Reducing anti-dive: Positives/Negatives?

69427

69427

The Artist formerly known as Turbo84
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Clinging to my guns and religion in KCMO.
Just coming up with my list of winter projects (now that I'm back in the midwest and expecting to be snowed in for a while). One item I'm curious about is the affects of antidive. I've got some decent rate front springs on the car, and don't know how much the anti-dive is doing for me. I'm also curious if I'd see any handling benefit from reducing the amount of anti-dive in the front suspension. My suspension textbooks are pretty slim on the downsides of anti-dive, but also note that most racecars don't use anti-dive. If there were no downside to anti-dive I would think that it would be added to racecars as a "freebie" (whether it was needed or not).

So, any thoughts on this topic?

Thanks,
Mike
 
The way to add more anti dive in your setup is to lower the rear upper a arm mount. What this does is it increases that arms angularity and makes the spindle rotate more than it does now. Rotating the spindle against the rotation of the brake (forward) gives anti dive.
The rotation of the spindle will try to pull the upper arm down, lifting the front of the chassis.
The stock C4 susp. has quite a bit of anti dive, you can see it in any pic of it. I don't know how much it has but I wouldn't be surprised if it was as high as 30%.
A problem is that this rotation of the spindle also messes with the tie rods and as such can (and probably will) induce bump steer like destabilizing effects.
 
Twin_Turbo said:
The way to add more anti dive in your setup is to lower the rear upper a arm mount. What this does is it increases that arms angularity and makes the spindle rotate more than it does now. Rotating the spindle against the rotation of the brake (forward) gives anti dive.
The rotation of the spindle will try to pull the upper arm down, lifting the front of the chassis.
The stock C4 susp. has quite a bit of anti dive, you can see it in any pic of it. I don't know how much it has but I wouldn't be surprised if it was as high as 30%.
A problem is that this rotation of the spindle also messes with the tie rods and as such can (and probably will) induce bump steer like destabilizing effects.
Click to expand...

I presently have less anti-dive than stock C4 settings. When I was putting the new suspension on I noticed the significant angle of the upper A-arm mounting holes in the stock C4 cradle. I built my A-arm mounts with 2 hole settings so I could get back to stock C4 anti-dive if the present reduced setting didn't work out. I haven't noticed any downside to the reduced anti-dive, and was thinking on reducing it further.
 
TT,
69427 asks about removing anti-dive not adding. I think the first issue is how are you going to use this car? I know where your coming from on the reading end. Most of what I have read is that in a race environment a more neutral setup is desired. Takes the mystery out of effect and cause I guess. But remember racing still requires different setups for different tracks. So if your going to street drive this car, your still chasing your tail. Your gains would be minimal on the road in my opinion. If your able to adjust your settings (angle) that's the way to go.
 
LOL! I did too!
69427,
So I guess your using a stiffer combination that offsets any dive. I'm thinking that when you change the angle you also reduce camber during cornering. That is when your suspension compresses and the spindle turns or rotates when cornering. The more caster or UCA angle will cause the spindle end to raise on the loaded side giving more negative camber. So as you reduce UCA angle you reduce the total negative corner cambering. Not sure where the line is? I'm sure caster effects the total camber more than UCA angle, but it is still part of the total.


"Excessive caster angle will make the steering heavier and less responsive, although, in some circumstances, "large caster angles can be used to improve camber gain in cornering."
http://www.rbevins.com/BRR/ILMS_Setup_Guide/Setup_Guide.html

Pyrometer tests maybe?
 
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I thought the dive comes in because of the heavily biased to front braking from the mauf. for safety. A prop valve to crank in a bunch more rear bias should cause less dive i would think.
 
it's the other way around, because of "weight transfer" towards front and that's why most of the weight is on the front wheels and you need more brake there and less in the rear so that you have max. brake effort without the wheels locking up. The weight transfer is always there, however the suspension reation is five and that can be reduced/eliminated with suspension geometry.
 
I always thought that decreasing anti-dive was done to improve bump compliance under hard braking, at the expense of requiring higher spring rates overall.
 
If the front doesn't dive much and being front braking is about 70%, doesn't that affect more pressure on the tires and increase braking power?
 
Bad Bird said:
I always thought that decreasing anti-dive was done to improve bump compliance under hard braking, at the expense of requiring higher spring rates overall.
Click to expand...

That's my perception, too.

I took a couple Skip Barber driving schools when I was younger. They stressed threshold braking, and the traction circle, combining braking and steering. I'm trying to see if I can get slightly improved braking/cornering traction by "freeing up" the suspension by further reducing the anti-dive percentage.
 
Here's a picture of the upper A-arm mount. You can just see the unused hole above the left (front) bolt. That's the original front mount when I initially was just duplicating the stock C4 geometry. That just looked like too much anti-dive for my taste, so I drilled another hole to reduce it. I might drill another hole over the winter to reduce it further just to see if I see any benefit or negative result.

IM001832.jpg
 
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