Board logo

What tyre pressures to improve self centring?
Sloan85 - 3/9/13 at 11:04 PM

What tyre pressures will improve self centring on an MK Indy with 13" wheels?

Cheers

dhutch - 4/9/13 at 04:28 AM

Not sometime I have looked into or done any work with, but my gut feel is that while is the is a slight amount, but not really enough, higher tyre pressures will help then wheels to turn and hence self center, tyre pressure cant really effect or correct geometry.

Daniel

deeceee09 - 4/9/13 at 06:56 AM

Seem to recall that I lowered the pressures to get better self-centering on the advice of Jeremy Phillips. Not sure if it helped but I passed.

pekwah1 - 4/9/13 at 07:09 AM

I pumped mine to about 35psi for the IVA, centred ok!
Obviously let them back down to 18ish again after the test!

skov - 4/9/13 at 07:19 AM

Have you tried playing with the front toe setting?
I had to give my haynes a few degrees of toe-out to get it to self centre for IVA.

pekwah1 - 4/9/13 at 08:16 AM

yeh i had a degree or two of toe out also for the IVA.
Now set to about 1 degree toe in

Not Anumber - 4/9/13 at 01:16 PM

To prove a point or to set up for the IVA changing the toe in and increasing the tyre pressures will help with toe in but at the expense of general handling and driveability.

The permanent solution is to do something about the caster angle by changing to adjustable top wishbones, There are several people on the forum who could make a set for you for under £ 100. I went for rose jointed ones from Phil at Talon, steering now self centres without any adverse affects.

pekwah1 - 4/9/13 at 01:53 PM

i think part of the problem is that on certain kits, the castor angle is more difficult to attain than on others.
I certainly had this problem on the striker because of the inboard suspension and chassis design. I adjusted my rocker arms back as much as i could which did increase the castor angle.

The other problem is that the IVA document refers to "evidence of self centring" but there are no specific guidelines of what is acceptable, so what one tester passes, another may fail.

Giving slight toe out and increasing the tyre pressures was in my mind, just to make sure the self centring was as good as it possibly could be, and then after the test put back to how it should be. My car does self centre with a standard toe and tyre setup, but again, is that acceptable enough for IVA?

dhutch - 4/9/13 at 02:43 PM

quote:
Originally posted by pekwah1
i think part of the problem is that on certain kits, the castor angle is more difficult to attain than on others.
I certainly had this problem on the striker because of the inboard suspension and chassis design. I adjusted my rocker arms back as much as i could which did increase the castor angle.

The other problem is that the IVA document refers to "evidence of self centring" but there are no specific guidelines of what is acceptable, so what one tester passes, another may fail.

Giving slight toe out and increasing the tyre pressures was in my mind, just to make sure the self centring was as good as it possibly could be, and then after the test put back to how it should be. My car does self centre with a standard toe and tyre setup, but again, is that acceptable enough for IVA?

Hard to say isnt it.

Although personally I would say, for normal operation, you would want self centering. I actually cant think of a time when you wouldnt want to self center, which is why to me its a surprise that there are ever any issues, and or, that people try to mask the issue rather than correct it.


Daniel

pekwah1 - 4/9/13 at 03:08 PM

Again, my car does self centre, certainly good enough for me when i drive it.
At low speeds it doesn't self centre too much (less than 20mph).

But again, just because i am happy with how the car self centres, different IVA testers will have different ideas of what is required. So i'm happy with the self centring during normal driving, so by tweaking the car so that mr IVA is also happy does not make a lot of difference for when i return to normal