Rear end feels squirly when accelerating hard

[rowdydaoudy]

As the title states, after getting my coils installed, new wheels put on, and alignment done, my rear end feels squirly when I am doing some hard accelerating.

Whether it be top end on the highway and even a downshift to 5 and laying into it or from a dig, it feels very unpredictable and sketchy.

I do not have the particular specs on the alignment at this moment, but all work was done at a very reputable euro shop where I live. I am taking it back for a realignment after the suspension has now settled for a weekish, but my assumption is the rear toe is out of whack.

Any other thoughts for them to check while it's there?

Specifics of work done (2016 ZCP M3):

- Fortune Auto 500 coils with Swift Springs (dampening set at 15)
- Mild camber added to the front and rear (nothing outrageous from factory)
- 18x9.5/11 Volk TE37SL
- 275/35 PSS, 295/35 PSS (all good tread and running ~36psi front, 38psi rear)
- New front tie rod assemblies
- Diff fluid changed

[Sahbatage]

Originally Posted by rowdydaoudy

As the title states, after getting my coils installed, new wheels put on, and alignment done, my rear end feels squirly when I am doing some hard accelerating.

Whether it be top end on the highway and even a downshift to 5 and laying into it or from a dig, it feels very unpredictable and sketchy.

I do not have the particular specs on the alignment at this moment, but all work was done at a very reputable euro shop where I live. I am taking it back for a realignment after the suspension has now settled for a weekish, but my assumption is the rear toe is out of whack.

Any other thoughts for them to check while it's there?

Specifics of work done (2016 ZCP M3):

- Fortune Auto 500 coils with Swift Springs (dampening set at 15)
- Mild camber added to the front and rear (nothing outrageous from factory)
- 18x9.5/11 Volk TE37SL
- 275/35 PSS, 295/35 PSS (all good tread and running ~36psi front, 38psi rear)
- New front tie rod assemblies
- Diff fluid changed

Squirly as in bouncing around/easy unsettled or mostly traction issues under acceleration? I'm not an expert but if it's not pulling to the right or left then likely not an alignment issue. 36-38 PSI seems very high, especially in the rear. I run 32-33 up front and 30-31 in the rear.

Also, not sure how long you've been running those tire sizes but the ratio seems less than ideal. I run 19's with 265/35 and 295/35. I've seen many do 265/35 and 305/30.

[rowdydaoudy]

Originally Posted by Sahbatage

Squirly as in bouncing around/easy unsettled or mostly traction issues under acceleration? I'm not an expert but if it's not pulling to the right or left then likely not an alignment issue. 36-38 PSI seems very high, especially in the rear. I run 32-33 up front and 30-31 in the rear.

Nope, no bounciness or anything; suspension feels amazing.

Only when I launch into it, it feels like traction issues and IS pulling left and right. The closest I can explain is the old E46 M3 RTAB issue.

I read in some other similar type threads to even increase psi. I was looking at the track alignment thread to see where I am at in comparison and I will be there checking alignment specs with them. (friends with the owner)

I hope that explains it a bit better? I can help and clarify more if I am missing details. Thanks for the reply.

[Sahbatage]

Originally Posted by rowdydaoudy

Nope, no bounciness or anything; suspension feels amazing.

Only when I launch into it, it feels like traction issues and IS pulling left and right. The closest I can explain is the old E46 M3 RTAB issue.

I read in some other similar type threads to even increase psi. I was looking at the track alignment thread to see where I am at in comparison and I will be there checking alignment specs with them. (friends with the owner)

I hope that explains it a bit better? I can help and clarify more if I am missing details. Thanks for the reply.

Oh really? Everywhere I read on here people advocate for lower PSI, I guess sometimes we have to take what we read with a grain of salt.

If they are looking at it again anyway they should be able to diagnose it. Do you know if those coils and springs are a good match?

[rowdydaoudy]

Originally Posted by Sahbatage

Oh really? Everywhere I read on here people advocate for lower PSI, I guess sometimes we have to take what we read with a grain of salt.

If they are looking at it again anyway they should be able to diagnose it. Do you know if those coils and springs are a good match?

Yeah, for sure! I just wanted to see if anyone had encountered anything that was similar in preparation before I take it so we can quickly try to diagnose before testing and tuning.

Yep! Tons of testing done on them. Definitely feels like a toe issue to me, but I wasn't certain if it could be something quirky.

[TopJimmy]

Get the tire pressure back to the recommended PSI of 32, morning cold. 36-38 will wear out your middles quickly.

You changed a lot at one time so it's hard to diagnose remotely. Hopefully your suspension shop can feel it out and then adjust.

[rowdydaoudy]

Originally Posted by TopJimmy

Get the tire pressure back to the recommended PSI of 32, morning cold. 36-38 will wear out your middles quickly.

You changed a lot at one time so it's hard to diagnose remotely. Hopefully your suspension shop can feel it out and then adjust.

After some digging, I am going to drop the PSI a bit to see if that helps some.

