tire pressure

[kar120c]

Am i an moron or what? what's with the low psi, doesn't this make the sidewall wiggle? just wondering:confused:

[slngsht]

Am i an moron or what? what's with the low psi, doesn't this make the sidewall wiggle? just wondering:confused:

 

Are you refering to sevens running lower pressures than normal cars?

 

typically with low profile tires on a light weight car, no.

 

ultimately if the pressure is too low, it will cause stability problems... at least that's what happens when you drag race heavier cars and lower pressure to increase the size of the contact patch.

 

In a 1300 lb car, you can lower pressures (compared to what you would run in a 3000 lb car) and improve performance. It's all trial and error, but 18-22 psi is not that uncommon

[Al N.]

Speaking of tire pressures...I went down to 21 psi all around vs. (the number stamped on the tire, which is higher than my age!) and I could instantly tell the difference.

 

Before, if I'd squeeze the throttle making a 90 degree turn onto a cross street, I could easily spin the rears in first and second. Now it just sticks.

 

Going to try 18 in the front and 21 in the rear...once I get that darn cooling hose clamped up better.

[MHKflyer52]

Al,

I run 20psi on the front and 22psi in the rear on my car. I find that those pressures work very well and keep the contact patch of the tires very even.

One way to check that is to rub some chalk across the tread and onto the sidewall then go drive the car. You want to see that the chalk is gone on the tread and just a little of the sidewall close to the tread from when you make a turn showing that the tire is flexing some but not rolling over onto the sidewall area.

Hope this helps get your pressure correct.

 

[kar120c]

Thanx for the tire pressure 101, i understand now, god i love this forum, ask a ? and get several replies to that ?

I would like to repay. I'm a aircraft structures AME, if you have ?'s concerning Aluminum please feel free to ask,

it's great stuff! STEEL SUCKS is my motto.:party:

[Flibbie]

Kar120C,

I have an Al ? for you. Also having an aviation background, I'm more familiar with 2024 than 5052. Seeing alot of posts about the hassles of polishing Sevens, I'm curious why not use 2024 Alclad. Much easier to polish. Jim

[jcm0791]

I realize that I am answering an old question ...

 

Two reasons I expect:

1) cost

2) the fiddly little corner at the back of the sill where it curves up is hand formed and welded (or used to be) in place on the car. 2024 does not respond well to being welded.

[southwind25]

We have used the chalk method for many moons, learned it at our first autocross and it works reasonably well.

[athens7]

On the Avon ZZ3s that came with my car, the fellows on Blatchat say that even at 18 psi the center rib will wear out before the shoulders (a common occurence with over-inflated tires).

[WestTexasS2K]

I would have to agree with everyones replies. I run 20 rear 19 in front. My car seems to really respond to tire pressure. If I have over 20 in the front I start to develope a push or understeer. I have run as low as 15 testing but didnt see much of a difference going that low. I suspect with that low a pressure a pot hole could damage a rim.

 

Another benefit of lower tire pressure it makes the car ride much smoother. I had a new set of tire put on a Discount tire they put the usual 38 psi in the tires. When driving home there is a very rough paved road. It was all I could do to keep the car on my side of the road. Got home dropped the pressure and it rode and tracked just like it was supposed to.

 

 

[JBH]

Although I agree lighter cars can run lower pressures, I think the tire makes a difference here. The Avon CR500 should run 16 front and 18 in the rear. I run my Hoosier radials at 26 front and 28 in the rear (on the recommendation of Hoosier). My Dunlop vintage tires on my FF I run at 15/17.

 

I don't think it matters much on the street, but on the track it is indeed trial and error best evaluated by taking tire temperatures.

[WestTexasS2K]

Although I agree lighter cars can run lower pressures, I think the tire makes a difference here. The Avon CR500 should run 16 front and 18 in the rear. I run my Hoosier radials at 26 front and 28 in the rear (on the recommendation of Hoosier). My Dunlop vintage tires on my FF I run at 15/17.

 

I don't think it matters much on the street, but on the track it is indeed trial and error best evaluated by taking tire temperatures.

 

I would have to agree that there is a difference between manufactures. Slicks especially do not have as stiff of a sidewall.