Check out this at http://www.kitcarmag.com/

Select menu KIT TECH and HOW TO to see article.
The srticle is courtesy of Held Motorsports.

And it is also a huge advertisement to sell this product.

If you want to eliminate bump steer, just install an '88 cradle. You will also have bigger brakes and a better handling car, no bushing flex on the cradle, and a different (read better) type of suspension.

Now, you can put aluminum bushings in the cradle, and poly up the rear of an early chassis, add one of Held's bump steer kits, and put on a swaybar - - and almost handle as well as with a bone bare stock '88 cradle/suspension.

But with just poly bushings in the links of the '88, you can easily surpass even the wildest modded early chassis rear suspension.

The costs for an '88 cradle swap do not have to be that much, either. The cradle itself will cost about the same as Held's bump steer kit. The adapter for the strut is around $85 from Held, and the adjustable perch strut can be as inexpensive as $250 if you do it yourself.

------------------
George Ryan
Performance Director
CFOG-I

[This message has been edited by cadero2dmax (edited 08-04-2002).]

No disrespect, but installing a '88 cradle will probably improve handling, but it will not "eliminate" bump steer.

Bump steer is caused by the changing toe end alignment of the rear suspension geometry as the wheels move up and down. It will still do this even with an '88 cradle.

While the '88 suspension is undoubtedly better than the earlier models, you're overly exaggerating the handling capabilities of the '88.

Poly bushings in an '88 will easily surpass even the wildest early chassis rear suspension??? All I have to say is prove it.

quote Originally posted by batboy: No disrespect, but installing a '88 cradle will probably improve handling, but it will not "eliminate" bump steer.

I don't know, batboy, but it sure looks like the 1988 suspension design virtually eliminates bump steer, if it doesn't eliminate it altogether. Looking at the 1988 geometry, I can't see how up-and-down can generate any yaw (yaw, sure ).

Anyway, I think "just bolt in a 1988 cradle" would end up being an awful lot of work. My guess is, better return on one's $ & sweat invested, to upgrade the existing pre-1988 suspension.

quote Originally posted by fierosound: Check out this at http://www.kitcarmag.com/ Select menu KIT TECH and HOW TO to see article. The srticle is courtesy of Held Motorsports.

You can also get a bump steer correction kit from RCC Specialties for $120. I have one on my car and it improves how the rear handles immensely. Their website is http://www.rccspecialty.com/fiero.html

------------------


Robert Beaubien
87 GT 5-speed

Every company claims that there is bumpsteer, granted - but what dimensions are they calculating for bumpsteer?

I tested the rear end of an 86 GT with bumpsteer calibration eqipment, and found the results quite laughable - the entire chassis flexes more than the greatest change in toe, which that in itself is experienced when the rear wheels are nearly off the ground.

But don't get ne wrong, I applaud anyone taking the time to convert craddle and/or spend thousands of dollars to correct 1/16" of bumpsteer, my only advice is that the money and/or effort could be better spent on something more beneficial for the vehicle.

------------------
( the above was the thoughts, views, and opinions of a disgruntled Fiero mechanic, and do not express or
imply those of West Coast Fiero, Fieros West, or any other organization - just that of this poor
bastard )

Eric Nelson
Technician,
West Coast Fiero
310-305-4111

[This message has been edited by West Coast Fiero (edited 08-05-2002).]

quote Originally posted by West Coast Fiero: Every company claims that there is bumpsteer, granted - but what dimensions are they calculating for bumpsteer? I tested the rear end of an 86 GT with bumpsteer calibration eqipment, and found the results quite laughable - the entire chassis flexes more than the greatest change in toe, which that in itself is experienced when the rear wheels are nearly off the ground. But don't get ne wrong, I applaud anyone taking the time to convert craddle and/or spend thousands of dollars to correct 1/16" of bumpsteer, my only advice is that the money and/or effort could be better spent on something more beneficial for the vehicle.

If the 1/16th is with a stock suspension, Does that mean when I lowered my car and stiffened up the suspension that I have less bumpsteer do to less movement? Or is this measured using the full travel of the suspension?

quote Originally posted by Oreif: If the 1/16th is with a stock suspension, Does that mean when I lowered my car and stiffened up the suspension that I have less bumpsteer do to less movement? Or is this measured using the full travel of the suspension?

excellent point Oreif!

