Overly active stability control after FLCA, caster bearing, alignment, and tires

[gcmak]

**Update**
Thanks to forum member @Msoupe - the shop fixed the mistake and I'm back in business.
The 6 spacers included with the FLCAs (3 for each side), are only to be used as needed, if the car is lowered. Since my car was is not lowered, no spacers should be used. SPL designed the part to work perfectly with the stock height so the roll center would not be messed up.

Simply removing the few spacers, the car has an on-center steering feel again, and remains planted on corners - only triggering VSC when I am actually overcoming tire grip.

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About a week and 130 miles ago I had a shop install the SPLC FCLA and adjustable caster bearings, mount and balance Advan Apex V601 tires (stock sizes on my original rims), and align the car. Install looks clean, they've worked on quite a few Supras, and have been helpful and responsive throughout.

Initial impressions with the changes are the car's turn-in is quicker/sharper. No issues with low/high speed straight line acceleration or braking, and no appreciable changes in NVH (everything else suspension-wise is original).

I did almost immediately start to notice stability control (VSC) was activating for highway on/off ramps; coasting on a curve. Then I had to do a U turn and noticed VSC was also kicking in. Drove more miles but kept noticing VSC would kick in before I could sense that I was losing mechanical grip. Asking the shop, they stated they aligned the car similarly to most other Supras they've had and no owners have reported issues. They hypothesize the caster settings could be causing the wheels to skip but are pretty doubtful. Cross checking alignment sheets posted by other Supra owners, I would say the alignment is within factory recommended spec and shouldn't cause sensor or other issues (and I have no errors/warnings).

In an empty lot I drove in circles with VSC and VSC Sport. While in VSC Sport, I felt like I wasn't losing mechanical grip at the speeds of ~8-10mph, when VSC would aggressively intervene. At ~15mph I could sense push and even faster led to pure understeer and that's when VSC Sport would kick in. The threshold for when VSC would previously intervene (in bone stock setup) prior to these changes, was a higher speed in all situations.
Video of circles with VSC ON:

I checked for sway bar interference - there's none - no witness marks on any parts.

Has anyone's experienced this in their Supra. I'm leaning towards this being a tire issue, because it could definitely be the case I need to put more miles on the tires for them to break-in, and unfortunately I don't have a second set of wheels (or the OEM tires) to test.

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[serialbooper]

wish i had a answer for your issue, i can only tell you i definitely have my traction light flash at me when aggressively driving on on/off ramps (long sweeping turns) with all safety systems on. i have fortune auto coils, spl front lca's and caster bushings. my caster is set at around 7.8 in the front due to 7.1 was rubbing my sway bar links to lca's just a touch. im on wider tires than you so i kind of expected to have some interference with a traction light. i think your alignment specs look good, just keep an eye out for rubbing on lca when really pushing the car to its limits.

what kind of tires did you go with? could be the car doesn't like the compound, just a thought.

 

[gcmak]

wish i had a answer for your issue, i can only tell you i definitely have my traction light flash at me when aggressively driving on on/off ramps (long sweeping turns) with all safety systems on. i have fortune auto coils, spl front lca's and caster bushings. my caster is set at around 7.8 in the front due to 7.1 was rubbing my sway bar links to lca's just a touch. im on wider tires than you so i kind of expected to have some interference with a traction light. i think your alignment specs look good, just keep an eye out for rubbing on lca when really pushing the car to its limits.

what kind of tires did you go with? could be the car doesn't like the compound, just a thought.

Thank you for your input. Definitely in a long sweeper, stability is grabbing like crazy.
I got these tires (Advan Apex V601). They're basically a PSS/PS4s equivalent. It could just be they need more break-in. I am going to Laguna Seca on Thursday anyways, so we'll see what happens.

Appreciate you sharing your alignment specs and your experience. I will keep an eye out for interference.

 

[Lude1888]

Thank you for your input. Definitely in a long sweeper, stability is grabbing like crazy.
I got these tires (Advan Apex V601). They're basically a PSS/PS4s equivalent. It could just be they need more break-in. I am going to Laguna Seca on Thursday anyways, so we'll see what happens.

Appreciate you sharing your alignment specs and your experience. I will keep an eye out for interference.

I am having a similar issue as you pointed out. In my scenario it is a very isolated issue as i had no previous mods prior to the issues you and i are seeing. It happened immediately after changing my rear tires to the Advan Apex V601. I reached out to Yokohama and will let you know what they say.

 

[gcmak]

I am having a similar issue as you pointed out. In my scenario it is a very isolated issue as i had no previous mods prior to the issues you and i are seeing. It happened immediately after changing my rear tires to the Advan Apex V601. I reached out to Yokohama and will let you know what they say.

Thanks, I look forward to hearing what they say.

 

[StudioRSR]

I might have missed it, but are you running the OEM shocks?
When you upgrade with a lower control arm, it will change the Roll Center of your suspension. The VSC system is using the sensors throughout the suspension (ie- ride height, steering angle, throttle %, load, differential, wheel speed etc.) to control everything and limit slip to maintain traction. If it's seeing a different suspension geometry and certain factors are going out of the factory set point for whichever measurement it wants to see in a certain range, then it will trigger the traction control. Any reason you went with the LCA w/o the tie-rod ends?

The bumpsteer tie-rod ends are a big factor when you lower the roll center with LCA's. I'm thinking that because the steering angle-to-ride-height is off from what the factory wants to see, this is triggering the traction system to kick on. Again, just a hypothesis..

