What do these pictures reveal about my suspention?

[Kevp]

I have only used these tyres on trackdays & sprints over the last 2 seasons. The car is live axle kit car.

Rear tyres viewed from the front.

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http://thumbsnap.com/sc/Hab3GsuM.jpg[/img]|http://t...

[Classic Grad 98]

I imagine this is because these tyres have spent much of their working life on clockwise circuits. It wouldn't concern me in the slightest. Cars with independent rear suspension would usually be set up with negative camber but of course this option isn't available to us live-axle abusers!

[Kevp]

I did consider the wear could be from going round in circles. But the other tyre has even wear across it, and I would have thought it too would have suffered (maybe to a lesser degree).

Only thing is part of the tyre has not been used at all, so down sizing for the sake of tyre costs may be worth it.

[Sam_68]

Classic Grad 98 said:

...this option isn't available to us live-axle abusers!

Yes it is!

Don't assume your live axle is completely 'true' (ie. zero camber and zero toe), because more than likely it isn't.

Some degree of ajustment can be obtained by localised heating (with and oxy-acetylene torch) of the axles tube... when you heat it, the metal expands, but it doesn't quite shrink back to its original length when it cools, so by localised heating of one side of the tube you can effectively 'bend' it to give a small amount of camber or toe. The bearings are usually quite capable of accepting the resultant slight misalignment.

[Classic Grad 98]

Cheers Sam, fair point. I was aware of the practice of introducing camber and/or toe by that method but didn't think to mention it. It's a fairly impractical measure for a trackday car and I'm not allowed to do it on my racecar!
Kev- what tyre pressures are you using? (hot and cold if you can). We run the Yokohama A048s at about 24psi hot in Caterhams. Remember that tyres warm up and increase pressure unevenly- so set your pressures with the tyres hot. If you're running them much higher than that you'll see more uneven wear. it is normal for the outer shoulder of the nearside rear tyre to wear the most as far as clockwise circuits are concerned.
If the car is handling properly and your tyre pressures are correct, then there isn't much else you can do to affect the way the rear axle works without getting drastic.

[Alan Kee]

You've got a sticky tyre there with plenty of sidewall height hence plenty of inner edge lifting .. that wear pattern is pretty much what youd expect to see.

[Sam_68]

Classic Grad 98 said:

...I'm not allowed to do it on my racecar!

Purely out of curiosity, how would they ever know?

[Classic Grad 98]

They wouldn't ever know- I've never known any of the scrutineers to check.

[Kevp]

I run 17psi tyre pressure - cold. So it will give a lot of side flex. I still cant believe that approx 2" of tyre has never touched the ground. Especially as 2 of our events have tight left hand bends (Llandow & Gurston Down).

The axle does have brackets welded to it for the suspension pick up, so the drive shaft tube cold be bent, by accident. I have looked & had a quick measure, but did not find any deviation (I know it will be very slight if there is).

[Sam_68]

Weslake-Monza said:

Protest by a fellow competitor and scrute produces a camber gauge.

And proves what? That you are lucky enough to have an axle with suspiciously consistent geometry?

Kevp said:

...The axle does have brackets welded to it for the suspension pick up, so the drive shaft tube cold be bent, by accident. I have looked & had a quick measure, but did not find any deviation (I know it will be very slight if there is).

The axle pick-ups are not always located with the finest accuracy either, mind you... unfortunately, it's not particularly easy to check the Sylva/Fisher live axle set up for deviation, since you do get a certain amount of roll steer (the asymmetric Watts linkages see to that), but you also get lateral deflection due to the arc of the Panhard rod that means the obvious way of checking for consistency side-to-side, by using a bump-steer gauge, doesn't really work.

Your best bet is simply to check for camber and toe in the same way that you would an IRS car, then carefully check the wheelbase both sides, both at static ride height and then with some squat (ballast the car, being careful to ensure both sides are equally loaded) and heave (jack, again making sure that the car is jacked evenly), to ensure you are not getting excessive rear-end bump steer.

...or simply put up with the slightly odd tyre wear (which I have to say looks more like tyre pressure and/or an oddity of the tyre carcass stiffness than a major problem with geometry).

I wish I could get 2 seasons track day use out of a set of tyres and still have that much tread!

Edited by Sam_68 on Tuesday 8th March 18:25

[Classic Grad 98]

You may find that 17psi all 'round, cold, becomes 23psi in the nearside rear and 21psi in the offside rear (not that I'd expect that difference to cause that tyre wear, but it may contribute). Next time you get the tyres hot, come in and quickly take the pressures. What your aiming for is even tyre pressures at the tyre's working temperature.
I'm not familiar with the suspension set-up in you car as Sam seems to be, but as he says a diagnostic geometry check might help if there is an irregularity with the location of the axle. Personally I've always accepted the unusual wear as a symptom of running an axle which actually has slight positive camber!