Skip to main content
Topic: Some info about bumpsteer (Read 3542 times) previous topic - next topic

Some info about bumpsteer

I emailed MM about my suspension problems here is their repsonse

Quote
It is a very common misconception, that when you  lower your vehicle you will acquire a bumpsteer problem. This is completely  FALSE!

First a quick explanation of what bumpsteer is. Bumpsteer is a  curve or graph made from taking several measurements of toe change (wheel  pointing in or out from center) as the wheel moves up and down through its  suspension travel. We always want this change to be as minimal as possible (zero  is best) to prevent the suspension from "steering" the car when it hits a bump  in the road. This adds stability and safety to the car and has been designed  into the front suspension from the factory.

Changing the ride height of  the car will place the suspension in a different part of the bumpsteer curve,  although it will not change the curve itself. While the bumpsteer at this  particular point in the suspension travel may not be quite as optimal as it was  at factory ride height, it is typically fine for street driven  vehicles.

Now as soon as you alter the relationship between where the  steering rack, control arms, and spindles are located, as with the 96-98  Spindles, you create a completely different bumpsteer curve. This is when you  need a bumpsteer adjustable tie rod end to re-tune the bumpsteer curve on the  car.

For your application, and due to the complicated, time consuming  process of bumpsteering a car, I highly recommend against installing these  spindles. They are a lot more hassle than they are worth. I would try and find a  set of 1994-95 spindles that have geometry closer the your original  ones.



In regards to your comment about bumpsteer, I think what you are  experiencing might be tramlining. This is the tire's tendency to follow ruts or  grooves in the road. It is typically accentuated by performance wheels, tires  and suspension modifications. It can be helped by a good alignment but it is a  side effect of adding more grip to the car, and is something that most  performance modified vehicles experience to some extent.
2005 Subaru WRX STi|daily driver

Some info about bumpsteer

Reply #1
That is one reason I only use the 94-95 spindles on my cars ;)

I've never had a bumpsteer issue with my cars, but the "tramlining" is an issue however.

On the 96-04 cars, the rack is 1" lower than previous years due to the mod motor...thus the lowered tie rod point. 

Fitting a bumpsteer kit and dialing it in can be tedious, and really those aren't meant for street use as they are just spherical rod ends. 

I'm not sure if a set of offset rack bushings installed so as to lower the rack (instead of raise it) would help, or even fit on the car.

The 94-95 spindle route is the best option, but I know they are harder to find.
Long live the 4-eyes!  - '83 Tbird Turbo - '85 Marquis LTS - '86 LTD Wagon

Some info about bumpsteer

Reply #2
That's interesting, it's the first I heard the 96+ spindles recommended against.  The thing is, the 96+ spindle is supposedly easier to mount brake ducts to, and better geometry somehow?  And they mount Cobra calipers with no grinding.  So when is it worth it?  I intend to modify my car for HPDE use and road racing, some autocross, so perhaps it would be justified for me?
Long time Turboford freak...
84 SVO
88 TC
87 XR4Ti

Some info about bumpsteer

Reply #3
If you're building a street car, or one that see primarily street use, like I mentioned, the bump-steer kits really aren't a good idea.  The geometry might be better when used on the appropriate K-member, but on a Fox? Not so much.  The "grinding" required is not required for the Cobra brakes....as the 94-95s used the same ones.  It's when you use the 11" 99+ PBRs that you need to do the grinding.
Long live the 4-eyes!  - '83 Tbird Turbo - '85 Marquis LTS - '86 LTD Wagon

Some info about bumpsteer

Reply #4
So if one were to, say, install a 96+ K-member in order to do a mod swap from, say, a Lincoln Mark VIII, one should use the 96+ spindles (and of course control arms) as well in order to maintain geometry?
2015 Mustang GT Premium - 5.0, 6-speed, Guard Green - too much awesome for one car

1988 5.0 Thunderbird :birdsmily: SOLD SEPT 11 2010: TC front clip/hood ♣ Body & paint completed Oct 2007 ♣ 3.55 TC rear end and front brakes ♣ TC interior ♣ CHE rear control arms (adjustable lowers) ♣ 2001 Bullitt springs ♣ Energy suspension poly busings ♣ Kenne Brown subframe connectors ♣ CWE engine mounts ♣ Thundercat sequential turn signals ♣ Explorer overhead console (temp/compass display) ♣ 2.25" off-road dual exhaust ♣ T-5 transmission swap completed Jan 2009 ♣

Some info about bumpsteer

Reply #5
Quote from: Thunder Chicken;134604
So if one were to, say, install a 96+ K-member in order to do a mod swap from, say, a Lincoln Mark VIII, one should use the 96+ spindles (and of course control arms) as well in order to maintain geometry?


