I upgraded my 930 to 22mm/30mm solid torsion bars and had the Bilsteins revalved to match. I'm also using Kokeln 22mm sway bars front and rear. For tires it's on P Zero Cs 235/45-17 and 175/40-17. It's a track/DE car that also sees some use on the street. But I don't care about the ride. It's a track car - "run what you brung".

ON the street it's fine. Driving fast on the track, the steering effort is huge compared to what is was with the stock 930 suspension. I'm fiddling with the bars but am not finding much improvement in the steering effort. I'm now at full soft on the front and mid way on the rear.

Out of curiocity, I'd like to hear what works for others. What are you using for bar sizes and where do you have them set? I wonder if I over-sprung it?

 

Peter,

I have 23/31 combination (I'd probably go with 33's if I were to do it again)with my car, lowered quite a bit. I found that when I put the ERP tie rod type bump steer kit in the front the steering effort increased noticably. Also, I've found that if there is more than about 1.5 degrees of rake it gets much worse.

I have smart racing products 27mm front and rear bars on the car with the front set in position 3 out of 7 with 7 being the loosest and the rear is in hole 7 out of 8 with 8 being the loosest. The car is very neutral. The ride is surprisingly good and is driven to the track.

 

Now why on earth would the bump-steer kit increase steering effort? I also have the kit. I got all the suspension parts including revalving from Smart Racing Products. Unfortunately, I tried to save a few bucks and got Kokeln 22mm sway bars instead. I really regret that. I'm not happy with them at all. I should have got the Smart Racing bars. Then I could have just asked "where should they be set?" and be done with all the fiddling...

 

I don't claim to be a math expert, but I think and am willing to be corrected that by moving the pivit point (tie rod end mating to the steering arm on the shock) down, you are in effect moving from a pivot that is in the same plane, to one that is now angled. Picture a right triangle where the shock is vertical, steering arm is horizontal, and the new pivot point is the long side (hypotenuse) of the trinagle. I believe that the angled plane requires more effort than if it were in the same plane.

I find that I really like the valving job Smart Racing did, it works very well and yet the car remains compliant rather than crashing over bumps. I have issues with the back of the car being sprung too lightly and occasionally bump the qtr panel with the tire on heavily loaded corners (the downhill at Lime Rock Park is an example).

With the larger 27mm bars you really notice a difference when you move them from position to position where the smaller ones are much less noticable.

 

I agree with Geoffrey's assessment as well about steering effort / pivot angle.

When I first bought the car, I simply had it aligned & lowered with stock suspension. I noticed an increase with steering effort after the lowering.

But subsequent change to the torsion bar (now @ 22/33mm) didn't change the steering effort (or at least I didn't notice any difference).

Geoffrey, I'm a bit surprised about your bar settings... seems like the ratio of front/rear stiffness in your car is quite a bit more than the stock setting then? And that might translate to more understeer (as you have increase the front stiffness compared to rear)?

 

So what you're saying is that after lowering you should move the rack up to be back in the same plane as the steering arms rather then move the attachment point on the arms down to the rack? I suppose that makes sense...

 

Here's my set up for the track:

Lowered, 18" BBS magnesium race wheels, 23 and 30 mm torsion bars, 22 mm adj. front and rear sway bars, urethane bushings thru out, adj. spring plates, Koni yellow sports, Bilstein HD front struts, and Camber Plates.

The sway bars are set as tight as possible in front and loose as possible in the rear. With fresh slicks, it sticks like glue. As the tires age, it has a tendency to push, which I counter by loosening my front sway bar. Unfortunately, the sway bars are Weltmeister, so there are no markings to go by. Won't be buying these the next go around.

I haven't found any differences in effort to turn the wheel and I have a really small Momo steering wheel for leg clearance. Maybe I've gotten used to it?

 

What have you done about bump-steer? Maybe the bump-steer kit is the problem after all...

 

Hi Peter:

This has been an interesting thread,....

I was asked to comment on steering effort so here goes,....

All things being equal, steering effort is determined by:

1) Front tire width and design/brand

2) Tire pressures

3) Camber settings

4) Caster settings

5) Front upper strut bushings

6) Front strut condition

7) Ball joint condition

Swaybars, being transverse torsion bars, usually have a negligible effect on the effort required to make a car change direction. Same goes for springs (torsion bars).

PT mentions his car's steering effort went up after alignment. I would ask; what is the car aligned to?

If tie rod angles get silly, the steering effort is altered but bump steer issues take center stage in cases like these. Using the ERP bump steer kits can reduce steering efforts slightly due to reduced friction at the junction of the steering arm and tie-rod.

Same goes for using the ERP front suspension and the spherical bearing in place of the factory ball joint.

Lastly (for Peter),....Let me know when you want me to send you a set of SR swaybars,... You will be VERY happy.

 

Steve,
First of all - thanks for your recommendation on my suspension setup
And, I have pretty much replaced all the components - shocks, torsion bar, ball joints, mono *****, spring plates, ... except the sway bar. Surprisingly, I find the car quite neutral in most tracks from the Glen, to Mosport to Tremblant.

Alignment-wise: I lowered the car by ~6cm than factory setting (using factory method of calculation). Front camber -1.5, castor 6 degree, toe 0 pressed. Rear camber -2, toe 15".

Other than the lowering, I didnt think this setting is overly aggressive though I (hopefully) set it to more a track/DE car than street. In fact, I do get fairly bad bump steer as expected, so ERP is the next thing (especially if it will lower steering effort!)

 

Hi Peter:

Your alignment settings looks fine to me, but I would reduce caster to 5 degrees if steering effort is a concern.

We used 4-5 deg on our 935's to reduce steering effort and those cars used a 12"-14" wide 16" slick.

Its really critical to bump steer the car on each side and correct that as needed. This is one of the main differences between an average handling car and a truly great one. (the other one is shock valving).

 

Interesting. I think I recall my mechanic saying he set the caster to the max -- whatever that is. I think it was also camber of -2 deg all around with some toe in the rear and a bit in the front. Maybe I'll get him to back the caster off a bit. I mean that is what it feels like. Too much effort=too much caster.

When the PZCs are done this weekend, I'm switching to Toyo RA-1s 235/40-17 and 275/40-17. I'll probably have to raise the front a bit as the Toyos are quite a bit shorter. Maybe I can get him to reduce the caster while he's at it. The PZC 235/45s were a pain anyway as they are really too tall -- always rubbing and binding.

 

Peter, the 235/40/17 tires are 24.4" in diameter and the stock is 24.9" in diameter. I've had some issues with the smaller ire size on my car. 235/45 are better, 245/40 are better, but both are hard to get in R compound sizes.

I've been running about .7-.8 degrees of camber in the rear with 315/35 tires (wider tires need less camber or so I'm told) and about 1/32 of toe in.

Front has been about 1.5 degrees negative camber, 5.5 degres of caster and 1/16 toe in.

ERP adjustable tie rod ends have been invaluable in getting rid of the bump steer. The rack spacers just don't do it for a significantly lowered car.

 

Solved it. Full soft on both front an rear bars. Go figgure. Less is more. This is for 22/30mm torsion bars... I may fiddle more but it's pretty good.