Bump Steer, Toe Steer, and Roll Center

[aleccolin]

So the S550 suspension design is a big step forward for Mustangs, but not exactly pushing boundaries. It's susceptible to the same effects chassis and suspension designers have been trying to mitigate for many years.

I plan on lowering my car about 1-1.5", first on springs then on coilovers. Goal is solid, predictable handling (lap times) first, aesthetics second.

I'm having trouble finding good information specific to the S550 chassis on the effect of lowering on bump steer and roll center. Some people have complained that the S550 has a lot of bump steer in stock form, but I haven't seen any real data to support that. At least bump steer is something I CAN measure for myself and decide if shimmed tie rod ends are needed.

Figuring out the roll center elevation however is a lot more complicated than with the old lower A-arm front suspension. I know Maximum makes some products for previous generations to raise the roll center back up after lowering your car, maybe it's not necessary for the S550? Anybody have any information on this?

Also, dialing in the toe and reducing toe steer is simple with Steeda's adjustable toe links, but for only 1-1.5" of lowering how much rear toe change should I expect? The stock toe links look pretty close to level at factory ride height, so lowering should induce just a little bit of toe-in, and the factory adjusters probably have enough range for that. If it can still be adjusted within spec I'll forego the adjustable links and only replace the knuckle side bushing with a spherical bearing (delrin) like the PP toe links already have. I saw a claim from a vendor that the stock toe links will flex under load, but it feels like they're just trying to sell their adjustable links. If flex is an issue, I can just weld in some gussets to fix that.

Thanks in advance, so far I'm finding some great info on this forum!

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[BmacIL]

**Place-holder for more detail after work**

 

[5.0_SD]

sub'd for Bmac's reply...calling [MENTION=6743]Norm Peterson[/MENTION]

 

[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

 

[Rebellion]

sub'd for Bmac's reply...calling [MENTION=6743]Norm Peterson[/MENTION]

Awaiting both of these replies too...super important topic here :hail::hail::hail:

 

[Bluemustang]

SUB’D

 

[Berstuck]

Awaiting both of these replies too...super important topic here :hail::hail::hail:

That was from 9 months ago.

 

[Rebellion]

That was from 9 months ago.

I know, but still...if I could do anything to spark the conversation again. Normally I wouldn't care much on geometry stuff, but recent developments have me researching more and more.

 

[aleccolin]

It would be great if someone from Steeda who was involved in the development could chime in. There's a fair bit of work to figuring out the change in roll center and how to get it back, but everything's going to be a compromise.

My guess would be this raises the front roll center back close to OE for moderate lowering .75 - 1.25", but if you really dump the car I doubt anything short of a full aftermarket subframe with revised pickup points will do the job.

Also don't forget this is a dual ball joint setup, which means the point along the steering axis you need to determine the instant center isn't just the lower ball joint center anymore, it's an imaginary point in space determined by the geometry of the two control arms together. Changing the just the lateral link (which is all you can do in this case) would have a less dramatic effect in raising the IC and RC than if it were just a single ball joint. LOL it gets nerdy real quick.

 

[5.0_SD]

So calling again.. [MENTION=10281]BmacIL[/MENTION] [MENTION=6743]Norm Peterson[/MENTION] damn I wish I remember some of the guys from S197forum...Norm and others had awesome suspension discussions over there.

 

[Roadway 5.0]

but for only 1-1.5" of lowering how much rear toe change should I expect? The stock toe links look pretty close to level at factory ride height, so lowering should induce just a little bit of toe-in, and the factory adjusters probably have enough range for that.

I lowered my car with Steeda Ultralite springs (1.15" front, 1" rear); according to my alignment sheet, the car increased in negative camber by roughly -.5 on all four, and the toe went OUT by .02. I was able to dial-in the toe to toe-in .1 with no additional parts and I let the camber ride (negative camber = to me).

As far as roll center, you can consult an engineer here: [MENTION=25806]SteedaTech[/MENTION]

 

[Bluemustang]

I know, but still...if I could do anything to spark the conversation again. Normally I wouldn't care much on geometry stuff, but recent developments have me researching more and more.

The bumpsteer from lowering is very real. I’ve experienced it on my car and know what it feels like when it goes away.

I am also still interested in more discussion about the roll center. If Ford decided to use different front control arms for the GT350 which has a different ride height, it seems logical it would also make a difference for lowered GTs.

The bad part about the bumpsteer kit is that it’s a very tedious process to dial in.

It also seems that these S550s don’t like being lowered very much.

 

[Barrel]

I ordered the Steeda roll center and bump steer correction kit. I'm lowered on the Steeda dual rate comp springs and I'm hoping this helps a bit. The stiffer springs and adjustable dampers definitely help keep the car stable but it's counteracted somewhat with other issues from lowering.

Hoping this kit does the trick.

 

[aleccolin]

Something to note: Raising the RC should have the effect of requiring less swaybar to do the same job, meaning some people might not need to upgrade sways unless they’re really tracking it hard on sticky ass tires. Another thing is running wide wheels with a smaller offset (moving the tire CL and “Dave Point” outboard) will raise the RC slightly, but of course increases your scrub radius which may not be desirable, but the steering feel kinda sucks anyway so most people don’t seem to care (myself included).

 

[tj@steeda]

I ordered the Steeda roll center and bump steer correction kit. I'm lowered on the Steeda dual rate comp springs and I'm hoping this helps a bit. The stiffer springs and adjustable dampers definitely help keep the car stable but it's counteracted somewhat with other issues from lowering.

Hoping this kit does the trick.

Keep us updated & if we can assist anyway, don't hesitate to ask!

Looking forward to your feedback.

Best Regards,

TJ

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