Homemade bump steer kit?

[KSUGreggy]

Has anyone made one? The ones you can buy don't seem terribly complicated to me when you really break them down but maybe I'm missing something. The search on here yielded a mention of someone making one back in 2001 but that was all I found.

If you've got any pictures of your setup that would be good too!

[MichiganMat]

The idea is simple, yes. Its just a changing of the geometry, something you could do with a long bolt and a stack of washers....

But the safe implementation of it is a different matter.

Heres a link to Elephant Racings bump steer kit: ELEPHANT RACING Adjustable Bump Steer Kit, 911 Series

You'll notice the amount of safety that is built into the products (ie a weld-on support bracket, machined extensions, etc). Im not saying you're not up to the task, there are plenty of inventive and capable members on this forum, but if you're going to try this yourself I would advise you do a lot of searching and reading here on Pelican. This is the cars steering we're talking about, and you don't want to compromise that with a weak bolt, a bad mount, or a poor design.

[Kevin Stewart]

You will need a bump steer guage to do it regardles of what anyone says, Kevin

[aigel]

OP is probably talking about the simple kit that Weltmeister sells, which simply lowers the steering rack by installing thick washers and longer bolts. That kit is very inexpensive, so why bother making it yourself???? ... but if you insist, I am sure someone on the forum can give you the dimensions of that hardware. The spacers won't be as purdy, but I am sure you can turn some yourself or use 3 thick washers. The only thing that needs good care if you reproduce that from home made parts is the proper grade and length bolts used ...

George

[aigel]

Here, this is what I meant in my above post.

$13 from Pelican Parts ...

Cheers, George

[KSUGreggy]

Originally Posted by MichiganMat

The idea is simple, yes. Its just a changing of the geometry, something you could do with a long bolt and a stack of washers....

But the safe implementation of it is a different matter.

Heres a link to Elephant Racings bump steer kit: ELEPHANT RACING Adjustable Bump Steer Kit, 911 Series

You'll notice the amount of safety that is built into the products (ie a weld-on support bracket, machined extensions, etc). Im not saying you're not up to the task, there are plenty of inventive and capable members on this forum, but if you're going to try this yourself I would advise you do a lot of searching and reading here on Pelican. This is the cars steering we're talking about, and you don't want to compromise that with a weak bolt, a bad mount, or a poor design.

I completely agree, and I know this is NOT something you want to half-ass. The rack spacers just don't seem like a great idea to me for some reason, just seems to easy though fundamentally they would work I suppose. You can see some photos of my situation below. Is there an easy way to measure on the car how much drop at the end of the tie rod or rise in the rack you need to get to the right alignment? I've been looking at an ERP (NOT elephant) kit but can't find many reviews of it. The Rebel Racing kit looks pretty trick and has adjustability...

Right:





Left:

[911st]

Are you having issues w steering kick back?

There are two things that some think is bump steer that are not.

One is the high level of caster a 911 runs. When on the track cornering this requires a lot of steering effort to conuter. Then with changes in traction that come with uneven surface condition, one feels changes in effort that are a result of caster.

The other is Scrub Radius. This creats leverage on each strut that wants to turn the wheel. On wide 911's like Turbos or cars w Turbo flairs the SR effect is quite significant. You can often feel this at low speeds when braking and it pulls at the steering wheel requireing effort to keep the car straight.

Bump steer is "Toe Change" that comes from suspention compression and extention that comes with the A arm and or tie rod lengthing or shorting with travel. One can have the car a bit low but if the tie rod is at about the same angle as the A arm, toe change on that side may be minimal.

It is more idea to have the A arm closer to level or a little positive mesured at the center line of the ball joint and the torsion bar. Note that the arm it's self can give the impression it is to low or saging even though it is close to netural. If the front is to low, rasing the spendle or using a smaller diamter tire can help ( smaller tire lowers front so less lowering needs to be done w the suspention). Once the spendle is rased there has to be some form of significant bump steer correction as the angle of the tie rod to the A arm are then way off.

