Hot Rods Tire Pressure

Just installed these Firestone bias ply tires on the hot rod. Was just curious what air pressure you guys are running on something like this ?? Thanks.

 

I am running 20 lbs on the front and 25 on the back of two vehicles with those tires.
Nice sedan. I yike it.

 

If not driving your car regularly bump the pressure up to 40# to help negate flat spots. Then lower it when you drive. I run 24 in front with 5:25x16 and 22 in the rear with 7"60x16 Firestone bias plys. The Pomona Fairgrounds is 50 miles from my home and when I didn't air up the tires when not driving and left them at the lower pressure it took 50 miles to get them round again.

 

The other way around would make more sense. The fronts should have more pressure because the weight distribution of the car will be biased more towards the front. An under-inflated tire will generate heat and be more likely to fail, and it is usually fronts that do because they carry more weight and do more work with steering and braking.

Just sayin'.......

 

Less chance of rolling a tire off of a rim on a turn also.

 

A model A has front/rear weight distribution that is almost 50/50. That being said I run 24 front and 22 rear. It helps a little with the steering and I want a little more grip in the rear.

 

I recently had cause to look for the weight distribution of a stock A Tudor (for this thread). Data for an actual car, recently weighed, suggests about 45/55. The V8 in the OP's car should shift that to around 50/50. Though: what does a banger weigh, anyway?

The principle of distributing tyre pressure proportionally to the car's weight distribution is sound, though. I use it on my DD, a light front-drive hatchback with a lot of forward weight bias. I run 38psi front and 23psi rear in the 50-series radials, which differs a lot from the stock specs. It tunes out the factory understeer nicely, and gives very even wear.

Remember that a tyre with less air in it acts like a tyre with more weight on it, as regards deformations and consequent slip angles, regardless of its construction. Lowering pressure might give you a longer contact patch, which helps longitudinal traction, but it also increases the slip angle at any given lateral force.

 

On my '30 tudor sedan about 3 or 4 years ago I was having a front tire bouncing problem. As soon as I got up to 20-30MPH the front tires would bounce like basketballs, I tried toe -in adjustment, new king pins, shaving the tires to make them more round, even new tires..... you know what fixed it? tire pressure, if I run 32 or more pressure it is fine but less than 30 and they will bounce.

 

That is strange. My experience with my car is just the opposite. When I try to run 30# on the front they bounce like basketballs. I usually run 22 front and 18 rear.

 

Yes, I have heard that before. I tried less pressure and it did not help I don't know what made me try more pressure but I did and it worked.

 

....It's all about harmonics and every car is going to be different.

 

Interesting view points. This gives me a lot to think about. I’ve never run higher pressures on the front end. I will try it.

 

Varying tire pressure a few psi can also be used to fine-tune handling.
>To increase understeer, reduce front tire pressure and increase rear tire pressure.
>To increase oversteer, increase front tire pressure and reduce rear tire pressure.

 

I think you got one of those backwards.

Re flat spotting, I think that is something that only occurs with steel belting, right? I've never had a flat spotting issue even after my A pickup has sat for 3 - 4 weeks, which is not often, but it happens. But even then the tires rode smooth right away. Bias ply firestones.

Re weight distribution, my A pickup weighed out at 1180# front, 980# rear.

 

Good catch. Corrected.

 

I remember flat spotting as a nylon tire cord thing.

Phil

 

During my old drag racing days always kept the fronts at 40lbs or more.....Less rolling resistance...

 

I had some Yokahama tires on my Toyota that would flat spot over the weekend. It took enough driving to create some heat before they rounded back out. Tire make probably has more to do with it them type.

 

Playing with tire pressure is fine if you're running bias ply, a bad idea if you have radials. Most of the tire 'flex' in radials is in the sidewalls, I'm convinced that most radial failures blamed on 'old' tires is really caused by underinflation in an effort to improve ride quality. Remember that the Ford Explorer/Firestone tire debacle was found to be caused by Ford recommending a too-low pressure and Firestone didn't catch it. Keep 'em at 30 PSI for safety...