P38A Tyre Pressures

domino · Aug 9, 2015

Hi all,

I remember reading a post on here where folks were disagreeing with the LR figures and using different tyre pressures...I just can't find it now!

Can you folks remember what the general consensus was regarding pressures?

tomcat59alan · Aug 9, 2015

28 F, 38R

domino · Aug 9, 2015

Thanks Alan

Saint.V8 · Aug 9, 2015

If on 18 rims, you'll have to play around until you get a good ride, steering and trim balance....for unknown reason the P38 on 18's was always fussy about tyre pressures.

domino · Aug 9, 2015

Ice gone for 28 front and 34 rear. Got a run to Newcastle today so we'll see how that feels. Only 2 adults so no load.

wammers · Aug 9, 2015

domino said:
Ice gone for 28 front and 34 rear. Got a run to Newcastle today so we'll see how that feels. Only 2 adults so no load.

Rule of thumb is increase pressure by 2 PSI for each inch reduction in side wall.

domino · Aug 9, 2015

I've got 18's on the car so adjusted slightly based on what Saint mentioned. If it feels craps I'll adjust in Newcastle and see what it's like on the return journey.

aj1954 · Aug 9, 2015

domino said:
Hi all,

I remember reading a post on here where folks were disagreeing with the LR figures and using different tyre pressures...I just can't find it now!

Can you folks remember what the general consensus was regarding pressures?

Sometime ago DATATEK said he runs his at 28 all round unladen, but not sure if that was on 16's or 18's

stopover · Aug 9, 2015

wammers said:
Rule of thumb is increase pressure by 2 PSI for each inch reduction in side wall.

So you recommend 32psi for fronts and 42psi for rears if on 18inch wheels? all loads?

wammers · Aug 9, 2015

stopover said:
So you recommend 32psi for fronts and 42psi for rears if on 18inch wheels? all loads?

No, how does the side wall on a 18" tyre decrease by 2 inches from and 16" tyre?

stopover · Aug 9, 2015

wammers said:
No, how does the side wall on a 18" tyre decrease by 2 inches from and 16" tyre?

I don't have a 16inch to compare with an 18inch assuming to overall diameter of the tyres is the same for both? Do you know the answer?

wammers · Aug 9, 2015

stopover said:
I don't have a 16inch to compare with an 18inch assuming to overall diameter of the tyres is the same for both? Do you know the answer?

Yes.

Saint.V8 · Aug 9, 2015

So do I....

stopover · Aug 9, 2015

wammers said:
Yes.

would you share? Please.

wammers · Aug 9, 2015

Saint.V8 said:
So do I....

Go on tell him Ant.

stopover · Aug 9, 2015

Saint.V8 said:
So do I....

Please, please

wammers · Aug 9, 2015

stopover said:
Please, please

I'll give you a clue. If you wanted to reduce side wall by 2" from a 16" tyre you would have to fit a 20" wheel and tyre.

Bix · Aug 9, 2015

Whatever the difference is in wheels, half it. Since you're adding that value top and bottom.

stopover · Aug 9, 2015

wammers said:
I'll give you a clue. If you wanted to reduce side wall by 2" from a 16" tyre you would have to fit a 20" wheel and tyre.

The penny has dropped. I also ran a tyre calculator and looked at the info on tirebuyer.com. So I have the answer. Many thanks

wammers · Aug 9, 2015

stopover said:
The penny has dropped. I also ran a tyre calculator and looked at the info on tirebuyer.com. So I have the answer. Many thanks

No problem. RAVE calls for the same pressures on both 16" and 18" tyres. Most tend to lower rear pressures when unloaded to stop the car bouncing about on things like speed humps, which are a bloody menace.

P38A Tyre Pressures

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