Bump steer and tie-rod end flip

[krispykritter]

Hello again,

In my continual battle to improve my LexusCruiser, I've lately been trying to figure out why I have wild torque steer and squealing noises if I ever floor the lexus. Today, my wife and I went outside and I did some 1st gear drag races in my neighborhood while she watched, and it rapidly became apparent that the issue is in fact, bump steer. The softly sprung LX lifts the nose a ton when the power comes on, and you can clearly see a metric buttload of toe in occurs as the nose climbs in first gear.

So, has anyone tackled this issue for real? I'm at max caster with the OEM control arms which gets me in spec. My lift isn't extreme - I'd guess around two inches? My AHC pressures are at the low end of the spec but in spec last I checked; I set them there on purpose so they're in spec when I've got the camping trailer and my whole family in the truck.

I'm leaning toward working out a way to flip the tie rods. As they sit now, they have a down angle on them already, so when I plant it, the down angle becomes extremely pronounced and toes in the front. If I flipped them, they'd be mostly level but with a bit of up angle, so raising the noise would toe them out al ittle before toeing them in, limiting the total toe change.

So, has anyone done this yet, or do I get to go off and try my hand at pioneering again?

Thanks for the help.

 

[abuck99]

No such thing as “bump steer” in an IFS truck- with rack & pinion steering. That would have to be a solid axle- pitman arm and drag link steering set up.

Your issue is Torque steer from too much lift up front. Adjust your torsion bars down to where your hub center to fender lip is 21” or less. Then see how it drives.

 

[JunkCrzr89]

No such thing as “bump steer” in an IFS truck- with rack & pinion steering. That would have to be a solid axle- pitman arm and drag link steering set up.

Your issue is Torque steer from too much lift up front. Adjust your torsion bars down to where your hub center to fender lip is 21” or less. Then see how it drives.

 

[jLB]

Hello again,

In my continual battle to improve my LexusCruiser, I've lately been trying to figure out why I have wild torque steer and squealing noises if I ever floor the lexus. Today, my wife and I went outside and I did some 1st gear drag races in my neighborhood while she watched, and it rapidly became apparent that the issue is in fact, bump steer. The softly sprung LX lifts the nose a ton when the power comes on, and you can clearly see a metric buttload of toe in occurs as the noise climbs in first gear.

So, has anyone tackled this issue for real? I'm at max caster with the OEM control arms which gets me in spec. My lift isn't extreme - I'd guess around two inches? My AHC pressures are at the low end of the spec but in spec last I checked; I set them there on purpose so they're in spec when I've got the camping trailer and my whole family in the truck.

I'm leaning toward working out a way to flip the tie rods. As they sit now, they have a down angle on them already, so when I plant it, the down angle becomes extremely pronounced and toes in the front. If I flipped them, they'd be mostly level but with a bit of up angle, so raising the noise would toe them out al ittle before toeing them in, limiting the total toe change.

So, has anyone done this yet, or do I get to go off and try my hand and pioneering again?

Thanks for the help.

“OE UCAs”

“My lift isn't extreme - I'd guess around two inches”

“AHC”

If your “lift” really is ~2”, that’s pretty extreme considering the rest of your “setup”.

The last time I measured, stock AHC was ~19.5” hub to fender in front while in “N”, and ~22.75” at full droop. If you’ve lifted “N” two inches, that would put you around ~21.5” in front, leaving you with ~1.25” (31.75mm) of droop.

As @abuck99 suggests above, I suspect the root of your issue is not enough droop, which I can say from experience really does make an 06 LX, with 5spd & VVTI, drive like s***.

 

[krispykritter]

No such thing as “bump steer” in an IFS truck- with rack & pinion steering. That would have to be a solid axle- pitman arm and drag link steering set up.

Your issue is Torque steer from too much lift up front. Adjust your torsion bars down to where your hub center to fender lip is 21” or less. Then see how it drives.

So I'm sure I'll be flamed pretty hard for this, but you absolutely can and do get bump steer in IFS/rack and pinion vehicles. It's an issue usually encountered by performance cars when you lower the vehicle, but the same dynamics occur when you lift a car as well. That all comes down to the suspension design and the alignment of the various control arms and steering gear, which I don't know on this particular vehicle. It was plain as day to see it even at low speed in my neighborhood by both myself and my wife. You can also see it on many 4wd shows (such as 4wd action) when the front end of an IFS vehicle bounces off the ground. I'll try to jack up the front end this weekend and get toe measurements with the tires resting on the ground and with the tires barely touching.

Yes, you can design an IFS to minimize bumpsteer but it's pretty difficult to remove it altogether, particularly as range of travel increases. From what I gather, you have a single point where all the suspension pieces align properly and you have 'zero' bumpsteer, but as soon as the suspension pieces move, that instant center moves as well. The farther from it you get, the more your bump steer comes into play.

