Bump Steer, Toe Steer, and Roll Center

[Norm Peterson]

You need to have decently accurate co-ordinates in 3-D for all of the pivot points in order to determine where the geometric roll center is (don't forget about the strut at its top mount). After that, getting a close approximation for conventional strut geometries is not that tough. This newer approach to strut suspensions using a pair of links instead of a control arm is a slightly different story, one that I haven't even tried to write a spreadsheet for. Same goes for the integral link IRS, as I don't have any coordinates for that either.

That camber goes about half a degree more negative per inch of lowering sounds about right. Could be a little more, might be a little less.

Likewise, strut geometric roll centers typically drop twice as fast as the car is lowered or a bit faster. SLA geo-RC's about the same as the amount lowered.

What the shape of the links themselves looks like is irrelevant geometrically. All that matters geometrically is where the centers of the end connections are. Link shape matters for link stresses, though.


(never saw this thread before)


Norm

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[wildcatgoal]

I have the Steeda front lower control arm (rear one) with the extended ball joint and the front one is the stock arm, stock ball joint, with the Steeda spherical bearing in it.

When I installed the lower control arm, I had to get an alignment immediately as it induced significant toe out. Once that was resolved, the car drove great except I had some bump steer on account of the geometry changes, and the guy that did my alignment didn't touch my prior bump steer setting, which I had measured myself.

Recently went down to Steeda in Valdosta and had the alignment re-done with bumpsteer adjustment, and the bumpsteer/tramlining behavior is effectively gone.

So, do have the bumpsteer kit installed and do plan on getting an alignment. And my recommendation is to self-align the car in your garage before driving it.

At this point, I haven't been on track yet with this new arm installed, but I do notice a tendency for the car to feel as if it is not rolling over the tire sidewall as much with all that weight up front. It does seem to change the balance I need to retain for understeer vs. oversteer, which is easily done with my sway bars, but this is an initial observation with about 2 months of not driving the car more than around the garage I keep it in in-between. Overall, the turn in on the street feels more natural and a little bit more "tight" or "fast reacting", but it is different enough that I've had to sort of re-learn how the car acted in some cases (to my liking, though).

Likely more to do with my alignment, but the car also tracks straight better. I kept the same toe settings front and back as before, and same camber and same tires/wheels, and the car feels like it'll drive itself in a straight line, but doesn't feel like it's in some kind of rut - like I'd feel some kind of resistance to start turning the wheel more than a little bit. It just smooths out of going straight very predictable, which I appreciate as I prefer to have the variable of doing much work for tracking the car straight on fast straights out of my head, but I don't want turning to be knee jerk and choppy, which it isn't.

Hopefully I've made some lick of sense. Probably not. I really need to go on track and see the effect it has on my driving confidence, body roll, and lap times.

 

[Rebellion]

At this point, I haven't been on track yet with this new arm installed, but I do notice a tendency for the car to feel as if it is not rolling over the tire sidewall as much with all that weight up front. It does seem to change the balance I need to retain for understeer vs. oversteer, which is easily done with my sway bars, but this is an initial observation with about 2 months of not driving the car more than around the garage I keep it in in-between. Overall, the turn in on the street feels more natural and a little bit more "tight" or "fast reacting", but it is different enough that I've had to sort of re-learn how the car acted in some cases (to my liking, though).

What's the effect on balance (over/under steer) with same sway bar settings?

Interested in the benefits of the arms, but don't want to deviate too much from my current balance, which took a while to get tuned there. In theory, the roll center and camber gain should sort of compensate, but it's impossible to know for sure without testing.

 

[apex15stangPP]

I like were this is going!

 

[boardkat]

bumpsteer and roll center correction are necessary and the difference in handling is more substantial than i'd thought. check the latest post in my build thread for more thoughts/info.

 

[Rebellion]

bumpsteer and roll center correction are necessary and the difference in handling is more substantial than i'd thought. check the latest post in my build thread for more thoughts/info.

Extremely interesting stuff right there...now I'm compelled to get the arms and bumpsteer kit!

 

[boardkat]

Extremely interesting stuff right there...now I'm compelled to get the arms and bumpsteer kit!

yep, the proof was in the pudding for me. i've been driving my car with the same suspension setup for the better part of a season now, so it was quite easy for me to see the difference in handling after making the change. the actual installation is cake, but as i mentioned in my thread, the setup and measurement is very tedious and time consuming. find a shop you can trust to make the necessary adjustments if you aren't planning on doing it yourself (but i definitely think you should!)

