Anti dive and anti squat

[Group3JDatsun]

Hi y'all,

I'm currently trying to wrap my head around how this geometry applies to my suspension.

MacPherson strut front end and anti-dive. As far as I understand, to gain more anti-dive, you need to move the front of the radius rod up in the mount. Ok, fine......but why? I'm sure there's moment diagrams for this, but I can't seem to find any - they're all using double wishbone. I think I've asked this before, but if you move the front of the radius rod up in the mount, can you drop the back of it....ie can you re-mount it below the control arm for the same effect (given that it seems to be all about angles).

Semi-trailing arm rear end and anti-squat. Ok, from what I can understand, you want the front of the trailing arm (ie the pivots) to be up - ie the arm slopes from a high front to a lower back. Is this correct? I'm 99% sure the answer to this next question is totally obvious, but I'll ask it just in case I'm wrong - other than moving those front pivots up, is there any other way to get anti-squat (other than stiffer springs of course).

Cheers

[Matty]

I won't claim any expertise, i'll just add my 2c...

dive and squat are the result of a torque moment being applied to the suspension.

as we know, a moment is the product of a force and a radius arm. The resultant deflection is determined by the stiffness of the system, which is a function of the spring rate.

The force is the horizontal friction force generated at the tyre/road interface. this can't change (without affecting braking or acceleration grip ability).

So the only other factor to work on is the radius arm: the closer the pivot line goes to the contact patch of the tyre, the less the torque moment that can be generated.

hope that's some food for thought...

[Billzilla]

Nah, TIm, you move the front of the radius rod down to increase anti-dive on the front.
Think of the bottom of the strut pulling against the rod and the angle at which that happens.
If you angle it up more at the front, it'll tend to pull the bottom of the strut up as well. If you make it flatter so that under brakes it angle up from the front to the bottom of the strut it'll tend to pull the bottom of the strut down, which is what you want.
You can make up simple spacers to try all this to find what you like.

[Group3JDatsun]

Matty, thanks heaps for that, it was actually EXACTLY what I needed to visualise it. :D

Bill, doh!!!! I see. So you can use spacers......interesting. This is something I'm going to have to play with. What do you know of the rear anti-squat side of things?
BTW, love you comment at the bottom. here, here!!!!!

[Billzilla]

Not off the top of my head, but I think it's pretty much the same sort of thing but around the other way, to lift the rear.
Best have a jolly good read of some Carroll Smith I think!
Tune to Win would be a good place to start.