salamander

The handbook and sticker on the door jam say to inflate tires to 32 psi. The max pressure on the tire says 44 psi. Which one do you use? My sense is to use the 32 psi but I want to be sure.

dis1

32

gambone

iTrader: (3)

Has been dealer tech... the door post says what ever and that's the one you want to use becouse the car maker goes out and buys lot of tires and test them all to see which one will give the best ride on averg for the buck.and tire pres is part of that testing ride and ware. So if you are useing the OME tire size then that is the rite setting , but if you are useing some other size then you need to do your own self testing for ride and wear

Fred Sickert

Max psi should be best for the track, but not for ride or tire wear.

rynberg

Woah, that is some really bad advice. Ever been to the track, there?

Fred Sickert

Just read tire tests, 40 psi was best in the test I read, even when max was 36.

rynberg

I don't buy it. No one at any track even I've been to runs pressures like that.

The real basis of setting tire pressures during track events is measuring tire temperatures and adjusting pressure to get consistent temps across the tires.

I guarantee you that running events with that high of pressures will result in you not running those pressures again. A lot of you guys need to quit reading questionable magazines and get out to the track for yourselves.

CarmonColvin

I suppose the test you read covered every tire type by every brand name, in every size, on every car on the road?


Using simple math you can come up with a base tire pressure to use. Going by the max pressure and max weight carring capabiltiy (because the volume of air in the tire has a direct effect on its weight carring capabiltiy).

Here are the stats off the tires on my wife's Mazda6
The tires are stamped with a MAX weight and max pressure as follows. (1356lbs 44psi). In theory at max pressure the tire can carry 1356lbs, giving a total of 5460lbs for 4 tires. A wild guess is that the car weighes around 3800 lbs.
3800 / 5460 = .70
.70 * 44 = 30.8 psi.
Then add 10% to cover pseudo weight changes due to bumps in the road and you get 33.8.
I keep these tires inflated to 34 psi.

Use this example as a loose starting number. Adjust based on tire wear and comfort. If the tires feel slopy add air, if they seem too hard lower the pressure. If after 5,000+ miles you see the inside/outside edges are wearing more then increase the pressure. Or if the middle groove of the tire is wearing more than the outside lower the presssure.

Bottom line is there is NOT just one presure that is good for street driving.

Tire pressure for racing/track conditions is a completely different can of worms. And from personal experience I can tell you that MAX pressure is not the magic number for every tire!

More Reading:
http://www.tirerack.com/tires/tirete...s_dryperf.html
http://www.tirerack.com/tires/tirete...l/pressure.htm
http://son.pca.org/Technical_Article...ssure_calc.htm
http://son.pca.org/Technical_Article..._pressures.htm

Fred Sickert

Well, when I get back on the road, i'll be looking for a track. Another thought, 32 is cold, right ? So what would that be after a few laps ?

Herblenny

iTrader: (13)

Fred, I don't know where you read that or whom you heard that from...

I agree with Carmon..
44 is to high..

just think of it this way.. too much pressure, tire will round out.. so, you will use more inner threads.. PSI needs to be in certain range to get max thread.. to high, less patch.. too low, less contact patch..

Most track people i've heard stick with slightly lower psi.. due to high temp created by brake caliper.. As temp increase, pressure increase..

I could be wrong on this.. anyone want to correct me??

Fred Sickert

It was Car and Driver, awhile ago. The calculator in the link above says 42 psi for 225/50 50/50 .98g 2800 lbs. I am guessing this would be at track temps.

Herblenny

iTrader: (13)

Damn.. You are right.. the calculator gives 40-42 PSI.. It just don't sound right??

Anyone else?? is this damn calculator wrong?? or I'm I missing something??

Also, I would think width of the wheel and diameter would make difference too..

skunks

nitrogen woudl take care of temps increasing pressure

as for what pressure to run, you gotta decide for yoru self, i have seen guys run 60-80psi and others run as low as 8psi of course for different applications but its jsut an example, i like to run 35 all around for normal and 45 for drift in the rears. it changes from tires to tire though. If you don't know what you want, just run 32psi.

rynberg

I have ran 32 psi (cold) at every single auto-x and track event I have been to. The wear on the tire has been right to the edge of the sidewall, just where it is supposed to be. The only time I had scuffing on the sidewall was when I just plain burned a turn and understeered really badly. At most, I've seen other FD drivers run 33 or 34 cold. We are talking street tires here, but I doubt R-compound tires would differ much from that.

