Rear Caster angle

[acermotorsport]

Hi All, I am very new to the forum (this being my first post).
I am running a pair of non downforce single seater cars, and have a fairly close relationship with the chassis manufacturer I use.

I am conversant with front caster and the affects it has, but I have noticed some (very few) of the competitors are using as much as 4 degrees of positive caster on the rear uprights, while the majority run 0 degrees, which is a figure supported by the manufacturer I use.

Everybody I ask can give me no definitive reasons why this is used, or any true theory behind it, hence I am asking here.

Is it another method of controlling anti-squat/anti-dive? is it a method of controlling traction? I am limited as to the testing time I have at present so I am keen to realise some of the theory behind it before I try anything... Many thanks in advance!

 

[sreid]

The only thing that comes to my mind is a better bump steer.

 

[acermotorsport]

thanks sreid. I have thought along those lines and cant really see why this would be the reason, as bumpsteer is very tuneable without disturbing caster and the cars in question were initially designed with zero bumpsteer @ zero caster. anybody else able to shed some light please?

 

[patprimmer]

Maybe it is the same as toe in. A slight toe in generating a slight pre load in one direction is better than straight ahead and flopping from one side of the backlash or compliance to the other.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[GregLocock]

Rear axle castor is a mystery to me. We try very hard to make the back end toe-neutral, so 'camber from toe' is a tiny effect.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[Fabrico]

For racing, castor in the rear, or extra castor in the front, is sometimes used to provide increased camber gain while cornering.

 

[acermotorsport]

Thanks all, your input is much appreciated. I will endeavour to post up any findings I may have on the subject after back to back testing later in the year.

Cheers,

Rob

 

[Aday]

Two reasons come to mind.
1. May be packaging to allow a longer rear toe-control arm to reduce rear toe-link loads & result in less toe deflection during cornering

2. Or the opposite reason may be a deliberate desire to induce toe deflection during cornering by increasing rear kingpin moments during cornering. This is done on production cars sometimes...