Bump Steer, How to tell...? Options

[gopack]

Elephant racing makes the tie rod end solution. Like everything they sell , it is high quality, and pricy: $335

[SirAndy]

Elephant racing makes the tie rod end solution.

We've been using a similar setup on the green 911 race car for years without any trouble.

Those work great and are easy to adjust.
(IMG:style_emoticons/default/shades.gif) Andy

[turboman808]

I really thought my car had this and just needed some adjustment. Guess I got to buy it sooner rather then later.

[jim_hoyland]

Does raising the spindles or using the ER bump steer kit end up doing the same thing ?

[SirAndy]

Does raising the spindles or using the ER bump steer kit end up doing the same thing ?

No. Raising the spindles allows you to lower the car past what is possible otherwise.
(IMG:style_emoticons/default/shades.gif) Andy

[turboman808]

Does raising the spindles or using the ER bump steer kit end up doing the same thing ?

No one has given a definitive answer and even elephant racing doesn't give one. I would really assume the goal is to get the tie rod close to parallel to the lower a arm.

In the pictures shown you can see it makes a trianlge. A arm is pointing down and tierod is pointing up. Correct me if I am wrong but that seems to me it would cause the tires to toe out over a bump. All the bump steer kits bring the tie rod down making this trianlge less severe.

I think moving the spindle up makes the problem worse.


Again no experience with this just looking at the pictures. (IMG:style_emoticons/default/smile.gif)

[J P Stein]

I hope all my work can help you understand what is happening with the 914 suspension: I have to keep reminding myselft that the car was DESIGNED around 100 HP and 165 radials....ONLY. So the best tip I can give is to run the car at STOCK suspension ride-height and setting......and if you PLAN to be "Up on the Wheel" maybe 1/6- 1/8" TOE-OUT in the rear.

Best of luck,
Terry

An old fat guy thinks your understanding of the 914s suspensions is pretty good.
Your conclusions are....well, *your* conclusions & thankfully, not mine.

Lowring the car is very worthwhile.....as long as it is done right & with consideration given to bump.

[J P Stein]

Angles..we gots em and it works. I'm at 4-3/4 inches at the doughnuts. I was lower but had wheel to A arm interference at a lot of steering lock & suspension compression..so back up we went.....who'da thunk it.....

Jim:
With raised spindles it takes either bending the steering arm.....which buggers up the Ackerman or tie rod extensions....these are by ERP. It can run into money to get both.

[SirAndy]

Angles..we gots em and it works.

Yeah, but your overall suspension travel is what, a micrometer? (IMG:style_emoticons/default/rolleyes.gif)


On a mostly stock suspension, with lots of travel, the more unparallel the arm is in regards to the tie rod the worser the bumpness steering gets ...
(IMG:style_emoticons/default/stirthepot.gif) Andy

[J P Stein]

I have 2 1/2 inches of front shock travel & use it all. 21 mm T bars ain't all that stiff.
What you want to avoid is going over center with the tie rod....and the A arm for that matter.

[cwpeden]

You need to account for the pivot points of the tie rod are constantly changing in relation to the a-arm, which is static.

Oh, and what about camber and caster..... (IMG:style_emoticons/default/stirthepot.gif)

[J P Stein]

You need to account for the pivot points of the tie rod are constantly changing in relation to the a-arm, which is static.

Oh, and what about camber and caster..... (IMG:style_emoticons/default/stirthepot.gif)

Ya gotta account for a lot of things. You won't find them all till you try something.....and, of course, it is possible to make a hash of it.....then go to plan B. (IMG:style_emoticons/default/biggrin.gif)

[ArtechnikA]

It binds things in other places...namely the upper u-joints.

you mean the steering shaft U-joints?

They're splined, and the shaft can be adjusted for length.

put in the spacers, loosen the clamp nuts, let the joint shafts retract into the outer shaft, retighten.

[jaxdream]

It binds things in other places...namely the upper u-joints.

you mean the steering shaft U-joints?

They're splined, and the shaft can be adjusted for length.

put in the spacers, loosen the clamp nuts, let the joint shafts retract into the outer shaft, retighten.

