Bump Steer Measurements

[JustinEET]

Hello, as promised I did my experiment with the Long Acre Bumpsteer Gauge



My car Suspension:
Yellow Speed Advanced Pro Circuit coilovers(Inverted Monotube)
ITR lower control arms
Lowered around typical track height(Lower control arms parallel with ground)
Area Motorsport Tie Rod ends used for Inverted and Non Inverted
SHG rack slider





Heres video
DC5/EP3 Tie Rod End(Inverted vs Nonverted) Experiment - YouTube

 

[James-T]

Interesting findings, as my results showed the opposite to yours.

This just proves everyones setup is different and changing these parts without measuring could in fact make your car worse.

 

[Lemons]

Interesting findings, as my results showed the opposite to yours.

This just proves everyones setup is different and changing these parts without measuring could in fact make your car worse.

James, would you remind us what your suspension set up was when you carried out your test achieving the opposite results?

 

[James-T]

James, would you remind us what your suspension set up was when you carried out your test achieving the opposite results?

Tein Advance Z Coilovers - lowered around 40mm
Hard Race Roll Centre Adjusters
Hard Race Inverted Track Rod Ends
Eibach Camber Bolts (no camber plates on top of shock)

 

[JustinEET]

My graph actually shows that I(Personally) would pretty much have very little change. My front sits at 12KG... so I don't think I even get 2 inches worth of movement up there. Especially with braking and acceleration(Which is important to nullify bumpsteer on).
Cornering actually having bumpsteer isn't such a bad thing. Especially with roll steer; the slight toe-in that I gain is ideal.

Explaining why we toe-in in the first place is why I expected Non inverted to show better results.
What essentially happens is that due to the kingpin inclination of our struts... they typically sit at an angle. (The same angle that gets influenced when using camber plates)
As you compress the strut; this causes it to go inwards towards the chassis. And this rate happens faster than the tie rod going inwards towards the chassis. Thus causing the Toe-in effect on compression. So outside of looking at typical bumpsteer geometry, this is why it happens in real-world. So that's why it would make sense having an angle should help versus straightening out the tie rods(which make the tie rod end stick out further away from the car).

I used the most expensive bumpsteer gauge I could find. One thing I found that was important was using levelers to make sure everything was level.(Which my bumpsteer gauge came built in with). This actually would have to be re-leveled as I was doing the compression(luckily it has it built-in). There's tons of factors here.

But I still recommend using non inverted UNLESS you are slammed to the ground. (Because I noticed that at the end of the 2 inches the inverted started to level out) but my non inverted was going upwards.

 

[Tuneboy]

Hey Justin, very nice information here, thanks for the effort. I already suspected that the inverted stuff is not suitable for 90% of the cars. Including mine. So i switched back from the hardrace inverted to oem.
Im currently rebuilding my DC5 as a rallycar so i am also intrested in the results for the Drop of the suspension.
Also a Sidequestion: How do you think would the values change if you would run castor bushings? Since the LCA is at an different angle, i think it would affect the Bumpsteer.

Cheers, Mark

 

[2Cent]

Hey Justin, very nice information here, thanks for the effort. I already suspected that the inverted stuff is not suitable for 90% of the cars. Including mine. So i switched back from the hardrace inverted to oem.
Im currently rebuilding my DC5 as a rallycar so i am also intrested in the results for the Drop of the suspension.
Also a Sidequestion: How do you think would the values change if you would run castor bushings? Since the LCA is at an different angle, i think it would affect the Bumpsteer.

Cheers, Mark

Good question. I had superpro caster increase bushings and had scary bump steer on uneven roads so I changed to the normal ones. On smooth roads it felt sharp at speed but very heavy maneuvering to park. My 2 cents, I feel like the teg is already sharp enough at speed and heavy at low speed, no need to accentuate those aspects.