Simple Bump Steer Fix?

[MacAllan30]

It’s a place called T & P Auto Body & Used Cars, 2360 W Main St, Grand Prairie, TX 75050.

It’s run by two older brothers. Cash only ~ $80 if stock/springs. I think $100 if on Coils. Super knowledgeable, lowered car friendly.. like… low. 3 month warranty. If you know who “Juan” is in the DFW scene, he’s the one that told me about them. He sees a lot of Supras.

+1 for T&P and they are good.

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[Lorre]

Thanks for the link, just watched the vid on the Verkline kit but don’t have $8k to throw at the moment As of now, it isn’t horrible by any means but I do plan to track this car and just don’t want it getting weird on me. I was hopping it could be pin pointed to a single part that could be swapped out for the time being. Still need to try a good alignment too

I think one of the core improvements is to swap out the factory rear subframe bushings with solid ones (millway etc). If you see the Verkline subframe, the mouting points to the chassis is much smaller - doing away with the factory rubber bush. This makes the subframe mount much more solidly to the body.

I haven't done it so don't have first hand experience, but i do think this is something worth looking into.

 

[Miko_Z]

I think one of the core improvements is to swap out the factory rear subframe bushings with solid ones (millway etc). If you see the Verkline subframe, the mouting points to the chassis is much smaller - doing away with the factory rubber bush. This makes the subframe mount much more solidly to the body.

I haven't done it so don't have first hand experience, but i do think this is something worth looking into.

Thanks for the input Lorre! You might be right, I plan to replace those when I get a chance to throw coilovers and sway bars in. A new alignment did help a lot but still want to improve where I can

 

[Thraxbert]

Guys, if it's actually bumpsteer, then no amount of working on the rear end is going to change anything. Certainly not new subframes or dropping the entire subframe to change the bushings wtf.

Solving bump steer, implied in the name to be a STEERING problem, which I'll remind people is at the front of the car, has 3 approaches at the front end of the car:

1. Get a better alignment.
2. Get a narrower front tire that is not so willing to follow the road.
3. New front tie rod ends with adjustable bump steer correction.

Now, the Supra can also have some rear end squirreliness depending on your setup. That is not bump steer. That is a separate set of problems. You can mostly solve it with front/rear differential lockdown braces and a new rear traction arm.

 

[Kujiwara]

Supras seem to come out of the factory with pretty badly set alignment, would only get worse after hitting the road, check out this thread before alignment https://www.supramkv.com/threads/solved-literal-bump-steer.20636/

 

[razorlab]

Guys, if it's actually bumpsteer, then no amount of working on the rear end is going to change anything. Certainly not new subframes or dropping the entire subframe to change the bushings wtf.

Solving bump steer, implied in the name to be a STEERING problem, which I'll remind people is at the front of the car, has 3 approaches at the front end of the car:

1. Get a better alignment.
2. Get a narrower front tire that is not so willing to follow the road.
3. New front tie rod ends with adjustable bump steer correction.

Now, the Supra can also have some rear end squirreliness depending on your setup. That is not bump steer. That is a separate set of problems. You can mostly solve it with front/rear differential lockdown braces and a new rear traction arm.

You can absolutely have bump steer in the rear. It's not connected to the steering wheel. It's the act of the car doing unintended "steering" (front or rear) when geo changes radically after disrupting the chassis from say, hitting a bump in the road. Basically, it's a change in the steering angle of the wheel (not the steering wheel) when the wheel is in bump or droop. Example, rear toe changing drastically when at full droop or under compression. Or front toe and rear toe changing drastically under hard braking. Front is at compression, rear is at droop.

That said, once I changed the rear toe and traction arms and put on MCS coilovers, all the oddness went away. I haven't touched the subframe. This is also on a 2020, which seems to have this more than 21+.

You can also tame this a little by just an alignment, if you know what is happening. Example, say, adding extra rear toe in to compensate for the suspension trending towards toe out under compression or droop.

