Club Cobra - Tire Pressure

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I received a gorgeous set of wheels from Vintage Wheels.

315/35/17
255/40/17

What is the typical pressure everyone runs on these wheels/tires ?

Input greatly appreciated.

whats it say on the tire?

Quote:

Originally Posted by csx wnab (Post 933427)

whats it say on the tire?

Probably too high for the weight of an SPF. :) I'm sure someone with 17's will check in.

I have the same on my Backdraft, try 29 lbs front, 28 lbs. rear, cold, and adjust from there.

I use 24# front and 22# rear w/ 17s. Mine weighs in at 2650 full up big block.

Remember, the air carries the load not the tire. Superformance recommends 18psi for every day driving and 25 psi for performance driving for the 15s that are typically used. I would see no reason to reduce the contact patch by going any higher than the pressures they recommend.

Bob

I would say 21-24 for daily driving

Quote:

Originally Posted by csx wnab (Post 933427)

whats it say on the tire?

psi rating on tires is always the max rating the tires can handle/are approved for. this is certainly not what we should run them on.......

I run 20 psi front and rear with my 17's. Tire wear seems even.

I run 26 F&R
I've heard that 10 lbs for every thousand pounds is a good starting point.

I run 23 to 25 psi. I have the 335 rears on 11.5" wheels. They don't contact the ground real flat on the back. My buddy has his 335 on 12" wheels. That seem's better.

Scott

Quote:

Originally Posted by scootter (Post 935412)

I run 23 to 25 psi. I have the 335 rears on 11.5" wheels. They don't contact the ground real flat on the back. My buddy has his 335 on 12" wheels. That seem's better.

Scott

Scott,

Your rear tires rarely have contact with the ground anyway. :LOL:

I'm running 20 in the back and 22 in the front. I've had it lower and higher, but this seems to be the right balance.

17's require much more air pressure than 15's. I don't recall the exact physics, but it's kinda like why a bycycle tire has like 60lbs, but they are so small. I think it has to do with the smaller the volume, the higher the pressure.

Quote:

Originally Posted by Got the Bug (Post 935428)

Scott,

Your rear tires rarely have contact with the ground anyway. :LOL:

I'm running 20 in the back and 22 in the front. I've had it lower and higher, but this seems to be the right balance.

Ditto......

That will vary a little bit from tire to tire. Don't go by the number stamped on the sidewall. That's the max inflation pressure.

Generally speaking you want about 1psi per 100#. If your car weighs 2600# wet and loade, you should start with about 26psi. But, that's just the starting point. There's two ways to determine the correct weight. Both of these work for any tire on any 4 wheeled vehicle.

1. Use a tire pyrometer. After driving down the highway, pull over and check temps on each edge and in the middle. If temp is highest in the middle it'sover inflated. If it's lowest in the middle, it's under inflated. If it's highest on one of the edges, the alignment is off. This will give you the most accurate results.

2. Use blackboard chalk. Drive down the highway and get the tires nice and warm. Pull over, and place a heavy chalk line across the tread. Drive foreward about 20'. Check the chalk line to see where it's been rubbed off the most. Thin in the middle means it's over inflated.

Be sure to check both front and rear. My car is almost perfectly balanced, so I use 26psi front and rear. I determined the pressure with a tire pyrometer that I bought off e-bay for $50