and plan to keep the old style tires. Those cars seem to handle fine with those old tires. I will never say never, and since I have seen some very attractive new radial white walls, I may try them someday on the older cars.
I have believed that "cheap" radials are not a great idea since they can come apart, like any other cheap tire, but that the steel belts can add to the sometimes disastrous outcome. I heard of a man who lost a '49 Cadillac to a roadside explosion after a disintegrating rear radial tire ruptured his gas tank, which was further exacerbated by sparks from the shredded metal coming in contact with fuel and vapors.
Cheap tires are never a good bargain. All tires need to be properly maintained.
Question from Neal (1959):
I recently acquired a 45,000 original mile '59 Crown. As we're going through the mechanicals, it's been determined that the car needs new tires. It has 15" rims. I was hoping to find wide whitewall radials to match the size of the worn bias ply tires, L78-15, which I believe translates to 255/70R15 or 235/75R15.
I priced them through Coker Tire; the mechanic contacted his tire sources, who said that the 1959 rims weren't designed for radials (true-they weren't commonly available for another 10 years) and that putting radials on the car would damage these rims. It would also harm the dynamics of the alignment, suspension, front end, etc. Is this true? A friend here in Virginia has radials on his '64 Crown Coupe and said they did nothing more than make the ride somewhat harsher.
Is any of what these tire people say true? I'd consider putting on newer rims, say from the early '70s, but I don't want to do it if it interferes with the integrity of the ride and handling. I'll put up with new bias plys if that's the case.
When I acquired my '64 Crown Coupe it had bias tires, and on a narrow street, especially if the right edges were uneven, it was a constant struggle to keep the car from veering off. And the tires were just like new. After replacing with radials, yes, the ride is a bit firmer, but what a difference in steering control. Believe me, like night and day. I would recommend the change.
It seems like this always comes up every couple of months or so . . . that was the knock against radials when they first came out - that they were harsher in ride - but no one seems to believe that anymore, or they have just gotten used to the ride that radials provide and no longer notice it. Perhaps the trade-off in terms of stability and increased cornering ability makes people overlook the difference in ride . . . or perhaps the idea that radials rode harsher was a myth. (But in the manual for one of my Imperials it warns of a harsher ride if radials are used, so evidently a lot of folks believed this.)
The consensus on the IML seems to be that radials are better for several reasons - at least on cars from the late 60's onward.
I do not believe radials will "harm" your suspension. I think older suspensions were designed with the tires that were available at that time in mind - when radials came along with their different characteristics, suspensions had to be changed somewhat to accommodate the new type of tire. And in fact they used to advertise that ("Radial Tuned Suspension"). But I don't think there is any harm to putting a radial on your Imperial. They will probably provide a lot more safety and would be the better choice in the long run, probably.
What does the car have on there now? I would be curious to hear what your driving impressions are, if you go from bias belted to radials. I think that would be the only way to know for sure if radials were harsher - drive the same car with 2 different types of tires on it and see.
I recently put radials on my 63 Imperial with out and bad results. It rides and drives much better. My 68 Plymouth has had radials for years with no ill effects for it either. I think they improve ride and handling.
There must have been a few old wives working at Chrysler in the late 60s/early 70s, 'cause this is the tale they tell in my 1971 Owner's Manual:
"RADIAL PLY TIRES
Your vehicle is designed for cross bias and bias-belted tires of the sizes indicated. The use of radial ply tires is not recommended because of their very harsh ride at low speeds and possible unfamiliar stability characteristics. Should these tires be desired, the maximum allowable size should be selected. Radial ply tires should always be used in sets of five and under no circumstances should they be used on the front only."
Again, I'm not advocating this position. I'm just saying this was once a widely held perception, and may have contained some small kernel of truth in it. However, I think what has happened is that the design of radials has progressed a bit since 1971, and the "very harsh ride at low speeds" statement probably no longer holds true with a modern tire.
Question from Rob (1964):
I have been running Goodyear radials on my '64 Crown Coupe for several years now. I just had the front-end rebuilt. With a solid and quiet front-end, I am finding that the radials seem to be giving a harsh ride when inflated to the tire shops recommended inflation level. I contacted Goodyear and they will not give me advice on how low the tire pressure could be set without causing tread separation. I know the FSM calls for 24 lbs of pressure for bias-ply tires, and 24 lbs in a radial does not look right on my car. Does anyone know whether the majority of IMLers are running on radials or bias-ply tires? Does anyone have any thoughts on tire pressure for radials on a 64?
I run the Goodyears on my '64 at 30-32. Love 'em.
I have radials on my Imperials & inflate to 29-30 PSI. I did have a '64 some years ago & did the same on that. My current '60 has had the same tires for nearly 11 years & still fine, the '69 for 6 years & fine also.
Question from Rich (1966):
I was wondering what the club thought of using radial tires on older Imperials like my '66 Crown?
I purchased the Firestone "721" with the 1.5" whitewall. I'm very happy with the ride, handling, and the quietness from road noise. A friend of my who
has a '55 Imperial coupe that's a AAA Senior has told me repeatedly that I shouldn't have radials on my '66, because the car didn't come with them. I explain many, many times about the advantages but I guess since he's a purist he doesn't think they belong on the car. He actually told me that if he were judging my car at a show he would knock 20 points off because of the tires.