Phil

Hey Stu, I'm not questioning the fact that the '88 suspension is better, my point was installing an '88 cradle like was suggested by Cadero, does not eliminate bump steering.

I have the RCC kit and it does a great job of "reducing" the effects of bump steering. I also have rear coil-overs, ST front springs all new ball joints and tie rods, and poly bushings everywhere.

Personally, I can't make any claims about how it'll hold up against an '88 since I've never tested it against one, but this is the best handling Fiero of all three that I've owned (all older models).

quote Originally posted by West Coast Fiero: Every company claims that there is bumpsteer, granted - but what dimensions are they calculating for bumpsteer? I tested the rear end of an 86 GT with bumpsteer calibration eqipment, and found the results quite laughable - the entire chassis flexes more than the greatest change in toe, which that in itself is experienced when the rear wheels are nearly off the ground. But don't get ne wrong, I applaud anyone taking the time to convert craddle and/or spend thousands of dollars to correct 1/16" of bumpsteer, my only advice is that the money and/or effort could be better spent on something more beneficial for the vehicle.

What were your testing procedures and how was the car set up?

Go change the toe by 1/16" per side in the front of your favorite Fiero. Drive it and notice how the handling changes. Then think that cars are MUCH MUCH MUCH more sensitive to changes in rear toe than front toe.

The '88 suspension does indeed have bump steer. The inner pivot of the toe link is further outboard than the inner pivot of the lateral link, making the toe link trace a more sharply curved arc. This causes toe in on compression and rebound. At the static ride height at which the suspension is set up from the factory, this assists the driver in keeping his line during longitudinal acceleration changes through a corner.

I have the RCC bump steer kit. It seems that the concept is sound, but the design and execution are lacking.

Usually I don't comment on threads that I know little about but please indulge me and let me make my point...

First, I don't know anyone who road races -- on a track with timers -- more than Cadaro2dmax. I'm more likely to believe his imperical data on the handling charactoristics of the Fiero than most anyone else. No flames, just facts.

Second, I know that most Fiero owners typically drive their cars just to and from work, shopping, etc. You know, just daily activities that can be done just a well with a Buick (but not as much fun). So, realistically, do you REALLY need to spend megga-bucks to try and eliminate a little bump-steer?

Would the average driver, even sport driveing on a daily basis, really notice the difference between a 88 cradle replacement and an 86-87 with solid cradle mounts and a rear sway bar? Throw in a good set of adjustable shocks and I'd bet most would not be able to tell the difference.

Third, I have no problem with bench racing. I have no problems with chassis, engine, or brake modifications. But, to basically call someone out who's actually time tested different chassis without have done so yourself, seems like your just looking for trouble.

Off my soap-box now. Peace,

------------------
Roy :D
Just another stock Blue 87 GT
Suncoast Fieros

YELLOW 1988 GT w/ T-Tops, 5-Speed, and Performance Sound.GONE!

quote Originally posted by Oreif: If the 1/16th is with a stock suspension, Does that mean when I lowered my car and stiffened up the suspension that I have less bumpsteer do to less movement? Or is this measured using the full travel of the suspension?

Yes and Yes

When you lower the car you essentially have less travel for these toe changes to take place, unless you modify the bumpstops so that you can retain stock travel ( i.e. flipping the bumpstop plates upside down ). Now I measured through full travel and articulation of all components on a stock 86 with poly bushings. Tonight when I have a bit more time ( its 1pm pacific now ) I will post the chart of numbers I have, but I want to make it boldly clear, I am only trying to add to a point/ counter point discussion, I embrace difference in opinions - thats how we all come to a solution

------------------
( the above was the thoughts, views, and opinions of a disgruntled Fiero mechanic, and do not express or
imply those of West Coast Fiero, Fieros West, or any other organization - just that of this poor
bastard ) :)

Eric Nelson
Technician,
West Coast Fiero
310-305-4111

quote Originally posted by West Coast Fiero: I tested the rear end of an 86 GT with bumpsteer calibration eqipment, and found the results quite laughable

I'm very interested to see your charts of this. Please describe the "bumpsteer calibration eqipment," too.

