What sort of numbers for scrub and castor?
What sort of numbers for scrub and castor?
(OP)
I've been reading through about suspension geometry, and advantages/disadvantages of big/small scrub, castor, kingpin angle, anti's etc. I've got Kingpin and anti-squat/dive sorted, but with tyre scrub what would be considered a lot of tyre scrub? Little is probably zero scrub. Same goes for castor, what sort of range is it usually in?
This is for an off road racer, 4x4. The Carroll Smith books and off road builders have said that off road these things have less effect (but camber curves and squat are still important important). But I still need to set my castor and scrub radius to something!
This is for an off road racer, 4x4. The Carroll Smith books and off road builders have said that off road these things have less effect (but camber curves and squat are still important important). But I still need to set my castor and scrub radius to something!





RE: What sort of numbers for scrub and castor?
Castor is much trickier. One rule of thumb is that under full pitching it should still be positive. That sets a lower limit of 3 or 4 degrees in your case. 12 is probably too much.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: What sort of numbers for scrub and castor?
RE: What sort of numbers for scrub and castor?
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: What sort of numbers for scrub and castor?
Also helps to have some jacking if you have a rear spool, to unload inside rear and enable turn-in.
je suis charlie
RE: What sort of numbers for scrub and castor?
I also got this from the Milliken textbook:
Will a four wheel drive vehicle need to follow this advice from Milliken as well?
My rig will have a lot of suspension travel, something like 14" depending on what my CVs allow. The tyres will be very big as well, 35" diameter. From what I'm being told it's important for the wheels to stay flat to the ground as the wheels bump over obstacles because traction is most important.
RE: What sort of numbers for scrub and castor?
RE: What sort of numbers for scrub and castor?
One OEM who used to pride themselves on their steering and handling has gone into production with an AWD that didn't self centre in various (realistic) circumstances.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: What sort of numbers for scrub and castor?
As I'm putting my design together it looks like various constraints are limiting my options down anyway. E.g. I need the CV centre to be on the kingpin axis to minimise the extension on the driveaxles, that fact is already constraining things.
RE: What sort of numbers for scrub and castor?
RE: What sort of numbers for scrub and castor?
I have to say my progress is very slow. I designed my last buggy with solid axles and that was much easier, just had to set my anti-squat and check my prop shaft angles were ok. Independent is a whole load more work!
RE: What sort of numbers for scrub and castor?
RE: What sort of numbers for scrub and castor?
Work out how much CV plunge you are going to get if the steering axis is offset from the CV axis. Put some numbers to it. Having the steering axis offset from the CV joint in side view will have significant effects. Having the steering axis offset from the CV joint in front view shouldn't be unless the separation distance is excessive ... which it shouldn't be. The practical need for having some "trail" combined with the practical need to have some "caster" usually works out with the steering axis in side view coming very close to the wheel centerline, so you really only need to look at the front-view situation.
If it is an upper-and-lower-A-arm setup, careful selection of the A-arm lengths (i.e. comparable to the length of the CV shaft between joints and at comparable angles) minimizes the CV-joint plunge. Again, it doesn't have to be exact, that's what the plunge is there for. "Somewhere near" should be good enough.
RE: What sort of numbers for scrub and castor?
If anyone is interested, the Milliken textbook actually has a step by step guide to design independent suspension geometry. It gets a little complicated at the end where you need to draw in the instant centre axis and then project those back into 2D for your swing arm mounting points. But with Solidworks 3D sketches you could probably do this much easier, as the Milliken procedure does the whole thing on paper using 2D drawings.
RE: What sort of numbers for scrub and castor?
BUGGAR, I'm using the spindle from a Mercedes Vito. Reason is that I bought a job lot of parts from a company that abandoned their off road project, and that's what they gave me. The parts were already customised to match up together, included narrow diffs with lockers (narrow to allow for long suspension arms), wheels with the Mercedes PCD, driveaxles all matched up to work together. There's a pair of custom uprights in that job lot, but I don't have to use them, they are set to zero scrub radius and zero castor, which the company said was because they were going to use full hydrostatic steering.
RE: What sort of numbers for scrub and castor?
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: What sort of numbers for scrub and castor?
RE: What sort of numbers for scrub and castor?