 

[Bluemustang]

Now I have a slight quandry. I had my bumpsteer adjusted when I had my Ford Racing springs on (1” drop all around). Now on BMR handling springs 0.88” and 0.75” drop and didn’t have the bumpsteer adjusted. And now I’m sensing a little bit of bumpsteer that I didn’t have before. But I am not entirely certain if it just tramlining. Plus, I can’t find the remaining spacers for my bumpsteer kit if they are needed to readjust.

Now I want to get the lateral links with the roll center adjustment from Steeda. If I do that, I know the bumpsteer WILL need to be readjusted. So now not sure what to do. Not sure if extra spacers will be needed to get the bumpsteer accurate with the new control arms.

Add to that- if I get the lateral links I want them with the bearings. But- I don’t see that Steeda offers only the lateral links with the bearings. I know they offer only the tension links with the bearings, lateral links with just bushings or tension and lateral links with bearings. But I don’t know if they offer only lateral links with bearings already installed. I don’t want to press them in afterwards if that makes sense and I don’t want to have to buy both.

 

[boardkat]

this is what i installed on my car (lateral link w/ extended ball joint and inner bearing):
https://www.steeda.com/Steeda-S550-...-w-Extended-Ball-Joint-2015-2018_p_14088.html

and i'm sure if you drop [MENTION=25806]SteedaTech[/MENTION] a line, i'm sure he can help you with your bumpsteer spacer problem

 

[Rebellion]

Now I have a slight quandry. I had my bumpsteer adjusted when I had my Ford Racing springs on (1” drop all around). Now on BMR handling springs 0.88” and 0.75” drop and didn’t have the bumpsteer adjusted. And now I’m sensing a little bit of bumpsteer that I didn’t have before. But I am not entirely certain if it just tramlining. Plus, I can’t find the remaining spacers for my bumpsteer kit if they are needed to readjust.

Now I want to get the lateral links with the roll center adjustment from Steeda. If I do that, I know the bumpsteer WILL need to be readjusted. So now not sure what to do. Not sure if extra spacers will be needed to get the bumpsteer accurate with the new control arms.

Add to that- if I get the lateral links I want them with the bearings. But- I don’t see that Steeda offers only the lateral links with the bearings. I know they offer only the tension links with the bearings, lateral links with just bushings or tension and lateral links with bearings. But I don’t know if they offer only lateral links with bearings already installed. I don’t want to press them in afterwards if that makes sense and I don’t want to have to buy both.

The picture on the website seems like they already have bearings, comparable to a stock PP arm, completely different from the stock arm in our non PP cars.

 

[wildcatgoal]

Ask Steeda if they'll include spacers. Why did you not just leave them all in?

 

[aleccolin]

So, turns out Steeda now sells front lateral links with extended ball joint studs to help correct the front roll center, in combination with their bump steer tie rod ends this is a step in the right direction.

The lateral links are the GTPP version with inboard spherical bearings, so this would be a double upgrade for anyone with a lowered non-PP car. Seems like a no-brainer for $160.

https://www.steeda.com/Steeda-S550-...-w-Extended-Ball-Joint-2015-2018_p_14088.html

I don’t make a habit of quoting myself, but yeah there you go.

 

[Bluemustang]

Ask Steeda if they'll include spacers. Why did you not just leave them all in?

Sorry, let me fully explain. I had the bumpsteer kit adjusted (by a shop) after I had the 1 inch drop FRPP springs. Now I’ve gone to a lesser drop, only by a smidge. I did not really think it was necessary to have them readjust the bumpsteer kit again for the 1/8” whatever difference. And I don’t know where the remaining spacers are (that weren’t used previously). I may have them somewhere.

But if I do go to the extended ball joint lateral links, I will for sure need to have that bumpsteer adjusted again. Idk if I need them or not, meaning I’m not sure if more spacers will need to be added or if spacers will need to be taken out. Idk the angles involved in order to understand that.

I certainly wouldn’t want to buy another bumpsteer tie rod kit just for a few spacers. I hope that makes more sense.

 

[Bluemustang]

this is what i installed on my car (lateral link w/ extended ball joint and inner bearing):
https://www.steeda.com/Steeda-S550-...-w-Extended-Ball-Joint-2015-2018_p_14088.html

and i'm sure if you drop [MENTION=25806]SteedaTech[/MENTION] a line, i'm sure he can help you with your bumpsteer spacer problem

This doesn’t make sense to me. How are the lateral links with bearings installed ($160) less than the control arm bearings that Steeda sells ($215)? Unless these are different bearings and are meant for other control arms (tension links).

 

[boardkat]

This doesn’t make sense to me. How are the lateral links with bearings installed ($160) less than the control arm bearings that Steeda sells ($215)? Unless these are different bearings and are meant for other control arms (tension links).

different bearings. the tension link inner bearing is HUGE.

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