Interestingly, I measured the bump steer on the back of my '85 a couple years ago and my results were completely different from yours. I don't have the numbers in front of me, but from memory I measured at least 1/2" of toe change per side, and if I remember correctly, a lot of this was near full compression. I'll dig my stuff up if I can find it.

My measuring method was simple:

With the car in the air I removed the spring and re-assembled the suspension. I put a jack under the tire and went from full extension to full compression in 1" increments. The car was parked close to a wall so I measured from the front and rear edge of the rim to the wall to calculate toe.

------------------
Doug Chase
Duvall, WA
'88 Fiero Formula 5-spd (autocrosser)
'88 Fiero GT 5-spd (daily driver)
'85 Fiero GT 4-spd (rally car)

quote Originally posted by Doug Chase: I'm very interested to see your charts of this. Please describe the "bumpsteer calibration eqipment," too. Interestingly, I measured the bump steer on the back of my '85 a couple years ago and my results were completely different from yours. I don't have the numbers in front of me, but from memory I measured at least 1/2" of toe change per side, and if I remember correctly, a lot of this was near full compression. I'll dig my stuff up if I can find it. My measuring method was simple: With the car in the air I removed the spring and re-assembled the suspension. I put a jack under the tire and went from full extension to full compression in 1" increments. The car was parked close to a wall so I measured from the front and rear edge of the rim to the wall to calculate toe.

just as you did, with a floor jack, in .5" incriments with a dail indicator mounted to a perpindicular stand-off measuring 7" from the center of the hub ( accounting for 14" wheels )

Doug, was that measurement on your '88 daily driver, your '88 autocrosser, or was it on your early chassis Rally car (86, isn't it?)?

Eric, on my Quad 4 GT/Prepared racer, I had stiffened the car up and lowered it almost to the ground. Koni's all around (adjustable perch on the rear), etc. - I measured 1/8" toe deflection on that until I changed to the '88 cradle. BTW, this was with 13x11 1/2" wide Hoosier slicks and 13x10 Keizer aluminum wheels with 4" backspace.

With the '88 cradle, same Koni's, same springs,same wheels/tires, and Helds Heims joints on the links, I had less than 1/32" toe deflection at full travel - - quite an improvement, I would think.

I also would think a stock Fiero with stock wheels/tires would be closer to the 1/2" that Doug measured.

(I tried to upload a snapshot of the Q4 to show just how low it really was, but PIP isn't working again!!).

G

[This message has been edited by cadero2dmax (edited 08-05-2002).]

quote Originally posted by cadero2dmax: Doug, was that measurement on your '88 daily driver, your '88 autocrosser, or was it on your early chassis Rally car (86, isn't it?)? Eric, on my Quad 4 GT/Prepared racer, I had stiffened the car up and lowered it almost to the ground. Koni's all around (adjustable perch on the rear), etc. - I measured 1/8" toe deflection on that until I changed to the '88 cradle. BTW, this was with 13x11 1/2" wide Hoosier slicks and 13x10 Keizer aluminum wheels with 4" backspace. With the '88 cradle, same Koni's, same springs,same wheels/tires, and Helds Heims joints on the links, I had less than 1/32" toe deflection at full travel - - quite an improvement, I would think. I also would think a stock Fiero with stock wheels/tires would be closer to the 1/2" that Doug measured. (I tried to upload a snapshot of the Q4 to show just how low it really was, but PIP isn't working again!!). G [This message has been edited by cadero2dmax (edited 08-05-2002).]

This is the first time that I have seen numbers and results from the Held eqipment, that is a significant improvement from what your previous numbers were.

