IRS....Rear Caster?| Grassroots Motorsports forum |

Opti HalfDork
10/29/16 9:28 p.m.

I was thinking about rear caster angle on an irs.

I know on vipers they have a weird thingamabob to measure it and ive seen specs for it on other cars like the sky/solstice.

But after extensive calculations, in which i thought about it for a few minutes and used my hands to try and visulaize a suspesion through it travel, i dont know why it matters.

All I could think of was it might affect the camber curve or toe during the travel.

So will you suspension gurus school me please?

mad_machine GRM+ Memberand MegaDork
10/29/16 9:53 p.m.

I can only think of it making a difference if the car has some way to affect the toe when cornering, but honestly, my non-engineering brain can't think of a good reason to have any castor in the rear suspension.

Unless it helps tame the rear on a tailhappy car?

aircooled MegaDork
10/30/16 12:17 a.m.

Since castor only real does anything when the wheel is turned, I cannot imagine it come into play much in a rear suspension. The only case I can imagine are those rear steer suspensions which I think have been gone since the 80's.

Driven5 Dork
10/30/16 12:56 a.m.

My understanding is that the rear caster measurement comes into effect when you run a 'front suspension' style setup in the rear, such that the use of anti-squat in the geometry causes undesirable toe changes in bump/droop if the caster is not correct.

sesto elemento SuperDork
10/30/16 8:23 a.m.

It also effects the way the tire responds to a bump. Keep in mind that the car is moving forward and that the bump is inherently wanting to push the tire up and to the rear. Caster seems like a good idea to me. This topic interests me greatly as I am in the midst of a irs swap using ifs as a donor. Lets hear some engineer feedback!