quote Originally posted by West Coast Fiero: Point being - the car flexes more than 1/16", spending hundreds to thousands of dollars to prevent 1/16" of bumpsteer is money best spent in other places - as you cannot prevent the vehicle itself from flexing over all.

Hey, Eric. I remember discussing this with you when I visited the shop back in October. I don't doubt your numbers, I just want to add an observation.

The first (and only, at that time) Fiero I owned was an 86 coupe. I test drove an 88 coupe, and could immediately feel how much more stable the car was. I'm not a knowledgeable enough gearhead to know all about bumpsteer and so forth, all I can tell you is my "seat of the pants" feel.

I now drive either an 88GT or (88) Formula on a daily basis. When I drive my wife's 86 coupe, I can feel a ton more body roll. The car feels like it's rocking side to side, with rotation along an axis down the center of the car. It may not be scientific, but I sure feel something going on. 88 coupes don't have a rear sway bar, so that couldn't have been the difference I felt when I drove it. So, what is it that I'm feeling?

Yo, BatBoy!

If you'll look at a pre-'88 suspension you'll notice that the toe-in link (note the correct spelling) is anchored to the cradle inboard of the pivot axis of the lower A-arm. This means the toe-in link is longer than the A-arm, & so doesn't undergo the same angular deflection as the A-arm. That means that from one extreme limit of travel to the other (up & down) the distance from the outer anchor point of the toe-in link to the centerline of the car varies MORE than the distance from the lower ball joint to the centerline of the car. This difference is felt as a toe-in change during suspension travel and can induce ( in test pilot lingo ) "unanticipated control system inputs."

If you look at an 88 cradle, however, you will see that the front pivot of the drag link and the inner pivot of both lower suspension arms are in the same plane & in a straight line. This ensures that therte is NO toe-in change during suspension travel, and so no Bumpsteer!

I have been looking at this problem for some time and it leads me to a question.
0" / 1/8" toe out
1" / 0"
2" / 0"
3" / 0"
4" / 0"
5" / 1/16" toe in
6" / 5/16" toe in
6.75" / 9/16" toe in

With the above numbers I see that if I am turning and I am going to fast if I let off the gas the rear end will lift and bump steer will toe out the rear wheel with the most traction causing me to spin. and if I go into a turn slow and give it more gas the rear will "squat" causing it to toe in on the rear wheel with the most traction making it harder to steer around the turn. Is it me or is this the reverse of what it should do? If you could relocate the toe link to the front of the a arm, move the inside pivot out a bit and install the tie rod end upsidown this should work verry well.

Any opinions? Please?

About the bumpsteer correction kits:

If you will examine the Fiero rear hub, you will see that the location of the "steering arm" places the center of the tie rod end above the center of the lower ball joint.

All the bumpsteer correction kits move the inner pivot of the toe-in link outward to line up with the inner a-arm bushings.

They also ensure that the height difference between the toe-in link's inner mounting point and the inner a-arm bushings is roughly the same as the height difference between the outer tierod end and the lower ball joint. If you can preserve this geometry through the full suspension travel, then you have no bumpsteer.

i have come to the conclusion after reading 40 something posts that the best way to eliminate bumpsteer is to have your engine run some very high powered fans and weld on some rotors to the rear to create a fiero hovercraft..

:O)

Don't mean to be disrespectful but you cannot eliminate bump/roll steer with a strut/tie rod combination(front or rear). This is because the top of the strut is fixed to the chassis and the bottom moves in an arc at the end of the a-arm. There is no place that the inner tie rod can be anchored that will not produce bump steer. Bump steer can be tuned so as to produce more desirable results. On an oval track we tune it to produce slight roll oversteer which helps make the car more drivable and have a more consistant feel to the driver. If the car doesn't feel right, he can never drive it effectively. Bear in mind we only make left turns. I've never tried this on a road race car. All that said: the average driver will never detect considerable roll steer in normal street use. Unless you're racing I would suggest leaving all the high dollar after market mods on the shelf. Good day!

Roll stear may be present with such an arraingement but it's also been demonstrated to be managed with proper engineering. However, I wish to defer authority on such subjects as independent rear suspension issues on a high performance street/road racing vehicle to persons familiar with such. I'm sorry if I offended you but coming off as the final authority with a background in oval racing (per your admission) falls on deaf ears. And I suspect many of the persons in this forum do demand more of their cars and encounter on-the-limit steering characteristics otherwise never encountered by the average motorist.

