Bump Steer Improvement Options

[gearheadE30]

I've got some ongoing bumpsteer issues with my lowered Tahoe Limited. I am making some assumption that it's actually a bump steer issue and not scrub angle, especially since these trucks also seem to have some pretty aggressive negative ackerman geometry once they are lowered.

IThe truck uses all stock, newish steering components with RideTech strong arms and DJM 2" drop spindles.

I know there are a lot of companies that make drop spindles. I have no idea if they are all the same, but I assume they are not especially considering some have an impact on wheel offset. I was not able to find any information searching, but does anyone know if there is a drop spindle that is known to have the best geometry? I have enough adjustment with the coilovers that I may also be able to go back to stock spindles and still have enough travel. Unfortunately I sold my stock spindles some time ago though, so I don't have any on hand that I can just throw on there to test out.

The only other option I have seen is the Baer Tracker setup, which does seem like it could work. Any firsthand experience with this or anyone who might have figured out if it works using a bump steer gauge?

At this point, I don't plan to go away from the stock steering box/drag link setup.

Considering a bump steer gauge is $300 I have not physically checked the bump steer on my truck. If there isn't some established solution, I suppose I might have to build or buy one to figure out what is actually going on, but this really seems like an opportunity to improve drivability of our lowered trucks.

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[someotherguy]

Was the alignment done to stock height specs or done by someone that understands how lowered trucks behave?

Richard

 

[gearheadE30]

It was not done to stock specs. -1.3 degrees of camber, as much caster as could be dialed in while matching both sides which I think ended up being about 5.5 degrees, and about 1/16" toe in. I know it's a lot of camber for a street vehicle, but it's necessary for fender clearance with 275-section front tires. The next set of tires and wheels will probably be a bit narrower so I can back it off to -0.75 or so.

It has had the bump steer issue through multiple alignments and multiple iterations of suspension parts, including some with less caster and -0.5 degrees of camber. It had the issue a bit before the drop spindles too, but I found enough other hidden issues after doing the drop spindles that I hesitate to draw conclusions that far back.

 

[gearheadE30]

Found my old thread by accident. I ended up getting rid of the DJM spindles and going back to stock spindles with RideTech upper and lower arms and coilovers. Bump steer is gone, and steering effort dropped. Scrub radius is significantly smaller, which helped get rid of offset bump feedback through the wheel.

The truck still has excessive anti-ackerman due to the drag link setup, and I don't think there is anything I'll be able to do about that without a rack conversion. Ultimately not a big deal, just makes for a really big parking lot turning radius because those fat 275-section front tires are fighting each other.

The truck still has a hunting problem, where it feels quite darty going down the road. Some of this is just because of wide tires, but it's still excessive. I think part of the issue is my rebuilt steering box still has play in it. I'm also going to try a little more toe in, but I'm trying to avoid too much to preserve tire life and fuel economy.

 

[Casey Price]

Found my old thread by accident. I ended up getting rid of the DJM spindles and going back to stock spindles with RideTech upper and lower arms and coilovers. Bump steer is gone, and steering effort dropped. Scrub radius is significantly smaller, which helped get rid of offset bump feedback through the wheel.

The truck still has excessive anti-ackerman due to the drag link setup, and I don't think there is anything I'll be able to do about that without a rack conversion. Ultimately not a big deal, just makes for a really big parking lot turning radius because those fat 275-section front tires are fighting each other.

The truck still has a hunting problem, where it feels quite darty going down the road. Some of this is just because of wide tires, but it's still excessive. I think part of the issue is my rebuilt steering box still has play in it. I'm also going to try a little more toe in, but I'm trying to avoid too much to preserve tire life and fuel economy.

Can we get some info from you? Whats your drop and what alignment numbers are you running? TY

 

[gearheadE30]

Can we get some info from you? Whats your drop and what alignment numbers are you running? TY

Roughly a 3.5/5.5 drop on a 4 door 2wd tahoe. Stock spindles, RideTech arms and coilovers. 275 section tires all the way around on 17x8.5 et6 wheels.