I also have radials on my '59 Ford Wagon wide whites. Before, I had the bias belted on the car, and the car would drift when hitting a road tar
strip, and you had to correct the steering wheel all the time. What a difference the radials made. I think the older cars look better with the bias belted tires, but that's the only advantage I see.
You basically have brought up all the pros and cons of having radials on your '66 Imperial. I personally also prefer them since the handling is so much better.
I don't think we have to worry about this on our cars, but there is another concern I have heard of that you didn't mention. The way that radial tires are designed, they stress the wheel rim in different ways than the bias ply tires. This can crack wheel rims if they are weak. I have not seen this with an Imperial rim, but that is not to say it has never happened.
Although I no longer have any Firestone 721's, I also liked the white wall on them. It is a nice looking modern tire, and there are other radial tires with that white wall style. I seek them out whenever I am buying a set.
Late '50s and early'60s had the white wall all the way to the rim, and these tires do not, but they look great anyway. On my '55 and '56 I have reproduction Allstate Guardsman bias ply tires and they look perfect for those cars, but the handling does seem to suffer under the circumstances that you describe, namely changes in pavement texture, and also grooves in the road.
It gets down to personal preference, and you are correct, judges in shows will subtract points for having the wrong tires. The kind of show I go to, there are no judges, and my cars are very beautiful "drivers". That said I want them to feel good when I am driving them.
Here's an alternate thought to considering a replacement WWW radial tire from a supplier such as Coker (expensive and not too high on quality, I've heard). Mostly for sidewall design and partly for tread design, I chose a premium set of Sears Roadhandler LX Voyager 235/70/R15's, with an original WW width of about 3/4", and took them to a professional specialty tire shop where a tire lathe neatly ground away enough surrounding black above and below the original WW to reveal a nice 1 3/8" result. Close enough to the ideal 1 1/2" that was stock on my '60 Imperial Crown. You have to be careful not to go too far into the black for fear of running out of underlying white. Take it a little at a time before going too far, and risk losing symmetry. Each manufacturer has a different quantity of white hidden away in the sidewall. Most premium, top of the line WW tires are well blessed. Have been told that a RWL (raised white letter) radial possesses the most underlying available white for lathing...up to 3"!!!! The process does not negatively affect the integrity of the sidewall. I personally do not care about losing judged points since I'm not much into "showbusiness". The end result is stunning as opposed to just barely there.
I had the same process done on a premium set of Sears Weatherhandler 235/70/R15's, again chosen for sidewall design more than tread design, for mounting on my '65 NY. This effort on this tire did accomplish the 1 1/2" WW. The only downside I am aware of, is the need to clean the WW with Blechewhite more often than normal. Apparently lathing the WW surface makes it more susceptible to oxidation and "browning". I know some of you will scoff at this idea, but sometimes "right" is better than "correct".
To each their own, but don't feel assured that radial tires will give better handling. I once put them on my 1964 Crown Coupe and could hardly hold it in the road. It wallowed so badly that I quickly replaced them with the original style bias tires. Perhaps my car with 160,000 miles was too worn out for radials but the handling was way too sloppy for me with the radials.
I think that for some it's easy to forget that we do this because we love it. It's a hobby that falls under the heading of "The pursuit of happiness"
for each of us. If one guy is a purest that's fine - for him. But I would suggest you do what works best for you. It's kind of like religion. We all do fine until someone starts thinking they have the right to push their views on others. Just a thought...be true to yourself.
There are a large group here that favor Radials, which is just fine.
Every time that this comes up, I try to offer my reasoning for going with Bias Ply on my 1960.
The car is a recreational "toy" and I will not be speeding, pulling off hard cornering, or the other antics that I do in my current car. I will normally try to stay as far away from other motorists as I can so as to avoid getting into a pickle. Not that it won't happen, but I'll be activly working to lower the odds of going into the car crushing business for a fellow road user.
That said, I want an old car that is "vintage". The taller profile tires and different appearance makes the car look and sit as intended. I had a 63 with radials, and it was lower, and the tires did not fill the wheel wells to my satisfaction.
Your car was tuned to use these tires as part of the shock absorbtion system. When I hit bumps on Radials, the car seemed to shiver and resonate in a way that was not plush at all. Your torsion bars are expecting to have only so much work to do, leaving the rest to either your tires or your seat springs and behind....
Radials can be tough on rims, throwing hubcaps more easily or developing leaks from stress cracks.
If you have not seen a car with bias ply tires, I encourage you to do so before making your decision. If you can go to a car show with chryslers, and you meet someone that has such, I bet that you'll get similar reasoning, and may even be able to score a ride based on that icebreaker? There have been many emails written over the years on this subject, and the tradeoffs listed in detail.
I went out of my way to take nice photos of what I put on my car on the 1960 epic (see the 1960 page). Those are BF Goodrich Silvertown Tires, and I think that the tread and shape are really cool looking....Whitewalls come in 2-3 widths.
I would suggest against the extended service warranties if you go mail-order. They only work if you can go to a local place. Probably cheaper just to skip them altogether.
Good luck, and hope that you're not "tired" of reading all this info.
Follow-up from Daryl:
I run 721's on my '64 Imperial convertible....I give lots of room on the road and do not try to brake too quickly...lets face it ...older cars do not behave/act/perform like modern cars do...im just glad when the car turns over and lets my partner and I ride for an hour in the rural areas of North Carolina...
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