Homemade bump steer kit?

[Flieger]

OK, I was typing while you posted.

Maybe it has something to do with using double-wishbones on the tube frame cars vs. the A-arm and strut on the 911s?

Whatever, I am not trying to ruffle feathers.

Happy Holidays.

[Flieger]

BTW, is that an Ultima in your photo? What kind of race car were you talking about (just curious, not talking about anti-dive)

[Kevin Stewart]

actualy i have both a older 911 with a 3.6 and a outlaw. I thought about it for a minute and we are both right i was thinking with a upper a frame. with a strut car its done different, no feathers ruffled, Kevin

[KSUGreggy]

soooo....does anyone have an opinion about the elephant racing vs. rebel racing bump steer kits?

[Kevin Stewart]

can you post pictures?

[KSUGreggy]

REBEL:


ELEPHANT:

[Steve W]

Although the idea is simple, by the time you source all the parts and fab the parts you can't buy, you'd have spent almost as much if not more than it would be just to buy either system, not to mention your time. I don't think you can go wrong with either, both systems are designed by Chuck and Clint, both very smart engineers.

My experience is with the Rebel Racing kit, and it's all top quality components, from the Kevlar/Teflon Aurora rod ends to the 14 mm grade 12.9 bolts. With the optional weld on second steering arms shown below, which puts the bolts in double shear, there is zero defection or stress due to moment torque - 100% reliability. Very easy to disassemble to make adjustments, and as an engineer myself, there's little I would change and how I'd design it.

[Kevin Stewart]

hi for the street or even the track i like the elephant simply because the heim has a cover to keep the dirt out.

but i like the rebel if your gonna use all the spacers because of the stiffening brace and the cotter key castle nuts.

with all those spacer you will have to make sure the bolt on the elephant or the carrot on the rebel are not bent if you have any contact.

but the gold box on the elephant apears to go over the spindle end which would explain why there is no carrot that needs a ball joint end on it.

it aslo looks like the rebel has a finer shim you can use.

so i like the rubber boot on the heim on the elephant and the support brace on the rebel. Kevin

[Chuck Moreland]

Originally Posted by Kevin Stewart

so i like the rubber boot on the heim on the elephant and the support brace on the rebel. Kevin

Kevin, sound like you're liking this kit from Elephant :

[Kevin Stewart]

Chuck , before you posted this i was thinking i would use the one he posted of yours for the street and the rebel for a track/street car, but seeing the one you just posted i would use it that is the best of both worlds. Can I ask if the heim is a teflon heim or is it a restricted mono ball. By the way really nice piece, also are you taking the insert out to weld the support on?, I am really glad you posted, I am sure the original poster is glad to, thanks for your time, Kevin

[Walt Fricke]

About two years ago I noticed a buddy had welded in a bottom plate in this application. Looked like the way to go if the bending arm from the long cantilever made one worry. I should have known Chuck and others would come up with that as well. One does not hear much about the unreinforced versions of these long tie rod connectors fatiguing or flexing or getting bent, but it sure looks like they could in hard track service coupled with some offs, curb jumping, and whatnot.

Next the question would be how many lightening holes can one drill (note the gusset in the picture of the green Bilstein mockup) in this part and still have decent strength? Unsprung weight and all that.

Chuck - why is the reinforcing plate bolt hole oval?

These are serious pieces, an order of magnitude plus above the old standby Weltmeister thick aluminum washers to raise the rack. I think those are the cost effective way to go with a street car if it has been lowered. All you need to do is have the front realigned after installing those. These beauties are for highly tweaked track cars.

Walt

[sc_rufctr]

Originally Posted by Walt Fricke

... Next the question would be how many lightening holes can one drill (note the gusset in the picture of the green Bilstein mockup) in this part and still have decent strength? Unsprung weight and all that...

Walt

Lightening this part wouldn't compromise its function as long as you're sensible.
I would be comfortable removing about 35% of the weight by drilling appropriate sized holes through the middle.

Leaving about 1/2 inch spaces between the outer edge of each hole at a minimum.

Why not make a clamp on version from Aluminium?

[KSUGreggy]

Originally Posted by Kevin Stewart

hi for the street or even the track i like the elephant simply because the heim has a cover to keep the dirt out.

but i like the rebel if your gonna use all the spacers because of the stiffening brace and the cotter key castle nuts.

with all those spacer you will have to make sure the bolt on the elephant or the carrot on the rebel are not bent if you have any contact.

but the gold box on the elephant apears to go over the spindle end which would explain why there is no carrot that needs a ball joint end on it.

it aslo looks like the rebel has a finer shim you can use.

so i like the rubber boot on the heim on the elephant and the support brace on the rebel. Kevin

The rebel can come with a rubber boot so that's not a big issue. I'm wondering which would be the most stable for a 19mm raised spindle. This is for DE/Autox car. I like that the rebel kit uses a tapered bolt through the steering arm. I'm curious how the gold box on the elephant adds stiffness to the assembly, I haven't seen a photo of it installed.