Don't take my word for it - there's plenty of information to google. This article describes it well but isn't for any particular front end suspension setup:

https://www.longacreracing.com/technical-articles.aspx?item=8162

There's definitely plenty of torque steer too but believe me, this is way worse than normal torque steer. I race a FWD car. I've spent most of my life messing with FWD cars. I've driven an 800hp FWD sentra. This is not just torque steer. Some toe plates and tape measures will get me some numbers tomorrow.

“OE UCAs”

“My lift isn't extreme - I'd guess around two inches”

“AHC”

If your “lift” really is ~2”, that’s pretty extreme considering the rest of your “setup”.

The last time I measured, stock AHC was ~19.5” hub to fender in front while in “N”, and ~22.75” at full droop. If you’ve lifted “N” two inches, that would put you around ~21.5” in front, leaving you with ~1.25” (31.75mm) of droop.

As @abuck99 suggests above, I suspect the root of your issue is not enough droop, which I can say from experience really does make an 06 LX, with 5spd & VVTI, drive like s***.

I'd have to go do some measuring as I don't really recall my numbers accurately, but I think I was around 20.75 hub-to-fender front. I also have welded on AHC spacers that add downtravel to the strut. I have what I think is plenty of droop. I'm absolutely not maxing out my down travel when I stomp the gas or blast over speed bumps. I'll attach some photos to this but will also do my best to measure my droop tomorrow.

I do believe more caster from aftermarket UCAs would help the situation but don't think droop is the problem.

Here's some photos for reference (just what I have on my work computer):

Sitting flat and level ish

Compression of front suspension (probably about max compression here):

Drooped almost off the ground:

 

[bamabrock]

If you are level, lower the front to put it back to an 0.75-1" rake and see if that helps the issue to eliminate that concern.

 

[krispykritter]

If you are level, lower the front to put it back to an 0.75-1" rake and see if that helps the issue to eliminate that concern.

I want to say I'm raked around an inch but can't say for certain. Will add it to my list of measurements for tomorrow morning.

 

[jLB]

But if it were simply “bump steer”, it would seem that I’d have all sorts of problems with our 99 LX (21.5” front hub to fender)

and at least some issues with both my son’s 00 LC (21” front hub to fender) and my 06 LX (20.5” front hub to fender.

 

[krispykritter]

But if it were simply “bump steer”, it would seem that I’d have all sorts of problems with our 99 LX (21.5” front hub to fender)

and at least some issues with both my son’s 00 LC (21” front hub to fender) and my 06 LX (20.5” front hub to fender.

I can't speak to your experience, only mine. It's entirely possible it's some combination of worn steering rack bushings and control arm bushing and loose tie rods. I can say we could clearly see the wheels turning towards the centerline but only one side at a time (my wife was obviously unwilling stand directly in from my the LX while I floored it towards her!).

Some measurements tomorrow should bear out one or the other viewpoint easy enough.

The statement that IFS/Rack-and-pinion vehicles don't have bump steer is false, however. I just have no idea if THIS rack and pinion vehicle has bump steer in a straight line.

Edit: on that subject, suspension stiffness matters a ton - less movement will always equal less bump steer. If all your vehicles are on much stiffer setups than my AHC lift, that would make a huge difference in bump steer characteristics.

 

[jLB]

I can't speak to your experience, only mine. It's entirely possible it's some combination of worn steering rack bushings and control arm bushing and loose tie rods. I can say we could clearly see the wheels turning towards the centerline but only one side at a time (my wife was obviously unwilling stand directly in from my the LX while I floored it towards her!).

Some measurements tomorrow should bear out one or the other viewpoint easy enough.

The statement that IFS/Rack-and-pinion vehicles don't have bump steer is false, however. I just have no idea if THIS rack and pinion vehicle has bump steer in a straight line.

Edit: on that subject, suspension stiffness matters a ton - less movement will always equal less bump steer. If all your vehicles are on much stiffer setups than my AHC lift, that would make a huge difference in bump steer characteristics.

If you’ve got some worn/bad bushings and/or rod ends in the front suspension/steering, it can definitely make life “interesting”.

For reference:
I drove the 06 LX with AHC ~13 years, and currently running an only slightly stiffer conventional suspension ( for the last ~2 years). I still occasionally touch the bump stops, and have an additional 2.25” of droop over AHC.

99 LX has a very similar setup to the 06 LX.

00 LC is currently running the basic OME kit, torsion bars, (2)860 light/medium springs and “light” nitro sport shocks. Compared to the other two, it rides like s***, extremely “stiff”.

Good luck chasing down this issue, but from my experience with my vehicles, I suspect that a tie rod end flip would be a wasted effort, that will not really resolve the issue that you’re experiencing.

 

[krispykritter]

If you’ve got some worn/bad bushings and/or rod ends in the front suspension/steering, it can definitely make life “interesting”.

For reference:
I drove the 06 LX with AHC ~13 years, and currently running an only slightly stiffer conventional suspension ( for the last ~2 years). I still occasionally touch the bump stops, and have an additional 2.25” of droop over AHC.

