Rear Wheel Hop / Bump Steer

[sprintamx]

I couldn't find an answer after a quick search.

Is some rear wheel hop / bump steer normal on a stock BRZ? I am not the first owner of the car, but as far as I know, all suspension components are stock. Stock wheels and tires.

The rear wheels hop and skitter a bit over road imperfections. It's more pronounced through turns as you'd expect. Nothing serious, but it's not a dynamic I expected.

Thanks.

[CSG Mike]

Bump steer is normal.

What kind of hopping?

[sprintamx]

Originally Posted by CSG Mike

Bump steer is normal.

What kind of hopping?

As a basic description, the car will slightly hop / skip to one side.

[olorin]

Perhaps the tires are over inflated?

[CSG Mike]

Originally Posted by sprintamx

As a basic description, the car will slightly hop / skip to one side.

Stock suspension? Sounds like a damping issue.

[sprintamx]

IIRC, pressures are 35 psi cold, square.

Stock dampers as far as I know. I bought the car with 12K on the clock only 1.5 months ago, and have not had the wheels off yet or put the car on a lift for a good inspection.

I can't detect any specific ride or alignment issues. But, the hop does surprise me a bit for stock car.

[Suberman]

The Torsen can deliver some weird little effects. If you've not driven with a Torsen before these can be disconcerting. Drive a Mustang GT (the 661 hp version) with a little vigour and you'll experience a demonstration of one reason why Torsen isn't preferred for racing applications. That car hunts like a dog chasing a squirrel if you goose it slightly on dry road. Once she breaks loose she settles down. Our cars don't put out enough torque to really settle down on dry pavement.

Hopping sensations could result from excessive toe in but the max achievable toe on these cars is pretty small I should think with no lower ball joint.

Otherwise, one video I saw on an upgrade to Ohlins revealed that the lower securing bolt for one of the rear sway bar links was stripped at the factory. A loose sway bar (roll bar) can certainly feel weird.

Finally, rear wheel hop is a classic symptom of a failed shock. At your mileage that would either be a defective part or the PO hammered a few potholes. How are the tires now I think of it? Tires can be damaged internally and no longer run round. Often you can't see this but a good balance man will spot it right away, especially with a road force balancer. Cheap diagnostic actually given the cost of a wheel balance.

[utekineir]

I've gotten that feeling you're talking about.

Easiest example was hitting a transition from old to new pavement (rise) mid corner while I happened to be on the gas.

I chalked it up to being a dumbass accelerating through a rough corner.

[Turdinator]

There have been a few threads on wheel hop on here. The stock suspension seems to do it a bit. My car on stock suspension, wheels and tires if I launch too hard will do it instead of spinning cleanly.

[sprintamx]

Thanks for the suggestions.


This is my first Torsen. I have had several limited slip diffs before--Porsche factory, BMW with an aftermarket LSD--but those cars spent the majority of time on track and had so many suspension and chassis mods I wouldn't assume there are enough similarities for a good comparison with the BRZ.


I'll be looking at the running gear, bushings and hardware in depth as I prepare to put the car on the track, but for now I can only go on assumptions.


I don't detect shimmies or other symptoms as if the wheels were bent or some defect in the tires. And, yes, the hop is most often in pavement transitions. Today, I noticed that the tachometer would bounce during the "hop" event. Probably means a wheel was losing contact with the pavement? Or is that an example of how weak the various bushings are reported to be?


Thanks again.

[mwjcyber]

OP...I've experienced the same rear wheel hop you're describing. There's this one section of pavement in town that's rutted from cars, and I would get crazy amounts of hip when turning and accelerating on it.

Since swapping out to Fortune Auto 500 coilovers, the rear wheel hop is gone. Definitely something wonkey with the stock BRZ suspension.

[sprintamx]

I don't know whether to be "relieved" that the mini-consensus seems to be that the hop is a factor of the stock BRZ suspension/setup, and may therefore be normal. Or . . . disappointed in the performance and a bit peeved that there may have a real reason to look at replacing the dampers, even with so few miles. On the other hand, there are some awesome options out there now; just need to decide which one I suppose.


I thought rear wheel hop was the defect of that out-dated live rear axle Mustang, not to be seen on an IRS. It's for another thread, but I shopped the Mustang/Boss/Shelby hard before pulling the trigger on the BRZ ...

[wparsons]

IRS cars typically suffer from way more wheel hop than live axle cars on hard launches, especially if the suspension has anti-squat geometry.

Does this happen all year round, or is it only appearing in the colder weather? Are you still driving on the stock tires? What's the average temperature in your area right now?

[sprintamx]

I've only had the car since December, so I can't comment on warm weather performance. The hop occurs over rough pavement and transitions. I haven't really launched the car hard--more of a twisty road guy than straight-line speed--so I can't comment on problems with a hard launch.


Polar Vortex notwithstanding, average temp range is 30-35 F. Stock wheels and Primacy tires.