Goodday.

[This message has been edited by SportscarBruce (edited 01-20-2003).]

I wonder if raising the mounting point of the RCC kit would help if I wanted to lower my car so that I don't aggravate the toe-in/toe-out movement it may cause...although I would guess the shift in toe wouldn't be as extreme as the stock setup?

I have to say something on this one. I built an 85 with a Northstar/Getrag. Same weight as the V-6. Lowered the car about 1 1/2" and used the RCC kit. It was better than stock, but the bumpsteer actually increased as the suspension traveled upward. I didn't measure it, but it looked like over 1/2". The car was like skating on ice, it went anyway it wanted to on a bumpy road.

I ended up redesigning my own rear suspension tubular a-arms, spindles, etc. and I measured the bumpsteer at now 0 at all suspension travels. I suspect the Held kit would do the same as the geometry is similar. The difference is that now the car goes where it is supposed to. We're talking everyday driving here, not performance. When powered up, at least now I go straight.

quote Originally posted by Doug Chase: My take away is this: If you lower your car your suspension is going to be working where bump steer is the worst. This may be negated somewhat by the fact that you probably stiffened up the car when you lowered it so you're getting less suspension movement. Still, you might want to check into changing the bump steer characteristics.

I do not agree with that. Your measures where taked with the normal hight, thats why your 0 deflect is in the normal position. If you lower your suspenssion you have to re-aling it. This will put back you in 0 deflect spect zone. The other side is that you will have more deflect when the car rises, like jacked or do some duke of harzards jumps.

Also we have to take in consider the position of the tie rod regarding tie rod radious vs normal ride high. This will influence in the radial movement that cause the bomp steer.

My 2 cents

DreX

I'ld like some more information before buying as well, as I'm looking at both the Held and RCC kit. The car will be lowered using Suspension Techniques springs, claimed drop 1 1/2 inches. The Held unit appears to be more complex (and more expensive), however the rear poly a-arm bushings are included and I woun't have to buy those so that is taken into account. The RCC kit appears to be a solution as well, but I am wondering if the shorter link does induce a greater toe change at the furthest range of suspension movement.

Help!

The sad truth is that without an upper controll arm in the configuration, we can never truely "cure" the bumpsteer effect, only minimize it. If an upper controll arm is added and the pivot point of the new shock & spring is modified, then we can come close.

David Breeze

quote Originally posted by opm2000: The sad truth is that without an upper controll arm in the configuration, we can never truely "cure" the bumpsteer effect, only minimize it. If an upper controll arm is added and the pivot point of the new shock & spring is modified, then we can come close. David Breeze

Opm,

Your diagram doesn't look right to me. First you can't use a upper control arm that isn't there for reference. It's throwing the geometrics off in your diagram. The tie rod is presently longer than the control arm on stock cars. Adding the "block" and moving the back of the tie rod out so it sits above the pivot point of the control arm and shorting the tie rod to just about the same lenght of the control arm the bump steer is greatly reduced.

There will still be some bump steer do to flex in the frame, but not enough in my opinion to be noticed.

Earl R.

[This message has been edited by FieroGT87 (edited 01-24-2003).]

Your right, something does look wrong. That diagram shows the essential elements required to correct bumpsteer, or better yet, how to "achieve zero bumpsteer effect".

Stock Fiero (84-87 anyhow)is based on the McPherson Strut, and is totally lacking the upper controll arm. This means that the instant center can never really be found.

When someone says the tierod length is way too long and they shorten it, don't think they have cured bumpsteer. They don't have an instant center or the other reference lines needed to accurately locate the points, which determine the length.

Since the McPearson Strut serves as the upper pivot point, the bumpsteer effect cannot be "dialed out" by properly changing the lengths of tierod arms, or the locations of their pivot points.

This can be done to a certian extent,however, and both companies that I'm aware of who sell bumpsteer kits, do a fairly decent job of minimizing the effect.

It all boils down to why you want to get rid of it, and what you are either willing to pay or fabricate to achieve it.

Hah! You silly persons! The crux of the matter is a geometry that will (duh) not alter toe-in through suspension travel. That means that everything must rotate around the same axis. The inner toe-in link anchor should line up with the axis of rotation of the lower a-arm pivot bushings. AND the center of the outer tie-rod end should be level with the lower ball joint!! Conceivable?? yes. Practical?? Maybe not, with the 84-87 suspension.

Put in an 88 cradle, you'll like it a bunch more.