May 10, 2024, 08:58:50 AM

Author Topic: Bumpsteer visualization  (Read 3145 times)

Offline Kevin Doe

Bumpsteer visualization
« on: September 04, 2010, 11:25:20 AM »
So since I was unsuccessful at finding someone to borrow their bumpsteer gauge, I decided I'd go the DIY route.  I did some reading online and it looked like all I needed was a laser pointer and mirror.  So I got to work.

Removed my shock/spring (my suspension geometry isn't dictated by the coilover so I can do this).  Cars with McPherson struts or similar will have to remove the spring form their shock/strut to do this.  What you need to do is mount the mirror to your hub somehow.  As long as it moves in the same plane as the hub face it will be fine.  I clamped a mirror to the rotor.  Then setup a laser pointer to reflect off of the mirror onto the wall.  The further you put the paper from the car the more exaggerated the visualization will be.

This is the mirror clamped to my rotor.  The mirror cost me $3 from Meijer.


Here is a picture of the laser pointer, aimed at the mirror.  Its taped to the level, and taped to the table to ensure it doesn't move during this.


Here is a picture of hte finished product.


There are two colored dots.  The pencil color is with maximum correction (thickest spacer able to fit).  The red dots are with only half of the bumpsteer correction spacers installed.  Here is how you read the chart. There is one dot for ride height.  I made dots for 1", 2", and 3" bump and rebound.  Vertical movement is due to camber gain.  Horizontal movement is due to toe changes (this is not good).  Ideally you'd want a purely vertical line.  So if you look at my results you'll see that the best possible solution for me is to use the thickest possible spacer that I can fit.  If I was able to fit more spacers I would, to get that line vertical.

This first video is using less than optimal spacers in the kit.  It follows the red dots on my paper.


This second video is using the maximum amount of spacers on the stud, this follows the pencil dots.
Steamroller

Offline MPbdy

Re: Bumpsteer visualization
« Reply #1 on: September 04, 2010, 12:47:04 PM »
I like that you're posting more again :)

Can you figure out from the distance to the paper how much the mirror is moving?  With the thickest spacer it could be an insignificant amount.

Do you ever notice bumpsteer while driving?

Offline mattster03

Re: Bumpsteer visualization
« Reply #2 on: September 04, 2010, 03:11:52 PM »
Nice work! Should have asked me! I've been renting it out to members for $50. Pez currently has it...
Current Car: 1993 Mazda RX7 Touring, LS1/T56, Stock Stock Stock

1993 Mazda RX7 R1, LS1/T56, EPS 230/238, TSP Ported heads
10.826 @ 128 , 1.53 60' - SOLD

Feature Article - http://www.importmeet.com/blog/2012/03/29/best-of-both-worlds-v8rx7guys-ls1-swapped-1993-mazda-rx-7/
Swap Info - http://www.cardomain.com/ride/2801662

1986 Mazda RX7 GXL, LT1/T56 "Retired"
Swap Info - http://www.cardomain.com/ride/641869

Offline paul_3rdgen

Re: Bumpsteer visualization
« Reply #3 on: September 04, 2010, 04:01:04 PM »
I have a bump gauge as well but shipping it from Canada probably wouldn't be worth it.  Good job on improvising.
93 RX7 R1 500rwhp
LS2, H/C combo... ARE drysump
Race Logic traction Control and 4 wheel Stoptech BBK
3.73 gears installed in the stock diff  :o

Offline Kevin Doe

Re: Bumpsteer visualization
« Reply #4 on: September 04, 2010, 05:13:17 PM »
Nice work! Should have asked me! I've been renting it out to members for $50. Pez currently has it...

I borrowed the laser pointer, and bought a $3 mirror.    :D
Steamroller

Offline mefarri

Re: Bumpsteer visualization
« Reply #5 on: September 04, 2010, 09:53:08 PM »
Great post Kevin.

So a question-
Like Daniel said, can you now measure how much bump is actually present in inches?  Like he said, it might already be within spec.

It would also be cool to be able to measure how much camber is gained just for shits.
"I'm not sure what your intent was because I don't speak "dumbshit", but next time, start your own thread. "

-Jimlab

"Otherwise it looks like something I can build over a weekend, if I spent the first day watching TV."

-Blake motherfucking McBride

Offline MPbdy

Re: Bumpsteer visualization
« Reply #6 on: September 04, 2010, 10:19:11 PM »
I think the camber curve is documented already somewhere.  It won't be different car to car unless you changed arm lengths.

Offline Kevin Doe

Re: Bumpsteer visualization
« Reply #7 on: September 04, 2010, 10:36:44 PM »
As to the question about the actual amount of toe change with suspension travel.  No, I do not know how much.  But I guess with some trig I could figure it out.  Not that it matters, I want it to be the minimum possible, even if its only a minute change.
Steamroller