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Micke · Post by **Micke** » Thu Jun 16, 2005 5:42 am

In theory (for steady state cornering), it doesn't really matter whether roll stiffness is done with AR bars or springs. Either way there's a force pressing the wheels to the ground and the tire doesn't really matter how.

You're right that there's a limit how stiff you should make the springs. Same rule applies to AR bars as well.

My point is (we ARE speaking race cars - right), that you need pretty stiff springs anyway to keep pitch under control.

The tire will be a part of the total stiffness already with moderately stiff springs. As some of obviously are interested in a deeper sight of this you can play around with the following numbers.
Vertical stiffness:
Typical 205/55R16 w 2.0 bar 200 N/mm
Typical 205/55R16 w 2.6 bar 225 N/mm
Typical 225/50R16 w 2.6 bar 260 N/mm
Typical slicks 215/620R17 2.0 bar 300 N/mm

So, as exersice you can reduce the spring + AR bar to the wheel and see how the effective stiffness is affected by the tires.

kterkkila · Post by **kterkkila** » Wed Oct 19, 2005 1:00 pm

Have anybody moved the front lower arm upwards to get roll-center higher?

Micke · Post by **Micke** » Wed Oct 19, 2005 9:55 pm

Yes.
It requires coil overs or bending the torsion bars.

kterkkila · Post by **kterkkila** » Wed Oct 19, 2005 11:14 pm

Hmm, do you mean bending it just a bit to allow the a-arm to move some amount or really radical bending to get past of the steering rack? It would be nice to see some pics about that. That radical one didn't even got in my mind before this.

We have both, coilovers and torsion bars due to the rules of the class. I'd like to dump the bars, but have to keep it legal

Mats · Post by **Mats** » Thu Oct 20, 2005 12:11 am

Ah, but do they state in the rulebook how small diameter bars you at least must have?

kterkkila · Post by **kterkkila** » Thu Oct 20, 2005 12:40 am

Type and material of main springs must remain as original, otherwise they are free. Additional coil-over springs are allowed when their spring rate is less than main springs.

I read rules like that the original type rule is fullfilled when using torsion springs which are made of steel, even if they would been bended in five bends

The spring rate rule cause more headache. There is also mentioned that the mounting plates of springs can be changed or modified to make it adjustable. I'm sure they really though only coil springs when they wrote these rules.. I'm not sure, if it would stay on rules, if use only 50 mm long torsion bars with VERY flexible modified mounting

Mats · Post by **Mats** » Thu Oct 20, 2005 2:41 am

Interesting, they don't say how many coil springs you can add only that they can only have the same or weaker stiffness then the main spring? Do they mean the original stiffness of the main spring or the factual stiffness of the spring mounted to the car?

I'd dare to say that if you only can run 200% stiffer front suspension compared the original it's still way soft.

kterkkila · Post by **kterkkila** » Thu Oct 20, 2005 8:10 am

Sorry for my unclear explanation

So, any stiffness on torsion bars is ok, but the coil springs over the damper must always be less stiff than those torsion bars used simultaneously. Dimensions of torsion bars are free, so they also can be shorter than original, not only larger in diameter.

There can be max. two coil springs in serial in every corner. I guess this isn't important anymore, after knowing that the comparison was done to actual main springs.

Maurizio · Post by **Maurizio** » Thu Oct 20, 2005 12:26 pm

Micke wrote:Yes.
It requires coil overs or bending the torsion bars.

why do you need to bend the torsion bar.

The torsion bar doesn't care at what height the axle is. read upright mounted from top or bottom towards the a-arm. Or am I overlooking something?

Micke · Post by **Micke** » Thu Oct 20, 2005 1:22 pm

We mean move the INNER end of the lower A-arm upwards.
As this is attached to the torsion bar, there will be a misalignment making fitting a bit tough. (OK for guys without power steering)

I can provide the parts needed to move the A-arm. I'll attach a photo.

About Kimmo's problem.
There's for sure nobody in the scrutineering being able to tell the stiffness ratio between the torsion bar and coil spring. So, I'd just go ahead and use the original or stiffest torsion bars available and then tune the suspension with coil overs.

Mats · Post by **Mats** » Thu Oct 20, 2005 1:24 pm

Yes, they're talking about the other end of the control arm, the one where the torsion bar is attached.

Maurizio · Post by **Maurizio** » Thu Oct 20, 2005 11:17 pm

OK, the difficult route, do rules take upside down ball joint option out?

A thought:
What about moving the front pickup point al lot more and the back pickup just a little. Then the torsion bar just has to be bent in a curve. The average height between the pickup points will be the distance be what the roll center moves.

kterkkila · Post by **kterkkila** » Fri Oct 21, 2005 12:15 am

Thanks for interesting picture. That gives some new ideas how to do the modification

Maybe the solution is going to be something like Mickes adapter in the picture, but somewhat higher to allow a-arm move more upwards. Maybe make also several pairs of holes to test which really works on track. Due to the bending effect of long distance, the higher adapter should been welded and boxed as a solid part of chassis.

The upside-down balljoint isn't allowed "original mountings on upright", so everything must be compensated on chassis mountings. To get a-arm in level, the movement should be about 45 mm, which means that the steering is just on the line of the torsion bar. Then there is needs to bend or cut and weld bars to make all of this even possible

Micke is also right that there isn't a guy on scrutineering, who really could say that torsion bars aren't stiff enough comparing to coils

Micke · Post by **Micke** » Fri Oct 21, 2005 12:42 am

Sorry Maurizio,

you want to do just the opposite. Raise the rear end more!

Why?
Anti-dive.

Mats · Post by **Mats** » Fri Oct 21, 2005 2:52 am

Ohh, anti-dive, now we're talking borderline rocket science.
I would definetly go for a very solid "zeroed" suspension before dialing in anti-dive.