Need tyre Pressure advice

[Red]

Last year I brought a new set of wheels for my Mark2 and I'm having a bit of trouble finding the correct tyre pressures to run them at. I got the new wheels toward the end of last year, and as the car dont get used during winter, the pressures will be out now. I should have taken note of what they were set at when I got the new tyres, but thats hindsight for you.

I know generally its down to drivers preference and many people say experiment with different setups, but trying out different setups on public roads is dangerous if you endup being way off the mark with your pressure settings and I'v never run tyres this wide before. As a rule I stick to manufacturers recommendations, but thats the problem here, there is little to no reliable advice for this car with this wheel/tyre combo.

The car is a 98 GT T-Bar N/A and the wheels are 17" fitted with continentals -
Front : 205/40/17
Rear : 235/40/17

I'v spent over an hour yesterday and about the same this morning tralling the net looking for a definitive answer. Theres plenty of info out there, but the problem is the answers Im getting are variying very wildly. So far the most prevailing advice suggests using the rule of +2psi for each inch over standard profile which would put the setup at:
Front : 205/40/17 - 35 psi
Rear : 235/40/17 - 39 psi
That seems really high pressures, especially on the rear to me.
I tried using a calculator on this site": http://www.alloywheelsdirect.net/inform ... _pressures" which gave me this setup:
Front : 205/40/17 - 37 psi
Rear : 235/40/17 - 36 psi
Surly a difference of 1psi between front and rear has to be wrong on a MR2.

Any advice on a safe baseline setup would be greatly appreciate.

[vinp182]

Rough guide line in the 'know your 2' section here http://www.mr2oc.co.uk/know-your-2/mk2. ... bartid=261

Set it at those pressures and go from there... Remember the tyres will need to be fully cold when adjusting pressures tho

[Red]

Rough guide line in the 'know your 2' section here http://www.mr2oc.co.uk/know-your-2/mk2. ... bartid=261

Set it at those pressures and go from there... Remember the tyres will need to be fully cold when adjusting pressures tho

I have hit that page before and found it very useful advice when I was coming up to buy my new wheels, but unfortunately it still leaves me having to work from assumptions based on spec for smaller wheels. I always do adjust pressure on cold tyres, shocking how many people don't even know about that.

You suggest setting at those pressures, which of the two examples was you refering to?

Thanks for the reply.

[vinp182]

There's setting for 17's with slightly different tyre sizes in there 27psi fronts and 29psi rear

[Red]

There's setting for 17's with slightly different tyre sizes in there 27psi fronts and 29psi rear

"Front: 215/40/17 @ 27psi
Rear: 245/35/17 @ 29psi"

I Did see that, but I guess I'm just looking for something more concrete. Thanks for the suggestion though.

[shinny]

There's setting for 17's with slightly different tyre sizes in there 27psi fronts and 29psi rear

"Front: 215/40/17 @ 27psi
Rear: 245/35/17 @ 29psi"

I Did see that, but I guess I'm just looking for something more concrete. Thanks for the suggestion though.

Toyota never fitted 17" tyres to the MR2, so there is nothing "concrete". You could do a lot worse than to start on any of the three stock pressure figures. I actually wrote the 27/29psi part on the sticky. However now I'm using better tyres, I'm running stock pressures again

[Red]

Obviously there wouldnt be any recommendations for these wheel/tires specific to this car, as you say Shinny, Toyota never fitted them in these sizes. After some hours searching for some more definitive figures for the tires in general, I'm rather surprised just how little support info there is from a manufacturer like Continental. I know this isn't exactly a common size tire, but it does seem to be left to guess work.

Iv been driving and maintaining my own cars for over 26 years now, and this is the first time I'v ever come across so little support on such relevant data...............This is starting to sound like a 'Points of View' letter

Anways, thanks for the advice guys.

