Setting my bump steer the right way (hopefully)

[RodS197]

After tracking my car for 4+ years on the hopes that the FR500S setup (control arms and tie rod ends) had OK bump steer settings, and not having any issues up to that point, I was going through the car before a track day and found a loose ball joint. (Of course it was the Monday before a track weekend, but that's another story...)

So on went the Steeda tall ball joints and bump steer kit, with the typical "That looks pretty good" bump steer adjustment with a bit of reference from other Mustangs at the track.

Well after one weekend on my new R1 tires and some funny tire wear, I decided to dig in and set the bump steer the right way. (Thanks to Fabman here...)

Here is a picture of my setup for checking the bump steer (without the spring installed, sway bar disconnected), and my before and after on my bump steer adjustments.

For reference 1.5 inches of compression is the static height of my car.

Before: .7 inch of spacers on top (This was the "guess" setting)
Inches compressed from full droop:
1.0 - +1/4 toe out
1.5 - +1/16 toe out
2.0 - +1/16 toe out
2.5 - +1/16 toe out
3.0 - + 0
So in total that is 5/16 of toe out bump steer from full droop to 3 inches compressed! And what was worse was the 3/16 from 1.5 (static height) to 2.5 compressed. Ouch! No wonder my tires were wearing funny.

Here is what I settled on after measuring .5 inch spacer, .3 inch and .1 inch.
After: .3 inch spacer on top of the rod end
1.0 - +1/16 toe out
1.5 - +1/16 toe out
2.0 - +1/16 toe out
2.5 - 0
3.0 - 0
3.5 - 0

My question is, from the pictures, anyone see anything terribly wrong with my setup? I know it isn't a Longacre bump steer gauge, but it was one of my own making. ($5 of aluminum and a $6 laser pointer.) I want to think that the numbers don't lie, but the setting has the tie rod end so much higher than all the other kids cars, I wanted to get some feedback here. I am totally sold on the process. Very worth the time. (Although I am one of those guys that thought it was fun...)

Thanks

 

[Grant 302]

I like your DIY rig...but I think the toe reading won't be very accurate. Changes in camber and arc from the control arm will skew the toe readings. I'm also a little surprised that ride height is only 1.5" from full droop. Well, unless you have 750+ lb. front springs.

 

[RodS197]

No, just a 450 lb spring. They are Ground Control coilovers, which are a shorter strut than stock, so they don’t drop as much. That is why there is only 1.5 inch from full droop to static height. It surprised me as well after the install, but I’m used to it now.

I was thinking the camber, arc and all the dynamics would be present in the bump steer action by running it through the travel and measuring the effect on toe. What piece do you think I am missing? I definitely want to learn and do it right.

 

[xr7]

I'm curious to about how accurate this would be. I would think it would be OK until the chassis comes off the jack stands? I would guess the bungy cord holding the hub in position could be a problem. Need to anchor the frame to the floor. I hate the thought of pulling the springs although it probably is the best way to do it. My brain hurts.

 

[Grant 302]

You'd need to add a second laser to the bar and take a separate reading at the back to simulate using a toe plate. The change in camber affects both front and back. So if you only record the front change, you aren't measuring the change in toe.

Hope that makes sense.

My brain hurts.

Then you're doing something right!

 

[racer47]

"I definitely want to learn and do it right."

Since you have coilovers, there is a much easier way. First buy this https://www.summitracing.com/parts/...MI18nSoeqU3QIVTrXACh0DJwMLEAQYASABEgINkPD_BwE

Then measure toe at normal ride ht. Next adjust the coilovers so that the ride ht is as low as possible (or practical). Measure toe again.

Adjust tie rod spacers equally on both sides until normal ride ht toe and low ride ht toe are the same. Since that probably won't happen, adjust until the low ride ht toes out a little more than normal ride ht. Bump steer out is more stable than bump steer in.

Every time you adjust something, roll the car back and forth so that the adjustments settle in and nothing is bound up.

This is really all you need to do. It does not take a complicated setup. Plus you don't need to worry about bump steer in droop because the tire is much less loaded in droop (say the LF on a left turn) and it will be close enough anyway if the bump toe is correct.

 

[Grant 302]

I *think* the OP is looking for 0º under compression.

 

[RodS197]

I'm curious to about how accurate this would be. I would think it would be OK until the chassis comes off the jack stands? I would guess the bungy cord holding the hub in position could be a problem. Need to anchor the frame to the floor. I hate the thought of pulling the springs although it probably is the best way to do it. My brain hurts.

I pulled the springs. The jack is simply to run the control arm through travel.

 

[RodS197]

You'd need to add a second laser to the bar and take a separate reading at the back to simulate using a toe plate. The change in camber affects both front and back. So if you only record the front change, you aren't measuring the change in toe.

Hope that makes sense.


Then you're doing something right!

Thanks for the input. The adjustment certainly made it much better from static to compression and I also see racer47 point about the weight distribution when the suspension is in droop. I’ll post a report after the track weekend.

 

[RodS197]

Saturday NASA Utah was on the Utah Motorsports Campus West track. To say I was surprised with the results of the bump steer change would be an understatement.

For reference, the only change I made between track days was the bump steer adjustment. I have a good feel for the car and it was (I thought) well balanced and pretty well setup for an amateur like myself. As an old motocross guy, I have a sense for suspension tuning and have put lots of time into dirt bike setup and have been fascinated car setup and getting a sense for the few commonalities and many differences between two and four wheels. For reference, here is my setup:

Ground Control Coilovers - 450 lb front, 250 lb rear - corner balanced cross 49.7%
FRPP front sway bar, full stiff
18mm rear sway bar
Koni Sport single adjustable dampers - Front 87.5% stiff - Rear 62.5% stiff
Prothane bushings throughout
Cortext Watts Link (third hole from the top)
FRPP 10” BBS Wheels with 275/35-18 BFG R1 Tires square (widest tires allowed in TT4)

My first session out the car was exhibiting tons of oversteer. It was like my front end suddenly had a bunch of grip that it did not previously have. Oversteer was present in every phase of the corner and under hard braking the car was very unsettled and I had the feeling that it was going to swap ends. (I have done it before and know what that feels like...) I had not expected any real noticeable change, boy was I wrong.

I certainly had options to move some grip to the back of the car, the first being the dampers, next the Watts Link, then the possibility of removing the rear sway bar.

I adjusted the rear dampers to 25% stiff and drove the next session. What a difference just that change made. The car now was starting to feel much more planted in all aspects of the corner, and felt much more positive under hard braking. Wanting to chase it a bit further I changed the rear dampers to 12.5% stiff. Under braking it was even better than before and started to feel very planted, where the entire car felt like it was almost planting all 4 wheels while braking and not giving any feeling of the back end coming around or excessive front end dive. Trail braking was very controlled and I could transition the car from a slight understeer during trail braking to planting the rear under throttle before apex and into track out.

Really happy with the results. Well worth the time and effort. Overall I was amazed at how much grip I was giving up by not having my bump steer set correctly, if that is a symptom of improper bump steer. I always thought that bump steer would be felt when hitting curbing or bumps, but it seems to be much more than that and effects the contact patch during all phases of driving.

One thing I love about this sport is the longer I am in it the more I learn about car handling and about improving the loose nut behind the wheel! I am looking forward to driving this new setup and pushing the car even further now. Push the driver, push the car, rinse and repeat…

Please share any advice or experience. If my experience does not sound consistent with proper bump steer adjustment I would like to know.