IRS caster -/+

[Westcoastrfg]

Why am I concerned w/ positive or negative caster, I think it should be neutral... RFI from my island please.

[Westcoastrfg]

What an island I find Sally, specs say -.125 to +.80, I have it, But why?

[mikedc]

"What an Island I find Sally"? Um . . . Is that some kind of auto-correct text error?


The big reason for caster in an IRS is for anti-squat.

On launch, the rear tires are trying to claw their way forwards. But the body doesn't want to move (inertia). So if there is caster in the rear geometry, then the wheels' attempt to pull themselves forward in the wheelwells is the same motion that raises the rear of the body upwards.




If you are struggling to visualize it, then try picturing it in the reverse - imagine that the rear wheels are moving forward as they go up (into the wheelwells). Imagine it being more exaggerated, like the wheels move forward at a 45-degree angle as they go up.

Now when this imaginary car tries to launch at a dragstrip, the body rears back (sinks down in back) and that lets the rear wheels claw forwards without moving the body forwards. So the wheel's forward pulling action is trying to pull the rearend of the body down when the car tries to launch. BA-A-AD.

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BTW that whole build looks really interesting.

Modern Mustang diff?

What parts are you using to fab the suspension itself? Nice alignment cams.

[Westcoastrfg]

Sometimes as I build my 65' Mustang "Sally" I feel isolated on an island. That is why I started a build post on pro touring, some humor for the post. I have a 2nd gen coyote, 6 speed, and IRS from Midway Mustang and a C6 on the four corners. I am building a full 11g. Chassis with ridetech coilovers to date. There are 3 dots on the lower control arm hostel that I marked plumb, 1 full +, 1 "0"' and 1 full -, caster change moves the arm on an angle forward and back. I have the C6 spec sheet parameters covered in movement for alignment but could not wrap my head around the need, thank you for the explanation.

[David Pozzi]

Rear caster affects the outer toe link height relative to the inboard link mount. This has a HUGE affect on toe change when the wheels move (Bumpsteer).