Tire pressure

[genolan]

Just took the Cobra for its first real ride since I purchased it in December and checked the tire pressure when done. 38 PSI waited an hour and 36 PSI. The car is a BDR and has the original Goodyear Eagle F1's. What pressure is recommended for this car?

[WardL]

I've been running 22# in my 17" 275/40 in the front and 335/35 in the back. After about 11k miles, I have ever so slightly more tread in the middle of the tires. The tire gauge shows 50 on outside, 58 in the middle and 43 on the inside of the front tires (tread depth). The rears show 53, 56 and 46 respectively. I can't find my tire gauge now but the numbers must be in mm. I think I'm going to bump the pressure up to 28#. I've got some autocross experience showing higher pressure would help. The tires are Michelin PS/2.

[pgermond]

Originally Posted by genolan

Just took the Cobra for its first real ride since I purchased it in December and checked the tire pressure when done. 38 PSI waited an hour and 36 PSI. The car is a BDR and has the original Goodyear Eagle F1's. What pressure is recommended for this car?

After weighing my car on all four corners by a Winston Cup crew member, the recommendation was 24/lb all the way around. That's what I have been running for years.

[bobcowan]

Originally Posted by genolan

Just took the Cobra for its first real ride since I purchased it in December and checked the tire pressure when done. 38 PSI waited an hour and 36 PSI. The car is a BDR and has the original Goodyear Eagle F1's. What pressure is recommended for this car?

A good rule of thumb is 1 psi per 100# of vehicle weight. For most Roadsters, that's around 24psi.

Originally Posted by WardL

I've been running 22# in my 17" 275/40 in the front and 335/35 in the back. After about 11k miles, I have ever so slightly more tread in the middle of the tires. The tire gauge shows 50 on outside, 58 in the middle and 43 on the inside of the front tires (tread depth). The rears show 53, 56 and 46 respectively. I can't find my tire gauge now but the numbers must be in mm. I think I'm going to bump the pressure up to 28#. I've got some autocross experience showing higher pressure would help. The tires are Michelin PS/2.

Your tire are probably under-inflated. In a perfect world, you'd have even wear across the width of the tread. In the front you'd like to see something like 50-46-43; a nice even spread.

Same thing in the rear. With IRS and a little camber, a closer spread like 53-51-49. If it's a solid axle, it should be a perfectly even spread, like 53-53-53 (in a perfect world).

You need enough pressure in the tire to create a flat contact patch. That's the real answer. How much that is depends on a lot of factors: type and brand of tire, temperature, wheel width, weight of vehicle, etc.

The best way is to check tire temps when the tires are hot. A probe type thermometer is best, but you can use a non-contact infrared thermometer to get you pretty darned close. When hot, stop the car on hot pavement and quickly check outside, middle, and inside of the tread. You gotta move fast, because the surface temp will cool quickly.

When you have camber, the top of the tire leans in. Obviously, that places more weight on the inside of the tire, and that part of the tread gets hotter. So you should see a gradual increase from outside to inside, and no more than 10*.

If there's no camber, like a solid axle, it should be (ideally) the same temp all across the tread.

My car does best with 24 front and 26 rear for street driving.

[lamaluv]

Per ERA's recommendation I have always ran 28 front and 26 in the rear tires. P235/60 TRX15 front tires and P295/50 TRX15 back tires. In normal driving conditions I have found this to be a good compromise for handling and ride comfort. Tire wear has been good also.

[motordean]

I run 26 & 28 all the time - works well.

[vatdevil]

Street 18 psig. Autocross 28 psig. Those settings just get full contact with 18 inch 285/35 front and 315/30 rear.

[Rjw289]

What tire pressure is recommended then for a 2300ish pound Cobra with BF Goodrich TA tires that are 275 60R 15 and 245 60R 15s?

Thanks

[Dwight]

I have ran 24 rear and 28 front for years (40,000 miles). I've tried 20 to 30 psi but the 24 / 28 gives the best traction and gas mileage.
Two pair of tires on the front but four on the rear

Dwight

[Z-linkCobra]

I find the best pressure to run is the one that will give you full contact as someone said in an earlier post. Grab you a can of white spray paint. Take your car out to a place that you can run in a straight line or really close to it for as long as possible. use the spray paint and put a line across the tire. Let the paint dray and drive normal for a mile or so. Check your wear pattern and increase or decrease tire pressure until you have even paint removal across the entire tread pattern.

Paint gone on the outside and not the center= under inflated.
paint gone in the middle and not the outside= over inflated.

Chalk works to but can sometimes rub off pretty easy and lie to you. This trick works for your daily drivers as well.

[vatdevil]

Originally Posted by Z-linkCobra

I find the best pressure to run is the one that will give you full contact as someone said in an earlier post. Grab you a can of white spray paint. Take your car out to a place that you can run in a straight line or really close to it for as long as possible. use the spray paint and put a line across the tire. Let the paint dray and drive normal for a mile or so. Check your wear pattern and increase or decrease tire pressure until you have even paint removal across the entire tread pattern.

Paint gone on the outside and not the center= under inflated.
paint gone in the middle and not the outside= over inflated.

Chalk works to but can sometimes rub off pretty easy and lie to you. This trick works for your daily drivers as well.

I use a red marking crayon.