New guy with a question on tire pressure.

I have a 72 coupe small block with Goodyear Eagle ST 225/70R15 tires.

Trying to get a good read on what tire pressure to run with. I’ve asked around the tire shops and received all sorts of answers from near the max psi, which is 44psi to whatever the sticker in the car states, which is 24 psi, even though I’ve told them what year car and what type tires.

Near 44 psi seems way to high, while 24 psi is the pressure for older tires and that seems to low, car feels mushy.

I ran across the following in a website about a year ago and I like the 32psi range. .

Vehicle Weight in lb/100) + 2 psi at heavier end + 2 psi all around if suspension and alignment are stock.
Example: Stock 911, 3,000 lb.
(3000/100) = 30 psi
Add 2 psi all around = 32 psi
Add 2 psi to heavy end = 34 psi at rear
With modified suspension, the result is 30 psi front, 32 psi rear.

Just had a tire shop balance and rotate the tires and they took them back down to 25 PSI

Any thoughts, trying to stretch the tires life out a bit, the car always comes up with other issues?

I’ve learned a lot over the last year reading this forum, Thank-you.

 

I usually run 32 psi in all 4 tires...

 

Me too

 

I have driven for years with 32psi cold. Never had any wear problems.

 

I used 32 PSI cold as my base, adding more air as it got down to 30 PSI. With the newer tires, it seemed a good compromise between long mileage and smoother ride.

Spike

 

Ahhh..... the good old tire pressure subject.

let me try to put it into a nutshell
1) The tire pressure should be sufficient to support the vehicle under all loading conditions and have the necessary reserve load capability. This really isn't an issue on a relatively light vehicle with relatively low weights.
2) The tire pressure should be sufficient to provide adequate resistance to heat build-up. Again, this isn't a huge concern with a C3. The car is relatively light for the amount of air volume in the tires. 24 psi should really be fine today if it was ok 30 years ago.
3) The tire pressure should be sufficiently high so as to provide an adequately low rolling resistance. THis increases fuel economy. Do we really care?
4) The tire pressure should be sufficiently low so as to provide an acceptible ride, primarily in terms of the tire's ability to envelop small bumps instead of transmitting that impact to the vehicle. So far, this is probably the biggest concern, and at least for me, it's a small one.
5) The tire pressure should be sufficiently high or low so as to provide the desired cornering coefficient. This will affect the steering feel, the cornering capability, and the time that the vehicle takes to react to a steering input. Sounds like this is probably the most important one for the bulk of us.

So where would I put the tire pressure? Without having real tire force & moment data, it's hard to say. Generally speaking, tire cornering coefficients are the highest in the 33-38psi range. Now, those are HOT tire pressures, so that translates to 30-35 psi cold. Find the spot you like in there and you're set.

In all actuality, there is a good bit of science and engineering that goes into developing tires and selecting OEM tire pressures for a given vehicle. We're well beyond the OEM stage, so it's really hit & miss as to how a given tire feels and responds at a given tire pressure.

Damn. Bug nutshell there!

 

I run 30psi

feels more firm

 

And don't forget altitude...
I used to run those exact tires and size here in Colorado on my 69 and ran 33-35 depending solely on how lazy I was checking tire pressure that wk... So anywhere in between 30-35 that feels right to you is correct.

 

I agree w/ the others. 32-35 psi cold what I use.