Handling doesn’t feel quite as predictable after installing a rear diff brace (more oversteer)

[dAPEX]

So I installed a rear differential brace made by black market race. Since then I have noticed that the rear end wants to rotate much more in corners. Car feels very stable with straight line acceleration, but I honestly felt the tendency to oversteer was more predictable and manageable previously. I’m kind of wondering if I should remove it. I’ve heard others mention that they felt the car wanted to rotate more after installing a brace but that they felt it was manageable. Has anyone else felt the same thing? Any remedies other than removing the differential brace? I’m also curious why this happened. I’ve heard people mention that perhaps there is more torque being transmitted to the rear tires because there’s less loss due to movement in the differential housing - that doesn't seem to make sense to me but I’m curious if that’s everyone’s understanding or if there were other theories.

The car is modified with a high flow down pipe and JB4 running map 1 with stock tires and suspension.

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[itzTang]

1. check alignment
2. check brace installation

 

[lucky phil]

So I installed a rear differential brace made by black market race. Since I noticed that the rear end wants to rotate much more in corners. Car feels very stable with straight line acceleration, but I honestly felt the tenancy to oversteer was more predictable and manageable previously. I’m kind of wondering if I should remove it. I’ve heard others mention that they felt the car wanted to rotate more after installing a brace but that they felt it was manageable. Has anyone else felt the same thing? Any remedies other than removing the differential brace? I’m also curious why this happened. I’ve heard people mention that perhaps there is more torque being transmitted to the rear tires because there’s less loss due to movement in the differential housing, but I’m curious if that’s everyone’s understanding or if there were other theories.

The car is modified with a high flow down pipe and JB4 running map 1 with stock tires and suspension.

Nope. You won't get more torque delivered to the wheels due to a diff brace. Same as you won't get more torque delivered to the driveline with solid engine mounts.
Phil

 

[dAPEX]

Nope. You won't get more torque delivered to the wheels due to a diff brace. Same as you won't get more torque delivered to the driveline with solid engine mounts.
Phil

That was kind of what I thought too. Didn’t seem to make sense logically. What do you think is the reason that the rear end feels like it wants to rotate more easily after the brace was installed? Is it just in my head because I read other people reporting that before I did my install?

 

[dAPEX]

1. check alignment
2. check brace installation

Would installation of the brace affect alignment generally? I will say that the hole in the subframe did not quite match up with the resting position of the differential when on jack stands. When I tightened the bolts to spec it definitely moved the differential slightly in relation to where it wanted to rest while the rear tires were not supported. I didn't see anyone else mention this in the installation instructions, youtube videos, or reviews on here.

I will get the alignment checked and report back.

 

[Loco38SUP]

Would installation of the brace affect alignment generally? I will say that the hole in the subframe did not quite match up with the resting position of the differential when on jack stands. When I tightened the bolts to spec it definitely moved the differential slightly in relation to where it wanted to rest while the rear tires were not supported. I didn't see anyone else mention this in the installation instructions, youtube videos, or reviews on here.

I will get the alignment checked and report back.

I raised mine and set the tires on race ramps to avoid locking in the diff with some sort of bias towards the alignment.

Mine has the front braces along with the rear brace (Twisted Tuning). I haven’t noticed oversteer at all. If anything it helped reduce the rocking back and forth on high speed turns.

-RJM

 

[lucky phil]

That was kind of what I thought too. Didn’t seem to make sense logically. What do you think is the reason that the rear end feels like it wants to rotate more easily after the brace was installed? Is it just in my head because I read other people reporting that before I did my install?

In my view yes. As soon as you have skin in the game it's extremely hard to eliminate bias, it happens unconsciously. The only true test is either a blind test or a means of measurement. When the engineering/physics doesn't support what you feel you are unconsciously biasing the result. Totally normal for the majority people to do. As a world famous MotoGP race tuner once said the key to his rider winning the world titles wasn't tuning the bike but tuning the riders head. He was dead right.
Phil

 

[Razors Edge]

No issues at all here, but I’m on PS4S because honestly, the stock tires absolutely suck. I would spin in 3rd gear on the highway in them. How they chirp and scoot.
I also have an alignment that’s spot on with Coilovers that were adjusted to my liking.
I would start with checking alignment and then swap tires for something better that doesn’t spin easily.

 

[razorlab]

Technically it shouldn't change alignment since all the suspension arms attach to the subframe. Shifting the axles from the diff shouldn't really do anything as they overall move independently of the hubs. (they flex in/out of hub/diff)

 

[itzTang]

Only saying check alignment cause they could have been off before installing the brace

 

[Razors Edge]

Only saying check alignment cause they could have been off before installing the brace

Exactly what I was thinking. Add to that stock tires that spin like they’re in a drift king commercial and you get more rotation. Just a thought…

 

[dAPEX]

No issues at all here, but I’m on PS4S because honestly, the stock tires absolutely suck. I would spin in 3rd gear on the highway in them. How they chirp and scoot.
I also have an alignment that’s spot on with Coilovers that were adjusted to my liking.
I would start with checking alignment and then swap tires for something better that doesn’t spin easily.

I had actually ordered PS4S’s before the install. Just need to get them on. Thanks!

 

[sinbad]

general rule of thumb: when you increase stiffness you need to increase grip to match.
I have the brace on my MT Supra, in my opinion whilst it can be more eager to let go, it does so in a much more predictable fashion. I guess its personal preference as to how you would like to setup your car.

 

[Twisted Tuning]

Would installation of the brace affect alignment generally? I will say that the hole in the subframe did not quite match up with the resting position of the differential when on jack stands. When I tightened the bolts to spec it definitely moved the differential slightly in relation to where it wanted to rest while the rear tires were not supported. I didn't see anyone else mention this in the installation instructions, youtube videos, or reviews on here.

I will get the alignment checked and report back.

Our braces were designed on a car with less than 1000 miles on it. Then test fit in our shop car with 20k on it. Wherever the diff locks to with the braces installed is where its supposed to be. We can not account for mounts that are a little more aged. Or even some oem inconsistencies. so some diff may move a bit while tightening it up, but diff is fine.

 

[lucky phil]

Would installation of the brace affect alignment generally? I will say that the hole in the subframe did not quite match up with the resting position of the differential when on jack stands. When I tightened the bolts to spec it definitely moved the differential slightly in relation to where it wanted to rest while the rear tires were not supported. I didn't see anyone else mention this in the installation instructions, youtube videos, or reviews on here.

I will get the alignment checked and report back.

Personally if I fitted such a thing which I wouldn't I'd fit it with the weight of the car on it's wheels which means a roll on lift. Youtube videos are classics for omitting the fine details. You look at a video to see how they overcame what you know is going to be a "challenging" part of the job and surprise surprise it's been edited out or skipped so they don't look too average.
Phil

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