[shinny]

Yeah, there's a gap here... but who fills it? Toyota won't, as we already know. But will the tyre manufacturers? Are they seriously going to experiment with every tyre size on every vehicle?

The thing with tyre pressures are there are so many variables. My BMW's manual has a couple of pages about it, where it gives different front and back pressures for all the different sizes they fitted at the factory... but each size has a different set of figures for summer and winter and for unladen and laden. That's a lot of experimentation that BMW did to come up with its recommendations... who on earth is going to do that systematically on our cars? And that's before we consider aftermarket suspension setups and those of us who run trackday tyres.

I know it sucks, but with so many variables that the best advice we can give is to start with stock pressures and adjust according to how you want your car's setup to feel, which is a combination of tyre compound, suspension setup, tyre pressures and tyre sizes.

[jimi]

I should have taken note of what they were set at when I got the new tyres, but thats hindsight for you.

What makes you think the place that fitted your new tyres had any more/better info than you can find ?
In my experience if you fit a non standard tyre/wheel combo to a car the tyre fitters use the standard (for the car) pressures unless you specify something else.
My car has 15" MK3 wheels fitted with 195 x 50 tyres, the MK1 was originally fitted with 14" wheels, the MK3 uses different tyres sizes on the front and back, none of which are 195 x 50. So there was/is no concrete settings available from Mr T and the only way the tyre manufacturer will provide settings is if the tyre was a OEM fitment on the car.
TBH it's not an unusual situation when fitting non standard wheel/tyre combo's to any car
What I did was what has already been suggested to you. I started with the standard pressures for my car, ran for a few weeks to get used to how it handled, then started experimenting (a few psi here and there) until I got a set-up I was happy with.
Since then after speaking to other owners with a similar wheel tyre combo's (who followed the same route) I've found that we are all running very similar pressures within 3 or 4 psi of each other.

[TonyleFrog]

I would like to know where the KY2 info for the UK GT 15" - 31psi front and 35psi rear - came from.
T2 was originally a 1999 UK n/a and I have the original Owners Manual for it which unequivocally states

Front -30psi
Rear - 34psi

It has always puzzled me why the equivalent stock JDM turbo figures are stated to be 2 psi less at each end. The logic of this escapes me. My white Rev 3 turbo came with the equivalent JDM Manual but it went with the car when I sold it in 2009 so I can't check. If anybody has one it would be interesting to find out what figures it specifies.

In KY2 the UK and JDM stock figures on 15" wheels both have a 4psi front/back differential. So does my Owners Manual (albeit with different actual figures). Toyota didn't come up with this just for sh*ts and giggles and imo there needs to be a compelling reason to depart from it.

FWIW I spent some time experimenting with T2 (turbo conversion on a UK car) which has 17" wheels (8J front and 9J rear and settled on:

Front 29psi
Rear 33 psi

Works for me. YMMV.

[baileydom]

For comparison i have the same rims at TLF and run 31psi front and 34psi rear. As has been said its personal preference.

[GazRev1Tubby]

I used to run 30f and 32r. I found it to be perfect

Sent from my SM-N9200 using Tapatalk

[Red]

I should have taken note of what they were set at when I got the new tyres, but thats hindsight for you.

What makes you think the place that fitted your new tyres had any more/better info than you can find ?

Well, they do it for a living. I know thats no guarantee its right, but I'd be willing to bet they know more than I do.

This isnt the first time I'v had aftermarket wheels fitted to a car, but in the passed I'v asked what they're set to and the cars felt fine. On the drive home it did occur to me that I should have remembered to ask this time, but I just assumed I could get the info from the net. My bad. Maybe I'll drop in and ask next time Im up that way(they're not local). Time to start experimenting I guess.

[jimi]

They do it for a living. I know thats no guarantee its right, but I'd be willing to bet they know more than I do.

I wouldn't trust a Quick F**k style fitter to inflate my tyres to the correct pressure and certainly wouldn't assume they know more than me about tyres (and I don't know much )