If the Held items make for this much inprovement then it is truly money well spent

------------------
( the above was the thoughts, views, and opinions of a disgruntled Fiero mechanic, and do not express or
imply those of West Coast Fiero, Fieros West, or any other organization - just that of this poor
bastard ) :)

Eric Nelson
Technician,
West Coast Fiero
310-305-4111

quote Originally posted by West Coast Fiero: This is the first time that I have seen numbers and results from the Held eqipment, that is a significant improvement from what your previous numbers were. If the Held items make for this much inprovement then it is truly money well spent

Well, all that were Held's products on that car were the links, and the '88 cradle adapter. Every iota of the improvement was from the '88 cradle, I'm afraid.

The cradle adapter just re-locates the top of the strut, a necessary mod in order to install the '88 cradle in an early Fiero. The only other things that must be done is the required adjustable perch strut with 2 1/2" springs, and relocate the existing brake lines. Everything else just bolts up!!

Just my opinion, but the early front end and '88 cradle are the best handling combo I have tried in many, many years of playing with these cars. And that includes the Ryane(Held) slolum front suspension. The car just drives fast easier than most Fieros when it is set up with this combo on it - - again in my opinion, and for my driving style.

G

With the exception of a few very limited scope race applications or very expensive kit buildups.... What's another few grand to a kit project... (That Kit article is a nice infomercial for Held...)

To most owners. The whole bump steer argument is a load of crap.

Fiero does have some Bump Steer, but it's not anywhere near as bad as some people keep claiming. Nor is it hard to make major improvments in handling. It can be done for less than $300-400 using off the shelf parts. (Less if you do the work yourself.)

The majority of owners do not need to spend the obscene amount of money some people want for a "Fix." They don't need to lower the car, which is actually a bad thing in many cases. They don't need polly all around, or $500-1000 worth of tires. (Obviously, bad bushings or tires won't help any... Either one needs fixing.)

The greatest cause of percieved Fiero Bump Steer, as reported in the rags and still piped by many of today's so called experts was the crappy shocks and struts that came on nearly all Fiero. (I understand that only WS6 got anything better for all years except maybe 88.) If you don't control wheel travel, the car will always handle like a giant turd. This applies to all cars.

GM found the cheapest POS shocks and struts they could for these cars. Bump Steer on the rear is especially bad due to the fact that OE struts had little or no compression damping. (Rebound damping only.) This type strut will allow the wheel full free travel all the way to stops when compressed. Even small bumps can and do throw the wheel completely off the road. Whatever bump steer is caused by other suspension parts will be tremendously exagerated by crappy struts.

Add to this the economy soft springs in many Fiero and the problems of a rubber mounted cradel, and it's a wonder the cars were ever drivable at all. The soft springs allow the wheel even more travel. The rubber cradel mounts are notorious for allowing the whole a_s end of the car to shift alignment due to uneven engine loading, especially in manual transmission cars.

For the majority of applications, the "Bump Steer Problem" and "Torque Steer Problem" can be greatly reduced or eliminated by simply replacing the shocks struts and cradel bushings.

Shocks and struts... Gas charged, bi directional damping and velocity sensitive valving. Gabriel, KYB, and Monroe all make products along this line. This will greatly limit wheel travel no matter what springs you have. If you have one of the sport or GT spring sets, even better.

I prefer Gabriel. KYB is good. Monroe's are good technically but the quality isn't so great. They've never lasted well for me.

Cradel... Polly, or if you can afford it metal. This will stop the cradel dancing with every twitch of the gas pedal. The off center dog bone can make the whole cradel twist reletive the car frame when engine load changes.

Manual transmission cars are horrible for this because they can shift from accel to brake almost instantly. The TC tends to damp allot of this in automatics but they can still do it.

------------------
11-Sept-01, The day the world as we knew it ended.

quote Originally posted by batboy: (1)...my point was installing an '88 cradle...does not eliminate bump steering. (2)...this is the best handling Fiero of all three that I've owned (all older models).

(1) That may be so... I was just making an observation based on the geometry, and not backed up by any measurements. Perhaps there isn't enough bump steer to worry about with either suspension design, as Ogre suggests. (2) Cool! I'm glad you are pleased with the results. One can't argue with success !

though some consider it an opinion - I consider it more of a fact.....

5 months ago when we had a mock up chassis for a Northstar install we wanted to see what the bumpster situation was all about, this is what we came upon.....