Do not be to concerned w the angles of the tie rod to the A arm at rest. Remeber the tie rod angle changes when the front wheel is turned.

Having the tie rod a little positive is a plus if the a arm is close to the same angle. The benifit of having the two close to level or positive is that there will be less effective shortening of them with compression and thus less toe change and less bump steer potental.

I suspect a lot of drivers are feeling the effects of Caster and Scrub Radius thinking it is Bump Steer.

A steering rack spacer and stiffer suspention are the first level of defense. With less suspention movement comes less toe steer.

As noted, to properly correct for bump steer it is not just bolting on a BS kit, it requires adjustment by someone that knows what they are doing. If not, one might end up with more bump steer than they had before the kit.

BTY, I am not sure if a rack spacer kit can be used on a Turbo as there front A arm atachment points are different from a 911's.

Still learning about suspention, just my opinion.

[KSUGreggy]

911st - thanks for the thoughts, interesting thoughts regarding the rack spacers on my car, it is a turbo-look and not a true turbo but I'm not sure if steering boxes are different between turbos and carerras? Please take a look at the videos if you dont mind and tell me if you see anything that looks like bump steer. I know that 911s are high feedback cars but just want to make sure all my bases are covered while I'm under the car this winter fixing my issues with the current coilovers. I have access to a laser bump steer gauge as well as it's owner who knows how to use it so adjusting is not a worry too me, although the ERP kit I'm looking at doesnt seem to be adjustable.









YouTube - KCRSCCA Event #9 Kansas Speedway

YouTube - KCRSCCA 2009 Event #5

[911st]

The TL's have the same suspension geometry as the 930's.

Porsche tried to put in some anti dive geometry in the front by raising the back of the front suspension connection and lowering the front.

Just look to see if there is enough clearance for the tie-rods and rack if it is raised about 7mm. Or, you might post a question on the 930 board if anyone has the rack spacer.

Why not put the Bump Steer gage on your car before you do anything and test to see if you have an issue.

You could then install the rack spacer and or disconnect the end of the tie rod and temporally relocate the end and see if you can make any significant improvement. Then you will know how much space you need from a bump steer kit when you go shopping. Just a thought.

If you want to get carried away, raising the front spindle helps the front by getting the A arm to an angle where camber gain in improved. Most increase the camber when they do this.

What a few have done is go the other way and reduce the amount of camber built into the front. This improves your front scrub radius for less pull at the steering wheel. However, you end up with to little camber if you do this. To correct for this camber boxes are needed to move the top's of the struts further in. The other way is to add some length to the A arms to push the bottom out to get the amount of static camber you need (apx -3).

A lowered 911 puts the front in a position in the camber curve where there can be less gain w compression. One can just dial in more static camber or by improving the A arm angles get about another .5 deg of camber gain. This mod seems to put the front's camber curve more in line with the 930's rear's which is more aggressive than the 911's. A 930's rear suspention because of its better geometry needs less static neg camber to equall a 911's. This depends on how stiff the car is.

[911st]

PS, widening the wheels to the inside improves scrub radius also. If one goes from 7" to 9" fronts it may move the SR in about 1".

A narrow body 911 usually has a better SR than a turbo.

Reducing Caster can reduce cornering effort and the perception of bump steer if you want to experiment.

Not an expert on this, just what I belive from my studies so far.

[Rusty Heap]

Actually I have some of those spacers for sale. Same size and dimensions as the Smeltmeister set in the picture above and made out of aircraft aluminum 6061-T6. You'll have to provide the two 12MM longer fasteners.

The simple spacer kit made a huge difference in my lowered below Euro height SC, and I was running 8" rims in front and 10.5 wide in back. I used to tense up and get ready for a jarring steering wheel bump steer hit when approaching a pot hole, after the simple spacers not a bit. Heck if you don't like 'em just remove them.