What type of steering shafts you using ?? (IMG:style_emoticons/default/confused24.gif) Mine do have the splined ends as most 914's I 've seen , but some also have a half moon cutout on them for the bolt that binds them to slide through and locate the u-joint on the shaft , adjustment , all I can do to mine is install a thinner hockey puck on the rack to allow for raising the rack to run spacers. The rack shaft to inside is covered up by a plastic cover and it would have to be trimed back as it butts up against the upper shaft bearing that's under the clamp behind the fuel tank. There maybe some adjustment there , but not much other than a thinner hockey puck.

Jaxdream

[dw914er]

This is what is on clubrsx from my searches while modifying my suspension on my rsx

First, I'll talk about what bumpsteer is NOT. It is NOT when the steering wheel moves when you hit a bump. That often is caused by high spring rates or high tie pressures. Imagine riding your bike with no tires. As soon as it hits a bump, you are going to feel it and it is going to push your wheel in a certain direction. When spring rates or tire pressures are really high, the suspension is really stiff and the car responds quickly and not necessarily in the right way. Remember, high spring rates don't = better handling. Race cars use high spring rates because they allow quick responding, but they also are racing on smooth surfaces and not on crappy city roads.

The short answer is that bumpsteer is when your wheels turn without input from the driver. It is affected by toe. On our suspension, when it compresses, toe goes in and the opposite happens with rebound. To control bumpsteer, one would want to keep toe settings pretty static throughout compression and rebound.

From what I understand, camber can and will affect toe, so the common results of bumpsteer from after lowering a car is bad alignment, creating what the quote said. Is this true, and could be why Jim hasn't noticed massive bumpsteer, because the alignment probably isn't that far out of wack? I don't really know, but alot of their stickies makes sense for the rsx applications, so I assumed this one was good also.

[jim_hoyland]

This is what is on clubrsx from my searches while modifying my suspension on my rsx

First, I'll talk about what bumpsteer is NOT. It is NOT when the steering wheel moves when you hit a bump. That often is caused by high spring rates or high tie pressures. Imagine riding your bike with no tires. As soon as it hits a bump, you are going to feel it and it is going to push your wheel in a certain direction. When spring rates or tire pressures are really high, the suspension is really stiff and the car responds quickly and not necessarily in the right way. Remember, high spring rates don't = better handling. Race cars use high spring rates because they allow quick responding, but they also are racing on smooth surfaces and not on crappy city roads.

The short answer is that bumpsteer is when your wheels turn without input from the driver. It is affected by toe. On our suspension, when it compresses, toe goes in and the opposite happens with rebound. To control bumpsteer, one would want to keep toe settings pretty static throughout compression and rebound.

From what I understand, camber can and will affect toe, so the common results of bumpsteer from after lowering a car is bad alignment, creating what the quote said. Is this true, and could be why Jim hasn't noticed massive bumpsteer, because the alignment probably isn't that far out of wack? I don't really know, but alot of their stickies makes sense for the rsx applications, so I assumed this one was good also.

The alignment is pretty close; forgot the numbers. Tire wear is even as well

[dw914er]

Then that's probably why...

when you drop a car, alignment gets off, and suspension parts get out of wack, like thetie rods work differently because of the angle, etc.

This is from my understanding though, I could very well be wrong

[SLITS]

HP Books - "How to Make Your Car Handle" - Fred Puhn

1981 - ISBN 0-912656-46-8

All the formulas, theories and headaches you could want!

Steve Smith Autosports Publications - "Advanced Race Car Suspension Development" - Steve Smith

1974 - ISBN 0-936834-05-6

More of the same

[jmill]

I like "Tune to Win" and "Engineer to Win." "Engineer to Win" gets a little more in depth as far as bump steer is concerned. "Tune to Win" might be a bit more applicable because your working with something already built.

[turboman808]

Wrote this long thing and then just made a diagram real quick. I need to install the 3d software already.

(IMG:http://i147.photobucket.com/albums/r283/turboman808/suspensiongeomertycopy.jpg)