99 LX has a very similar setup to the 06 LX.

00 LC is currently running the basic OME kit, torsion bars, (2)860 light/medium springs and “light” nitro sport shocks. Compared to the other two, it rides like s***, extremely “stiff”.

Good luck chasing down this issue, but from my experience with my vehicles, I suspect that a tie rod end flip would be a wasted effort, that will not really resolve the issue that you’re experiencing.

I do appreciate the input. There's no doubt there's some sort of dynamic steering going on but whether it's truly bump steer or some other combo of worn parts I can't say yet. I replaced the passenger tie rod end last weekend but the one that came out didn't have much play in it.

It drives perfectly fine in a straight line and under normal moderate throttle, it's only at WOT that the weird tracking behavior manifests. I'd say I've probably got something like an extra 1-1.5" droop over normal AHC but nowhere near your 2.25". I know the wheel bearings are good as I rebuilt them recently and checked them a couple weeks ago. I don't THINK the control arm bushings are bad but that's a bit harder to check since they take stupid forces to get decent deflection in them.

I've never flipped tie rod ends before so I have no experience with that. I've heard of that as a solution to bump steer many times but since it doesn't sound like anyone has tried that on a 100 I'd be hesitant to dive into that. Knuckles aren't cheap.

Step 1 will be to take measurements and see if I'm crazy or not. Step 2 will be ?????

 

[krispykritter]

I come bearing news.

I decided to attack this real quick once I got off work. This is what I measured:

Front measurement: 21.5 inches hub to fender
Rear measurement: 21.75 inches hub to fender

On ground toe (front measurement 21.5"):
front edge 73.75 inches
rear edge 73.75 inches

Nearly lifted front toe (front measurement 24.5" = 3" droop)
front edge 73.375 inches
rear edge 73.8125 inches

Total bump steer = ~1/2 inch

So, as before, easy enough to measure. Definitely some toe in under extension, however, what we can see is way more than a half inch of toe in. Realistically, half an inch of toe in would probably help stability when standing on the throttle, so the issue isn't with the static geometry.

Also, I'm definitely low on rake. I thought it was more like 3/4 of an inch but it's really only about 1/4 which is probably too low.

I believe 3 inches of droop is fine?

While I was out there, I yanked, prodded, and pulled on everything I could. The passenger side wheel has some play in it but nothing crazy. The driver's side, however, I was able to manually toe in an inch or more by hand.

I realized as I yanked on the driver's side wheel that I could see the steering linkage moving up and down through the wheel well. I had my wife yank on it, and I can see the steering rack itself shifting up and down with just the force of my 4'11" tall wife pushing on it.

So...it looks like my steering rack bushings are dead dead. I loosened the bolts and tightened them back down and it made zero difference. I think the rubber has just complete detached from the sleeves, and when I stomp the gas, the up angle on the tie rods translates into an upward force on the rack that pushes it a long way away from the frame.

So....it's bump steer, but it has nothing to do with the geometry of the suspension and everything to do with worn out parts! Thanks for the input, once I have new bushings in, I'll report back.

I'm working on uploading some videos of the issue, I'll try to post them up later.

 

[krispykritter]

Video where you can clearly see the toe in occur under heavy accel.

 

[RedesKat]

Only solution I can see is to SAS convert it with portals

 

[ramangain]

Video where you can clearly see the toe in occur under heavy accel.

That is waaaay excessive

It may be worth your time to check all nuts and bolts are torqued to spec just to start.

 

[cruisermatt]

Woah. That video is crazy.

Let me know if I can help with a tie-rod flip if you do end up wanting to do that, I think I have a pretty good idea for how to accomplish that

 

[krispykritter]

Edit: for anyone who trips over this in the future; this post was wrong. On a lift, at full droop, I ended up measuring 3ish inches of toe in.

That is waaaay excessive

It may be worth your time to check all nuts and bolts are torqued to spec just to start.

I checked everything I could get to yesterday and it's all tight. Pretty sure it's the steering rack moving a ton under acceleration forces.

Woah. That video is crazy.

Let me know if I can help with a tie-rod flip if you do end up wanting to do that, I think I have a pretty good idea for how to accomplish that

I appreciate that. The actual measured bump steer (from geometry) isn't large at all, certainly nowhere near what you can see in that video. I've ordered new poly rack bushings to stop my rack from moving all over the place first then re-evaluate!

If I still get crazy acceleration behavior I'll look into what else it could be. I'd really like to avoid a tie-rod flip unless it turns out to be absolutely necessary.

 

[Bisho]

I’d guess your inner tie rods are also shot. At least the driver’s side based on your description.

 

[gatormark91]

TRE's are tapered, pretty sure. No way to flip them easily (I looked at them when I did my lower ball joints with this thought).

What is your toe-in set to? It should be zero. Also, check the bushings on your steering rack.

 

[Mike NXP]

Wow that video is wild, I agree with the previous suspension comments but this appears to be a different issue all together. Can you get it on a lift and give it a good shakedown to see if anything is worn out?