Bump steer!

So I've been lurking on here for a while now, and after a lot of reading I decided to go with Bilstein 6112's at the 4th notch(about 2.5"), LR UCA's along with new oem LCA's(worn bushings/seized cam bolts). Without having the alignment sheet in front of me I can tell you my camber and toe specs were close to 0* and my caster is 2.5, and it's got pretty annoying bump steer and is a little sketchy on the highway. I read somewhere on here that too much caster can actually cause bump steer but a lot of people recommend 2.5+ of caster. So should I try 3* or try going down a bit?

P.S. Tires are 265/75/16 Falken Wildpeak at3w on SCS f5

 

I would try to set caster as high as possible.. do the right side 1st then set the left side about 1 degree lower than the right to compensate for road crown. i would try and keep camber as close to zero as possible...

 

Thanks for the response! I think I may try 3-3.5 but I really don't want to pay for multiple alignments to get it riding right.

 

Anyone else have some suggestions??

 

I had been battling bump steer ever since I lifted my Tacoma with LR UCA's too, and what Tommie said is spot on. While 2.5 degrees of caster is good, staggering the caster is even better. I finally found an AWESOME alignment shop, and they took their time and road tested it a few times and ended up with 2.5 degrees on one side and 3.5 on the other. It really did make a noticeable difference. I was sure to mark everything really well with a white-out pen as soon as I got home.

It's also worth mentioning that this was at the only shop that ever adjusted the angle of the ball joints in the control arms. I found them by calling around and asking if they have ever worked with the LR UCA specifically. Lots of shops said sure, we've worked with shims before, and tried to explain to me how how cams and shims work. NOPE. Not what I asked. In my experience, most alignment techs won't touch the ball joints even if I give them a diagram and explain how they work.

As for too much caster, I think you have to go REALLY overboard with these trucks to achieve that. After one shop really screwed up so bad they didn't even charge me (kept me waiting 3 hours for an alignment that was still out of spec), I had 2.5 degrees on one side and almost 6 on the other. It was tolerable, even on the freeway. I drove it like that for about a month before replacing a control arm under warranty and having the alignment done again. I can't say if the bad alignment contributed to the control arm breaking, but it was a typical break for the older design that has since been corrected.

 

I don't really feel the truck pulling away from the crown in the road. So do you think I should try *3.0 on the left side and *3.5+ on the right?

I forgot to mention I also installed a 1/4 spacer on the drivers side if that's something I should try to compensate for as well?

 

I have a 1/4 spacer on the driver side too, and I didn't feel it pulling to one side more than the other either honestly. The manager didn't give a great reason for the difference in castor, but said sometimes uneven weight can do that. Our trucks definitely have more weight on the driver side. I didn't hear about the road crown argument until just now, but I didn't talk to the tech either, just the guy in charge.

 

I wold like to hear other people's experiences who have had bump steer and their alignment specs. I know some people have stock UCA's and get about 1.8 caster and like how it drives but then other people have aftermarket UCA's at 3+ and like it. I've also read that too much caster can cause bump steer so I don't want to go in the wrong direction.

 

Dont compensate for road crown... freeways are flat or banked in both directions depending on the curve. Compensating for "road crown" is a joke IMO and will only lead to a truck that doesnt track straight.

Get each side as even as possible.

I had stock ucas on my 1.75in lifted front at ~ 1.5* of caster with no negative camber.

Put on SPC UCA's and had the alignment guy do 3.4* Of caster with -0.4* of camber (for more even inside to outside tire wear) and 0.1* of toe in per side. Man o man, ignorance is bliss, truck drives SOOOOO much better now.

 

6112's up front on 4th notch but with the allpro UCA's.

Truck drives great at these specs.

 

Thanks guys! I'm going to try 3.4 caster and see how that handles!

 

Well... Freeways are crowned, at least around here. Obviously not in curves but on straight road they are. That being said I wouldn't adjust for it either, because if you are in the passing lane it is adjusted in the wrong direction and will make the pull worse. Secondary streets generally aren't crowned either so it won't be quite right.

 

+3 Caster. 0 Toe. 0 Camber. Perfect # to me.

 

I'm not going to say that even caster is a bad thing, because usually it is important for handling, but I think that for certain applications there really is a solid argument for less caster on the heavier side. My reasoning relates to how caster works:

Caster is the angle of the axis of rotation that your steering knuckles rotate on when you turn. This means that caster values different from zero tilt the tire slightly onto its shoulder when you turn, giving it temporary pos or neg camber. Since the weight of the vehicle on that side is pushing straight down, it's trying to force the tire back down to zero camber, which in turn forces the tire to point straight ahead (to help visualize it, imagine having 90 degrees of caster--your wheels would just tilt side to side instead of turning left or right). This means there is more 'straightening force' on the heavier side, which pushes the tire more aggressively towards flat/straight.

In reality the tire just deforms slightly instead of lifting up onto a corner, but the effect is the same. The tire is acting like a spring when you turn, trying to level out and point straight. This extra resistive force that tries to point one wheel straight more than the other is kind of like bump steer, since bump steer is caused by unbalanced forces trying to direct the tires (if you hit a bump at an angle with the left tire, then there is more force directing the left tire, and the truck pulls to one side). If you give the truck less caster on the heavier side, you will get closer to equal resistive force on either side of the vehicle when you turn, making it comparable to an evenly weighted vehicle with even caster on both sides.

I looked at my alignment spec sheet, and sure enough the shop gave my truck a full degree less of caster on the driver side, which is by far the heavier side. I have a 1/4" spacer on the driver side to compensate for the weight, and my truck is still sagging more on the driver side from the uneven weight distribution. My handling was tolerable (for me) when I had even caster, but it really did improve after the shop I went to gave the passenger side more caster.

As for too much caster, some cars (like BMW's) are specified to have 6-8 degrees of caster stock. I had close to 6 for a while due to a tech who didn't know what he was doing, and it honestly wasn't that terrible (still bad, just not as bad as 0 caster).

 

Does this look good? I'm still getting a little bump steer. I'm playing around with the tire pressure now to see if that helps.

 

Anyone have any suggestions on what else could be causing bump steer?

 

I wouldn't go quite as high as possible. I did this initially and ended up at 6.1 caster on both sides. I didn't really notice bump steer but it was noticeably more difficult to turn the wheel and I was concerned it was putting added stress on the power steering system. I since adjusted my LR UCAs and got my caster down to 3 3. Very happy there.

 

Anyone else battle bump steer? I'm starting to think it may be my tires? I had my tires installed before I got my suspension, but I also got an alignment at the same time, I thought it was the alignment because I never got a printout of the specs. So I went to another shop to get another alignment and they told me my my LCA bushings were going and my cam bolts were seized. So I got new OEM LCAs and while I was at it I got new suspension and UCAs. The bump steer isn't bad, the steering wheel moves an inch or two left or right, and it's only when the wheel is straight.

 

So I've searched like a mad man and narrowed it down to either the tires themselves or something in the steering column/shafts. But there is no play in the steering itself, And there are no noises whatsoever. So does anyone have experience with any issues in the steering column that didn't have play or make noise?

 

What is your tire pressure at? When I got my new Duratracs, I was running them at 42 psi. Dropped them down to about 35 psi and it got rid of the bump steer.