[Mk2] [Turbo] Tyre Pressures for 17" alloys?

[timecorp1]

How do I know what my tyre pressures should be?

7Jx17 front with 205/45 17 tyres
9jx17 rear with 235/40 17 tyres

Should they be much higher than pressures with standard wheels?

[fearless]

should be writen on tyre what preasures you need, but i used to put 32psi all round in my 17" when i had them on my calibra and omega if that helps, tyre wear was spot on with no problems

[ancient mariner]

pretty certain (but stand to be corrected )that you don't need to increase pressure,from standard setup.paul.

[Leon.]

You need to lower them against standard.

I'm not 100% sure on the science but with the footprint area increasing (wider tyre), pressure on the tyre at any given point decreases.

I had mine about 29F and 32R (stock recommended pressures) and got central wear on the rears, lost a couple of 1000 miles because of it. I'd go 27/28F and 30 rear, from my experience. But don't let the fronts drop from 27 as you'll lose grip.

You should probably experiment +/- a couple of psi as everyone's setup is different.

HTH

[Harry]

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[Harry]

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[fearless]

i was about right then never had any problems with uneven tyre wear, like you said get the suspension set up by a pro elite have done a couple of my cars and are very good thats probably what helped me

[Kongaroo]

I've been using slightly higher than stock pressures when I use my 16's or 17's based on what I read in this article for 'plus-size' fitments:

http://www.sportcompactcarweb.com/tech/ ... index.html

It's quite a useful article and there's also some general advice for setting tyre pressures based on vehicle weight from a BFGoodrich engineer.

[Leon.]

Interesting article.

It really does depend on your individual setup. If I go even to Toyota recommended pressures for 15s on the front of my 17s (29psi), I get ABS kicking in all the time when braking on smll bumps etc. 27 is perfect for my setup.

Rears don't seem to make that much difference but as I said I had high central wear before when running at 33 psi...

[Kongaroo]

Interesting article.

It really does depend on your individual setup. If I go even to Toyota recommended pressures for 15s on the front of my 17s (29psi), I get ABS kicking in all the time when braking on smll bumps etc. 27 is perfect for my setup.

Rears don't seem to make that much difference but as I said I had high central wear before when running at 33 psi...

Hi Leeroy, what does the problem with the ABS feel like? Is it very obvious? I read other posts on IMOC regarding it but have never experienced it myself and I've had all sorts of tyre sizes on the car (I have 7 sets of wheels crammed in the flat at the moment )

[Leon.]

Hi Leeroy, what does the problem with the ABS feel like? Is it very obvious? I read other posts on IMOC regarding it but have never experienced it myself and I've had all sorts of tyre sizes on the car (I have 7 sets of wheels crammed in the flat at the moment )

Its basically the ABS kicking in, so juddering under the brake pedal. I'm on Tein's so when I hit small bumps with higher pressures, the front end bounces up, loses traction and so the ABS thinks I'm skidding... its a PITA not to mention dangerous!

[Kongaroo]

Yes it sounds like an annoying problem mate. Odd that just a few PSI difference would cause the ABS to activate though. Maybe it's just the Teins that are setup a little too hard for the street?

33PSI is also not exactly high pressure for the rear though. I recently used 36PSI on my 255/40/17 rears and 32PSI on my 225/45/16 fronts all through the winter and when they came off the car I didn't find any unusual wear in the centre of the tyres.

I've also been using 35PSI on my 235/50/15 R888 rears and so far the wear is even across the surface of those too.

I tend to favour slightly higher pressures as the car sees a lot of daily motorway use so it makes sense for me to have the tyres well inflated, especially with petrol being so expensive now

[timecorp1]

The pressures were set by the tyre fitter at 34psi all round and the car seemed to be understeering a lot.

I then increased the rear pressures to 36psi 'cos I thought the rears should be more. This seemed to make the cornering a bit better but I did think the car seemed hard as f*ck, especially as I've got the Tein adjustable kit set pretty stiff as well - small potholes were starting to snap my spine!

I'm now going to massively lower the pressures based on the above advice so will report back soon!

[Leon.]

Yes it sounds like an annoying problem mate. Odd that just a few PSI difference would cause the ABS to activate though. Maybe it's just the Teins that are setup a little too hard for the street?

No, they're near their softest setting. Poly bushes probably add to the bounce. But its fine tbh, handles great and even tyre wear. I get good mpg too, did 250 miles on just over half a tank the other week, driving 70 mainly...

33PSI is also not exactly high pressure for the rear though.

No the back isn't so much of a problem but like I said, I was seeing central wear on the rears so 33 was too high for my setup, unless I just need to take it easier round bends

My main point was to play around with pressures a bit and see what works best for your driving and setup

[timecorp1]

tried 27 front 29 rear for the last couple of days and the car is behaving loads better!

[Leon.]

tried 27 front 29 rear for the last couple of days and the car is behaving loads better!

Good news

[Kongaroo]

Yes good news Although I still think it sounds like you are using lower tyre pressures to compensate for an overly hard suspension setup. This was something I was trying to do a while ago (without much success)when I still had my adjustable KYB dampers - they were also an extremely harsh ride and were too bouncy even on the firmest setting because although the compression could be adjusted you could not adjust the rebound. I had them changed for adjustable Konis which has a rebound that much better suited to the street and I can run higher tyre presures without feeling like my fillings are going to fall out - my car's ride comfort is now much less bouncy/crashy than my wife's low mileage Citroen C2 VTS

One more link that gives some explanation as to why you usually run higher tyre pressures on plus size wheels:

http://www.tyrepower.com.au/tyre_pressures.aspx

Btw they are referring to pressure as KPA - to convert to PSI:

http://www.csgnetwork.com/presskpapsicvt.html

"I get good mpg too, did 250 miles on just over half a tank the other week, driving 70 mainly...

Wow, 250 miles on a little over half way while driving 70MPH is incredible
It suggests you can achieve about 450+ miles to a tank though. Do you mean 150 miles? I think most Rev 3 tubbys only get in the region of 250 to 300 miles on a full tank.

I set my power FC to run a slightly leaner AFR (about 15.1) at low load motorway cruising than a standard ECU but the most I have ever got was about 350miles from full tank to yellow light and that was on a super long motorway journey and cruising mostly at about 60mph. I thought it was pretty good at the time.

[Leon.]

Wow, 250 miles on a little over half way while driving 70MPH is incredible
It suggests you can achieve about 450+ miles to a tank though. Do you mean 150 miles? I think most Rev 3 tubbys only get in the region of 250 to 300 miles on a full tank.

No mate, 250 Ended up about 330 for the tank with town driving mixed in, and I never let it go to the light. I do have a very smooth style though on long journeys - never slow down or speed up (anticipation...), unless something grabs my attention