EIRE

Just a quick question about the my 07 wrx tyre size... why is a car which has a 2.5 litre engine, awd and 230 bhp horse power got such a narrow tyre ie 215/45/17... When you look at other lesser powered cars like golf tdi"s etc have standard 225/45/17"s..Surely the wrx should come standard with the wider tyre for more grip on the twistys as that is what it is renouned for among other things.. ..and finally are there any pro"s or con"s to upgrading to the 215/45/17"s that are the standard sti size...???

Bugatti

I'm no expert here, but here is me uneducated view: Some of the lesser powered cars with wider tyres are front wheel drive therefore are putting more power down at each of the front wheels than a scoob does on each of the 4 wheels as its AWD.

For example, if say a front wheel drive car has 200 bhp, then each powered wheel is having to cope with 100 bhp. A 200bhp scoob's wheels only have to cope with 50 bhp each.
I know the above example is unreal as theres transmission losses and stuff but hope the thoery makes sense.

I'm sure someone will come and give a more thorough explanation in a bit thats in English.

Naz.

EIRE

Thanks for that mate...you"ve got the ball moving..i suppose that makes sense but i still think subaru should have opted for a beefier tyre for the wrx ie 225/45/17 unless there is a mechanical reason why or maybe economic...???

EIRE

Come on guys there must be someone else out here that has some more info on this...???

Hoppy

It's a very complicated subject (and has been hotly debated here before) but grip is a function of friction and load. Size of contact patch is not - all other things being equal, which of course they aren't - part of the basic equation which is why it's complicated

In other words, big tyres don't automatically give you more grip and possibly less, as after-market wheels often mess with the geometry and are usually heavier and not matched to the suspension.

Webby Simon is the expert on this and has written an article, but that area of the site seems down at the mo.

Richard.

EIRE

Well that all sounds very interesting so the original size wheels and tyres may well have more grip than upgraded 18"s...hmmm the plot thickens...!!!