[Jimbobeast]

I put Coker steel belted RWL tires that look like the original fiberglass units. The service manual states 24-28 psi for the front. Should this be increased due to the steel belts? I will probably call Coker on Monday.

[b-man]

Those are bias tire pressures.

Way too low for radial tires.

I would bump up the pressure to 30 or 32 and see how it drives.

I’m running 32 psi all around with my 215/75-14 Coker Classic radial white walls, it handles nicely on canyon roads and has a good ride quality.

[tjs72lemans]

Doesn't everyone just go by what the side of the tire recommends?

[Jimbobeast]

I think that's just the max load pressure

[The Champ]

Originally Posted by Jimbobeast

I think that's just the max load pressure

100% correct.

You don't want to run the MAX pressure (typically 50 or more pounds).

I typically run 35 pounds on my GTO and the Camaro.

[Pershing]

I have always used the bias-ply pressure plus 4 psi. That has worked well for me. The sidewall psi is max pressure and not normal driving pressure.

[GordonGeesey]

I run the new Firestone Wide Oval RADIAL tires in size GR70-14. I run them at 32psi, and that seems to be a good pressure for street use.

[b-man]

Originally Posted by Pershing

I have always used the bias-ply pressure plus 4 psi. That has worked well for me. The sidewall psi is max pressure and not normal driving pressure.

Seems quite reasonable, close to my initial recommendation.

With any radial and especially in non-stock sizes you can start there and adjust pressures to suit your driving style.

Pump them up until they’re wearing in the middle, which isn’t as much of an issue with radials compared to bias plies, or until the ride is too rough for your liking.

[chrisp]

32lbs is good

[tjs72lemans]

I'm glad this post came up. As a younger lad, I always thought 32 lbs. was the desired pressure. Now, my 55 Chevy has Goodyear radials and the 44 lbs. max pressure on them I thought was the cold pressure setting. My 72 Lemans has BF Goodrich and they say 35lbs. max pressure. Should I be running both these tires the same, at 32 lbs.?

[b-man]

I’m pretty sure the 215/75-14s on my Le Mans are 35psi max pressure rating. Most tires with taller sidewalls usually have lower max pressure ratings than lower profile tires do.

Either way just run whatever pressure works for you, the max pressure on the sidewall is just there as a general guide and for liability.

You’d probably be shocked at how much air pressure your tires can withstand before they fail. The tire manufacturers won’t tell you for obvious reasons but it’s high enough to probably scare you.

You could run them higher than the indicated maximum if you can stand the harsh ride. A lot of hyper-milers do this to achieve as much fuel efficiency as possible.

Actual real-world tire pressure story:

I bought a new 2006 Civic LX 5-speed and the Bridgestone 205/55-16 tires had 44psi max pressure rating on the sidewalls. The recommended pressure on the placard inside the door jamb was 32 psi all around.

I was on a forum with a lot of hyper-milers, some of whom were running ridiculously high tire pressure to squeeze out the maximum miles per gallon so I decided to up the tire pressure.

After putting 5k break in miles on it and doing the first oil change I started a 28 day 7,145 mile vacation trip around the USA. I pumped the tires up to the 44 psi sidewall max and ran the entire trip like that. The car drove and handled fine, didn’t ride harshly and got stellar fuel mileage getting an average of 40.955 mpg for the trip.

Some tires depending on brand or size ride better at higher pressures than others. Since changing out those original Bridgestones which weren’t the greatest but fine enough I’m now only running 36 psi in the two different brands of replacement tires.

So just do whatever works for you, there are really no hard and fast rules.

[Shiny]

Just curious..

How does tire pressure affect braking and/or traction?

To me, the higher the pressure, the lower the contact area. So at what point does the reduced contact area degrade braking and/or traction?

I would expect a tire to have an "optimum" footprint to meet all the "ratings" I see on the tire sites.... mileage, braking, snow traction, etc. Some of these are actually warranted. So can a tire warranty claim be rejected for running too much or too little pressure and causing uneven wear?

[b-man]

Too many variables to nail it down concisely but I do know that for performance driving you want to up the pressure considerably beyond what you would use for normal driving.

Tires act like a spring so too much pressure makes the car ride rougher and the tires will want to bounce and skitter over small bumps.

I had a set of aftermarket 18x8s on my Civic for a time with 225/40-18 tires that had a 51 psi max. I ran them at 51 psi for a little while and it wasn’t too bad but sometimes it felt a bit like driving on bowling balls.

Just do whatever you think is reasonable, evaluate how the car responds to different pressures and go with whatever feels right.

I have cars with wheel and tire combinations that are far different from what they came with from the factory, I just do whatever seems to work.

1966 VW pickup - originally 14x5 wheels 7.00-14 bias, now 16x8.5 on 205/50-16. In the bed is a 1957 bug chassis with 15x3.5s 135/80-15s and 15x6s with 215/65-15s, originally had 15x4s with 5.60-15 bias.

Tempest had 14x5 and 6.50-14 bias, went to 17x8s with 235/45-17s all around then to 18x9 all around with 245/40s and 275/40s.

So where do you start?

Just do whatever seems to make sense and go from there.

[Jimbobeast]

The off road tires on my TRX recommend 70-80 PSI.

[Jimbobeast]

They are noisy and very difficult to balance and are only rated to 85 mph. I hate them. I'm never going off road in that truck but the only brand close to a highway tire in 12.5 x 22 is a Nitto, and they are $600+ each. I may end up changing wheel and tire both.