journo

Been trying to suss this out for ages but stil not there.

I'm picking up a new WRX with PPP in the next couple wof weeks. I've asked the dealer to supply the 18" PFF7 wheels. Subaru also do a package which includes this wheel and P Zero Nero tyre. But after reading some comments on here I quite fancy Goodyear GSD3's and I've told the dealer I'll supply them if he can't get them.

What I can't find from the Subaru web site is the size of the tyre for these wheels. I'm guessing it's likely to be 225/40/18?

Also could someone explain where the width of the WHEEL comes into play - the standard WRX wheel is 7", the PFF7 is 8" - how does this affect the size of the tyre.

And finally - when changing tyre size how do you/dealer know what pressure to use - I'm fairly sure the guide in the manual is just for the standard 17" wheel.

So many questions!!!!

Help appreciated.

Mike.

Claudius

Hi Mike!

Good to hear you're getting an Impreza

Let's take a look at your concerns

A friend of mine had PZero Neros. They are awful tyres, really. No grip, melt away, etc. Good you arent getting them! The PZero YELLOWs however are very good. Why dont you check how much they are? Especially now that the weather is getting better, you'll like those, much better dry grip than Goodyears or Toyos (with the V thread to evacuate water, good for wet road use).

As for you wanting 18 inch wheels, I'd like to point out that while they look nice, they will actually reduce the performance of the car because they are heavier, and because the main part of the wheels' weight is further away from the center of the wheel. This makes it more difficult for the car to get the weight going, ie acceleration will be slightly less good. This is especially important as wheels and tyres are unsprung weight (weight you cannot compensate by adjusting the suspension). If you want to be really **** (like me ), compare tyre weights.

Yes, absolutely.

Generally, for fast road use, you want the rim width to be about 85 - 90% of the tyre width. In other words, you need to convert the rim width to mm (since that's what tyres are given in) and compare the two.

For instance, in your example, 8 inches wide rim = 8 x 25.4 = 203.2 mm. If you divide that by 225, it comes 90.3%. That's excellent for fast road or even track use

Be warned, however, that the higher this % I outlined is, the better the car will grip but also the more abrupt it will become on the limit of adhesion.

Yes, that's only for the standard wheel. The lower stiffer sidewall will enable you to run somewhat higher tyre pressures, about 10 - 20%, ie 2.3 bars instead of 2.1. Play around and see what suits you.

journo

Claudis,

Excellent response - thanx very much. Especially the bit about the wheel width - I thought the width of the wheel should be the same as the section of the tyre - but of course the tyre overhangs the wheel a bit.

Reason I'm going for 18" is at the suggestion of the Prodrive web site which suggests using 18" wheels for the PPP (both WRX and STi).

Mike

Claudius

You're very welcome

I can see that, but I guess you can see what I said about weights? Dont believe Prodrive. It's simply not accurate.

I'd suggest you go for 17 x 8 wheels with 225 x 45 / 17 tyres.

Anyway, you do as you please, just thought you might want to hear this.

Take care

Danny Fisher

Mike, follow the link and ler it work it out for you.

http://www.tyresave.co.uk/tyresize.html

Dan

Dyney

http://www.tyresave.co.uk/tyresize.html

For the incapable