Technical The old Bias-ply verses radial tire debate again, with a twist.

I’ve been driving my roadster for a several years now on county roads , two lane highways and occasional short trips on less congested sections of I-70. My questions is one of safety. The roadster weighs around 1,500 lbs., SBC, tri-power, Muncie M-21. Super Bell dropped axle in front , with traverse springs and tube shocks. Rear made up of 3-link ,traverse springs, tube shocks, S-10 Blazer rear. I’m running bias-ply tires. Gulf Cruisemaster A78-15 with 18-20 lbs. air . Rears are 8.20-15 General Dual 90 with 24 lbs. The front tires have been trued and balanced. The rears balanced. The car handles well except when the road is not smooth., which is a lot of the time. Expansion joint bumps are the worse. The car leaves the ground if going 50 MPH or so if the bump is a couple of inches tall. Crowns in the roads from heavy trucks is another concern. The car will dart a few inches left/ right.

I’ve learned how the car will handle in these situations but still it can be unnerving at times, especially in traffic. Cruising at 55-60 MPH is not an issue on smooth roads. I’ve had the car up to 75 MPH on a flat county road. It was a little hairy and I’ve not gone that fast again.

I was wondering if switching my current bias-ply to radials. Would there be a big difference in how the car handles or do I need to look at the current chassis set up? The wife has been wanting to drive the car but I’m afraid for hers and mine safety. She’s never driven it and once she gets behind the wheels, she’ll question me about driving an “unsafe” vehicle.

Wondering how the roadster, coupe guys address these issues in their hot rods. I see several hot rods in mags. and the net running my combo on the street. Are these traditional straight axle traverse rear suspension bias-ply setups safe going over 70 MPH , on interstates, etc.?

 

We drive our truck quite a bit. Just did 1300 miles to Colorado and back and then another 300+ the next weekend to the Hamb drags. All of this at about 75-85 mph on bias plies. I will admit that it takes some getting used to but it is an 80 year old truck that was never intended to go above 45 mph anyway . I honestly don't know if radials would help but they are not an option in my case as it would just not evoke the same feeling visually.

We jump bridges and expansion joints a lot too but I think that has more to do with the short wheelbase and stiff suspension rather than the tires.

 

interesting subject...I'm getting ready to go on Drag Week again, and the (stupid) plan is to drive my altered wheelbase Chevy II from Arizona to St Louis, then another 1300 miles of driving and racing for a week, then drive it back home.



it's kind of quick, runs low tens. I've had bias ply tires on it for over 4000 miles, and the handling on the highway is a bit iffy...kind of like what you say, although the car is heavy enough (2700 lbs) that it doesn't leave the ground. But I've had some excitement with it changing lanes all by itself in a crosswind, etc.

For the trip, I decided to switch to radials. I put some tires I had laying around on it, and went for a couple test drives. The difference is amazing, it takes no effort or concentration to keep the car going straight on the higway with the radials. With the bias plys, I had to always pay attention and keep both hands on the wheel.

I had radials on the car when I first got it running last year, so I kind of figured it would be worth the switch for this trip. The other thing is the spare tire deal...you can't find bias ply tires anywhere, they come mail order in a week or two. That had me thinking about what to do. Now I'm bringing the bias front tires, and the slicks, in the car. and I'll have to swap all 4 wheels/tires every time I race. My son is coming along with me, and he's going to be driving the car on the highway too, so I feel more comfortable with the radials on it when he's driving. And he's the "trunk monkey", in charge of doing the wheel swaps and pulling the exhaust off at the races.

 

First, a woman driver is unsafe on any road, in any car, period. Second, why would you think that doing 80 mph will be safer with different tires. 80 mph is dangerous, period.

 

I don't know what kind of women you hang out with, but my wife is a heck of a lot safer driver than I am

 

My wife has a 33 coupe with Firestone bias plies on it and she has driven it in all sorts of conditions and manages OK. Have had some hairy rides at times, tram tracks and bias plies don't go well together. Was funny tho. I've got a 32 coupe with American Classic radials fitted and when we've swapped wheels/tires her coupe is a completely different car re ride and handling. She suffers from motion sickness and is not happy riding in my car at freeway speeds but is happy if she's driving. Most long trips I end up as passenger-happy wife, happy life.

 

I don't think tires would make that much difference in such a light car with a short wheelbase.. Besides, bias-plies look so much better...

 

Jim...let us know how it goes.....I was an early radial guy in the 70's....and they blew - going to post a thread one day....you were lucky if they didn't tare up something in the process when they blew.....they still as "new equipment tires" blow and tear up vehicles often....hopefully the after market or what you choose are better made tires.....

 

Radial tires these days seem to be pretty decent...although they don't age as well as bias tires. I've only had one radial come apart on the road in recent memory. Although I had an old one come apart when it was sitting in the garage, not mounted on a car.

 

I agree that radial can make a big difference. yes, you can learn how your ride handles with bias ply. but, they give a stiffer ride, which maybe part of reason for leaving the ground in some situations. but, sounds like you need to examine your suspension to figure out if it set up right. shocks too long/short/ weight rating - springs have the correct weight rating-etc

 

Good god! Try driving a lifted jeep with bias tires and a flexy suspension. It requires paying attention!

Cars are easy to drive.