PM me if interested, I sell 'em cheap and take paypal

[Kevin Stewart]

bump steer is just that you hit a bump and as the wheel compresses or rebounds the toe changes in and out. I havent done a stock 911 but have done a couple dozen rack based race cars. the goal is getting the tie rod arm and lower control arm to act as if they are bolted at the same mounting spot. the problem with the 911 is the the tie rod length and lower control arm length(mounting hole to center of ball joint) are not the same.

I would use an adjustable tie rod end instead of a rack plate(you may need both) but i would definately not just add shims and try and see as mentioned above, take it some where and have it done if you dont have a bump steer guage, Kevin

[Chuck Moreland]

those are raised spindle RSR struts. Raise spindles make the bump steer problem inherent in stock 911 suspensions into a profound bump steer problem.

A rack spacer kit is not adequate to correct this with raised spindles.

You need a proper tie rod end kit, and it should adjustable to best tune out the bump steer. As Kevin says, this is best done using a bump steer guage. But you can make your own measurement tool using a couple strings and bit of thought.

[Steve W]

You might want measure your toe changes before deciding on the degree of bump steer correction if needed. Four concrete blocks placed around each corner of the car with some string, or even better the SmartStrings setup, or if on a budget, replicate something similar with $20 worth of 3/4" PVC pipe and fittings.

[911st]

Originally Posted by Chuck Moreland

those are raised spindle RSR struts. Raise spindles make the bump steer problem inherent in stock 911 suspensions into a profound bump steer problem.

A rack spacer kit is not adequate to correct this with raised spindles.

You need a proper tie rod end kit, and it should adjustable to best tune out the bump steer. As Kevin says, this is best done using a bump steer gage. But you can make your own measurement tool using a couple strings and bit of thought.

There you go. If your spindles are raised, you do of cource need a proper BS kit no mater.

Chuck, How much are the RSR spindles raised over stock?

Just an note, bump steer or toe steer changes with changes is steering wheel angle because the ends of the steering rack moves and the angle of the tie rods change.

Being at the zero point with the wheels are straight I am guessing is not the ultimate goal. Under braking toe change is not going to be noticed much. Over a full on sweeper with undulations is where I suspect we want to minimize toe change.

You do need the kit as noted but if you are running 400/600# springs in a lightened car I would guess you are probably not going to have a lot of BS to worry about if you just get close.

Still learning.

[MarkRobinson]

I am making anti-bump-steer tie rod ends for the 928: I will tackle the 965/964/911/951 once I'm done testing. Will replace your tie rod end & should be $150-ish for the entire kit, & will allow you to dial in a perfect "horizontal-to-the-ground" tie rod angle.

Mark

[911pcars]

Installing a bump steer spacer kit, raising the spindles or other bolt-in, tie-rod kit will just get you closer, but that's not the same as measuring and correcting bump steer accurately.

A proper measurement requires one, maybe two dial indicators, a jig bolted onto the suspension and a method to raise and lower the suspension easily (easily = no shock insert).

Accelerating Performance: Bump Steer & Bump Stops

That's why most folks settle for a convenient bump steer adjustment "kit".

Sherwood

[MarkRobinson]

nobody's gonna install a jig & use dial-calipers to work against bump-steer. The bump steer spacer kits only help in getting the tie rod angle closer to what the factory had intended & only "generally" work with barely-lowered cars: let alone track cars sitting on the ground.

Most will, like I have done, lower the car to the height they want it, then install a bump-steer correcting kit. If using my kit (assuming I release it for 911's), they can use a level to get the tie rods parallel to the ground, having full adjustability on each end. Bump-steer would not be noticed after a proper alignment.

[911pcars]

Serious racers will fully measure and adjust to minimize.

"Bump-steer would not be noticed after a proper alignment. "

You will notice by elapsed lap time.

Sherwood

[MarkRobinson]

My mistake: I meant to say:

"corrected bump-steer (with my kit) would not be noticed after a proper alignment", even if using rough measurements. (ie, tape measure).

I type faster than I think sometimes