 

[Thraxbert]

Bump steer is a front axle problem. What you're highlighting in the rear is bump toe.

//edit: or crappy OEM trailing/traction arm bushings for you people who launch the car.

 

[i3igpete]

Bump steer can occur in the rear. Attaching a copy of "Tires, Suspension and Handling" by Dixon, where the expressions are in section 5.16.

Dixon also refers to what brian describes with the traction arms as "compliance steer". But kinematically, it's the same thing.

edit: file too big. maybe this will work.

https://pdfcoffee.com/qdownload/tires-suspension-and-handling-1-56091-831-4-pdf-free.html

 

[Vertex]

I never had an issue with bump steer but did just get an alignment done on mine finally a couple thousand miles after I got new tires on where I work.

We found that the rear end alignment was a fair amount out of spec and was basically tracking the whole rear end to the right on both rear wheels. Fortunately at the time I hadn't taken it to the track yet so I never really noticed much of an issue. We also adjusted the front toe enough to essentially get it to a point where it was much more flat or better for tire wear up in the front as well.

End results picture of before and after measurements

Also wanted quick add I was at the track this past weekend. Not sure the car could have driven any better except for more seat time/driver mod for myself. I wish I would have gotten two dry days but day 2 was very rainy and I only had part of a session where it was just kind of starting to dry up and then started to rain again.

 

[razorlab]

Bump steer is a front axle problem. What you're highlighting in the rear is bump toe.

Agree to disagree, and I agree that you are wrong.

Bump toe can happen front or rear, and that leads to bump steer, front or rear.

There are countless documents on this.

 

[i3igpete]

Verkline subframe WILL adjust the bumpsteer curve, since you are changing the pivot point locations. i.e., move pivot point inboard and lengthen arm to compensate, will give a smaller magnitude of toe at the endpoints. Moving the pivot point up or down will change the bump/droop position of max toe-out, but will NOT change the max toe-out magnitude.

That being said, I would never buy it because they (verkline themselves) took an entire day to install it, and then took another day and a half to do the kinematic alignment. That tells me that it would be incredibly easy to fuck up and make worse.

 

[Jah29]

I have an email from verkline where they said just using their subframe with adjustable toe arms got you to 90% of their full setup.

 

[Michael-Dallas]

FWIW-

A buddy and I were talking about this the other day. He rented a Supra and drove it on the Nurburgring back in 2019 and commented about the rear bump steer.

Some time later, the owner of the rental company (and Supra) posted this video in his YT channel:

 

[FLtrackdays]

Verkline subframe WILL adjust the bumpsteer curve, since you are changing the pivot point locations. i.e., move pivot point inboard and lengthen arm to compensate, will give a smaller magnitude of toe at the endpoints. Moving the pivot point up or down will change the bump/droop position of max toe-out, but will NOT change the max toe-out magnitude.

That being said, I would never buy it because they (verkline themselves) took an entire day to install it, and then took another day and a half to do the kinematic alignment. That tells me that it would be incredibly easy to fuck up and make worse.

Great find Iggy Pete! I was actually considering purchasing that Verkline subframe. But it makes sense the more you complicate things, the more you can fcuk it up. And since I’ve been really satisfied with the performance of the car, I’d rather just get the bolts Robert/Thraxbert kindly located for us (fantastic link below ?) & replace when needed.

https://www.supramkv.com/threads/oem-suspension-bolt-kit.17261

I do like Verkline’s product line better than the others. Luckily Bryan/Razorlab shared that great find. I’ll keep using their stuff when things need replacing.

 

[kyle9]

Lowering the car messes up the rear toe curve, ie it changes the way that toe changes through the range of motion of the rear wheel (yes, this is called bump steer - your wheels changing direction under bump)

As @razorlab pointed out, the rear toe and traction arms can be replaced to correct both the toe and toe curve, respectively.

no need to touch the subframe or believe dumb YouTube videos to make a simple geometry change. Also, if you leave your car at oem ride height you won’t really have issues.

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