Crazy bump steer with 37s.

[II Sevv]

Have a 2011 super cab and just installed 37” KM3’s. In the front I have king coilovers set to about what top perch would be, Camburg upper arms, and brand new tie rods. Obviously this is to be expected with heavier, larger diameter tires, but steering response is now absolutely atrocious. Above 70 on the freeway, any bump or dip in the road generates massive bumpsteer that almost feels like driving a solid axle. This only happened immediately after installing the new tires. Any solutions? I’m assuming this is now because the rack cannot exert enough leverage on the tires given the angle of the tie rods with the front height and the leverage the now larger tires are able to exert on the rack.

 

[CoronaRaptor]

Interesting, bumping this to see what the response is. Do you mean shaking in the front or ....?

 

[PlainJane]

I suspect your alignment is set to "stock" specs instead of the revised specs for raised suspension. You might try more caster and toe.

 

[zombiekiller]

sounds to me like too much preload and overinflated tires.

 

[BillVickers]

Bumpsteer is a direct relation to geometry. As Plainjane suggested, I'd call upon the suspension manufacture and inquire about their recommended alignment specs.

 

[Muchmore]

I completely agree. I'm used to calling it "rut steer" from heavy trucks leaving ruts in the roads. "Usually" the width of tires are what gives that bad pulling in rutted roads. I mean you could go with a 40x12.50 and it will pull the game as a 35x12.50.

Just like motorcycle tires the height of a tire is what makes it hard to turn left or right because of the rotating gyroscopic effect. Usually, the contact patch is what gives that bad rut steer. As if a 12.50 won't pull as bad as a 15.50 regardless of how tall is is.

I would check alignment for sure if the tires are the same width as your old ones.

 

[CoronaRaptor]

Are you guys confusing Bumpsteer with Tramlining? Tramlining is when the vehicles shifts left to right when riding up and down on the crown of a road path.

https://www.tirerack.com/tires/tire... tramlining,uneven pavement or severe rutting.

 

[Vader]

Post a picture of the tie rod from rack to spindle. If the angle is pronounced you will have bump steer.

 

[Jakenbake]

Directional bump steer (L or R) on an IFS would only occur when only one tire catches a bump or rut, correct? Otherwise it would only result in a toe in or toe out equally with both tires.

 

[zombiekiller]

Directional bump steer (L or R) on an IFS would only occur when only one tire catches a bump or rut, correct? Otherwise it would only result in a toe in or toe out equally with both tires.

no, that won't cause bump steer on IFS. ( at least not unless the bump encountered with a singular tire is significant enough to make the tire turn. the steering tie rod design should compensate for the up/down motion on an IFS suspension and not be impacted. higher travel designs tend to use a heim to provide for more wheel travel.) It can on an i-beam suspension though. On IFS, The rack should exert enough force to not cause the other tire to change direction

As stated above by another poster, If the angle of the tie rod from rack to the spindle is too steep, you will experience what "feels" like bump steer.

The reason that I would start with lowering the preload is that the suspension is most likely close to full droop with the preload ratcheted that high. The effective spring rate will be overly stiff.

going over a bump will be quite stiff and with the angle of the tie rod due to the excessive preload, you'll feel bump steer because the rebound force from the over-preloaded spring will cause EVERYTHING to feel quite jarring being that a lot of additional force would be needed to actually compress the suspension. ( which would soak up the bump if adjusted to be within spec. )

The stiffness of the suspension will also lead to feeling every loose tolerance in the entirety of the front suspension/steering systems.