With the 86 chassis ride height of 14" ( measured at the center of the hub ) we measured all dimensions through suspension travel from 12" ( wheel into the fender, considered as a harsh bump ) to 16" ( wheel essentailly at the end of its travel, commonly seen when raising the car with a floor jack )

ride height / amt. of bumpsteer
16" / 0.000-.000"
15.5" / 0.015-.020"
15" / 0.025-.038"
14.5" / 0.060-.080"
14" / 0.070-.055"
13.5" / 0.060-.055"
13" / 0.070-.065"
12.5" / 0.050-.055"
12" / 0.038-.025"

For a point of reference, 0.065" = 1/16"

So what does all this math mean, well in conclusion to this testing we found that the car has the most extreme bumpsteer ( 0.080+ - just over 1/16" ) at 14.5" which is roughly the midpoint of up travel before hitting the bumpstops

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.

------------------
( the above was the thoughts, views, and opinions of a disgruntled Fiero mechanic, and do not express or
imply those of West Coast Fiero, Fieros West, or any other organization - just that of this poor
bastard ) :)

Eric Nelson
Technician,
West Coast Fiero
310-305-4111

quote Originally posted by theogre: With the exception of a few very limited scope race applications or very expensive kit buildups.... What's another few grand to a kit project... (That Kit article is a nice infomercial for Held...)

On that we agree, the entire article was just one big advertisement for Held. My guess is that Dave wrote the article himself, or coached the author heavily.

quote To most owners. The whole bump steer argument is a load of crap. Fiero does have some Bump Steer, but it's not anywhere near as bad as some people keep claiming. Nor is it hard to make major improvments in handling. It can be done for less than $300-400 using off the shelf parts. (Less if you do the work yourself.) The majority of owners do not need to spend the obscene amount of money some people want for a "Fix." They don't need to lower the car, which is actually a bad thing in many cases. They don't need polly all around, or $500-1000 worth of tires. (Obviously, bad bushings or tires won't help any... Either one needs fixing.)

Had you not said "to most owners", I would have to disagree. But with that disclaimer I would have to go along with you.

To the show-n-shiners, or the grocery getters, it isn't an issue. But for those that try to push their cars to the edge, there is a great deal of concern. The inherent bump steer in this chassis is what makes this car so uncompetitive against the likes of the MR2 and RX7, both in the same class as a V6 Fiero in the SCCA.

quote The greatest cause of percieved Fiero Bump Steer, as reported in the rags and still piped by many of today's so called experts was the crappy shocks and struts that came on nearly all Fiero. (I understand that only WS6 got anything better for all years except maybe 88.) If you don't control wheel travel, the car will always handle like a giant turd. This applies to all cars. GM found the cheapest POS shocks and struts they could for these cars. Bump Steer on the rear is especially bad due to the fact that OE struts had little or no compression damping. (Rebound damping only.) This type strut will allow the wheel full free travel all the way to stops when compressed. Even small bumps can and do throw the wheel completely off the road. Whatever bump steer is caused by other suspension parts will be tremendously exagerated by crappy struts. Add to this the economy soft springs in many Fiero and the problems of a rubber mounted cradel, and it's a wonder the cars were ever drivable at all. The soft springs allow the wheel even more travel. The rubber cradel mounts are notorious for allowing the whole a_s end of the car to shift alignment due to uneven engine loading, especially in manual transmission cars. For the majority of applications, the "Bump Steer Problem" and "Torque Steer Problem" can be greatly reduced or eliminated by simply replacing the shocks struts and cradel bushings. Shocks and struts... Gas charged, bi directional damping and velocity sensitive valving. Gabriel, KYB, and Monroe all make products along this line. This will greatly limit wheel travel no matter what springs you have. If you have one of the sport or GT spring sets, even better. I prefer Gabriel. KYB is good. Monroe's are good technically but the quality isn't so great. They've never lasted well for me.

So far, so good - - for all but those that use their cars for something other than competition. But this isn't enough for those of us that have to try to keep up with smaller displacement, better handling cars. We have to become their equals in handling, and what you are advocating here will not do that when "on the edge".

