darksider

should i air up my tires to the max to what it states on the outside of the tire? the max permiss on my front says 44 psi and my rears say 51 psi. the tire shop who mounted the tires siad he put 40 psi or somthing like that. is that ok or should i pump it to the max?

darksider

tires are 225/40/18 front and 235/40/18 rear. this car is for DD and i just want the correct psi for good tread wear. so is 40 ok? i dont care about ride comfort. i think it states 32 psi on the sticker, but that was for the 15" wheels.

rynberg

NO!

Run 32 psi. The tire shop guy was a complete idiot.

darksider

im not trying to argue but want to explain why? i would suggest tires pressure closses to the max would be ideal...

again im running 18" wheels not 15". tires are 225/40/18 front and 235/40/18 rear on a 9" wide rim so YES im stretching if that had anything to do with tire pressure.

32 psi seems to be too low from the max. but since you say im running over standard (about 8 psi) how does this effect it?

thanks for the reply

Mahjik

iTrader: (1)

Over inflation can cause:

* incorrect tire wear
* excessively uncomfortable driving (i.e. bumping, bouncing all over the place)
* increased steering responsiveness but less grip on turns

just to name a few... I don't know what FC's usually run, but I would start at around 32-35 PSI. Pick a number and start there. You can check the tire wear for improper inflation signs as well as the feeling on the road while you are driving.

darksider

so im concluding that tire size does not matter, it will alwasy be 32-35 psi for an fc?

thanks for the replies.

Mahjik

iTrader: (1)

Tire size can matter. However, you really only have a few ways to determine optimal pressures:

* tire Pyrometer
* checking tire wear

Like I mentioned, pick a PSI to start with and watch the wear (and feel how the car is on the road); then adjust accordingly.

Now, whether or not you run the same PSI all around, front more or front less is another discussion.

maxcooper

That max pressure listed on the tire means "don't exceed this pressure or you will have problems!" -- it doesn't mean "run this pressure".

-Max

RETed

I am one of those guys who runs against convention.
Running higher tire pressure will get you better gas mileage.
In Hawaii, we got some of the highest gas prices in the nation - 92 runs about $3.40 / gallon right now.
I try all the tricks in the book to get the gas mileage to go up.

A trusted autocrosser runs insane tire pressure on his MkIII and MkIV Supra.
I trust his experience.
He has run up to 60psi on his tires just to get the pyrometer to go even across the face during runs.
Now, this blows away the convention about running over the max tire pressures listed.
I DO NOT RECOMMEND DOING THIS.
This was just purely an anecdote for this thread.

I try to run my tires pressures right below maximum.
You really need to know what you are doing; you need to watch the tire wear religiously - as long as you're getting even tire wear it's okay.
My 225 / 50 / 16 Bridgestone S-03 Pole Positions are running at 40psi of tire pressure.
Maximum recommended is 44psi.
They are running on 16" x 7.0" GAB Sports.


-Ted

darksider

so where do you suggest i start for my application? 40-45 then adjust (what should i look for outer wear or inner?) or start lower and adjust from there (again what where should i look for wear?

thanks fo rthe replies

Mahjik

iTrader: (1)

IMO, I would start lower, like around 35-36 PSI.

slow_2ed_gen

you can mess around with tire pressures to fit your tire and suspension set up.

i know i run 38F 33R with my autocross tires and a little higher on the street

i really dont care about wearing them down faster i just like to have fun on the street, i do have 4 sets of wheels and tires though...

rynberg

auto-x is NOT street driving!!!!

I guarantee for 99% of drivers, running higher pressures means you are reducing grip and excessively wearing the middle of the tire. And living with a harder ride. For what?

If you are running 18s but they are wider than stock, you likely have the same volume. You should run the same pressure. I still say to start with the manufacturer recommended pressure and adjust from there.

Howard Coleman even suggests running slightly under 32 psi for best performance (he is a 22-year SCCA racing veteran).

BridgePorted12A

iTrader: (6)

34psi all around, anything highter than like 40 IMO for the street is pointless. Like everyone else is saying you will cause abnormal tire wear and your car will handle like ****. Do yourself a favor and pick up a SCCA book at your local bookstore or Amazon, they explain the physics behind it all and why it is extremely important to know.

Ryan

RETed

Mazda recommended is 32psi.
OEM manufacturer recommendations are a compromise of gas mileage, comfort, and tire wear.
You can easily run 10% higher pressures without weird tire wear.
Most people can run 35psi easily without any complications.

Another note is that I tend to drive my car hard on occasion.
We're talking 4 wheel drift here just to keep the rubber fresh.
This is probably why I can get away with the higher tire pressures.
You're not supposed to be doing 9/10ths... 10/10ths on the street in the first place, so you can throw away all the "race" tire pressure recommendations.

(I just reread the original poster's questions is, and I'm getting OT now...)

I'd run it at around 35psi.
Most people aren't sticklers for monitoring tire pressures, so in a few weeks it's going to easily drop into the Mazda recommended 32psi anyways.
"35" is an easy number to shoot for with almost any gauge since it's half away in between "30" and "40".


-Ted