Yuppers.
Long live the 4-eyes!  - '83 Tbird Turbo - '85 Marquis LTS - '86 LTD Wagon

Some info about bumpsteer

Reply #6
"Tramlining" was a huge problem for me when I had spoogeho tires. The tires would catch a groove and literaly yank the wheel. It was cured instantly when I went to a different tire (riken raptor). I'd say tread pattern plays a huge role in "tramlining."

Some info about bumpsteer

Reply #7
Tire pressure can also effect tramlining. Often it's the edge of the tire catching craks and grooves that will cause issues. try adding a couple pounds of pressure.

Some info about bumpsteer

Reply #8
Quote from: Chuck W;134555
If you're building a street car, or one that see primarily street use, like I mentioned, the bump-steer kits really aren't a good idea.  The geometry might be better when used on the appropriate K-member, but on a Fox? Not so much.  The "grinding" required is not required for the Cobra brakes....as the 94-95s used the same ones.  It's when you use the 11" 99+ PBRs that you need to do the grinding.


You're right, I have read that.  The Cobra calipers should bolt up.  So I guess the only advantage that leaves are (supposedly) making it easier to bolt up brake ducts, and maybe better (or just different) geometry and a wider track.  So I see what the best choice is here, but let's say worst case one ran the 96+ spindles, IF (big if) you could offset the rack down 1", you'd be close on the geometry? 

I don't know if there's any point to that, but just depends on how hard 94-95 spindles are to find.  I have some 20mm offset wheels and apparently the 96+ spindles may push them out too far anyway.
Long time Turboford freak...
84 SVO
88 TC
87 XR4Ti

Some info about bumpsteer

Reply #9
I'm not sure you can move the rack down 1".  You may start running into things (K-member), and the steering shaft might be too short. 
Dropping it, even if it's 1/2" would help though.
Long live the 4-eyes!  - '83 Tbird Turbo - '85 Marquis LTS - '86 LTD Wagon

Some info about bumpsteer

Reply #10
Remember you can also pull your wheels in with Fox Stang Arms if needed.

I think I am just going to run the 96-98 Spindles. I'm tired of digging for parts. Plus, I don't recall the bumpsteer being that bad on darkthunder or the mustang that they are on now. 
It think it was more tramlining than anything. Except on slow bumps... the steering wheel would turn out of my hand if I wasn't paying attention.
2005 Subaru WRX STi|daily driver

Some info about bumpsteer

Reply #11
Quote from: Chuck W;134712
I'm not sure you can move the rack down 1".  You may start running into things (K-member), and the steering shaft might be too short. 
Dropping it, even if it's 1/2" would help though.

You don't have to worry about the steering shaft. The column portion is collapsable/expandable. :punchballs:

Some info about bumpsteer

Reply #12
id like to know how you can extend it. ive seen a few collapsable steering shafts, and my bird aint got one. the column portion may be collaspable, but that is for impact absorbtion and is on the interior side of the firewall. that wont help in this situation.

my kmember extended the wheelbase 1" and i am gonna be either extendin the stock shaft, or gettin an aftermarket unit.
gumby - beauty may fade, but stupid is forever!

Some info about bumpsteer

Reply #13


See parts #45 and #47? You can move 47 in/out. At least I can on mine. It has gone in 3-4 inches. Maybe I broke something. :o

Some info about bumpsteer

Reply #14
hrrrmmmm, ive pulled on the steering shaft(#50, bolted to 47) pretty hard and it hasnt budged. it should only collapse not extend AFAIK. maybe i need a bigger hammer.....
gumby - beauty may fade, but stupid is forever!