orangecurry

I have a classic prodrive wagon, and have been very happy with the OE wheels, moving from
- OE Bridgstones to
- Eagle F1s (in 2003) in 205/50/16 87w (which were truely excellent) then
- P-zero assimetricos 205/50/16 88w (not as good, especially not in the wet but at least predictable and just as good/firm going round corners as the F1s as far as sidewall was concerned).

I decided to treat myself, and got some OE Prodrive OZ racing 17" WRC-1s, and for various reasons fitted 215/45/17 91Y tyres (I won't tell you the make yet).

I know the rolling diameter is slightly bigger, but it's a very small change.

I now find the car is pants if you push in through a sharp corner - it seems like the front is moving, but it isn't, then the back, but again the car *does* go round the corner.

It has removed my confidence is the cars abillities, which I know are excellent.

BTW I had a four-wheel track/alignment done by GCS in Horsham after I fitted the P-zeros, but nothing since fitting the 17" wheels.

So...
1) do I need to change anything on the suspension, to get back to where I was?
2) Is it simply the tyres are rubbish? Even with a 91Y rating which I understood would give it stiffer sidewalls?

thanks guys/galls - I am miserable to have spent loads of money and the car handles worse

911

I swop from 16's to 17' with very different tyres on my very (suspension) modified Classic Sti V3 with no probs at all.

The only thing you have not mentioned is the wheel offsets.

I have stock 16'' Sti and stock Prodrive P1 17's which are from the same era of classic.

I think this may be where your issue is?

Graham.

orangecurry

thanks for the reply - both sets of wheels are made for the classic; both are 7" wide, and IIRC they are offset 52 and 53.

Any more?

911

Interesting!

The 50 section tyres are much the same wall height so unless the basic tyre wall is weaker then I'm out of ideas already other than the blatent obvious: Tyre pressures?

I use the same pressures on the 16's as the 17's. (32 Fr/28 Rr)

The way to irradicate things now are to swop wheels with another Impreza, 17's for 17's.
That will remove the tyre question for sure.

So what 17's are on there now?

Graham.

orangecurry

OE Prodrive OZ racing 17" WRC-1s - I did say in the original post

I find slightly higher pressures work better (and it's a wagon) so everything is/was at 34/32 F/R, on all tyres/wheels mentioned.

911

Be the tyres then.
Nothing else has changed?

Graham.

Jay m A

iTrader: (2)

Is there a large difference in weight between the 16" wheel/tyre and the 17" wheel/tyre?

You may be noticing this if it is significant

orangecurry

weight of OE 16s is a very impressive 7.5kgs, and the Prodrive OZ (P1) WRC-1 wheels weigh 9.1 kgs, so a significant %age difference, but why would that affect cornering abillity? - accelleration and braking yes I agree.

OK - time to come clean on the tyres....

the 17s are 215/45/17 91Y Goodyear Eagle F1 GSD3s, so the same as my previous excellent 205/50/16 87W Eagle F1 GSD3s?

No, because they are made in China from different materials, whereas the older 16s were made in Germany.

Opinions anyone?
Superb german versions, with a Rayon sidewall


wobby chinese version, with a Polyester sidewall

911

That's the difference, BUT

Om my car the handling on identical settings is the same for

16' using crossply slicks
17 using radials

Couldn't be more different.
Graham

Jay m A

iTrader: (2)

The way I see it is the gyroscopic effect the rotating wheels have. If you have 2 gyroscopes spinning at the same speed, but one is heavier than the other, then it is harder to deflect the heavier gyroscope. So it would be harder to turn the heavier wheels left or right, they'd rather keep going straight on.

Having said that the 16" tyre may be heavier than the 17" tyre, also the weight is more significant the further it is from the centre of the wheel.

p1mark

It will have a small affect gyroscopically (that you may notice on turn in) as Jay says but different wieght wheels can have an affect in other ways.

You are not talking a massive %age here so it will be minimal, but your wheels are unsprung wieght i.e they have an affect on damping characteristics.

the heavier wheels obviously will add extra load into your dampers as they try and follow the ups and downs of the road surface, so if you take the theory to the nth degree you should revise rebound and compression damping rates.

I don't think for one minute in your case this will be required because of the small wieght change and you are really talking track car set up here........but you never know.

Its the same as putting a massive brake kit on (again, unsprung wieght), the theory says you should adjust suspension rates but in reality its just not noticable and probably impractical.

If you don't have adjustable coilovers or the like you are stuffed anyway.

p1mark

By the way, have you seen the thread regarding F1's from different countrys in the general section?

https://www.scoobynet.com/scoobynet-...-f1-users.html

By all accounts the chinese ones are good, but avoid Thailand tyres.

orangecurry

thanks for the thoughts - I was expecting slight effects (which is why I weighed everything before and after; I should weigh with the tyres as well), but the sidewall flex is just so huge.

I think I'm going to have to put my money where my mouth is, and buy some other manufacturers tyre and replace the F1s.

Mark - thanks for the E-mark link; yes I know all about that too.