Avon tyres less stable at speed?

[FatBoy]

Hi,

I've just replaced my Goodyear Billboards with a set of Avon CR6ZZ tyres and the initial feeling was that they are much better at normal road speeds and much less inclined to follow bumps and white lines.
However, over the weekend I took it for a 200 mile drive and a variety of different roads and had the opportunity to stretch its legs a little and I found that the new tyres are less stable than the Goodyears at higher speeds e.g. >100mph.
The Goodyears were always rock solid at higher speeds and I would like to get the same feeling with the Avons if possible.
I had the suspension thoroughly setup to the figures provided on the Kirkham website for the Goodyears, but has anyone found that different settings work better for the Avons.
There isn't any vibration, so balance isn't the problem, but maybe the radial prefer a different toe in/out setting.

Paul

[FatBoy]

Anyone??

[Mark IV]

You are changing from a bias ply tyre to a radial. The radial will be more sensitive to toe in/out so I would look at a good alignment with thrust angle correction.

[Cobra #3170]

Originally Posted by Mark IV

You are changing from a bias ply tyre to a radial. The radial will be more sensitive to toe in/out so I would look at a good alignment with thrust angle correction.

Excellent advice, especially getting the thrust angle correct, you will need more camber too.

[FatBoy]

Originally Posted by Cobra #3170

Excellent advice, especially getting the thrust angle correct, you will need more camber too.

Do you have any suggestion as to how much more camber?

Thanks,
Paul

[Cobra #3170]

Originally Posted by FatBoy

Do you have any suggestion as to how much more camber?

Thanks,
Paul

I would probably try -2.0 front and -1.5 rear as a start, watch inside tire wear and if is excessive go to -1.5 and -1.0. I run -3.5 and -2.5 and get even wear but the tires are seeing corner loading the majority of time.

[FatBoy]

Originally Posted by Mark IV

You are changing from a bias ply tyre to a radial. The radial will be more sensitive to toe in/out so I would look at a good alignment with thrust angle correction.

Thank you. That, I understand, but I was l hoping for some numbers based on personal experience. The car was REALLY well setup on the Goodyears and I just want to get some of the straight line stability back again.

Paul

[mdross1]

It has been a long time since our car was on the rack but do remember it was set with toe-in and 4 to 4 1/2 degrees pos. caster. Our car has BFG radials it is steady and solid well beyond the triple digits.

[mickmate]

Good info from Bruce but remember his is a track cornering type set up. He knows more about these suspensions than anyone I've talked to.
Rear toe also is adjustable at the rear lower inner which has much less effect on the other setting like changing radius rod lengths does.
I think Paul my first adjustment for speed stability would be more caster, especially if the steering feels pretty light at low speeds with the radials.
Check the pitch on the threads, use a ratio to make it closer to a true measurement. A good method is adjusting an upper ball joint and simply measuring between pivot points. Translate it into an angle change rather than a distance using a ratio. Best way to do that initially is on an alignment machine and noting the change. Of course that's what you were asking for initially, it's a matter of whether anyone has done this and also remembered it or written it down. When I was racing I had my own code on the decamber plate graduations so no one could read my numbers.