Castor angle advice please

[steve-v8s]

Got the standard off the shelf Griff Niton kit fitted. Fiddled with the dampers and have arrived at two settings one for the hill and one for the road. Car now a lot nicer, and set a personal best at Gurston this weekend, I now feel that I am driving the car rather than going along for the ride. However… I notice that after 8 enthusiastic runs at the hill, my fairly new A032s show more wear on the inside edges at the rear than the outside edges, which look just like new. If I clean the tyres and drive slowly across some dust this again reveals that the outside edges are not in use. The ride height is set to about 1cm lower than before but the castor angle has not been reset. Is 1cm sufficient to cause this effect ? I Guess that it is simply a case of accurately measuring between the wheels top and bottom and calculating the angle. The fronts show an equal contact patch. Seems a shame to be wasting half an inch of grippy rubber.

[Guillotine]

interesting.

1degree in use will dissapper during hard acceleration as the back squats down. but will increase under braking as the weight transfers to the front offloading the rear. exciting but not fast and certainly not good for a hill climber

i would suggest that you are looking for camber not caster.

caster is the top wishbone leading or following the lower (1 oclock or 11 oclock), whereas camber is the top of the wheel over or underhanging the bottom. which is usually negative. standard spec for camber front and rear is -1 degree. ie top smaller than bottom.

i run -2 front and -1 rear. but the stiffer the suspension set up, the less camber you'll need.

as your tyres will be cold i'd go for -2 and +2psi on tyre pressure at front and standard -1 degree and =1 psi on rear.


stand by for a "guru" shooting me down here.
i'd always defer to jools and steve if they're online


>> Edited by Guillotine on Wednesday 23 June 22:13

[GreenV8S]

Second what Guillotine says, you're talking about camber. If you change the ride height this will affect the camber, which will therefore need to be reset. Since you're driving the car competitively you will presumably be looking to optimise the suspension geometry for performance/handling not for wear. There is a compromise here because more camber is usually better for cornering but less for acceleration and braking. The traditional way to assess whether you have too little or too much camber averaged over acceleration, cornering and braking is to measure the temperature distribution across the tyre after a run. Normally, the optimum performance is achieved with the outside edge running a little hotter than the inner edge. If you set the suspension up for optimum grip, you will almost certainly end up with too much camber for even tyre wear when driving gently on the road, so you might consider backing off the camber for road use. Personally I can't be bothered so I drive like a wally on the road and like a granny on the track, and somehow it all averages out with even tyre wear and reasonaly good temperature distribution.

>> Edited by GreenV8S on Thursday 24th June 00:13

[shpub]

Agreed. The toe will also change and this can cause inside wear. The problem with the Griff is the technique to change the camber is not that straightforward to do in a paddock. The bible has details and also a piccie of me throwing the Griff round Silverstone and you can see the inside edge taking the brunt of the road contact.

The amount of camber will depend on how much roll the tyres and the car experience. Get someone to photograph/video the car to see what is happeneing.
Inside wear is also caused by toe problems.

Basically changing the ride height means resetting the camber and toe otherwise there will be funny wear and handling problems.

[marco]

Ah

That (as I suspected!) would be the reason that having raised my ride height by 20mm the car now tramlines and bumpsteers all over the road like a shopping cart.

I'm guessing I lose camber by going up on ride height yeah?

I'll try Chemix in Stourbridge who have a full laser geometry rig and apparently plenty of experience with TVRs. Anybody used them?


Marco