I don't have caster numbers, but I knocked out the punchouts, maxed out the caster, and then pulled it back to hit -1 degree of camber. Toe is 3/32" in. If I was having issues with the truck pulling consistently one way or the other, I would be concerned about my caster, but on a smooth road it tracks straight.

I did check the steering box and ended up loosening the sector gear slightly. The input gland nut checked out. The sector gear was a little tight causing some steering drag. Loosening it helped. I don't have time to pull the steering box to do the 'real' drag setting, but I can tell it is still hanging very slightly. I'm sure 'sticking' steering near center was/is probably contributing to the problem. It still tramlines a bit, and haven't done any highway driving since adjusting it to see if there is much improvement there.

 

[Pinger]

The truck still has excessive anti-ackerman due to the drag link setup, and I don't think there is anything I'll be able to do about that without a rack conversion. Ultimately not a big deal, just makes for a really big parking lot turning radius because those fat 275-section front tires are fighting each other.

Correct me if I'm wrong, but isn't anti-Ackerman unavoidable when the steering linkages are ahead of the axle line?

The truck still has a hunting problem, where it feels quite darty going down the road. Some of this is just because of wide tires, but it's still excessive. I think part of the issue is my rebuilt steering box still has play in it. I'm also going to try a little more toe in, but I'm trying to avoid too much to preserve tire life and fuel economy.

What profile are your 275s?
I have 245/65-17 and am thinking of going to 265/65-17. Good idea or bad idea?

Couple of steering issues I have with my C2500 is steering shimmy under braking - but usually only at very low speed - just before coming to a stop.

And a slightly weird feeling at the wheel on fast sweepers where it feels as if the tyre contact patch moves relative to the steering axis at a certain cornering force. Like it tucks under and/or rearwards making it feel slightly 'over centre'. (I have the speed sensitive (EVO?) steering).

I've had a good poke around and kind find anything amiss and it's just been through it's annual (UK) safety inspection where it got a pretty thorough going over. As it sits - by eye, without measuring - camber is slightly positive. Something amiss or are those things just what these trucks do?

 

[HotWheelsBurban]

Correct me if I'm wrong, but isn't anti-Ackerman unavoidable when the steering linkages are ahead of the axle line?



What profile are your 275s?
I have 245/65-17 and am thinking of going to 265/65-17. Good idea or bad idea?

Couple of steering issues I have with my C2500 is steering shimmy under braking - but usually only at very low speed - just before coming to a stop.

And a slightly weird feeling at the wheel on fast sweepers where it feels as if the tyre contact patch moves relative to the steering axis at a certain cornering force. Like it tucks under and/or rearwards making it feel slightly 'over centre'. (I have the speed sensitive (EVO?) steering).

I've had a good poke around and kind find anything amiss and it's just been through it's annual (UK) safety inspection where it got a pretty thorough going over. As it sits - by eye, without measuring - camber is slightly positive. Something amiss or are those things just what these trucks do?

Have you ever changed the shocks? They do more for handling than people think. I noticed a big difference on our Burb with the new shocks, even if they're not as heavy duty as I would like.

 

[Pinger]

Have you ever changed the shocks? They do more for handling than people think. I noticed a big difference on our Burb with the new shocks, even if they're not as heavy duty as I would like.

Not yet!
It's on the list but tyres are ahead.
Could shocks be the cause of the braking shimmy?
On sweepers (to be more accurate, one very long downhill lefthander) I don't think it could be shockers as I have it loaded up constantly for ages in steady roll but if I just tweak the wheel a little bit more that over-centre feeling is there. I can do it as often as I want and it's there - in and out of it and in again. And the truck doesn't turn much tighter (not enough to roll more) as I do it.

 

[HotWheelsBurban]

Could be a combination of the tires and shocks. Ours handles a little worse than it used to, but I feel like once the bushings/control arms are done and new front tires are installed, it'll be good. The 400 series trucks do handle differently than the older square body trucks though; the chassis is more flexible.