Checking tire pressure and spraying them with water

[kuwakuwa]

Whats up guys,

This might be a dumb question, but what is the usual purpose behind checking your tire pressures after a run? Is to make sure that you haven't lost a tremendous amount of air, or is it to relieve air due to the higher pressures from the tires heating up?

Also, what is accomplished by spraying the tires with water?

Thanks.

Oh yea, final question... do you need to have your car number posted during practice?

[nalbar]

Hey Satoshi!

After a run your tires heat up, causing the air to expand. By bleeding the air out you get your pressure back down to where you want it to be. Washing also cools them, which prevents large heat build up over your runs, which would cause you to bleed more air than you might like.

Some tire also get a 'greasy' feel when they are hot, and washing them (cooling them) removes this, helping grip.

I can go over all this in person at the next event.

Yes, you need a number at a practice for sound violation and safety reasons. Some don't bother (which is irratating a heck), but stricly speaking, you should have them.




nalbar

[kuwakuwa]

Hows it going Warren, thanks for the info.

I better keep an eye on my tire pressures this time around.. especially since we're doing 8 runs within a pretty short time span. I'll be sure to find you to check out how things are done.

Are there any specific tire brands that are notorious for getting greasy? Just a thought, but how about hitting the tires with some armor all.

Cant wait to run next saturday.

[frosty]

There is a point where your tires won't gain much pressure from heat. If you have an idea how much pressure to keep in your car and you aren't dropping seconds each lap, it's something to keep in mind.

If you are fairly new, you might find your in-between lap time better spent talking to other people on technique or whatever. That's what I did at my last practice.

[nalbar]

If you are fairly new, you might find your in-between lap time better spent talking to other people on technique or whatever.


This is pretty much true. Just advice on the correct path around the course will save more time.

A couple years ago we have a novice school I attended. Each group of about 5 people got an instructor. My instructor (whom I have not seen at an event since) was asked about tire pressure. He said; "Forget about it for now. It makes maybe a 2-3% difference. Your novices. Concentrate on fundementals. You can make up more time there."

IMO he is right. But don't forget, 2-3% is 1 to 2 seconds on a 50 second course. That's a LOT. So once you DO get an idea of what your pressure should be it makes sense to stay there.


That said, you usually don't need to worry about pressure or heat at a practice. The time between runs is so long your tires cool down. It's also winter, and many of the top drivers are BEGGING for warm tires because the lot is cool.


nalbar

[nik]

Are there any specific tire brands that are notorious for getting greasy? Just a thought, but how about hitting the tires with some armor all.


Falken Azenis are probably the worst. Armor All is greasy all on its own. I can't stand the stuff. It would have no performance benefit but some people like the look I guess.

[Andrew]

Armor All is greasy all on its own. I can't stand the stuff.
The guys in tech hate the stuff too. Gets all over your hands when you shake the wheels.

[cshodges]

Umm.. I hope you don't mean ArmorAll on the treads, that would be dangerous.

Most street tires don't have much of an issue with heat, and as a Novice you probably wouldn't notice the difference anyway. I'd talk to someone who runs a similar car to you, set your tires to a pressure they recommend at the start of the day, and leave them alone beyond that. Get a couple of events under your belt before you worry about adjusting your tires between runs.

And there are no dumb questions... they've all been asked before many times over. By all of us. :)

[froggy47]

I would add, so far as spraying tires, take the temp. of the tires IMMEDIATELY after the run - that is the key to finding out if you are getting all the use of the tire. Take outer/mid/inner on each tire. If temps are close that is good, if they vary by say 20 or 30 deg that's not so good. You may need alignment changes, tire pressure changes, or choice of tire needs to be looked at.

Usually someone in grid will have a tire temp. gauge you can borrow.

My tires don't get that hot unless it's 85 or 90 deg day. Usually it's the opposite for me, trying to get the tires heated up to a grippy operating temp. so I rarely spray.

YMMV

[kuwakuwa]

right on, thanks everyone.

i think i'll just check the tire pressures to make sure that they haven't gone beyond what I set them at initially.

how much fluctuation can you see anyway?

for example on a hot day, if your tires were at 40psi before running, could they get up to about 46psi?

[frosty]

right on, thanks everyone.

i think i'll just check the tire pressures to make sure that they haven't gone beyond what I set them at initially.

They will go up, and it will not matter.



for example on a hot day, if your tires were at 40psi before running, could they get up to about 46psi?

Unless you have azenis or r-comps, you'll probably just see 4 or 5 lbs increase. Odds are, you won't notice it.

[froggy47]

right on, thanks everyone.

i think i'll just check the tire pressures to make sure that they haven't gone beyond what I set them at initially.

how much fluctuation can you see anyway?

for example on a hot day, if your tires were at 40psi before running, could they get up to about 46psi?


Yes.

[DelSolBurrow]

i was wondering how i could check to see if i had to much camber... duh....tire temp differences from inside to out, not sure why i never figured that out! thank you

[frosty]

i was wondering how i could check to see if i had to much camber... duh....tire temp differences from inside to out, not sure why i never figured that out! thank you

Hmm... interesting idea. I'll need to find someone who has one of these tire temp guagues on Saturday because, well, I'm curious. I'm pretty certain I don't have too much camber, but maybe I'll find out if I have way way too little camber.

[woodrufj]

Stock class rarely has too much camber.

Jay W
505/287 Dakota

[frosty]

Stock class rarely has too much camber.

Jay W
505/287 Dakota

But can it have too little camber? Or does this method not work for that?

[Sebastian R.]

There are differing opinions on the accuracy of guaging too little or too much camber by the tire temps.
I've been told and becuase it makes sense believe, that because of the variety of angles a tire encounters on course the only sure way to tell if you have too little or too much camber through temperature measurement is on a true skid pad, where you can eliminate course variables and give the tires a constant angle.

[MX5bob]

Another aspect to this is that measuring the temperatures across the tire method is based on bias ply tires, not radials.

[frosty]

Ok, so basically the idea wouldn't work. Thanks.

[MX5bob]

Ok, so basically the idea wouldn't work. Thanks.

Yeah, pretty much. Consider that autocross is about transitions more than about steady-state cornering, so even skid-pad testing is of limited use.