Avon tyres less stable at speed?

[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.

[DanEC]

Wow - that's a lot of negative camber! Is that for the track or street?

[Chilibit]

You did not mention tire pressures. What are running the Avons at cold? I don't a Kirkham so I hesitate to suggest an optimum pressure.

[Cobra #3170]

Originally Posted by DanEC

Wow - that's a lot of negative camber! Is that for the track or street?

Yes it is, but a Kirkham is very much like an original and has very little camber gain in bump, as a result you need to run more static camber to get steering response and cornering capacity. If the car is used in "spirited" driving you will get even tire wear, if it is driven on freeways or with very little cornering load you will get inside shoulder wear. That is why it is best to drive it for awhile and adjust camber for relatively even tire wear. It all depends on the owners driving habits, that set up will give optimum handling on the street but maybe not optimum tire wear. Radials need more camber than bias plys because of the construction and can still have a relatively even foot print with 1 degree of negative camber, adding cornering load increases the camber requirement especially with stock Cobra suspension. The only way to know is to try it, I can't imagine a Cobra owner who wouldn't hit a round about hard when the opportunity presented itself, otherwise why have a Cobra? Getting perfect tire wear is like getting good gas mileage who cares?

[Bobcat]

Bruce ... speak about timing on the Avon subject . Just got an answer from the Technical Manager of Avon Tyres Motorsport/UK about using the CR6ZZ tires on the track ( I do VIR ) . Common thread for both of you is that radial tires want/need a lot more negative camber than most people are running , or are comfortable with . For example , the Hoosier R6`s a friend ran in SVRA , needed a minimum of 2 1/2 to 3 degrees negative and higher pressure than most others run . Realizing that there is no silver bullet and not all cars and drivers like the same thing , Avon suggested ( as you did ) that , a minimum of 2 degrees negative camber . They were comfortable with tire pressures of 32 to 34 psi hot in front and 30 to 32 psi hot in the rear , depending on the balance of the car . Monitoring tire temps will then be your guide . The range I was given was to shoot for was a delta of 10 to 15 degrees C with the inside warmer .
I also run 1/16" toe in per side on the front and 3/32" toe in per side for the rear for track and street .
I spend more time on winding roads and the track than Interstates and if I get 4000 miles to a set of tires , I`m happy .

[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