 

I guess my car is a lot like a Jeep

 

Got bias ply on one car and radials on the other,they both drive fine. HRP

 

I worried that running the Coker Firestone grooved rear and ribbed front bias ply tires would make my coupester handle badly, but was pleasantly surprised when they actually improved the handling and ride over the previous radials. I drive it at highway speeds on the Texas freeways as well as on two-lanes and rural roads with no issues whatsoever. I drag race the car on the 1/8 mile with a rough shut-down with no problems at all. In short, all the horror stories I'd heard about bias ply dirt track style tires were simply not true for me. The car runs straight and true.

I run 32 lbs. all the way around - maximum recommended pressure - and while the ride isn't cushy smooth the handling couldn't be better.

The only complaint I have is that the ribbed front tires tend to flat spot when I park it with the tires hot. I solved that problem by raising the front end on a floor jack when I put the car away for the day.

I suspect that much of the bad-mouthing of bias ply tires is from people who don't have a handle on the alignment specs or chassis design features of their hot rods. The ills they experience are not due to the tires but of shortcomings in the adjustment or design of their suspension.

 

And what is the reason for this out of line crap?

 

What a load of BS that is. I can assure you that there are plenty of women who are better drivers than you.
And 80 mph can be perfectly safe at the right time on the right road.
What is even sadder is that you actually believe your own nonsense.

 

It is all about proper suspension setup.

My rock rig's rockers at 32" off the ground, and I had no trouble driving 36" Super Swamper TSL bias-plies, from new to bald, on California freeways.

 

My wife is a better race driver than me, and she could easily drift circle around you, at 80, on bias-plies.

 

To the OP.. why dont you borrow some radials to see if they help your issue or not. As you can see there are a lot of different opinions.

 

For fun I took off some 16" bias plys off my coupster and put on some billet wheels bfg radials ... And believe it or not was ..... SCARY! I could go 100mph on the bias plys ... The fronts had a harmonic at 60-70 then was fine if you drove through it ... But I put the radials on and the car darted, bounced and carried on .... 20 miles was enough

 

It's really tough to say that this or that tire will cause a certain handling problem. Camber, toe-in, shock valving, and wheel offset can all effect how a given vehicle reacts to a tire type. On a OT car I had, it drove/handled great on the OEM 215/70R15s, still did fine after upsizing to a 225/60R16, but got twitchy on 17s. Guys with the same car that tried even larger wheels had worse problems.

I'd say the OP's problem is probably too-stiff front shocks, coupled with the fact that bias-ply tires have less 'give' in them. Radials do absorb irregularities better, so they might help with his particular problem.

 

you say that the car will "dart" right and left at times, while you may not have a bump steer problem as you do not say this happens when you hit bumps, you may have a caster problem. Caster helps keep you straight. Also, if you don't have enough toe in the car will wander. Now, I'm no front end expert but this is what I have read. Too many cars out there running 70-80 mph with belted tires for your problem to be just the tires. This is not to say radials will not help, but they may just mask another problem. My tudor has no problem doing 80 - 90 or even over 100mph no wander no bump steer no problem and I'm running 600 X16 up front and 750 X 16 rear.

 

but that could still mean that you are both unsafe

 

My roadster has the bias ply Coker BFGs on it that were on it as a mocked up, unfinished project when I bought it 8-10 years ago, 5.60X15 & 8.20X15. Wish I had access to a durometer, as they just don't wear out and I'm getting concerned about their age, although the car is stored inside out of the sun's rays when not being driven, and there aren't any signs of cracks or other aging.
70 is a common cruising speed fo0r me and have been well above 100 before it began to be "twitchy". Rough roads are no fun though! But I've always figgered it was the light weight, short wheelbase and stiff, transverse springs and beam front axle.
Tudor, a fellow HAMBer and SFCC member has a '32 coupe that is super fast with a blown 383 SBC, and he went through a bout of death wobble a couple of years ago and tried all sorts of things with suspension and steering components before finally taking off the bias ply front tires and replacing with radials, and he says it's great now. Rears for street are Radir cheater slicks IIRC.
I plan to install radials when I finally get too scared of the bias ply ones I have now.

 

I went from bias ply to the American classics radial(bias ply look) Best improvement I made! Can't explain just how good it drives,Back roads its like a go cart and highways its one hand on the wheel,A totally different car!! I find myself going faster because it drive so nice!! Pete

 

IMHO, you've got too much air in your rear tires.
and maybe to many leaves both front and back.

 

X2 on the average statement maid by everyone else. When I read the OPs query my first thoughts where... Setup. Last thoughts would be tire type. Although all tires are different and will change a cars feel and handling to a degree, leaving out condition of course, chassis and suspension setup or design will trump all this. We're talkin about the effects firm at best rubber with meer inches of grip can effect the hard firm posisitioning of steel. What I mean is if the caster, camber, alignment, toe in, toe out, shocks, bushings, springs, shackle angles, and things don't jive the tire type doesn't have a chance in hell at saving your ride quality.
My second thought that came to mind was do you have a pan hard bar? Not that I think you "need" one. But yes they help. Oh yeah and a 1500 pounder can get light on its four feet.

 

Radial tires usually give a smoother ride, but if your ride is leaving the ground when it hits a sharp bump( two inch tall bump and fwy speed is pretty harsh) I wound say start with the suspension ,its probably sprung a bit too stiff , suspension is binding, shock angle incorrect or shocks have way too much compression dampening. standard hot rod shocks are fine, but if your running a nitrogen charged shock that could be a problem. increasing the caster should help with the darting issue.

 

Me?(avatar) Pete

 

No Pete, Dave29 the original post!