Project CMS

CMS-GT4

Active member
Here is the video and blog post for bump steer readings. The blog has the data from the video, as well as lots of links for research. I had to reshoot several times but I tried to keep as much of it a concise as possible. Hopefully I didn't botch up my explanations. Much of the video covers setting up the car to measure. I'll be taking more readings with my new setup so I can near zero the bump.
https://youtu.be/2zwOlxDBZo4
http://cmsgt4.blogspot.com/2015/03/rese ... r-and.html
 

MWP

New member
So ive finally had a little time to look at this.
Nice work producing the video.

First, are you 100% sure your steering rack is centered?
You can have wheels straight, correct toe, and steering wheel in the center yet not have the rack centered.
It is very important that the rack is centered for the bump steer measurements to be correct. It can change the result by quite a lot if its not.

The point at which you had the minimum amount of toe-in (the point at which it goes from toe-in to toe-out) is the optimum ride height as far as bump-steer is concerned.
The optimum point should also be the factory ride height.
You should find this location, then call it the 0 height point for your measurements.

Can i also suggest you take a lot more readings.
8-10 readings each side of the 0 point would be ideal. That way you can see any errors in the readings, and also any non-linearity.
 

CMS-GT4

Active member
Thanks. I checked the rack when I set it up, and it measured centered. I am using a tape measure though, and I would like to look into a more accurate tool for large measurement, preferably in mm. I am just not sure what that tool would be.

I did take the readings about 4 other times for this side, I just did not record it. I had a lot of recordings of failed measurements as I was figuring out the angle of the frame against the plate. While the numbers were different from the final results, the toe change in and out were consistent at the heights.
I will do the other side once I get the new parts in. My control arm is not right on the other side and has a degree of caster difference, so I will measure that when its replaced.

The height I chose was the ride height I had measured off the car. I made a cap with a slot cut into it to measure off of so my measuring points from the axle would be consistent. Due to alignment at the height the toe change is 0 and is the lowest point but 0 is achieved again at 1.25" of compression. I had looked at some other cars bump steer readings and talked to a couple tuners on the subject, and supposedly its common for a production car to have bump toe changes like that.

I am going to try and measure droop the next time too. The problem I had with that is the shock wheel did not want to drop hardly below the ride height without assistance. I had to put weight on it, and I was afraid I would mess up my reading that way.

In other news I tried a camber curve experiment. I have a magnetic digital level used for alignments and I put it on the car and measured and went through the 3" of compression, and 3/4" of droop to see what I get. The gauge is zeroed at ride height. Here is the numbers, and they may also explain why I have more wear on the outside of my tire. I want to do more research on how to test it though. I expected a curve that added negative camber then would go to positive when deeper in compression, but it seems to go straight into positive on compression.

-3/4" -.30
0 0
1" +.25
2" +.40
3" +.55
 

MWP

New member
CMS-GT4":16onyie2 said:
Thanks. I checked the rack when I set it up, and it measured centered. I am using a tape measure though, and I would like to look into a more accurate tool for large measurement, preferably in mm. I am just not sure what that tool would be.

You could slide the rack boots down over the tierod and measure the distance from the rack end to the rack casing on each side.
I think that would be the easiest way.

I did take the readings about 4 other times for this side, I just did not record it. I had a lot of recordings of failed measurements as I was figuring out the angle of the frame against the plate. While the numbers were different from the final results, the toe change in and out were consistent at the heights.
I will do the other side once I get the new parts in. My control arm is not right on the other side and has a degree of caster difference, so I will measure that when its replaced.
The height I chose was the ride height I had measured off the car. I made a cap with a slot cut into it to measure off of so my measuring points from the axle would be consistent. Due to alignment at the height the toe change is 0 and is the lowest point but 0 is achieved again at 1.25" of compression. I had looked at some other cars bump steer readings and talked to a couple tuners on the subject, and supposedly its common for a production car to have bump toe changes like that.
I am going to try and measure droop the next time too. The problem I had with that is the shock wheel did not want to drop hardly below the ride height without assistance. I had to put weight on it, and I was afraid I would mess up my reading that way.

Try pushing it all the way to droop (hopefully it'll stay there due to stiff bushes), then use the jack to raise it from droop to full compression.

You need to plot a graph like this, then everything will become clear:
toe.jpg


You should get a shape pretty close to that.
In that graph, the 11.5 inch mark is the ideal settled ride height for the minimum amount of bump steer.

So using a graph like that, you would set your ride height to 11.5in, then do a wheel align to set your normal wheel align toe in/out amount (0 for me).
Once you've done that, you'll have the perfect front ride height & wheel alignment to achieve the minimum amount of bumpster.

In other news I tried a camber curve experiment. I have a magnetic digital level used for alignments and I put it on the car and measured and went through the 3" of compression, and 3/4" of droop to see what I get. The gauge is zeroed at ride height. Here is the numbers, and they may also explain why I have more wear on the outside of my tire. I want to do more research on how to test it though. I expected a curve that added negative camber then would go to positive when deeper in compression, but it seems to go straight into positive on compression.

If you corner hard (ie, >1G) a lot, then its a camber/caster issue. If you don't corner hard much, then its a wheel align issue.
Camber change through suspension travel is a macpherson strut weakness. There is nothing you can do about it without completely changing the suspension setup to double A arm.
 

CMS-GT4

Active member
MWP":2un8met2 said:
You need to plot a graph like this, then everything will become clear:
http://www.rudmanworld.com/cobra/blogge ... ta/toe.jpg

You should get a shape pretty close to that.
In that graph, the 11.5 inch mark is the ideal settled ride height for the minimum amount of bump steer.