And I am not talking pure racers, either. There are many that take their daily drivers to the Solo course, or race track on weekends. To those of us in that catagory, bump steer is real, it is damaging, and it is necessary to reduce or eliminate it as much as we can.

I have found the most effective method is the use of an '88 cradle. Just my experience, nothing scientific.

quote Cradel... Polly, or if you can afford it metal. This will stop the cradel dancing with every twitch of the gas pedal. The off center dog bone can make the whole cradel twist reletive the car frame when engine load changes. Manual transmission cars are horrible for this because they can shift from accel to brake almost instantly. The TC tends to damp allot of this in automatics but they can still do it.

And the '88 cradle doesn't have those cradle bushings at all, they bolt directly to the chassis. Therefore, the combo of the dogbone twist against the cradle bushings is minimized. Even with the '88, the dogbone can be a problem with rubber bushings, But with the '88 cradle and poly bushings, that phenomenom is greatly diminished to the point of not being that noticeable, even when dancing the Fiero through a slolom.

BTW, here's that photo of the Q4 racer, forgot what I was trying to say about lowering, but remember I couldn't post the image earlier!!

G

[This message has been edited by cadero2dmax (edited 08-06-2002).]

Ok, I now see what Cadero was sort of getting at when he was referring to swapping in the '88 cradle in the older models. I reckon this would "reduce" a fair amount of flex and deflection. I thought he was somehow trying to suggest that just a cradle swap corrected the rear suspension geometry. Certainly it would not completely eliminated bump steer. Another thing I did was to weld extra steel plates onto the bottoms of the rear control arms to reduce any possible flex there. I'm planning on adding a second dogbone to my V8 Fiero too.

Ogre makes some good points. The Fiero in stock form does handle quite well. Trouble is, a 15-17 year old car will have lots of worn out parts and bushings. The first step like he mentioned is to get rid of the worn out junk parts. But, some of us like to drive in a "spirited" manner, even if we don't go to the track on a regular basis. The point is, there are a few things that can be done to improve older Fiero handling.

Nice tires and good shocks and struts are probably the best bang for the buck. A smooth handling car is like a wonderful wet dream. All I can say is that I feel all the money and work I did to my suspension was well worth it. Hey Orgre, I currently have Gabriel shocks and struts too. They do seem to handle quite nicely and hold up well too.

Actually, my experience has shown the biggest problem with most ill handling daily driver Fiero's is from a poor alignment, especially in the rear.

Just a few weeks ago I helped a couple that complained about what they thought was bump steer "the back end did wierd things - seemed to have a mind of it's own". It turned out to be they had toe OUT on the rear, and that in itself will mess up any Fiero's handling big time! I was able to get it pretty close and make it drive a lot better with the old fishing wire and jackstands alignment. BTW, that original alignment was done by a Pontiac dealership!

In agreeing with Ogre (except for competition cars), I would first recommend good tires, good shocks, and check all the bushings, tie rod ends, and ball joints for security. Then I would get an alignment from a shop that SPECIALIZES in alignments, and one that will do it to your specs, not theirs.

G

[This message has been edited by cadero2dmax (edited 08-06-2002).]

Correct me if I'm wrong, but I was under the impression that the major cause of rear bump steer in the early-model Fieros was the toe link rod. Well, aside from the cradle wiggling and stuff. You'd think that this could be solved simply by moving the inboard mounting point of the toe link rod, and shortening the rod to match the radius of the control arm. That shouldn't be too hard to do.

quote Originally posted by Blacktree: Correct me if I'm wrong, but I was under the impression that the major cause of rear bump steer in the early-model Fieros was the toe link rod. Well, aside from the cradle wiggling and stuff. You'd think that this could be solved simply by moving the inboard mounting point of the toe link rod, and shortening the rod to match the radius of the control arm. That shouldn't be too hard to do.

www.rccspecialty.com makes a bump steer kit which does exactly that. However, it loses effectiveness rapidly as the car is lowered.

