anti squat

[smcferran]

what is a good starting point for a % anti squat
at the moment i have 32%
this is asuming the cog of the car is at the middle of the flywheel

n.b.
car is an escort mk2

does more anti squat = more grip?

Thanks
Stephen

[Bunman]

Hi Stephen, are you doing an initial set up or are you trying to get rid of a handling issue?

What do you use the car for and what is current spec / suspension / engine box etc. I will try and point you in the right direction.

[carl talbot]

Originally Posted by smcferran

what is a good starting point for a % anti squat
at the moment i have 32%
this is asuming the cog of the car is at the middle of the flywheel

n.b.
car is an escort mk2

does more anti squat = more grip?

Thanks
Stephen

anti squat is mostly to do with the rear suspension geometry
there is a lot of good, easy to understand info on here http://www.racetec.cc/shope/

[smcferran]

thanks
it is a tarmac rally car

with a warrior engine type 9 box

i have a base setup which has the lower link arm pretty much level

front pivot 234 mm above ground
rear pivot 243mm above ground

top links
123mm apart at front
142mm apart at rear

height of instant center 181mm above ground

with this setup
it might only be in my head but
the car is very light of the rear under breaking and then wants to break (spin off) on initial throttle application
any help would be usefull

[PumaWestie]

The sensation that you are experiencing under braking is brake hop as a result of too much anti squat and / or too softer rear dampers which is effectively the opposite of anti squat. AS is really for dragsters and not recommended for circuit cars due to the axle binding up in roll. If you car is a tin top, then the CoG height will also be much higher than the crankshaft centreline in any case and thus your calculations are not giving the real picture

[carl talbot]

Originally Posted by smcferran

with this setup
it might only be in my head but
the car is very light of the rear under breaking and then wants to break (spin off) on initial throttle application
any help would be usefull

are you sure its not excess dive under braking ?

[smcferran]

maybee dive
but ive got 250lb front springs
which is quite hard

could it be excess front camber / caster
the front really bites and turns in well
its just the rear which wants to swing out

so to recap
what it the approx cog height of a typical tin top like an escort mk2
what percentage or range antisquat is to be expected

[wight jr]

its not got much to do with your COG,
do your run a anti roll bar at the front, is your front dampers up to the job, (does it dip on turn in) are you running a high rear ride hight, are you running stiff rear springs?????

[smcferran]

ride height is as normal
it does dip and i run an arb
front springs are probibly as hard as i can go
local supplier wont sell me any harder
he says i run harder springs than anyone else

rea springs are fairly normal
180lbs
i think the issue is with the rear 4 link setup

ive helped (i think)
by narrowing the front pick up points
previously the inst center was behind the car
but i dont know if this was correct or not

[Rob Stevens]

I don't think that the anti-squat will have much to do with the issue you have, sounds more like a spring/damper issue, I'd suggest the wheel rates are checked to make sure they are sensible, I'd also have a look to make sure you haven't somehow introduced bump steer into the front or participially rear suspension. Also just confirm that your rear bump and droop travel is ok.