Kirkham specific tire pressure

[4pipes]

You guys that run 15' radials on your Kirkham 427 with aluminum FE's that weigh about 2400#'s, what tire pressures do you run on the street and track?

[Tom Kirkham]

30 psi is a good place to start.

[Ronbo]

It will vary depending on the tire. Best thing to do is get one of those infared temp guns and take readings of the tread after driving for about a mile or so (no turns, straight line). You want a consistant temp reading across the tread. Too low and the center will be cool, too high and the center temp will be higher.

The temp reading can also reveal alignment problems when one half of the tire is hotter. Too much toe-in will cause the outside of the tire to heat up for example.

[4pipes]

Originally Posted by Ronbo

It will vary depending on the tire. Best thing to do is get one of those infared temp guns and take readings of the tread after driving for about a mile or so (no turns, straight line). You want a consistant temp reading across the tread. Too low and the center will be cool, too high and the center temp will be higher.

The temp reading can also reveal alignment problems when one half of the tire is hotter. Too much toe-in will cause the outside of the tire to heat up for example.

Ronbo, if you've measured those temps on your car, what pressures are you running? What tires?

[RodKnock]

For running around town, I typically run 35 psi in my Avids.

[4pipes]

Originally Posted by RodKnock

For running around town, I typically run 35 psi in my Avids.

I used to run 30psi, but I think that is way too much for an SUV tire size loaded with half an SUV's weight. These tires are specified for a vehicles that typically weigh 4000-5000 pounds.

[Got the Bug]

Interesting that people who are running Avids on different cars run their tire pressure anywhere from 18 to 25. Is there something specific to the Kirkham that would dictate a higher tire pressure? I think SPF recommends 18 to 25 and I'm running 22F and 20R for street driving.

[Tom Kirkham]

Everything is a trade off. Steering response increases with higher pressure. The best way to determine where the pressures should be, is as has been stated by measuring the tire temp. Another very good method is watching the wear pattern on the tires. Our cars have typically worn very evenly at about 30 psi. A trick autocross racer use is marking the corner of the tire with white shoe polish to make sure that the tire is not rolling over onto the side wall...

[4pipes]

Originally Posted by Tom Kirkham

Everything is a trade off. Steering response increases with higher pressure. The best way to determine where the pressures should be, is as has been stated by measuring the tire temp. Another very good method is watching the wear pattern on the tires. Our cars have typically worn very evenly at about 30 psi. A trick autocross racer use is marking the corner of the tire with white shoe polish to make sure that the tire is not rolling over onto the side wall...

You're right about tire wear. Tom. I measured all four this morning with calipers and wear is very uniform across the tire after 7k miles. Up until now, I've maintained 30psi F/R. I'm going to try 26F/24R for a while.

[RodKnock]

Originally Posted by Tom Kirkham

30 psi is a good place to start.

Then that's what I'll run.

[4pipes]

This morning I went for a long ride and measured my tire temperatures with an instantaneous reading temperature probe. I measured at three points across each tire. With my tires inflated to 26F/24R the temperatures were quite even. I never measured them while they were inflated to 30psi all around.

What I did observe was slightly more steering effort, but noticeably less steering wheel shake. My car used to feel a bit nervous when holding a turn through a corner, know that's all gone. Also, the back end used to stutter around a corner on an uneven road and that's all but gone.

I think I'll leave the inflation pressures at these new setting for a while and see how I like it at the track next week.

[Tom Kirkham]

Originally Posted by 4pipes

My car used to feel a bit nervous when holding a turn through a corner, know that's all gone. Also, the back end used to stutter around a corner on an uneven road and that's all but gone.

You might want to have your alignment checked.

[4pipes]

Originally Posted by Tom Kirkham

You might want to have your alignment checked.

Thanks Tom. My alignment is pretty fresh...completed last year.

[PANAVIA]

wish they still sold Avids in the correct size.---

[Randy Rosenberg]

Originally Posted by 4pipes

I'm going to try 26F/24R for a while.

This is what I'm running in my signficantly heavier SPF (I'm 600lbs heavier). The lighter the car, the less air pressure needed, so IMHO, 30lbs in a Kirkham has got to be too much, however air pressure settings are rather "personal", and everyone has their own preferences.

Taking tire temps is the best way to judge inflation. I did this consistently when I ran GY Slicks on the track, and this led me to inflate them to 21F/19R. I took the tire temps after each 20 minute session. BTW, I believe that tire temps need to be taken after agressive/spirited driving, not just straight line.

Before I had a pyrometer, I used the "white shoe polish" method to see of the tires were rolling over onto the side wall. This process worked fine, however it's not as accurate as taking tire temps.

IMHO, I would not worry about wear. I drive my SPF so little (about 3k per year) that my old tires died of old age before they wore out.

YMMV,
Randy...

[Tom Kirkham]

Tire Rack's suggestions on tire pressure when autocrossing:

http://www.tirerack.com/tires/tirete....jsp?techid=58

[Tom Kirkham]

Tire Rack's suggestions on tire pressure and high speed driving:

http://www.tirerack.com/tires/tirete....jsp?techid=72