I have a quick question for you guys here at the forum, today I took off rather quickly and popped my clutch and I could feel the entire rear of my car bouncing, I have summer tires and it's about 29° so they're probably very hard for the weather, but my question is, is this bouncing normal?

 

Seems like you're describing wheel hop. Happens on cold pavement when the wheel catches traction intermittently

 

Happens to me on the track alot. Has been described as a problem that affects cars with no LSD, along with shaking tail in braking. It's really annoying to me at least. I've read people's opinions that porsche intended the 911 to rely on PSM to be fast with an Open Diff....even the GT3 LSD is somewhat worthless...most rebuild with guard internals if tracking seriously. Just what i've been reading on rennlist/6speed.

 

yes, I've done research with the correct term you have given me and wheel hop it is, I'm almost having to replace tires and being in Chicago with summer tires probably doesn't help, time to break out the 4x4 and put the trickle charger on the 997, come spring I'll buy new tires, thanks! Having my hardtop on probably didn't help with the shaking

 

have the same problem, turning off PSM help?

 

It is not just a tire-related phenomena, there are multiple contributing factors having to do with the twisting torque load on the springs and suspension components as well as the tires. It is not uncommon on most wheel drive cars capable of significant wheel spin. Undoubtedly tires have something to do with it; if they are relatively slippery there isn't enough grip to make them grab again after the spinning starts and the hop can't happen. If they are grippy enough they stay hooked up and won't start grabbing/releasing.

There is less chance of hop if the application of power comes as less of a shock to the drive train... going from completely unloaded to fully loaded in an instant is tough on any mechanical system. Introduce springs, bushings, and slightly flexible metal components and a shudder in the system isn't all that inevitable, leading to the by-product of hop.

While you can try to launch even harder to set the wheels into a full spin (with PSM traction control disabled), this is undesirable since traction is lost in full wheel spin and you just waste rubber. Very moderate wheel spin gives the most launch traction... this is what launch mode on 997.2 PDKs tries to do. If you are interested in knowing about the effect of wheel spin on power application, google the term "slip ratio".

I'd suggest a less severe dumping of the clutch if this is important to you. You'll actually get a faster launch in most cases, and the shock to the drivetrain and suspension will be less and you'll get less (or no) hop. You are also less likely to break the drive shafts which can happen with the shock introduced when hop is occurring. Of course, it is a fine line between dumping the clutch and slipping the clutch excessively and thus burning out the clutch. I think the bottom line is that our cars aren't really intended to do these clutch-dump drag race burnout starts.

 

I think the bottom line is that our cars aren't really intended to do these clutch-dump drag race burnout starts.

here here...

 

Same thing happened to me the other day. I was like "wtf was that?" Never experienced that before (not even in my 2600 lb 400hp car)

 

The 911 will wheel hop in wet conditions if tires are not warmed up. It also has to do with what tires you're using and the age/tread.

The 911 wheels hops like no other RWD car since the car is RR.

Think of the 911 like a Honda/Acura Integra, but backwards .

In an Integra, the center of gravity is extremely low because the engine is placed right behind the front wheels. This also makes the car handle much better and mostly importantly gives superior traction up front .

In wet conditions, everyone know a Integra can wheel hop easily.

In the 911, the exact same wheel hop is happening in the rear.






If driven properly, the 911 drives great in the wet !

 

Wheel hop on hard launches is a well known trait for the 911's. Motortrend's review of the 991 said that the wheel hop was pretty much eliminated from the new model - perhaps because of the longer wheelbase or updated PASM? I think the root cause is the RR design - the immense rear traction advantage has its drawbacks in some situations such as hard launches. The shock of dumping the clutch initially digs the rear wheels in, but then as the rear bounces back up it loses traction, then repeats as the rear oscillates on its springs and the weight of the car shifts backwards. Also perhaps the toe and camber change rapidly because of the quick change in compression. Perhaps the new 991 has a more sorted rear suspension geometry? Could also be worn suspension bushings that have some play.

As for the integra, the engine is fully in front of the front axle just like almost every other front-wheel drive transverse-mounted engine car I think. Not sure why it would be more susceptible to wheel hop than other FF cars, maybe the double wishbones in front have much more dynamic camber change than the more common strut front which causes traction to be lost under rapid compression?

 

what does RR mean...?

 

Rear engine Rear wheel drive

 

Front engine/rear drive cars would simply spin their wheels and produce smoke. There is a lot of traction with a rear engine/rear drive car and the net result is wheel hop.

Dumping the clutch is abuse. It is very stressful on the drive-train and will eventually result in $$$$$$$ repairs.

 

Your tires hopped cause you dumped your clutch on a 29 degree day on older summer tires.