I go in Thursday, so hopefully we can figure it out then.

[whitstap]

Check the rear diff bushings, also excessive toe in at the rear exacerbates the pulling back and forth under hard acceleration... lastly I will say that the GTS diff tune helps chill the locking action on the diff (helping it pull straighter and/or carve under power exiting a turn w/out stepping out) which is what you’re feeling when it is going back and forth... the higher psi recommendations were for steering feel on PS4S not traction issues or PSS they seem to like lower pressures but I believe you have grip when you’re feeling the pull left and right if I understand you correctly... good luck

[rowdydaoudy]

Deflated the tires a bit from where I had them at and after the springs had settled on the coils, my alignment had gone totally out of whack. Rear toe was the worst (as expected), it was ~ -.3

We got it set pretty solid, based on research in the track section of the forums for a daily with my specs and occasional track use. Front and rear camber are sitting around -2 all around and ~.2 toe in the rear and just below .1 up front.

Test and tuned it last night after we got it off the rack and its never felt better. Had full control and felt very planted at all speeds.

Thanks for all the assistance and ideas on things to look out for. Made last night much quicker.

[MineralWhiteF80]

My car does this. It's like it is rear end torque steer. If I'm going 45mph down the road in 3rd gear at very light throttle and then floor it, once it comes up on boost, the right rear wheel tucks/squats down and the left rear lifts/raises as the tires start to break traction and start to spin. All the while, the car is doing a sketchy mini drift when accelerating. As soon as you let off, the car stabilizes again and tracks straight. Basically the car wants to slightly turn left and getting crossed up under full throttle, almost like one tire grips and one spins and upsets the straight line tracking. This doesn't seem to be a road crown issue but is very repeatable on a variety of different roads. I'm thinking about stiffening the rear suspension on my KW V3 coils to see if firming up the rear helps the squatting and torque steering.

BM3 stage 1 93 octane tune. Nothing crazy.

[TopJimmy]

Do you have the GTS diff coding? Wondering if the added straight line clamping action would reduce your kicking out the back end.

I'm trying hard for 60-130 times and whenever my tires don't stick (too cold) the back end kicks right. Since I'm pushing about 600whp it's hard to stick any street tire...guess I need Mickeys now.

[fiveohwblow]

Originally Posted by TopJimmy

Do you have the GTS diff coding? Wondering if the added straight line clamping action would reduce your kicking out the back end.

I'm trying hard for 60-130 times and whenever my tires don't stick (too cold) the back end kicks right. Since I'm pushing about 600whp it's hard to stick any street tire...guess I need Mickeys now.

I’ve the GTS diff coding.

I need to dyno mine because on my full E85 Cary tune I can full rip third no issues. Still the 285 tires we talked about and last night it was all of 42 degrees. Either I’m way low on power or I’ve magic grip. I’ve been talking about a dyno day in January. Might just do that.

[hC1001]

Have you guys tried calibrating the steering wheel angle?
I updated all the modules with a 7/2020 istep from a 2017 istep and the rear end started stepping out when punching it. It was fine before the update. Performed a steering wheel angle calibration with ista and now it doesnt step out. Give it a try if you can, doesnt hurt. You just turn the steering wheel all the way to one side and then do it to the other side and then return it to center.

[TopJimmy]

Originally Posted by hC1001

Have you guys tried calibrating the steering wheel angle?
I updated all the modules with a 7/2020 istep from a 2017 istep and the rear end started stepping out when punching it. It was fine before the update. Performed a steering wheel angle calibration with ista and now it doesnt step out. Give it a try if you can, doesnt hurt. You just turn the steering wheel all the way to one side and then do it to the other side and then return it to center.

Hmmmmmm. Worth a try!

[hC1001]

My theory is that traction and diff uses steering angle data. The firmware update reset my calibration. Before the flash i would spin tires but the car stayed straight. After the update it would twitch the rear end like power wasnt distributed evenly between the two wheels.

Goodluck.

[GregSM3]

Interesting I just upgraded to stage two and I'm having the same issues with my stock ZCP suspension. Under heavy acceleration the backend feels very Squirrley as soon as I back off it settles. The back end just seems to twitch back-and-forth it's very unsettling. I have bootmod3 should I try gts transmission or some other code changes?

[jmg]

Originally Posted by GregSM3

Interesting I just upgraded to stage two and I'm having the same issues with my stock ZCP suspension. Under heavy acceleration the backend feels very Squirrley as soon as I back off it settles. The back end just seems to twitch back-and-forth it's very unsettling. I have bootmod3 should I try gts transmission or some other code changes?

OP posted it was his alignment and that would be one of the first things to check regardless.

[PayamFSU]

I had this problem , I jacked up the car after I had new tires / alignment done , they hadn't properly torqued the bolt so it was loose and hence the loose back end on acceleration. I was pissed. I laid into the shop.

[icegrill]

Welcome to VTEC bro!!

[jmg]

Originally Posted by icegrill

Welcome to VTEC bro!!