I'm not following this. How does swapping in an '88 cradle into, say a '85 Fiero, change the rear suspension?

the cradle that they are talking about is the rear frame. It holds the rear struts , brakes rear wheel and of course the engine. Now, swap the cradle, and you swap the entire rear suspension of the car

------------------
"You obviously have a great economy with words, I look forward to your next syllable with great eagerness"

Blacktree,
Do you mean something like this? http://members.aol.com/cfogikitcar/bump1.jpg http://members.aol.com/cfogikitcar/bump2.jpg http://members.aol.com/cfogikitcar/bump3.jpg http://members.aol.com/cfogikitcar/bump4.jpg http://members.aol.com/cfogikitcar/arc1.jpg

I'll try pip, but the links are good.

David Breeze

George: As I said in my message above "I measured the bump steer on the back of my '85 a couple years ago".

Blacktree: This seems like an obvious and simple fix, but it won't eliminate the bump steer, it will only change the bump steer curve. The reason is that the strut doesn't stay completely vertical as the suspension moves. Since the top of the strut is fixed, as the control arm moves up or down from horizontal the bottom of the strut moves inboard.

Eric / Everybody: I found my bump steer measurements. On my numbers 0" is topped out suspension -- car off the ground and wheel hanging. 6 3/4" is bottomed out -- wheel up in the wheel well and strut against the bump stop. Normal ride height is around 4" on my chart. I measured with a tape measure so I don't have three digits of precision like Eric and his dial indicator.

Travel / toe

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

I don't think these numbers disagree with yours, Eric. Throughout the middle of the travel travel there isn't enough toe change to measure with a tape. There's a little bit at suspension top out, and a lot in the last inch of compression. Total change from bottom to top is 11/16" per side, and that's a lot.

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.

Since I raised my car about an inch (this is my rally car), I'm not worrying about the bump steer because I'm normally working where it's pretty linear. Since I race on dirt I don't see as much suspension movement from cornering forces as pavement racers. The only time I get into the bad bump steer zone is on severe bumps and since it's toe in, that doesn't upset the car a noticeable amount.

I hope somebody finds all this useful.

------------------
Doug Chase
Duvall, WA
'88 Fiero Formula 5-spd (autocrosser)
'88 Fiero GT 5-spd (daily driver)
'85 Fiero GT 4-spd (rally car)

OPM2000: That's EXACTLY what I was talking about. But as others have pointed out, you'll still have some amount of bump steer. The reason is because the pivot point for the toe link is higher up than the pivot point for the ball joint. So as the suspension moves up and down, the hub will swivel left and right relative to the control arm. Which means that the pivot point for the toe link will swivel too. Since the toe rod can't change its length to match the swivelling of the hub, it ends up pulling and pushing on the hub, hence bump steer.

quote Blacktree: This seems like an obvious and simple fix, but it won't eliminate the bump steer, it will only change the bump steer curve. The reason is that the strut doesn't stay completely vertical as the suspension moves. Since the top of the strut is fixed, as the control arm moves up or down from horizontal the bottom of the strut moves inboard.

OK, got it. So if you were to move the outboard pivot point of the toe link rod downwards so that it's horizontal with the ball joint, that should fix the problem. The hub could swivel back and forth on those two pivot points just like the A-arm swivels up and down on its two mounting points. If you were to draw a line between the ball joint and the toe link joint, and likewise draw a line between the two bushings on the control arm, those two lines need to be parallel.

And you could probably tie off the inner mounting point of the toe link rod directly to the control arm, kind of like the Held kit. This way, you wouldn't need to worry about the placement of this pivot point, because it would pivot with the control arm. But instead of using a fancy tubular A-arm and custom-fabbed bracket, you could just drop a bolt down through the toe link rod's mounting hole (in the hub) and attach the end of the toe link rod to the end of that bolt. As long as your bolt didn't flex, you'd be set.

Sound feasible?

[This message has been edited by Blacktree (edited 08-07-2002).]

Eric, you're wrong about the bumpsteer being laughable.

1/16 an inch is 1/16 an inch too much for me. My suspension is tight and I think it's more than that.

I have an 86GT with WCF aluminum cradle bushings(Awesome product), poly in the control arms, eibach springs, fresh KYB struts and a good alignment.

All I can say is the bumpsteer is NASTY

by the 3rd cone of a slalom, I'm fighting the car to keep it going strait.

