Bump Steer Kit Necessary?

[Doc76]

I just came from a local well known custom suspension shop. He's is recommending a bump steer kit when he does the alignment on my car and adding 1/8" wheel spacers to get the rims away from the UCAs. When I asked why regarding the bump steer kit, he said "its just good practice" and will assure no "sloppy, squirrelly" feel in the steering.
I thought this feeling that I have experienced was the nature of a short, light car with power steering.
This is the first time I am hearing this could be bump steer. (Used to modern cars)
I can appreciate the value in the 1/8" wheel spacers but bump steer kit?
Would this actually resolve the feeling in my steering or is this the nature of our platforms?

They're available locally for ~$300 CAD so rather not spend the money needlessly

[Jeff Kleiner]

So let me get this straight…the guy hasn’t measured to determine whether the car even has bump steer and he wants to sell you a bump steer kit…to correct a problem which you may not have. That’s like a heart surgeon wanting to do bypass surgery before even determining whether you have a blockage! At the risk of you thinking that I’m sounding like Rich (who is actually one of the most knowledgeable guys here) get the car to somebody who knows what the heck they’re doing—the guy trying to sell you a bump steer kit isn’t that guy—-and do as I said earlier by establishing a baseline with proper alignment, ride height and corner weights.

Jeff

[Doc76]

So let me get this straight…the guy hasn’t measured to determine whether the car even has bump steer and he wants to sell you a bump steer kit…to correct a problem which you may not have. That’s like a heart surgeon wanting to do bypass surgery before even determining whether you have a blockage! At the risk of you thinking that I’m sounding like Rich (who is actually one of the most knowledgeable guys here) get the car to somebody who knows what the heck they’re doing—the guy trying to sell you a bump steer kit isn’t that guy—-and do as I said earlier by establishing a baseline with proper alignment, ride height and corner weights.

Jeff
He doesn’t sell them nor any affiliations with anyone that does. Didn’t even try suggest where to buy.
I believe his suggestion was based on frequency he sees them needing to go into FFR cars

[Jeff Kleiner]

He doesn’t sell them nor any affiliations with anyone that does.

But he wants to sell you the installation labor.


I believe his suggestion was based on frequency he sees them needing to go into FFR cars

Well, he must frequently work on Mk1 and Mk2s because the geometry changes made to the Mk3 and Mk4 made bump steer virtually nonexistent.

Carry on.

Jeff

[edwardb]

He doesn’t sell them nor any affiliations with anyone that does. Didn’t even try suggest where to buy.
I believe his suggestion was based on frequency he sees them needing to go into FFR cars

What Jeff said... recommending you "fix" something without know whether it's broken. To be fair, Factory Five builds for many years used Mustang donor spindles. Some were better than others. But bump steer typically was something that needed improvement. When Factory Five tooled up and released their own design spindles (https://www.factoryfiveparts.com/14850-mk4-two-piece-spindle-set/) in the range of 10+ years ago, the issues were addressed and bump steer isn't an issue. I've had multiple builds with these spindles, after my first build with Mustang donor spindles, and I can confirm they are rock solid with no bump steer. Probably the "frequency" he mentions is from prior times. Not current builds.

Edit: Jeff beat me again. But we're on the same page.

[Doc76]

But he wants to sell you the installation labor.



Well, he must frequently work on Mk1 and Mk2s because the geometry changes made to the Mk3 and Mk4 made bump steer virtually nonexistent.

Carry on.

Jeff

Thanks for the info

[Doc76]

What Jeff said... recommending you "fix" something without know whether it's broken. To be fair, Factory Five builds for many years used Mustang donor spindles. Some were better than others. But bump steer typically was something that needed improvement. When Factory Five tooled up and released their own design spindles (https://www.factoryfiveparts.com/14850-mk4-two-piece-spindle-set/) in the range of 10+ years ago, the issues were addressed and bump steer isn't an issue. I've had multiple builds with these spindles, after my first build with Mustang donor spindles, and I can confirm they are rock solid with no bump steer. Probably the "frequency" he mentions is from prior times. Not current builds.

Edit: Jeff beat me again. But we're on the same page.

Makes sense as to why he may have suggested it. He asked and I told him I was on donor spindles
My kit was purchased just prior or likely during that change.

[GoDadGo]

FYI:... I've been driving my MK-4 legally for four (4) years and have experienced NO SIGNIFICANT bump steer.

..........My ride height is set so that the tie rods are pretty much level with the ground with a front ride height of roughly 3.75".
..........The car is aligned to near factory specs for the manual rack which is 3.85 Caster, .6 camber and 1/16 toe.
..........Though I'm no serious corner carving auto-crossing fiend, I do like curvy roads as most owners do.
..........I do not have a Bump Steer Kit on my car but did add a .75" front sway bar to create a little push.
..........Our biggest issue down here here in the South are the roads themselves.
..........I did upgrade to 200 TW tires this past spring to gain some grip.

Hope This Helps!

https://youtu.be/iwslgKJUaKc

[Jeff Kleiner]

Makes sense as to why he may have suggested it. He asked and I told him I was on donor spindles
My kit was purchased just prior or likely during that change.

FYI, even with donor spindles Mk3 and 4 bumpsteer is minimal. My new Ram pickup has more bump steer than my Mk3 with Mustang spindles ever did.

Jeff

[CraigS]

I agree, bump steer is a really fine tuning tool, but it needs to be measured before even considering spending the $. I'd file the thought for maybe 2026.

[rich grsc]

FYI, even with donor spindles Mk3 and 4 bumpsteer is minimal. My new Ram pickup has more bump steer than my Mk3 with Mustang spindles ever did.

Jeff
Even my 2020 Subi STI has mild bumpsteer. It's a NON issue, I just don't get why everyone gets in a tizzy about it.:confused: