Wheel hop - what more can I do?

[Funkjaw]

2023 manual - stock power

My car has struggled with wheel hop since the day I got it. The wheel hop was so bad any amount of traction loss in 1st or 2nd gear the rear wheels would hop, violently at times.

I have done the following at an attempt to get rid of it, and each mod has helped to some degree

Powerflex engine mount insert - helped
Twisted tuning differential brace kit - helped, but not as much as I thought it would kinda disappointed in this one
Verkline rear toe arms - maybe helped
Verkline rear traction links - helped a good amount

Now the car is at a point where wheel hop will only happen under extreme traction loss. Say a very cold rainy day flooring it in 1st gear on bald tires. This is a substantial improvement from how it was... but it's still there

Before you say new tires, they are in the works! But also that's not really fixing the problem, more just avoiding it by providing better grip.

Anybody have luck solving wheel hop in their car? What would you suggest next? I've looked around on the forums but most people seem to be in my boat where they only reduced it but didn't get rid of it entirely.

Thx a ton

BIG EDIT:

I received a response from Verkline that provides an wealth of information on the issue. I am sharing it here in hopes it helps those battling wheel hop like myself:

"
Generally speaking, to decrease the wheel hop You can tune a lot of different factors:

1. Increase the stiffness and/or damping of drivetrain, suspension and chassis (uniballs, polyurethanes, solid bushings, chassis braces, coilovers damping and spring rates etc.)

2. Change the forces which are applied (alignment, tires, tire pressure),

3. Change the direction of movement (wheel path - anti squat) and/or forces (static alignment, bump steer, camber gain, elasto-kinematics)

I found and read Yours very good, constructive thread on the GR Supra forum regarding the wheel hop - https://www.supramkv.com/threads/wheel-hop-what-more-can-i-do.27820/. I believe that it would be best/easiest to find someone who will know the root cause of the wheel hop in Your supra to effectively eliminate it. I like the idea of setting a go pro to look at different components to find out which vibrates the most and in which direction. If the wheel is moving mainly vertically, the cause may be the tune of the dampers/springs (maybe manual supras have softer dampers/springs?). And if there is a lot of longitudinal movement of the knuckle, it may be good enough to increase the stiffness of the traction arms even more.

Unfortunately we do not know what is the cause that some cars suffer from significant wheel hop and some with similar setup don't. However, this shows that the root cause of the problem is probably not in the stiffness of the control arms. Stiffer arms and uniballs instead of rubber bushings will help for sure, but we can not guarantee that they will completely get rid of wheel hop.

In terms of mentioned anti-squat - You can increase it by increasing the length of the lower traction arm and/or by decreasing the length of the upper traction arm. The problem is that this way You will also change the bump steer in a significant way, so if You do not measure it, I recommend to set the length of traction arms to be the same as OEM. Generally speaking it would be also hard to significantly increase the anti-squat without messing up bump steer if You do not relocate the pickup points.

In terms of products which should help with wheel hop, we have two more besides lower traction arm (WAS-421) which You already have:

1. Rear Knuckle Bushings (WAS-426) - it replaces the rubber bushing with spherical bearing on the knuckle pickup point of lower traction arm. Assuming similar stiffness of both lower traction arm OEM bushings (knuckle and subframe pickup points), this product should give a similar upgrade in terms of wheel hop as WAS-421.

2. Upper Traction Arms (WAS-422) - I checked the forces calculations and during acceleration there are about 2 times higher loads on this arm in comparison to the forces acting on the lower traction arm. Also this OEM arm consists of rubber bushings on both sides, instead of 1 so I would expect that it should help with wheel hop roughly 4 times more than WAS-421.

In terms of direction of forces mentioned in the forum thread (picture in the attachment) - User @i3igpete would be right if we would consider the braking scenario or the acceleration with some engines mounted directly to the knuckles (outboard drivetrain). In our acceleration scenario (inboard drivetrain) we can apply longitudinal force in the wheel center instead of contact patch. Thanks to that we will take into account the torque coming to the wheels from the halfshafts. In reality, during acceleration, there will be the same direction of forces acting on both upper and lower traction arm (please see the picture in the attachment)."

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[Loco38SUP]

2023 manual - stock power

My car has struggled with wheel hop since the day I got it. The wheel hop was so bad any amount of traction loss in 1st or 2nd gear the rear wheels would hop, violently at times.

I have done the following at an attempt to get rid of it, and each mod has helped to some degree

Powerflex engine mount insert - helped
Twisted tuning differential brace kit - helped, but not as much as I thought it would kinda disappointed in this one
Verkline rear toe arms - maybe helped
Verkline rear traction links - helped a good amount

Now the car is at a point where wheel hop will only happen under extreme traction loss. Say a very cold rainy day flooring it in 1st gear on bald tires. This is a substantial improvement from how it was... but it's still there

Before you say new tires, they are in the works! But also that's not really fixing the problem, more just avoiding it by providing better grip.

Anybody have luck solving wheel hop in their car? What would you suggest next? I've looked around on the forums but most people seem to be in my boat where they only reduced it but didn't get rid of it entirely.

Thx a ton

What are the rear alignment numbers?

-RJM

 

[Funkjaw]

What are the rear alignment numbers?

-RJM

here ya go

 

[Loco38SUP]

Maybe you need the new bracing offered on the US version Final Edition. It looks like they’re tying in the rear differential to the body of the car.

The video circulating of the track testing showed it improved the rear stability.

-RJM

 

[Funkjaw]

Maybe you need the new bracing offered on the US version Final Edition. It looks like they’re tying in the rear differential to the body of the car.

The video circulating of the track testing showed it improved the rear stability.

-RJM

Whoa! How cool is that. Gonna add that to my list! Thanks for sharing it.

 

[razorlab]

Maybe you need the new bracing offered on the US version Final Edition. It looks like they’re tying in the rear differential to the body of the car.

The video circulating of the track testing showed it improved the rear stability.

-RJM

The Z4 has had that since inception. Not new, easy to get.

It's not to the diff, it bolts to the bottom of the battery box.

 

[SoDakMk5]

What psi are u running in the tires?

 

[i3igpete]

since you noted that the rear traction arms had the largest effect, you could also replace the upper trailing arms that run parallel to the traction arms. These also resist thrust loads from the tires, though counterintuitively, I think they are loaded in tension when you're accelerating (?)

(thrust forces are drawn w. r. t. hub frame)

 

[Funkjaw]

What psi are u running in the tires?

38-40
Just whatever the computer yells at me to do.

 

[Funkjaw]

since you noted that the rear traction arms had the largest effect, you could also replace the upper trailing arms that run parallel to the traction arms. These also resist thrust loads from the tires, though counterintuitively, I think they are loaded in tension when you're accelerating (?)

(thrust forces are drawn w. r. t. hub frame)

Thanks for the insight, you could definitely be onto something.

https://verklineusa.com/products/was-422

Guess that is going on the list!

 

[exe36m3]

My 2-cents as a 20+ year BMW owner, get a better alignment shop not more parts.

BMWs are VERY sensitive to alignment and toe settings absolutely need to be matching. I used to track and commute in my 95 and 96 BMW M3s and just plain thrash my M435i and now Supra. If the toe setting (direction tires are pointed in) is off, the whole car is off.

Looking at your alignment settings if viewed overhead...
Your fronts (toe 14/12) are pointing like this / \.
This is slows down the turning response and makes the rear end react more under power. Generally Supras like fast turn in, less resistant front like this I I. (Or zero toe.)

Your rear setting (toe 12/14).
If viewed overhead, tires pointed inward (positive toe) / \ is ok. And generally this is good because the Supra is a stupidly short wheelbase car (less than a BRZ or E30 M3) but with 400ft/lb torque. So that rear end will dance around if not aligned right.

Simplified, your toe looks like this / |.
So under power, you have one wheel going one direction, the other wheel another direction. So the rear hops, slides, etc.

So caveat, I haven't raced or tracked my Supra... yet.
But as soon as I got it (April 2024), I had the car aligned. Because on the test drive the rear end was all over the place, even under 1/2 throttle.

When I took my car into a known BMW shop (20+ years, owner and I in BMW Car Club and have done track days together). He asked me how I wanted the car to handle. We couldn't do anything about camber or caster (static, not adjustable), so all there was, was toe. I said I don't have a commute, so let's concentrate on handling. Crisp turn-in front, rear end glued to the tarmac.

I got .05 toe up front (straight but slightly pointed inward, some higher speed stability) and 13 toe rear (pointed inward). This gives me good crisp turn-in and the rear end predictable and planted. Under power, I can feel the center of gravity around me the driver.

Get your alignment solid before throwing more parts at it.
-Dad

 

[TBK]

The Z4 has had that since inception. Not new, easy to get.

It's not to the diff, it bolts to the bottom of the battery box.

What's the reason the aftermarket hasn't pickup up on this?

 

[i3igpete]

Get your alignment solid before throwing more parts at it.
-Dad

His rear toe has side-to side variation of 0.02 degrees. I would bet real money that if the alignment tech were to roll the car off and back on, there's a good chance to it would register as dead-on. and yours would come back as misaligned again.

 

[Funkjaw]

And generally this is good because the Supra is a stupidly short wheelbase car

I couldn't agree more. Why they decided to build this car on a short wheelbase platform like the Z is beyond me.

Get your alignment solid before throwing more parts at it.
-Dad

I do agree that a more aggressive alignment might help... BUT going outside of OEM specs is off the table at the moment.

However when thinking about it...
The wheel hop on this car seems to be fundamentally solved at the suspension geometry level, rather than just a matter of grippier tires and better alignment. I say this as I've owned over 20 manual RWD sports cars, including an E46 M3 with a cracked rear subframe that I drove very aggressively, and none of them exhibited wheel hop like this; even the cars with more torque/power or an alignment as crooked as Steve Buscemi's eyes.

I think at this point I am going look into what @i3igpete suggested about the upper lateral links from Verkline.

I also think the differential in this car would be better if it were a regular mechanical clutch based LSD instead of whatever BMW magic is in there. But that might be a topic for another discussion.

 

[SoDakMk5]

38-40
Just whatever the computer yells at me to do.

That’s way too much. Try 32-34 psi

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