So using a graph like that, you would set your ride height to 11.5in, then do a wheel align to set your normal wheel align toe in/out amount (0 for me).
Once you've done that, you'll have the perfect front ride height & wheel alignment to achieve the minimum amount of bumpster.
I see what your saying. I'll look into doing a graph like that. I may also do one for the camber curve just to compare before and after extended ball joints.

MWP":2un8met2 said:
If you corner hard (ie, >1G) a lot, then its a camber/caster issue. If you don't corner hard much, then its a wheel align issue.
Camber change through suspension travel is a macpherson strut weakness. There is nothing you can do about it without completely changing the suspension setup to double A arm.
Honestly I only corner hard in this car. Its the only way I know how to drive it. I don't know how much I go over a G though. I'll have to hook the accelerometer up when I finally get to my next autox. I was reading on camber curves and suspension types and it does seem that mac is awful. It seems caster is the trick to fight it since you getting camber in turn conditions from the caster. I had not seen ways to measure the gain though, I imagine some of the techniques we have been using so far might apply here.

I spent yesterday at junk yards pulling control arms from 5th gens to send for having the new LCA made. I will likely send them off once I get back from holiday as well as a new special part I am picking up on the way home. I finally pulled the trigger and ordered my feals. I collected all my data I had on the car and sent everything in as well as mailed them my t3 camber plates. T3 had given my a nut that was 12x1.25 that fit perfect in their bearings, and that happens to be the same thread pitch as the Feals so hopefully it will go on without a hitch. I wanted them to figure out the preload on the springs with the T3 parts so that I was not doing any guess work. I expect to have them in a few weeks. The weather is nice, and I am starting other projects on the car. I am hoping before the parts get here I can drop the rear end and swap the subframe for the 205 one I have. I will also get weights to compare. The main subframe is the same PN, but the section that supports the diff is lighter.
 

MWP

New member
Mac isnt awful... its just a bit limited :p

Caster is a huge help. I know my 4.5deg has improved front grip a lot.
Going up to 8deg, and maybe more would be great.

If you up to it, have a look at susprog3d. Its suspension modeling software.
You give it all the suspension pivot points (not easy, but worth doing), and it gives you all the calculated dynamics information.
It'll be really interesting to see how close your measurements are against its calculated results.

Im going to use it to help with positioning my new steering rack.
Ive started entering the chassis info, but still have a lot more to do.
 

CMS-GT4

Active member
It looks like that software is pretty expensive. Seems like a good tool, but I still wonder if I can find something open source. I talked to adrian a bit and got some specs from his car he had in his notes to verify a few things on part weights and such.

I just got home, I am sick as a dog, but I did manage to go pick up my new part. A fiber images hood. It will go on the wall until I decide to paint it or make covers for my headlights. I also took a look at initald93's alltrac he is selling. Motor needs rebuilt from sitting for 10 years, but for $3k, you get blue alltrac in god shape, and redone interior. If I had room I might had picked it up.

11084937_357618441099046_1281966079_n.jpg
 

aus jd 2703

New member
Are FI still making replicas or is this one from the GB? I've heard the early ones were identical but the later ones don't have the bulge in the right spot
 

MWP

New member
CMS-GT4":3ro8bcm8 said:
It looks like that software is pretty expensive...

At $300 its on the cheap end for something like this.
The Lotus suspension software i think is closer to $10k.

Anyway.... they both can be found for free :wink:
(PM me if needed)

I just got home, I am sick as a dog, but I did manage to go pick up my new part. A fiber images hood. It will go on the wall until I decide to paint it or make covers for my headlights.

Niiiiiice.
 

CMS-GT4

Active member
I did a quick bump reading with the flip kit with interesting results. I didn't take any video or many notes I just wanted to observe the change quickly before I pulled the car apart. It no longer changes bump out to in. It now goes toe in for compression and toe out for extension. Reading up on the toe condition it looks like if the IC affect this as well. If the steering arm is pointing above or below the IC then that effects the toe in or out condition. Based on my readings I don't think the length of the arms are as much an issue, but the angle vs IC. So here is the nitty gritty. I need to plot my IC, then look at my steering arms and figure out a ball joint length that will work in a positive way with my steering arm angle.
 

CMS-GT4

Active member
Kicking around dying the carpet black and getting black mats. Did a quick PS just to see.
 

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CMS-GT4

Active member
If I can match the carpet to the charcoal mats that are made that would be another option. Black will be the easiest.
 

CMS-GT4

Active member
Got the rear end out. What a pain in the ass. Swapping in a 205 subframe and new bolts. While its out I am cleaning any grime and hunting for any rust to wipe out.

11111541_1380668198899432_1879859559_n.jpg
 

CMS-GT4

Active member
Cleaning a lot and hunting for any rust to por15. Got new spindles, but I need to prep them for being reamed, then new bearings since I didn't do a good enough job on the last set. Starting to dig around for parts and stuff to sell to increase my budget as it is tapped out. I got pretty frustrated with the project this week, and I am tried of the car being on jackstands. I am going to simplify some of my plans, and maybe put some things off just so I can enjoy the car more this year, and the next.
St185 vs St205 rear subframe part weights video is up. http://youtu.be/asHtEDcgaDg
 

88st165

New member
So you went with the Feals, awesome. I'm curious to hear your review on them. What spring rates did you end up going with?
 
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