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I was reading a fantastic article on anti-squat in RC cars (all the concepts apply to full sized cars) the long and the short of it is that anti-squat is the angle at which the rear suspension travels in relation to the road. If the suspension travels perpendicular to the road there is no of anti-squat. If the suspension travels back slightly as it travels up there is anti-squat and if it travels forward as it travels up there is pro-squat. the effect of anti-squat and pro squat are as follows: (Copied from the web site)
The Effect of Anti Squat Angle Changes
Increasing Anti-squat Angle
1. Increases rear traction during acceleration.
2. Reduces off-power traction.
3. Best used on smooth and/or slippery tracks.
Reducing Anti-Squat Angle
1. Reduces on-power traction.
2. Increases off-power traction.
3. Best used on rough and/or bumpy tracks.
A few other subtle effects of anti squat, especially with on-road cars are:
1. On corner entry the rear suspension will resist lifting.
2. If you use a stiffer front spring and have little rear droop may result in less off-power steering.
3. The maximum roll point of the rear suspension is reached faster.
4. Off-power steering mid-corner will be reduced until power is applied.
5. On corner exist the rear suspension resists squatting.
6. With reduced rear weight transfer on-power steering increases as throttle is applied.
7. Reduces rear grip on corner exit.
8. The rear suspension has a better ability to handle large or successive bumps.
How Pro-Squat can affect your on-road handling.
1. With transferring less weight rearward and more weight forward off-power steering improves.
2. Off-power steering increases mid-corner until throttle input is added.
3. With more weight being transferred rearward increases rear grip, but reduces on-power steering upon acceleration.
4. The rear suspension has little or no ability to handle large or successive bumps.
5. Best used on rubber tire setups.
6. Best used on low-bite smooth tracks.
Anyway we have talked here about how Jaguar and other manufactures built in some anti squat by using the trailing arms and other connecting links to change the squat angle as the suspension goes through its travel. In my particular case that is not an option because the wishbone squat angle is dependent on the differential angle and the differential is solidly mounted to my sub frame. So the squat angle can not be changed as a result of suspension travel however because my sub frame is bolted directly to the the spring mount pocket in the front and is shackled in the back I should be able to make those shackles adjustable turning the front mount in to a pivot which would change the angle of my subframe in relation to the chassis and thus allow me to adjust the squat.
Now I know what you are thinking, "by changing the angle of the subframe you are changing the pinion angle in relation to the transmission angle and this will cause drive line issues" Yes this is absolutely a true fact however it is also true that in the real world a set of u-joints can absorb MAX 3º of mismatch with little to no effect on u-joint life and vibrations. In my case my drive line and transmission angles are parallel to begin with so I am at the ideal setting. I did some rough calculations and If I make my shackles adjustable and adjust them about 1" (would never adjust them more than that) I am only increasing my pinion angle by about 1º which means I should be well with in the tolerances of what kind of a mismatch the u-joints can absorb.
I must be telepathic because I know what you are thinking now "if you increase the shackle length it will have the same effect it does on a leaf spring car and you will increase the ride height on the rear end" This also is absolutely correct, but in my case my coil over shocks are also adjustable so I will be able to lower the ride height at the shocks to compensate for any increases in ride height due to shackle adjustment.
I have defiantly thought this through but I am sure I have missed some things... OK probably lots of thing 
, so what do you think?? Also got any ideas of what would be the best way to make my shackles adjustable?? I am thinking rigidity is the most important and that maybe I should just make several different shackle plates with different hole spacings that way I can bolt it in solid but I am open to other options.
Last edited by Daze (10/27/2011 6:38 pm)
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Here is an interesting responce I got to this thread. It came as an email from a friend of mine from Sweden
Håkan from Sweden wrote:
Day,
Your conclusions and thinking is absolutely ok as far I can see! I am impressed about the way you are approaching different new topics with in depth pre studies and research! Gives you a good theoretical background to refer back to the whole time.
To be really honest though I don't think you will have any noticable difference at all with different anti squat settings unless it's completely off as you have it now. On a race car where they are hunting 10th of seconds on lap times on different tracks it might be motivated to have adjustable anti squat. I don't want to sound negative in anyway, but I remember back in the eigthies when I asked a very knowledgeable guy about how to make design adjustments to a front end geometry to avoid anti dive, he just answered: "Are you going to race at Le Mans?" and when I said "No!" he just said "Ok, just forget about it!"
But still you of course got my thinking going about how to maybe build adjustable anti squat into the way you have designed your IRS setup. To not have to worry about changing the pinion angle or ride height I was thinking about making the piece of the subframe where the upper shock mounts is rotateable and then make the inner lower A-arm attachment points also adjustable. I made some rough drawings of what I am thinking about and I also know that the deisgn I am thinking about will mess up some of your existing design, but it is what I came up with that wouldn't be too hard. It might look like you would get everything in bind, but thanks to the sleeves in the new inner attachment bar for the lower A-arm I think you should be able to get it right, the size of these sleeves and where to drill the holes in them will probably be critical.
Håkan
After reading that my thoughts were:
Håkan,
"I am impressed about the way you are approaching different new topics with in depth pre studies and research! Gives you a good theoretical background to refer back to the whole time." That is how I approach everything in my life I am always thinking, some times to the point where I overt think things and it gets in the way of my actual doing however when I am "doing" I usually don't run in to any major issues because I have thought most of it out already.
Your points on the need for the adjustment... or in most cases the lack there of make total sense and I will have to weigh that out when I make my final decision weather or not to make anti-squat adjustments.
As to your solution, that is brilliant!!! Probably more modification than I had in mind, but brilliant nun the less As I think about it the lower mount would concern me the most. Not only would the bracket need to angle but you would also need to be able adjust its for and aft positioning so that the now parallel angles of the upper and lower shock mount could be lined up. The other thing that would concern me is getting the two sides identical. with so much free adjustment on the lower bracket it would be a challenge, not impossible, but a challenge nun the less to get both the drivers side and passengers side brackets lined up.
Still... brilliant!!! would you mind if I posted your info on the IRS forum?? I think others on the board would be interested in what you have come up with.
Thanks!!!
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