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Tyre Pressure

BLACKGTR33

By BLACKGTR33,
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Galois Veteran

Galois

Posted
Posted

hey mate,

i have nankang ns2's on my r34 gtt, on the rear i have 265/35/r18's on 10" rims which i was told by the shop (tyrepower newcastle) should be at 40psi, on the front i have 235/40/r18's on 9" rims which apparently are supposed to be at 38psi.

i'm guessing the difference in pressure has something to do with the differing height, not sure, but the pressures have suited me okay.

the back is a handful in the rain though

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Galois Veteran

Galois

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^ a 235/40 and a 265/35 have the same height of sidewall.

ahh ok, what do the 35 and 40 refer to then?

You all realise your tyre pressure will rise a few PSI after driving when the tyres have heat up...

and even more for a track day or drags, or on a hot day or cold, or day and night. it'd hard to allow for all conditions tho.

back in my karting days we ran roughly 13 psi, but we'd adjust it till there was a 2 psi difference between hot and cold to find the ideal setup for the day

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Munkyb0y Grand Master

Munkyb0y

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Posted
ahh ok, what do the 35 and 40 refer to then?

It is the height of the tyre sidewall as a percentage of the width. ie. aspect ratio.

265/40 would be a higher sidewall than 235/40. thats why the common size is 265/35. keeping the rolling diameter similar across the 18" range. u see?

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Galois Veteran

Galois

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Posted
It is the height of the tyre sidewall as a percentage of the width. ie. aspect ratio.

265/40 would be a higher sidewall than 235/40. thats why the common size is 265/35. keeping the rolling diameter similar across the 18" range. u see?

i do, thanks mate, i'm still on the steep side of the learning curve lol

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some_cs_student Veteran

some_cs_student

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Posted
You all realise your tyre pressure will rise a few PSI after driving when the tyres have heat up...

My new tyre pressure monitoring system can see anything from 33psi to 39psi depending on weather / tyre temperature.

During warmer weather it was closer to 36 - 39psi.

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Galois Veteran

Galois

Posted
Posted

before this thread gets out of hand with people asking what pressure they have for their tyre size (including myself!)

how much does a couple of psi matter? ok, so if we imagine the pressure is meant to be 40psi, for ease of numbers, and it runs at 38 psi. that's a difference of 5%, which would make fk all difference compared to other parameters, like temp, speed, cornering and driving style

and more importantly, how much does it vary between companies? because i'd imagine each company builds to it's own spec, which might vary by a few psi anyways

as a side note, my r34 was bought and after some dramatic events i checked the tyre pressure, it was 26psi, it was after that my worries about the prior owner began...

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getyayayaout Enthusiast

getyayayaout

Posted
Posted

There is no one answer to this question. Ideally you want to run a tyre pressure that balances the car and feels good when you drive it. Typically tyres heat up and expand when you drive, so if you stand on the throttle at every set of lights i'd expect the rear tyres to heat up a little bit, however its mostly the front tyres that heat up more than the rears because you have the load of the car thrown forward under braking and also the fronts are constantly working harder that the rears because the turn and slide (if only slightly). Also this is in theory what could happen, in reality it doesn't make a difference when you're stuck behind a bus.

Secondly, with a gtr, I personally think you should run all four tyres with the same pressure because otherwise it may trick the g sensor into thinking you've got wheelspin.

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(OO)SKYLINE(OO) Grand Master

(OO)SKYLINE(OO)

Posted
Posted
Yea. I'm running 38psi "cold" (just driving from home to servo). I'm guessing it'll be around 40psi when hot?

Yep, pretty much and when the tyres have cooled down, it will go back to 38 psi.

and even more for a track day or drags, or on a hot day or cold, or day and night. it'd hard to allow for all conditions tho.

back in my karting days we ran roughly 13 psi, but we'd adjust it till there was a 2 psi difference between hot and cold to find the ideal setup for the day

Yes, true.

I just pump an all round 34 psi and seem fine.

:)

My new tyre pressure monitoring system can see anything from 33psi to 39psi depending on weather / tyre temperature.

During warmer weather it was closer to 36 - 39psi.

:D WTF!

:)

You got any pics of that, where did you get that?

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