[Chuck Moreland]

Kevin, it is a teflon lined precision rod end from Aurora. We do pull the insert for welding.

Walt, the hole is oval so that it can accomodate differing spindle heights. Taller spindle heights need bigger spacers. The bolt is not parrallel to the strut, and the oval accomodates the changing bolt/strut distance.

Did I just disclose another soon-to-copied design feature?

We offer kits with bolts and spacers sized for 19mm, 30mm, and 40mm spindle heights and one could customize that for virtually any height.

Yes some material could be removed from the center. However the arms aren't especially heavy and the 'holes' even less so.

[911st]

I suspect the amount of bump steer adjustment has more to do with how much one raises the spindle on the strut than how much one lowers the car.

The RSR struts are 19mm and the 930 seems to have the steering rack raised something less than 13mm already. One might suspect some correction will be needed but not as much as for a strut that has raised the spindle some 35mm.

Adding the reinforcement would keep the steering arm from receiving twisting forces from steering input and braking forces that probably want to pinch the steering arms together.

I wonder how much twisting force the arm receive from the cantiliver effect of a bump steer kit?

I would guess we might get some 50 ft lbs peak thought the leverage of the steering wheel. Then that is multiplied by about 3 through the steering rack for about 150 lbs against about a 2" lever at most created from the bump steer kit. So maybe 25# of twisting force. I have not taken any engineering classes so I could be way off here. It would be interesting for someone to run the numbers add see if adding a second arm is a perceptual need or an actual need.

Braking might create the most load but I think the pull on the steering wheel I have felt is more in a full on corner from the forces created by caster than if one front wheel hits something slippery under full stop. However I have noticed the pull at the steering wheel is higher on a turbo with its increased scrub radius.

Interesting.

[Walt Fricke]

Thanks, Chuck.

Peter:

I think it might be a design challenge to come up with a clamp system which resisted rotation as well as a few welds will. The strut at that point is cylindrical, nothing I think to key on.

I have wondered, for radical changes, whether one could chop off the steering arm, and use just a piece like Chuck's. Perhaps the torsional forces on the strut tube would be too large? Steering arms historically have been stout forgings rather directly incorporated into the hub.

Heating and bending the stock arm used to be the method of choice. Seems that if you do more than just a little bending you reduce the radius of that arm, though. That should quicken the steering a bit, but perhaps that introduces other changes - Ackerman, for instance, which you might not want.

Walt

[KSUGreggy]

does anyone have photos of the elephant system shown above installed? I'm curious as to how the gold "box" for lack of a better term, braces around the steering arm on the spindle.

[burgermeister]

I once measured my bump steer (ride steer). For reference, the steering rack was not centered for this measurement. I later discovered that the steering wheel was installed 1 spline off by the PO and tie rods were used to re-center the wheel, leaving one tie rod long and the other short. The curve becomes a wee bit less of a straight line with the tie rod at the correct length.

Ride Steer / Bump Steer

Note that tie rod angle (changes as a function of suspension travel) has little to do with ride steer.

It seems to me the ride steer is a form of negative feedback - as the car rolls as a result of lat accel, some steering input is taken out by the suspension movement. Porsche probably did this to help keep people like me (slow-reacting drivers with a +- 0.3g sensitivity internal accelerometer lacking any yaw functionality) from killing ourselves in their cars . Others blessed with more cat-like internal instrumentation can probably benefit from reducing said ride steer ...

[Kevin Stewart]

burgermeister
i disagree with you again. the angle of the tie rod arm has everything to do with bump, if your wheel is going out then in you have a problem. you always want some bump out. i have looked at your board a couple times and still can not figure how your measureing it with no marks on the board as this isnt something you can measure to the ground may be i didnt read it but it is also import that the spindle hieght is exact. if the board is not perfect level at all times your measurement will be wrong. in a perfect world the lower control arm from pivot to center of ball joint will be in the exact same height and length as the inne and outer center of the heim/tierod end this will create zero bump, and there is even more to it then that if the two are exactly parallel the ackermen will be off creating toe in as you turn at static heigth. caster can also play a part as you give more caster it moves the spindle and changes the heigth of the tie rod end heigth. Even the if the car is not at its exact ride heigth can play a part. Kevin

ps i dont wanna argue with you, you can do it your way ill do it mine. there is just more to bump then what people think.

[burgermeister]

Kevin,

No argument taken

We're saying the same thing in some respects: The angle of the tie rod relative to the lower control arm, as well as length differences of the tie rod compared to the LCA, are of paramount importance. I'm just suggesting the angle of the tie rod relative to ground is meaningless.

I'm measuring suspension travel with the angle finder level stuck to the bottom of the LCA. There is another one stuck to the tie rod which I used for unrelated purposes. Converting the angle to travel in mm is pretty accurate. Differences in dial indicator measurements divided by the distance between dial indicators measure steer angle (in radians). So there's the x & y axis of the graph.