 

[gcmak]

I might have missed it, but are you running the OEM shocks?
When you upgrade with a lower control arm, it will change the Roll Center of your suspension. The VSC system is using the sensors throughout the suspension (ie- ride height, steering angle, throttle %, load, differential, wheel speed etc.) to control everything and limit slip to maintain traction. If it's seeing a different suspension geometry and certain factors are going out of the factory set point for whichever measurement it wants to see in a certain range, then it will trigger the traction control. Any reason you went with the LCA w/o the tie-rod ends?

The bumpsteer tie-rod ends are a big factor when you lower the roll center with LCA's. I'm thinking that because the steering angle-to-ride-height is off from what the factory wants to see, this is triggering the traction system to kick on. Again, just a hypothesis..

Thanks for the detailed response. The only suspension changes made are the FLCA and front adjustable caster bearings. As I'm aware, those are the only two modifications required to adjust camber and caster in the front of the vehicle. Everything else suspension related is stock. I did not consider tie-rod ends nor did two shops I spoke with recommend them.

My alignment specs fall almost entirely within factory specifications. I wouldn't think the ride height of the car would be affected (not by more than a tiny bit). Of course I'm not the expert.

 

[StudioRSR]

Thanks for the detailed response. The only suspension changes made are the FLCA and front adjustable caster bearings. As I'm aware, those are the only two modifications required to adjust camber and caster in the front of the vehicle. Everything else suspension related is stock. I did not consider tie-rod ends nor did two shops I spoke with recommend them.

My alignment specs fall almost entirely within factory specifications. I wouldn't think the ride height of the car would be affected (not by more than a tiny bit). Of course I'm not the expert.

Gotcha. We're running the same setup on our shop supra. LCA and caster bushings, but we also have the bumpsteer tie-rod ends. We also started with the tie-rod ends and had no issues with VSC triggering unwantedly during our test laps in all three VSC modes (on, 1-press traction, and hold VSC OFF)

I agree that your alignment is within spec, but that is in a static condition. When the suspension travels and the roll center is changed without the needed tie-rod ends, that geometry changes exponentially throughout the suspension's movement and is what, I suspect, is causing the issue. Feel free to PM or call us and we'll be glad to help out. I'm very curious to see what the solution will be.

 

[gcmak]

Gotcha. We're running the same setup on our shop supra. LCA and caster bushings, but we also have the bumpsteer tie-rod ends. We also started with the tie-rod ends and had no issues with VSC triggering unwantedly during our test laps in all three VSC modes (on, 1-press traction, and hold VSC OFF)

I agree that your alignment is within spec, but that is in a static condition. When the suspension travels and the roll center is changed without the needed tie-rod ends, that geometry changes exponentially throughout the suspension's movement and is what, I suspect, is causing the issue. Feel free to PM or call us and we'll be glad to help out. I'm very curious to see what the solution will be.

Thank you - I'll see what happens at Laguna and then if the problem continues, I'll work with the shop I had the work done at first. I always believe in working with the original team first. I think you've given some additional information which could be helpful.

The other member in here started getting vsc issues with just a tire change. I haven't ruled out that the V601s could be a contributing factor.

 

[Msoupe]

As I understand SPL's design, the use of just the FLCA tapered spacer alone should retain the OE outer pivot point height. When lowered, it can be advantageous to add the provided SPL spacers to drop the outer pivot point which will raise the roll center height back up. I can imagine if the FLCA spacers were used without also dropping the outer tie rod pivot (via SPL bumpsteer rod ends), you could introduce a bumpsteer issue.

Did your shop install the SPL spacers (Items 5 & 6) ? They should have left them out if you are not lowered and if you do not have means to also adjust the outer steering tie rod height down.

 

[gcmak]

As I understand SPL's design, the use of just the FLCA tapered spacer alone should retain the OE outer pivot point height. When lowered, it can be advantageous to add the provided SPL spacers to drop the outer pivot point which will raise the roll center height back up. I can imagine if the FLCA spacers were used without also dropping the outer tie rod pivot (via SPL bumpsteer rod ends), you could introduce a bumpsteer issue.

Did your shop install the SPL spacers (Items 5 & 6) ? They should have left them out if you are not lowered and if you do not have means to also adjust the outer steering tie rod height down.

It looks like 5 & 6 were installed. However, there are two 5's in the diagram and it looks like my shop did not install the second 5. In my box there are two washers that look like 5 (one for each side is my assumption).

Do you have the installation manual? I cannot find it online for the A90 specifically.

 

[Msoupe]

It looks like 5 & 6 were installed. However, there are two 5's in the diagram and it looks like my shop did not install the second 5. In my box there are two washers that look like 5 (one for each side is my assumption).

Do you have the installation manual? I cannot find it online for the A90 specifically.

https://www.splparts.com/content/SPL FLCA G29.pdf

 

[gcmak]

https://www.splparts.com/content/SPL FLCA G29.pdf

Thank you sir! I just emailed SPL and they emailed right back crazy fast....

"Do not use the round spacer above the bearing between the tapered spacer that goes into the knuckle. The tapered spacer puts the control arm at OEM location"

 

[gcmak]

https://www.splparts.com/content/SPL FLCA G29.pdf

Thank you again. The issue is resolved. I believe you're in SoCal, but if we ever cross paths absolutely my treat for a meal or beverage. Cheers man - love this community.

 

[Msoupe]

Thank you again. The issue is resolved. I believe you're in SoCal, but if we ever cross paths absolutely my treat for a meal or beverage. Cheers man - love this community.

No worries man! Glad it helped.

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