Best Way to Measure Bumpsteer?

[JESSE_at_TLT]

Hard numbers are hard to come by. So what is the best (most accurate) way to measure bumpsteer? I would like to compare the suspension characteristics/geometry of a few different suspension/steering setups. Specifically, a Total Chaos LT 4WD/Prerunner Tacoma front suspension kit with stock extended tie-rods vs. the Total Chaos heim steering upgrade (stock inner joint and outer heim) vs. the ESB heim steering upgrade (inner and outer heims). I know that the stock Tacoma front suspension has a good amount of bump-steer to start with, so I was planning to cycle that for a base-line comparison.

So how should we set this up to get some objective/reliable numbers? I was thinking about setting the frame level on jack-stands and bolting a piece of angle-iron or something to the wheel-studs, oriented so that it would point towards the front of the truck and be set parallel to the ground. Then if I set something with a straight edge vertical alongside the piece of angle-iron, wouldn't that give me a good 0-point to measure bumpsteer from as we cycle the syspension? Is there an easier way? Something like a digital/laser angle finder that could track horizontal movement against a wall or something?

Follow-up question: I hear people refer to bump-steer in inches all the time, but wouldn't it be better measured in degrees? Like when measuring toe-in in inches, you have to be talking about a specific tire size if you're measureing at the tread. There's a lot of difference between .5" toe-in on a 31" tire and a 40" tire.

Thanks in advance for any helpful input.

[CRAIGHALL]

I haven't seen any of the kits first hand but ,how would one have more or less if they all use the original attachment points?Except of course the difference in height that may come from ball-joint center line to mount surface as opposed to a heim.

[Ramsey_ElWardani]

[ QUOTE ]
Follow-up question: I hear people refer to bump-steer in inches all the time, but wouldn't it be better measured in degrees?

[/ QUOTE ]

Buy, beg, borrow or steal a Camber/Caster Gauge and measure in degrees.

[JESSE_at_TLT]

The steering shouldn't change too much between the stock and Total Chaos steering, but the ESB steering geometry is a little different because it replaces the stock inner joint with a heim/clevis. It's definately a stronger setup, and I would like to measure the trade-off between strength and bumpsteer.

[JESSE_at_TLT]

I'm not too familiar with the different tools that are available to take these measurements. I know what camber/caster are and I've been able to improvise using what I've got, but what are some of the better tools and methods?

[ntsqd]

One way to do it:
Longacre Bumpsteer Guage (http://www.longacreracing.com/catalog/item.asp?id=156&catid=5)
Might try supporting the spindle at the lower BJ/SB and jacking the chassis up and down rather than making a really big plate.

[dadunc205x]

the only way i can think of getting inches of bumpsteer, and not having variations with tire size is to have a straight line from the axis(lower BJ) that travels directly under the outer tie rod/ or heim joint centerline. and measure the amount the center of the tie rod/ heim crosses the straight line in either direction. maybe use a plumb bob or something similar to get the center of the tie rod end, as it crosses the fixed line off the BJ. maybe??

bumpsteer should be around the same unless the clevis on the rack has a pivot angle more inward towards the frame.
the center of the pivot is about an inch from the end of the rack, so it seems hard to eliminate much bumpsteer at the rack.

[hoeker]

that is exactly how i set my truck up. i used 2 almost 8' sections of angle bolted to the hub. i put the angle iron level at full droop and marked lines on the floor with a verticle level, then leveled it(the angle iron) again at ride ht and full bump and marked accordingly. because of your suspension geometry the lines will not lie on top of each other, but need to be parallel. i went the next step farther and used the bars to check my ackerman angle at roughly 45 deg steering angle(the max i could get before hitting the frame). with such long bars i was able to check if they were pointing the right direction when i turned. athough not very scientific, and very time consuming the results were superb.

most people measure bumpsteer in inches and off the diam of the tire. ie."1/8" of bumpsteer" they are typically checking this with a tape measure off the tire tread. when i designed my steering around the use of a gauge like you described i was able to build my steering to less than 1/8" of bumpsteer over an 88" bar! the results are unmeasureable at the tire with a tape measure.

if i was simply trying to gauge different kits i think i'd find an alignment shop that could cycle the suspension while on the rack.

[racer_dude]

havent checked bumpsteer in a while but this is how we used to do it..

we would take 2 pieces of angle iron and set them ontop of the hub and vice grip them to it so they didnt slide around. then we would have 2 people on each arm and lift the arms to the same height and have the third check the distance between the two pieces of angle iron and let the tape measure pull itself out with the bumpsteer ( as close to the hubs as possible ) and move the arm up a little more and repeat all the way untill full bump.. not scientific but it gets the job done.. and as far as it being in inches or degree's it is just easier to say inches because not to many people have the tools or the knowlage to know how much a 45 degree angle change is....

as far as toe we measure from rim to rim, not the outside of the tire or the tread, we go from inside of rim to inside of rim. thus giving more of a genral distance no matter how big the tire. and there is only a 2" difference between most rims so the distances are perty universal

[Jkrell]

on RG 4 seater buggy i did it the same way as Hoeker mentioned. Bolt square or angle to the outside of the hub and plumb down to the ground at full drop, ride height, and full bump. VERY time consuming since you have to re-square the stearing every time you move the inner/outer tie rod pivot, but it definately gets the job done in a low tech environment. You can also check scrub and ackerman with this as Hoeker mentioned.

jk

[JESSE_at_TLT]

Thanks for all the replies.

[steveG]

I know most people don't have access to one, but one of these days when I'm feeling really energetic (and my front end is done) I'm going to measure it on our aligment rack at work. It'll be in degrees.