RSR struts raised spindles and bump steer

[RayM]

My car is sitting about 1/2" below Euro height. NO bump steer kit yet but I'm gonna do something so I don't get tennis elbow with the feedback through the steering wheel.

I am considering two options 1) replace stock boge inserts with bilstein sports and a bump steer kit with washers or 2) Bilstein RSR struts, since the RSR has spindles that can be raised, can I do without a bump steer kit or would I need a drop link bump steer kit. I thought of the RSR strut so I can have the option of coilovers in the future and lose the torsion bars. Any advice on that too as well as spring rateswould also be appreciated Thanks in advance

[Jeff Alton]

The RSR strut spindle is already raised. They come in 12mm and 19mm. This makes your bumpsteer problem worse. You will definately need a bump steer kit of some direction. I used the long srp one and extended it some more and welded and gussetted it to the steering arm.

Cheers

[Tyson Schmidt]

Like Jeff said, raising the spindles makes the tie-rods even less parallel with the lower control arm, making bump-steer even worse.

With raised spindles, it's a good idea to have the steering arms bent ala 935-style to get them back to proper geometry. You may still need rack spacers too, depending on how far the arms are reconfigured. Most places just bend them the same amount the spindles are raised, which give you stock bump-steer, which is still too much, IMO.

[Steve@Rennsport]

Ray:

Depending on your precise ride height, you can use the Bilstein inserts with a rack spacer kit.

If your car is that low,....you should consider the RSR raised spindle struts for 3 reasons:

1) Restoration of lost suspension travel from lowering

2) Raised front roll center location for reduced lateral weight transfer and less tendency to pick up the inside front wheel in a corner

3) Improved bump steer curve although you'll need an adjustable bump steer kit such as the Elephant one

One thing: the regular RSR struts as delivered fromt Bilstein have terrible valving and we always redo that for MUCH improved road-holding.

Regarding coilover conversions: one needs a complete & triangulated roll cage in any car that will be converted to coil springs. This is required to properly stiffen the chassis due to the different load placements in the body. There is a LOT more to this than meets the eye,....

Spring rate choices depend on wheels/tires, vehicle weight, aero package, and how the car is used.

[Steve@Rennsport]

Originally posted by Tyson Schmidt
Like Jeff said, raising the spindles makes the tie-rods even less parallel with the lower control arm, making bump-steer even worse.

With raised spindles, it's a good idea to have the steering arms bent ala 935-style to get them back to proper geometry. You may still need rack spacers too, depending on how far the arms are reconfigured. Most places just bend them the same amount the spindles are raised, which give you stock bump-steer, which is still too much, IMO.

Hi Tyson:

One makes Ackermann changes when the steering arms are recurved (and therefore shortened) so thats something to consider here,...

I really like Chuck's bump steer kits for their adjustability.

[widebody911]

Originally posted by Steve@Rennsport
I really like Chuck's bump steer kits for their adjustability.

I concur

[Jeff Alton]

Take Steve's word the valving, he did mine and they are great! Even with my ERP crossmember (which raises the rack quite a bit) and the SRP extended bumpsteer kit, I still lengthened the bumpsteer kit a little.

Then I made a gusset and welded it to the arm. That little trick I learned from Tyson. I saw a pic he posted once on the gusset after Craig had his bumpsteer kit fail at the track. thanks tyson

Cheers

[RayM]

Thanks a lot guys, great info. A LOT more there than meets the eye. As I peer over the edge, switching to RSR struts looks like a very steep muddy slippery slope. Thanks for keeping from sliding down that one!

I think I'll be going with Bilstein inserts w/ bump steer kit and since I am putting on a Ruf front chin spoiler I'll be raising it up a little closer to euro height so I don't rip it off. Car might see a DE event but mostly street.

Tyson we miss you in So Cal. You actually did the PPI on my car last July. Best wishes in your new endeavors.

[Jack Olsen]

Originally posted by RayM
My car is sitting about 1/2" below Euro height. NO bump steer kit yet but I'm gonna do something so I don't get tennis elbow with the feedback through the steering wheel.

Just so you know, the wheel jerking in your hand doesn't have much of anything to do with bump steer. The term refers to changes in the wheels' toe angles that take place during the suspension's travel. The tell-tale signs would be that the car behaves as though you've given additional steering input during a turn when in fact you're holding the wheel steady -- because the car's suspension is compressing and uncompressing due to changes in the road surface (namely: bumps) and the toe angles are changing in less-than-optimal ways.

At least, that's how I understand it.

[Tyson Schmidt]

Originally posted by Steve@Rennsport
Hi Tyson:

One makes Ackermann changes when the steering arms are recurved (and therefore shortened) so thats something to consider here,...

Yep, and in a good way, since it increases Ackerman.

