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They sound like the stock rims right?

42psi is pretty darn high, probably the max tyre pressure it can handle (check the sidewalls). On my S14, the tyre placard recommends 29psi but thats a bit too on the comfort side. About 32-34 should be cool :)

I run FM901 225/50/16 on a 7.5"rims, 32-34psi gets the best out of them :D

Over 40 is a tad too high, and your tyres will wear the middle out a bit quicker. Also should get less grip at lower pressure too, but all depends on the tyre itself

I think 42 is a little high, but I would be aiming for around 38 (we are talking cold, right?) They should then come up to 42-44 once hot for nice handling :D

Can vary depending on the actual tyre tho, you may want to check with the manufacturer

42 is not too high, in fact 40 is the minimum you need if you hit the track regularly.

In fact 36-40psi is the majority of operating pressure of most tyres. Tyre placards are

a conspiracy used by car manufacturers so they can sell cars, since customer will feel comfortable bounce on their bums when test driving a car from the showroom.

For the street it all depends on rims and tyre combination. if you fit a wider tyre 225 onto a narrow rim like 7", then you need to pump it up to prevent too much sidewall flex, e.g. I find 36psi on my 225/50/R16 on stock R33 16" rims gives the best turn in response. If you put 225 tyres on 7.5" or 8" wide you may be able to run less pressure, maybe 32-34.

you'll need to experiment to find the best. I always find running at least 2-4psi above recommended pressure on the tyre placard works best.

decided to put it back down to 36...though at 42 the car felt slightly less sluggy in the rear end. will try 38 next time. i assumed 42 cause when i got my front tyres swapped over to the new rims they were pumped at 42 by the tyre guys.

by the way...has anyone used those auto pumps..the one with the digital display?? i aint too sure about those things. i set it to 36 so it would deflate the tyres from 42 rite...then i get an error then it says its 32 so it starts pumpin then i get another error and it says the tyres now 50psi so it deflates for a sec then another error and it says 35 so it pumps again and then another error and it says 59psi..WTF?? i felt the tyres and shat myself thinkin it would explode or something. took the hose off and deflated the tyre with my keys. who knows how long this would have gone for...sheesh.

Those digital ones are generally more accurate since the pressure sensor is not being thrown around to the ground like some older conventional ones.

However they are not perfect as I found:

- They cannot be used to inflate a totally flat tyre as it needs some pressure

feedback from the tyre to sense how much air it needs to pump into the tyres

to reach the target pressure.

- If the target pressure is too far from your current pressure (e.g. from 24psi to

36psi) they often overshoot and had to deflate, overshoot the deflation and

has to inflate again.

by the way...has anyone used those auto pumps..the one with the digital display??  i aint too sure about those things.  i set it to 36 so it would deflate the tyres from 42 rite...then i get an error then it says its 32 so it starts pumpin then i get another error and it says the tyres now 50psi  so it deflates for a sec then another error and it says 35 so it pumps again and then another error and it says 59psi..WTF??  i felt the tyres and shat myself thinkin it would explode or something.  took the hose off and deflated the tyre with my keys.  who knows how long this would have gone for...sheesh.

if you don't connect the hose properly this can occur, I have to hold the hose in position and then it works fine.

  • 2 weeks later...

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