how do bump steer kits work?
Nov 15, 2007, 08:40 PM
#1
how do bump steer kits work?
i understand the idea of relocating the inboard joints to match up with the control arm length and angles, but those are steering rack relo kits.
what do bump steer kits do? what measurement are they shifting? and how does that even help if they can't do some massive relocation?
what do bump steer kits do? what measurement are they shifting? and how does that even help if they can't do some massive relocation?
Nov 17, 2007, 09:59 PM
#2
i understand the idea of relocating the inboard joints to match up with the control arm length and angles, but those are steering rack relo kits.
what do bump steer kits do? what measurement are they shifting? and how does that even help if they can't do some massive relocation?
what do bump steer kits do? what measurement are they shifting? and how does that even help if they can't do some massive relocation?
Nov 18, 2007, 02:31 PM
#3
apparently what needs to be understood about all this is that when the tie rod is most parallel it gets the largest toe out condition it can as parallel creates the longest arm.
the tie rod (bump steer) or control arms (roll center adjustment) must be placed (mounting points) in such a way as to be above or below the parallel points in order to create favorable resultant geometry despite the to unequal lever arms changing things during suspension motion.
if the tie rod (toe arm) is pointing upwards (toward the outside of the car) then as the suspension droops the toe arm goes toward parallel (increasing tow). this is good for a rear suspension geometry because at a corner entrance situation (after some braking) the rear is less loaded (more droopy) and with some toe out in such a condition the car becomes more maneuverable. (this is the stock set up for the evo)
this is why the toe correction kit from whiteline makes an eccentric sleeve that relocates the inboard joint slightly lower (makes the tie rod point up more). this may or may not be reliable though because it relies on the stock system to "hold" (torque down) on the sleeve to keep it from flopping around inside the bushing.
the tie rod (bump steer) or control arms (roll center adjustment) must be placed (mounting points) in such a way as to be above or below the parallel points in order to create favorable resultant geometry despite the to unequal lever arms changing things during suspension motion.
if the tie rod (toe arm) is pointing upwards (toward the outside of the car) then as the suspension droops the toe arm goes toward parallel (increasing tow). this is good for a rear suspension geometry because at a corner entrance situation (after some braking) the rear is less loaded (more droopy) and with some toe out in such a condition the car becomes more maneuverable. (this is the stock set up for the evo)
this is why the toe correction kit from whiteline makes an eccentric sleeve that relocates the inboard joint slightly lower (makes the tie rod point up more). this may or may not be reliable though because it relies on the stock system to "hold" (torque down) on the sleeve to keep it from flopping around inside the bushing.
Last edited by trinydex; Jan 4, 2008 at 05:32 PM.
Nov 18, 2007, 02:38 PM
#4
so you can see that the whiteline front bumpsteer adjustment kit relocates the mounting joints at the tie rod (toe arm from steering rack) and spindle to put the control arm back in a more like stock orientation (sloping angle) after you have lowered it
these examples are from a mustang but the idea is the same. they're known as tie rod ends or rod ends or pillow ball ends.
these examples are from a mustang but the idea is the same. they're known as tie rod ends or rod ends or pillow ball ends.
Last edited by trinydex; Jan 4, 2008 at 05:28 PM.
Nov 18, 2007, 02:41 PM
#5
the roll center correction kits are there to relocate the joint at the control arm and spindle, lower. this is to get the control arm to point downward on the outboard end of the car. as you lower the car the control arm gets more and more parallel or past parallel (pointing upward). after this happens when the suspension compresses the lower control arm will move up further. as we can imagine camber is related to the difference between offset of the upper and lower control arms. so if the lower one is moving up more (past parallel) then it is reducing camber (all else equal).
remember parallel is the longest the arm is going to "seem." pivoting anything beyond parallel in either direction and you're you're shortening the lower control arm's length (this is of course dynamic cuz the suspension moves) with respect to the outboard joint. but also remember that we don't care about a droop condition too much (you don't want an increase in camber for droop) you only care when the suspension is loaded (in turn). the preference is to let the droop lose all kinds of camber so you can gain or maintain camber under compression.
that's why when you lift your car you lose tons of negative camber.
remember parallel is the longest the arm is going to "seem." pivoting anything beyond parallel in either direction and you're you're shortening the lower control arm's length (this is of course dynamic cuz the suspension moves) with respect to the outboard joint. but also remember that we don't care about a droop condition too much (you don't want an increase in camber for droop) you only care when the suspension is loaded (in turn). the preference is to let the droop lose all kinds of camber so you can gain or maintain camber under compression.
that's why when you lift your car you lose tons of negative camber.
Last edited by trinydex; Jan 4, 2008 at 05:36 PM.
Nov 18, 2007, 03:00 PM
#6
so the moral of the story is that all these things can be had in fully adjustable tie rod ends. this is really the only way to overcome overlowering and suspension geometry changes based on the stock suspension architecture.
http://www.deck-japan.co.jp/List%20Suspention.htm
deck mechanical makes a lot of these items for the evo.
you need to be careful running spherical jointed stuff. dust and dirt can destroy these joints and make them loose.
also you need to be sure items like these are made well. the problem is many times roll center kits are just a small rod that connects the control arm (big) to the spindle (big and iron) and there needs to be some confidence that these items will hold up otherwise you'll lose 'em under load and crash badly.
look for boots for the joints like this http://www.sealsit.com/rodend.asp
http://www.deck-japan.co.jp/List%20Suspention.htm
deck mechanical makes a lot of these items for the evo.
you need to be careful running spherical jointed stuff. dust and dirt can destroy these joints and make them loose.
also you need to be sure items like these are made well. the problem is many times roll center kits are just a small rod that connects the control arm (big) to the spindle (big and iron) and there needs to be some confidence that these items will hold up otherwise you'll lose 'em under load and crash badly.
look for boots for the joints like this http://www.sealsit.com/rodend.asp
Last edited by trinydex; Nov 18, 2007 at 03:03 PM.
Jan 4, 2008, 05:55 PM
#13
on my old car, we would shim the steering rack instead of changing the tie rod end. so long as when you shim the rack it keeps the same arc as indicated in your first thumbnail.
i.e. 1" drop. .75" - 1" shim under the steering rack.
Great write up tho.
p.s. triny, im going to use some of your thumbs for my suspension thread i pointed you to.
i.e. 1" drop. .75" - 1" shim under the steering rack.
Great write up tho.
p.s. triny, im going to use some of your thumbs for my suspension thread i pointed you to.
Jan 5, 2008, 08:53 PM
#15
not necessarily shimming, in my case when i lowered that front end of my 914/6 i placed two spacers about an inch thick between steering rack and were the rack mounts to the unibody.