6 replies to this topic

[miniman24]

Last question from me tonight

 

I have recently bought a gauge that allows me to adjust my own camber and caster and am keen to try out different set-ups to find my ideal set-up (I know that the camber and caster affect the toe, I am in the market for a set of tracking gauges too) I understand what caster is and what it affects but what I dont know is this: Do I lengthen or shorten the tie rod to increase caster? Is it more positive caster or less positive caster (so shortening or lengthening the tie bars) that gives better self-centering to the steering and more stability? Thanks :)

Edited by miniman24, 21 June 2013 - 09:39 PM.

[KernowCooper]

Caster Angle – viewed from the side of the car, the top ball-joint should be positioned behind the bottom one. The angle made by a line drawn through the ball-joint centres and vertical describes caster angle. Its effect is a self-centring action that causes the car to run straight where no steering input is made and pulls the wheels back to straight ahead when exiting corners. Controlled by tie-rod length, shortening it will increase the self-centring effect, lengthening it the opposite. Increasing it also helps reduce the positive camber induced by body roll. On the downside, increasing caster decreases camber and induces body-roll by virtue of lowering the inner wheel and raising the outer wheel when cornering. Having said that, a big caster angle can cause the inner edge of the inside tyre to re-engage the ground where the wheel goes 'light' in a tight corner, helping to restore some grip. A further effect of increasing caster is a very slight lengthening of the actual wheelbase, increasing in effect as the wheels are turned on the outer side in a corner. Perhaps very slightly increasing stability.

 

Sorce KC

 

As listed here in the forum by Cooperman and others the castor for a road car should be 3-3,5Degs max

 

And something else due to manufacturing tolerences of standard conponents if you have adjustable tie rods and set the castor angle side for side, you could have a different wheel base side for side.

 

And remember if you increase the negative camber then you increase the castor

Edited by KernowCooper, 21 June 2013 - 11:18 PM.

[miniman24]

Thanks, just what I needed :) I have a feeling that I am going to favour a slightly larger caster angle - I like my steering to self center very positively and to have some resistance when turning left and right - Ive just been reading through other geometry enquiry posts and the member "icklemini" who knows hos way around a geometry set-up prefers a caster angle of 5 degrees - I suppose its just messing around until she feels spot on :)

[KernowCooper]

5degs may be a bit excessive for the road, but you have the kit and can see what you think works in your car.

 

The more positive castor you run, (shortning the front tie rod) the better the steering feedback at the wheel. Again this is a trade-off, as too much positive caster will make the steering very heavy in use. It will also cause the inner wheel to rise and the outer wheel to drop resulting in the transfer of weight from the inner wheel to the outer wheel when cornering, resulting in a loss of steering feel. The more positive castor you run, the less the steering will self-centre.

 

 

Edited by KernowCooper, 21 June 2013 - 11:38 PM.

[miniman24]

Dont know if Im using the tool wrong but I measured the caster today and its telling me that I have about 3 degrees negative caster - thought it was supposed to be positive?

[KernowCooper]

These are the figures I have and also I have a N.B beside the info- Caster should be checked with the tracking set at parallel

 

standard the mini has:

Front camber = 2degs positive +- 1 deg
Front castor = 3degs positive +- 1deg
Front toe = 1/16" toe out
Rear camber = 0.5 to 2.5 degs positive
Rear track = 1/8" toe in

 

 

Front camber and caster have the +/- degs due the manufacturing tolorences, but what you don't want is a big diggerence is caster left and right as it will make the car pull.

[miniman24]

Think Ive realised my mistake, I turned the front wheel in 20 degrees first instead of out 20 degrees so the reading was reversed - it seems to be in order, but Im going to try a touch more positive caster as I would like the steering to self centre faster than it currently does. Thanks for the help :)