The calculator at Car & Driver is bullshit. I guarantee you that running 40+ psi in your tires will NOT lead to good handling....

cpa7man

iTrader: (2)

I run 38 front 37 rear at the track. I've even run 40/39. Sounds like your saying thats too much. This is on SO3's (245/45/16). Next event I'll try 34/33 or so. It would be interesting to see what all the real racers run with R compound tires.

rynberg

Are those cold or hot temps?

AMRAAM4

OK, lets diversify

Appropriate pressures for:
245/255/265/275 - 17's
45's
40's
35's

245/255/265/275 - 18's
40's
35's
30's

All tires covered?

redrotorR1

R-compounds are a whole different ballgame. The sidewalls in R-compounds are generally much stiffer than street tires and can withstand lower tire pressures without significant rollover. For example, on my Kumhos, when fresh, I'll run 33psi(F) and 31psi(R) ... and adjust tire pressures accordingly to grip and tightness of the course. As the Victoracers start to wear down, I find that I have to run even lower pressures to maintain grip ... like 30psi(F) and 27psi(R). Hoosiers and Ecsta V700's tend to like higher tire pressures however .... Hoosiers, I usually run 40psi(F) and 38psi(R). But the same pattern for worn tires ... lower tire pressures. I'm guessing that has to do with the heat cycling ... as the tires get older, it takes more heat to get them tacky ... lower tire pressure = less volume of air to heat.

But for street tires, you'd probably want to run a setting that induces slight understeer. So if you're running 225/50's or 245/45's all around, I'd recommend running 35-37psi(F) and 32-34psi(R). Better safe than sorry.

Herblenny

iTrader: (13)

wow.. I think this thread is becoming very interesting..

I would of never guess running higher than 32 on my car..

SO, what would you run if I have 275/35/ 18 contisport2 for the rear and 235/40/18 in the front.. same tire??

Should I run 38-40PSI??? iT seems so high??

CarmonColvin

Racing tire pressures diserve a new thread for each brand of tires.

Sometimes properly designed race tires give more grip with lower presssure. When I was running 15"x10" tires with Yokahoma slicks I would run ~16psi front and ~15psi in the rear.

adam c

iTrader: (2)

There are way too many variables here to give someone an exact tire pressure. For most street tires, and non performance driving, somewhere in the mid 30's will be fine. The difference between 34 and 36 psi doesnt mean much.

As you increase pressure, the tire will tend to roll over less in turns. Too much pressure, and the center will start to bulge, giving you less of the outside of the tire on the road.

For road racing/autocross, its a whole new game. Weight of the car, width of rims, FWD vs RWD, tire construction.....etc.

I was running 24/22 psi with 225/50's on 8 inch rims. This was on a CSP 79 RX7, and BFG "R" compound tires. I think lighter cars can run lower pressures with SOME tires. I think front wheel drive cars tend to run higher pressures in the front, with a larger differential to the back.

For what it's worth, I run my 245/45/16 Bridgestone 750 tires, on stock FD rims at around 34/33 psi for daily driving. When I go to my next autocross, I will bump up the pressure about 3-4 psi per tire, and see what happens.

Adam

Herblenny

iTrader: (13)

Carmon, thats what I usually hear from people autoX and do tracks..

I usually hear people lowing there pressure than increasing it.. Just as Adam C mentioned.. and I said before, increase in pressure tends to round the tires.. and use less contract with the road.. Maybe when turning the roundness helps?? i don't know..

But this topic is getting interesting..

adam c

iTrader: (2)

Some tires require a lot of pressure to keep the sidewall from rolling over. For racing, you cannot have your tires rolling over very much. Many higher performance tires are now being built with very stiff sidewalls, so increased pressure is not needed to keep them from rolling over. The "average" tire requires more pressure.

If I were unsure of what pressure to run (for racing), I would error on the side of a little too much pressure as opposed to not enough. Having your sidewalls roll over too far will mess you up worse than too much pressure.

cpa7man

iTrader: (2)

Cold temps.

Fred Sickert

I saw a neat trick for rollover, put chalk or shoe polish on your sidewall, then make some runs. If it rubs off, your tires are rolling over so increase psi.