On transitions into curves, if I make the slightest mistake, the back will come around before I know it.

keep in mind this is at the limit of adhesion.

I can run at 9/10ths of my ability all day without a hiccup.

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quote Originally posted by Howard_Sacks: Oh and where exactly does the RCC kit relocate the rod? If I get ambitious, I can plug it into "Racing by the Numbers" to get the exact amount of change in bumpsteer.

Here are pics of mine. It changes the pivot point out to almost where the lower control arm pivots. This keeps the bumpsteer at near 0 for all but the last 1.5" of strut travel which should only be seen when the car is jacked up.

This kit with the poly cradle kit really tightened up the rear end at speed (100+ mph). You don't really notice any improvement at low speeds.
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Robert Beaubien
87 GT 5-speed

[This message has been edited by RBeaubien (edited 08-08-2002).]

[This message has been edited by RBeaubien (edited 08-08-2002).]

Has anybody measured the deflection on an '88? The toe change is substantially less than the 84 - 87, But how much less? Just wondering if anybody had the actual figures for comparison (seems like there are several that have measured the 84-87!).

Of course not!! That would only validate the '88 cradle upgrade i am running and advocate

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George Ryan
Performance Director
CFOG-I

I'm posting a reply to this old thread because I had a recent event in the rain that involved bumpsteer, a spin, and a lucky ending (didn't hit anything). My suspension budget is modest at best, right now I have the following that haven't been installed yet: a new set of Gabriel Gas Ryder VST (velocity sensitive) shocks and struts, Suspensions Techniques lowering springs, and poly cradle bushings. Am right now trying to decide on poly a-arm bushings or Del-A-Lum (want a way to regrease w/o disassembly).

My question is look at the pic above of the RCC bump steer kit. It appears to be aluminum with a spherical bearing. Does this look durable enough for street duty? I'ld hate to imagine what would happen at speed if the thing broke.

Knowldgeable answers or guesstimates are appreciated.

It is not (at least ours isn't) aluminum. That's a steel square bar with very good quality greasable Heim ends on the inside. The outer ends of the rods take the stock Fiero Rod Ends.

I didn't measure our bumpsteer before and after, but you do notice that the bulk of it is at the very end of the suspension travel (extension). Typically, this is not a problem because if the suspension is at the extended end of the travel, by nature it has to be very lightly loaded. What you really don't want is a lot of toe change under compression when the suspension is heavily loaded.

John Stricker

quote Originally posted by SportscarBruce: I'm posting a reply to this old thread because I had a recent event in the rain that involved bumpsteer, a spin, and a lucky ending (didn't hit anything). My suspension budget is modest at best, right now I have the following that haven't been installed yet: a new set of Gabriel Gas Ryder VST (velocity sensitive) shocks and struts, Suspensions Techniques lowering springs, and poly cradle bushings. Am right now trying to decide on poly a-arm bushings or Del-A-Lum (want a way to regrease w/o disassembly). My question is look at the pic above of the RCC bump steer kit. It appears to be aluminum with a spherical bearing. Does this look durable enough for street duty? I'ld hate to imagine what would happen at speed if the thing broke. Knowldgeable answers or guesstimates are appreciated.

We seem to have quite a few suspension experts posting to this thread and I really find the info interesting. When I first purchased my 87GT I was very disappointed in the way that it was affacted by bump steer. I purchased and installed a used ACCO rear sway bar and it really improved the handling. I don't know if this is the total solution but it seems to make a substantial difference.

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87GT 3.4 Turbo Best 0-60 5.2 seconds
http://turbofiero.fierojoe.com/turbo.htm

Thanks to both respondents, as I'll be looking to get the bumpsteer linkage and, in a few months a 3.4 (turbo or NA, haven't decided yet).

Again, thanks.

You know what's really weird? You'ld think GM engineers or beancounters would have looked into such an effective and low cost fix earlier in the Fiero's history. Well, if they were really smart they would have continued the Fiero line beyond 1988 (as Toyota did with the MR2).

[This message has been edited by SportscarBruce (edited 01-19-2003).]