[928uk] wheel offset

[Phil Chadwick]

nicholas skudder wrote:
> 
> i am running mille miglia cup 2 replica rims in 17" and they have the 
> technicaly wrong offset.  i know plenty of others also use this wheel and im 
> interested in opinions as to whether you experience more tramlining with 
> them than with the standard wheels.  at first i was prepared to accept this 
> on the basis of the wider rim and tyre contact patch but driving the SE with 
> its 8" wide front rim and similar tyre contact patch is much better in this 
> regard ie it dosent tramline as much.
> 
> is this because of the offset?  how do you guys with 18" rims get on??

Hi Nick,

There's a lot of factors at play, but I reckon that front offsets
less than 55 mm will usually cause noticable tram-lining, particularly
on 1986/87 and later cars with 4-piston Brembos (where the scrub radius
was changed from -16 mm to -10.2 mm to accommodate the bigger brakes).

What offsets do you have?

When people change offsets initially, they often go from 16" to 17"
wheels, get new rims, new tyres, and new alignment.  With all these
variables, not to mention a lot of pride in the "new look", the wider
rubber, and the money spent, objective assessment of the outcome
might be difficult.

This is why I think that the "back to factory" test is a good one.

I have recently seen observations from two different 928 owners who
"went back" to wheels with 65 mm front offsets (both started with
"third party" wheels and front offset not greater than 55 mm).  They
also kept the same tyres, so the only variables were offset and metal
wheel weight.  One, a 928 S4, went back to factory standard S4
(7-slot) 16" wheels.  The other, a 928 GT, went to factory standard
GTS 17" cup wheels.  Both observed that they thought the steering was
OK before the change, but were *stunned* at how good it was after.

Note that factory standard 928 metal wheels are quite light, typically
17 lb front and, on later cars, 19 lb rear.  The GTs had lighter wheels
than that (down as low as 16 lb on the early ones, I think).  Not sure
about the SE, but I expect it had GT wheels?

I think I have heard that that the Mille Miglia cup 2 replicas might
be a wee bit heavy, but not sure of my facts there.


-- 
Phil

Herblock's Law: if it is good, they will stop making it.