Geometry Settings

[London Bill]

Hi from London,

we are having a discussion at the LSOC UK on how fitting 18" rims is taking the SC suspension way out from it's operational design, has anyone got new geometry settings for running with 18" rims and 35section tyres (tires).

TIA.

[DoubleWhoosh]

Properly fitted wheels and tires do not alter the suspension geometry or function. They will, to a certain extent, change the handling characteristics due to the different behavioral characterstics of certain wheel/tire combinations.

Although in theory it can be slightly affected, in a nutshell, NO wheel and tire combination will change your alignment. The alignment is a function of the control arms, steering arms and spindles, which (to a certain extent) do not have any play in them which is what would alter suspension geometry. Of course, if your tires are sticking out 2" past the fenders you will have handling issues, but it is not because of a change in alignment or suspension settings.

Todd M.
TM Engineering
http://www.tmengineering.net

[London Bill]

Hi Todd,

Sorry, I did not mean to infer that the 18" rims would change the geometry but that there are optimum settings to cater for the changed handling characteristics when fitting bigger rims and lower section tyres.

Iain Wiltshire (LSOC) has done extensive testing to produce optimum geometry settings for 17" rims, he has warned that 18" & 35section will drastically alter the handling due to the loss of compliance in the tyre sidewalls and the factory suspension rates do not account for this.

Another fly in the equation is altered ride height, my TT was "slammed" when it arrived, actually riding on the bump stops (I found it had adjustable struts and lifted it 2"), even now I get slight cone shaped wear across the front tyre tread but nowhere as bad as before.

I suppose the question should be, how do you arrive at optimum suspension geometry settings after making drastic changes to the factory setup - is it just trial and error with lots of track testing.