I am looking to give my car a little more castor. I have rose jointed the front suspension (which is inboard with a rocker arm) so i can move the lower wishbone forward to increase it. (its 3.5 at the moment)

I just wondered how much movement on the wishbone will give me about 5 or 6 degrees castor and how do i measure it?

Also, apart from self centering, what does more castor do to the steering?

[Edited on 21-9-09 by Antnicuk]

castor is the angle from the top to bottom ball joint, measured against vertical.

hope that makes enough sense, without drawing it out lol

edit, this should help


[Edited on 21/9/09 by blakep82]

One method of measuring is to hang a plumb line from the top outer ball joint (upright removed) down past the lower ball joint then measure against a large set square using trig to calculate the angle.

Increasing the castor will affect the dynamic camber change on turns and possibly the dynamic toe in/out on turns. I'm guessing these effects will be greater when moving the lower bone rather then the top bone as the uprights steering arm/TRE will move forward/backward to a greater degree. Might pay to re-check you static toe settings after you've move the bones.

If you know both sides are set the same to start with, might be simplest to move both lower bones by the same increment (1 washer?) and road test to see how it feels.

[Edited on 21/9/09 by nick205]

I wouldn't worry too much about measuring it, just adjust and try it until it feels right to you.

Castor will make the steering heavier especially at low speeds as it's lifting the car a little while turning the wheels. It can make it appear to have more 'feel' but that's really just the extra self centering you're feeling. It also changes the camber while steering so giving more neg camber on the outside wheel while turning in, giving better grip theoretically.

This is just theory and in the real world you may not feel the same effects...

i'm not sure if you'll be able to get as much as 5 degrees without new brackets, but push the top wishbones all the way back, bottom all the way forward, you might just about manage it

Hi, Thanks for that, i understand that bit but i mean how do i actually physically measure it?

Its difficult to get a digital spirit level (what i normally use) up against the upright which is not straight.

edit as its been answered now, thanks.

I have about 10mm of movement available, will that give he extra 1.5 degrees?

[Edited on 21-9-09 by Antnicuk]

You should be able to work that out roughly by measuring the distance between the top and bottom ball joints then draw a right angle triangle with that distance as one side of the right angle and your 10mm as the other side. Join the two lines to form a triangle and then measure the angle at the long pointy end. That will give you the max. adjustment you're going to get then you can fiddle around and work out the change in dgrees per mm of adjustment.

As above though it's probably more important to make sure both sides remain the same and you can get back accurately to your current setting. Then just adjust a liitle/test in increments.

The proof is in the fell, not the number as they say.

[Edited on 21/9/09 by nick205]

Another way similar to nick205's, but without having to remove the upright is shown by Mark Allanson here

God bless inginuity

HTH

JB

Been a while since I measured castor but IIRC you need to put the front of the car on turntables , attach castor gauge and zero then turn 20 degrees left using the turntable to measure angle turned, take a measurement then turn right 20 degrees (40 in total) take a measurement which should give you the total castor. If?? I can find it I have a Dunlop instruction sheet which may be of use