Twin Spark wet weather setup

[Colin Edwards]

Rarely is wet weather setup discussed and the freedoms allowed by TS regulations in this regard. 
The most recent Twin Spark Cup rules allow camber adjustment up to a maximum of 3⁰ and adjustable brake bias.
The camber (and caster) is allowed to be adjusted via offset / eccentric control arm bushings, however the brake bias cannot be adjusted by the driver while seated in the driving position.
These freedoms though, allow significant wet weather setup adjustment.
Whatever camber setting you feel is quickest in the dry will be no good in the wet.  Same can be said for brake bias.  Camber should be at least halved in the wet and brake bias adjusted to maybe 30% less to the front and 30% more to the rear.  Given the tyres will produce less grip in the wet and therefore distort less, heaps of negative camber means less rubber is in contact with the track surface.  Excessive camber when not needed is also no good for grip when braking.
As the reduction in grip when wet also increases braking distances / reduces load on the front tyres, some of the front braking effort should be transferred to the rear to re-balance braking. 
Try it.  I'm interested to hear back from those who have tested this.
A bit of toe out in the wet cant hurt either!

[warsch]

How do you adjust front camber though? I have eccentric upper arms bushes which I'm yet to install, but adjusting them seems a bit of a pain. Another option is lifting the front axle which is just as painful. Even more so that here in QLD I had like 4 wet events out of almost 60 over four years. Not exactly worth the hassle. Even if the overall first place is at stake. Especially that wheel alignment has to be done too and what if it doesn't rain?

But I'm curios to here about other's experience too.

[Colin Edwards]

Hi Warsch,

When you install eccentric bushes to the upper arms you can adjust both camber and caster.  Assuming the "mid" point (nil offset) of the eccentric maintains "factory" geometry, rotating the eccentric pivot points equally towards the centre line of the car will pull the upper control arm in causing an increase in negative camber/decrease in positive camber.  Conversely, rotating the eccentric pivot points equally away from the centre line of the car will push the upper control arm out causing a decrease in negative camber/increase in positive camber.

If you adjust the front eccentric out and the rear eccentric in, the top ball joint of the upper control arm will move to the rear of the car increasing caster.  Conversely, if you adjust the front eccentric in and the rear eccentric out, the top ball joint of the upper control arm will move to the front of the car decreasing caster.  Increasing caster can increase steering axis inclination and builds into the geometry a degree of camber management and recovery under roll.  This scenario can allow us to run less negative camber which is a bonus with regard to putting more rubber on the road under braking.

A good wheel alignment facility should be able to "map" the camber and caster migration versus eccentric position.  Once this is "mapped" and the impact camber/caster adjustment has on wheel alignment is "mapped" adjusting setup at the track is a piece of cake.  Either that or you purchase one of these. 

http://www.revolutionracegear.com.au/?PCID=17705&PSO=245&PSID=3100005013&PSV=Primary&CDO=

We have one.  Its in continual use during a race weekend - wet or dry!  If you don't believe its worth the hassle you'll never get the best out of your tyres.