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There is an interesting thread on one of the Imperial club sites re radial vs bias.imperialclub.com/Repair/Wheels/radials.htm
Seems to be a decent explanation/opinion of the term radial tuning that makes as good a sense as any and also a bit of history and some recommendations. Changing the toe in seems to be the main item recommended for a successful switch.

That radial tires can only be used on a car with "Radial Tuned Suspension" is hogwash. "Radial Tuned Suspension" was simply a marketing term introduced by GM back in the early 1970s. Radial tires were actually introduced in the US market several years before that.

As the webpage cited by HH56 indicates, "Radial Tuned Suspension" simply refers to a (then) new performance suspension package that included matched front/rear sway bars, Pliacell (gas-charged) shocks, wider wheels with 70-series radial tires, and different alignment settings.

Most of the features in that package are simply add-ons that take advantage of the characteristics of radial tires.

However, I would agree that radial tires installed on a vehicle that was previously fitted with bias-ply tires require less toe-in - to decrease oversteer - as radials are more sensitive to toe.

Yet, because our Packards weren't originally fitted with "safety rims", I would NOT encourage stunt driving or performance competition with radials mounted on the OE rims.

Keep in mind, I don't go to shows and judged events. I drive my cars, and radial tires make a BIG difference. My '52 Mayfair had bias plys on it when it was purchased and it actually jumped from side to side. Without any suspension changes, the radials made this car driveable...you don't even need to hold the steering wheel now and it goes so straight as an arrow. My '41 Clipper is now fitted with Diamondback WW radials too, and they actually look like the old bias plys. My grandkids travel in my old cars with me quite often and I consider radial tires as safety equipment...like seat belts!

I read most of the Imperial Club post.

I have to agree with BH that the "radial Tuned Supension" is just so much gimmick.

Such points about shock absorber valving is again just gimmick. One can buy a variety of shocks for ANY ONE SPECIFIC car and get a wide variety of valving or other technical changes in the shocks. So shock absorber variation/valving is a moot point.

I'm not sure about the toe-in issue either. Most modern cars (rear wheel drive) run at least 1/16" toe-in spec.


What no one has addressed here is the foot print of the tire while under operation. Foot print of the bias ply tires tends to move REARWARD and further rearward as the speed of the car increases. Radials tend to move rearward much LESS than bias ply.
What this affects is the CASTER setting of the front suspension. The bias ply tyres tend to create THE EFFECT of more negative caster than the radials. Most cars built prior to the early 60's are spec'ed for neg caster. So the putting radials on a negative caster car will tend to give the EFFECT of zero or s0mething closer to positive caster.

The negative caster of pre-60's cars coupled with the rather large stering wheels was an attempt to make the cars steer ez at low speeds and parking. THE DRAWBACK is that negative caster creats alot of wander or hunt in the steering at higher speeds of say 45+ mph.

Most manufacturerss moved toward POSITIVE caster during the early to late 60's WHILE PROMOTING power steering and makeing smaller steering wheels because the car sihoutte was dropping. I'state hwy commision was born.

All of these 1965'ish driving environment and manufaturing evolutions allowed for and demanded the positive caster setting. POsitive caster alllows for a more stable high speed steering control.

So the so called "Radial Tuned" suspension is just so much nonsense. Makes for good coctail party buzz words but that's about all until someone can be more specific as to what changed in the radial tuned suspension other than a cheap pair of shock absorbers.

Radial tyres made their debut ca. 1967. Radials were offered as OPTIONAL to already existing bias ply by new car manufaturers. That is to say that one could have a new car either way: bias OR radial.

SO, IF there is any truth to the so-called "Radial Tuned Suspension" then where is it in the service manuals or parts catalougs that indicate some different service procedure or parts for cars with radials or Bias ply???

I don't ever remeber seeing ANY service manual nor parts cataloug for Chevy, Buick, Opel indicating any special treatemnt or parts depending on tire configuration.

PackardV8, Thanks for that information. It was very enlightening.The first radial tires I had were Michelins on my 1960 Desoto Adventurer in 1969 and by then they were already several years old.

Also note the last statement in the post above by BH about the 'safety rims'.

There is a difference in the OEM 56 wheel and the more modern nearly identicle 1980 Dodge wheel. The difference is a stamped safety bead that runs radialy around the wheel near the outer flange of the 1980 Dodge wheel. The OEM 56 Packard wheel does not have it.

NONETHELESS, since REpop bias ply tires are not to OEM spec then how do we know that such REpop biasply tires are any better for the 56 OEM wheel than the modern radial tire would be????

MOREOVER, i'm not sure the stamped 'safety bead' in the more modern wheels (such as the 1980 Dodge wheel) has anything to do with radial tires at all. I don;t really know. More research needed here.

Simply looking at the Dodge wheel with it's 'safety bead' i am more inclined to think that it is just a reenforcment to strengthen the wheel.

I have NOT checked the metal gauge difference between the 56 OEM Packard wheel and 80 Dodge wheel yet.

Very likely that the 56 wheel is heavier gauge than the 1980 wheel and therefore the safety bead exists only for extra strength due to the liter gauge of steel in the more modern wheel????? I don;t know.

Sean:

A few months ago I was exactly where you are now. My 1941 180 limo was getting ready to roll and it needed new tires. I read all the opinions, asked everyone I could and it was just about 50-50. I do have radials on my MGA 1600 and Morris Minor woodie and love the way they handle. Driving my friend's MGA with bias-ply I do notice the road "pull" at times which I don't experience with the radials.

But in the end I went with Firestone 700-16 bias-ply with the 4" whitewall from Coker.

A few weeks back I went to the restoration shop for a test drive. The car handled perfectly. I drove it for over three hours - in town, along the highway, up hills, down hills, around curves etc. I never even gave a thought to the fact that I was on bias-ply tires. They look great, they felt great, I had no mis-givings about my selection.

Hope this helps,

Neal

The safety rim wheel was invented by Chrysler corporation and first used in 1941. The idea was by putting a ridge around the tire bead, the bead would stay put in case of a blowout. This would make the car much more controllable. In those days a blowout often meant the tire came off the rim and got wound around the axle, throwing the car completely out of control.

Chrysler offered the industry free use of their patent, in the interest of hiway safety but no one took them up on their offer for years. The reason was the slight increase in manufacturing cost, less than a dime per wheel.