Porsche used carefully calculated bump-steer to achieve Ackerman, rather than use the traditional steering geometry method. (The car toes out progressively with the compression of the suspension. This makes the outside loaded wheel turn in slightly less than the driver intends, which is much more predictable to the driver. Also helps the driver avoid over-correcting) The reason was to tame down the twitchiness of the original short wheelbase cars. (It of course stayed that way pretty much unchanged through '89.)

So if you eliminate all "bump-out" (toe-out under compression) bump-steer, you need some Ackerman from the steering geometry.

[Tyson Schmidt]

Originally posted by Jack Olsen
Just so you know, the wheel jerking in your hand doesn't have much of anything to do with bump steer. The term refers to changes in the wheels' toe angles that take place during the suspension's travel. The tell-tale signs would be that the car behaves as though you've given additional steering input during a turn when in fact you're holding the wheel steady -- because the car's suspension is compressing and uncompressing due to changes in the road surface (namely: bumps) and the toe angles are changing in less-than-optimal ways.

At least, that's how I understand it.

Jack, you're spot-on in your assessment of what bump-steer is.

But RayM is actually correct about kick-back.

One-wheeled bumps will turn suspension jounce into steering wheel movement when you have bump steer. Reducing bump-steer will reduce these kick-backs through the steering.

So will stiffer shocks and springs, simply by reducing the amount of suspension travel, and therefore all the geometry changes that go along with it.

[Jack Olsen]

Originally posted by Tyson Schmidt
RayM is actually correct about kick-back.

I stand corrected, then.

[Tyson Schmidt]

Originally posted by Jack Olsen
I stand corrected, then.

No please, have a seat, you look exhausted.


Hey, I'm still proud of your explanation of bump-steer. It's better than my explanation would be of (insert screenwriter vernacular mumbo-jumbo here)

[Bobboloo]

Originally posted by Tyson Schmidt
No please, have a seat, you look exhausted.

Bucket-o-fishhh!





Just a little sound effect for your, ahem dare I say, stand-up bit.

[Wil Ferch]

Wait a minute !!!

Since the original poster has his car lowered by only 1/2" below Euro...wouldn't this be the rare "sweet-spot" to cost-effectively use rack spacers ( limited to 13mm thickness due to space limitations)...to regain stock steering geometry??

Raised spindles speak to getting full range of shock motion and re-establishing the original camber curve, roll centers, etc. This is independent of the bump steer ( or "parrallel-ness" of the steering arm) issue. The rack spacer at 13mm nicely matches the amount of lowering done to his car. The spendy ERP or Elephant bump steer kits allow a fine tunability if the lowering is much below 1/2".... no ?????

-Wil

[Tyson Schmidt]

Wil, the accepted "Euro" ride height is actually quite a bit lower than factory spec.

That said, the rack spacers are fine with stock spindle height. You'll have near-stock bump steer curve. Still not ideal, but at the stock compromise.

But with raised spindles, the bump steer gets worse no matter what height the car is at, because when you raise the spindles, the steering arms move with them. That makes the bump-steer curve even steeper, due to even less parallelism between the tie-rod and the lower control arm.

[analogmike]

Originally posted by Tyson Schmidt

But with raised spindles, the bump steer gets worse no matter what height the car is at, because when you raise the spindles, the steering arms move with them. That makes the bump-steer curve even steeper, due to even less parallelism between the tie-rod and the lower control arm.

I don't think so. If the car is set to the same ride height with normal and raised spindles, the spindle and steering arms are at the same place, no difference.

[Tyson Schmidt]

Originally posted by analogmike
I don't think so. If the car is set to the same ride height with normal and raised spindles, the spindle and steering arms are at the same place, no difference.

Right.

But the control arms are not. It is the difference between the arc of the outer tie-rod end and the lower ball joint that cause toe changes as the suspension moves.

So if you move the lower ball joint farther away from the outer tie-rod, without moving the inner tie-rod end farther away from the lower control arm's inner pick-up point, you make bump-steer worse.

[lateapex911]

Tysons right, IMHO. I built a set of blocks so I could do all the under car setting and alignment in my shop while looking at things from unde the car as it sat on it's wheels.

When you crank down the front T bars, you can watch the control arms go from the outer ends down, to level to up as the ride height drops. Of course the steering linkage does the same.

Which means that bump steer worsens. If that outer tie rod is higher than the inner, there will be issues, no matter how it results. Moving the inner end up solves it, which means the rack needs to move up relative to the body, OR some other method needs to occur.

[Tyson Schmidt]

Close Jake.


It's really just about the relationship between the tie-rod and the control arm. It has nothing to do with their relationship with the ground, or the car, or magnetic North for that matter. Just each other.

There will always be bump-steer. The only way to completely eliminate it, is to have equal-length upper and lower control arms, and tie-rods that are not only the exact same lenth as the control arms, but are also parralel to them.


Outside of that, you're just trying to minimize bump-steer, and get the bump-steer curve close to where you want it, whatever that may be in your application.