Cheburator

Design 911 in the UK will make you a set of replica wheels for £690 - 4 x 10" ET65 all round. That is the best way to go, as it will allow you to run 255/35/18 at the front and 265/35/18 at the rear. The handling will improve no end...

Bret, I dunno how your handling can improve when you fitted wheels with ET49? My car, no disrespect to your good self, is much better sorted suspension wise and would still tramline like crazy on anything but the smoothest of surfaces... For the record, I am running 18" x 8.5" wheels with 235/40/18 rubber, Leda custom shocks + Ott ARBs and -1.75 deg camber +02 deg total toe in and -5 deg castor

Discuss...

Brett928S2

Hi

I know it seems silly...lol

It was running and handling ok (NOT TOO MUCH TRAMLINING) with 52 offset and no spacers , then someone gave me some 3 mm spacers from a GT2 ....

I thought , well they could do with moving out a little so lets try the spacers....

Put them on and it handles MUCH BETTER......tramlining almost vanished and definitely all round better handling....

And I KNOW the spacers SHOULD have made it worse......but they didn't....and no idea why lol

All the best Brett

dprantl

A 255 wide tire on a 10" ET65 wheel is 62.5mm from the wheel hub. A 225 wide tire on a 7.5" ET49 wheel is 63.5mm from the wheel hub. If you took the 3mm spacers off, they would stick out 60.5mm. Also, a 255 tire on a 10" rim looks kinda silly; the wheel lip actually sticks out further than the tire itself.

Dan
'91 928GT S/C 475hp/460lb.ft

Brett928S2

Hi

On my fronts I have 225/40/18s on a 52 offset with 3 mm spacers....on a 7.5 inch wheel

Tried 245s but they locked on half lock on the rear of the front arches on my S2.

The 225/40s are fine, protrude beyond the wheel lip and if you look down from above ,you can see the tyre slightly protruding from the arch...

As I said...they work BETTER with the spacers than without lol....

No idea why as they should be worse.....

All the best Brett

dprantl

Brett, you would be able to fit those 245 tires if you had a ET57 or higher offset front wheels. My avatar has them on with no issues and 160mm ride height in the front.

Dan
'91 928GT S/C 475hp/460lb.ft

Brett928S2

Hi Dan

You may be right, but don't forget I have an S2....which has a different front end to an S4 or a GT, although as mine is the last year of S2s it has S4 brakes and suspension....

At the time i had 245s fitted, I did not even realise they would not work until I tried to reverse out of the tyre fitting place and the wheels locked on the rear of the front arches lol....

I promptly drove back in and had the 225s fitted , I would have tried 235s but they had none in stock....

All the best Brett

Cheburator

How do you measure the distance?

Who cares what it looks like? Mine is a race car... The 928 is SEVERELY undertyred up front from the factory. You really need 255+ if you want to make it go around corners properly. Moreover, if you ask me, fitting 245/255 on anything less than 9.5 to 10 inches is asking for the tyre wall to be rolled under whilst cornering... I have seen 8" wheels with 50 offset and once you set up proper ride hight - 110mm all round - for track work, they will foul the fender lips if fitted with 235+ tyres...

My 2c...

dprantl

(Wheel or tire width / 2) - offset

Of course if you have width in inches you must first convert to mm (*25.4).

Dan
'91 928GT S/C 475hp/460lb.ft

Cheburator

Dan,

I know how to use ET (offset) - what do you mean when you say that the tyre is Xmm from the hub? Measured from where is my question...

Alex

dprantl

The above is the answer to your question. The tire must sit evenly on the wheel. The wheel bolts directly to the hub. The measurements I was stating was how far from the hub does the wheel or tire extend towards the fender. It's pretty much like taking a ruler and placing it on the wheel hub, then following it outwards until you reach the end of the tire or wheel.

For comparison purposes, a stock 225 tire on an ET65 wheel will be 47.5mm from the wheel hub. The width of the actual wheel will have some variation in the value, but not much (due to the ratio of wheel to tire width and the resulting tire bulge).

Dan
'91 928GT S/C 475hp/460lb.ft

Cheburator

Ok, that makes sense. However, once you start messing around with the offset, even though your tyre will be roughly in the same place, you are changing the scrub radius of the front axle, which then affects handling and can manifest itself in excessive tramlining and wandering under braking to name a few...

Ispeed

Another issue is when your overall diameter keeps going up with 18 or 19" wheels. This can lead to some rubbing when turning or at the fender lip that you wouldn't have with a smaller diameter.
The stock diameter is 24.7"... Look at the specs of your tire before you buy. I am at 25.3" and have no issues with 265/35/18 and 68 offset.

dprantl

Yep, that's also true. I am really pushing the diameter (25.7") with my 245/40-18 fronts on ET57. When I'm doing a sharp turn there is one specific point on the steering wheel where the tire just slightly rubs on a part of the wheel liner if I take the turn fast enough and there is enough body roll. It is the outside front tire, so I know it's not contacting the fender top. It also only happens on the left tire when doing left turns, not vice versa which I find difficult to understand since my ride height is the same on both corners front and back. Having a passenger doesn't change the situation either.

Dan
'91 928GT S/C 475hp/460lb.ft

dprantl

I don't disagree with you. However, a 10" ET65 front wheel should really be used for a track-only car. It's guaranteed to stick out past a stock unmodified front fender, even with a 255 wide tire. I suppose if you have extremely aggressive negative camber it would work with a very low ride height.

Dan
'91 928GT S/C 475hp/460lb.ft

jon928se

Thats a function of the handbuilt nature of our cars - the "chassis" probably gets jigged during manufacture for a precision check - but the alu fenders are assembled by eye to get the gaps to match and the liners are just installed.

My 90GT left front tyre (235/40/18 on a 52ET rim 170mm ride height) just catches on left turns at about half lock.