tires skipping during hard acceleration with psm off

[ohhh my]

Just curious if this is normal.

I purchased my car about 6 months ago and i have never turned off psm before. It was a quite foggy earlier and the ground was a little moist. I wanted to see what type of traction and how hard I can accelerate before the rear tires break loose. I recently purchased some hankook v12's about 1,000 miles ago.

In all my previous cars that i've tried this one, when you lose traction it just feels like you're not moving and the rear tires spin with traction control off and eventually it gets grip and you start moving.

When I tried this earlier, my rear end skipped, feels like going over a really bumpy road, except in my case, the road was smooth.

Is this normal and is it because my tires are fairly new? thoughts?

[rene525d]

I get the same feeling when PSM is on.

[ohhh my]

No, when PSM is on, the power to the rear wheels get cut off not allowing you to spin the wheels or just slightly.

[Spinnaker]

What you are experiencing is called axle tramp. It is common on cars with independent suspension.
A Boxster is not a drag racing car and the suspension is not configured for tire spinning starts.

[ohhh my]

Thanks for the explanation. Perhaps i wasn't clear in my original post, the reason for me trying this was just to see how much traction I have before the tires breaking loose. I believe it's good practice to know your cars limitations/capabilities, especially if you change brand tires.

[Spinnaker]

Now that I re-read your original post, I understand what you were doing. I did the same thing when I first got my Boxster, wanted to see how much traction the tires had when the road was wet so I could get a better feeling for the amount of grip to expect. Didn't want to get too tail happy by accident.

[fatmike]

I get wheel hop when I leave my neighborhood on occasion.

I have to turn right and accelerate rapidly up a steep hill. It's noticeable when there is bad traction if the road is wet or sandy, etc. But, if you modulate the throttle it's easy to prevent. That is the only spot that it happens, and it won't happen if you're even a little aware of the potential.

[ProjectM96]

This happens to me too. Another thing. Is the Boxster's traction control really that effective?

With my traction control on, I still spin out the tires when accelerating in cold weather(because summer tires), and in parking garages(because smooth cement). I barely hit the gas and the wheels spin and my traction control light blinks rapidly.

Is the traction control supposed to allow some wheel spin?

[rene525d]

http://www.deter.com/porsche/PSM.txt

A very good explanation of how PSM works.

[blue2000s]

Originally Posted by Spinnaker

What you are experiencing is called axle tramp. It is common on cars with independent suspension.
A Boxster is not a drag racing car and the suspension is not configured for tire spinning starts.

+1 and it's very hard on your drivetrain. The impact of the little jumps in traction can break joints and gears. It's very common on Porsches in general from what I understand.

[thstone]

Its also called axle hop or wheel hop and yes, its normal on our cars (and many, many other cars).

It happens because the suspension allows the wheel to move up as its reaching maximum traction (the torgue winds up the suspension) rather than keeping the wheel firmly on the ground and having the tire spin. The net result is that the tire "hops" up and down as it grips, loses grip, and grips again.

Blue2000s is correct that this is VERY hard on the transaxle and CV joints. Don't get me wrong, the car is built to take some abuse but damage can occur so you're best bet is to minimize axle hop to avoid any problems.

Unless you are willing to do some suspension mods (usually starting with at least new shocks), then you'll have to live with it. Drag racers go so far as to install special "torque arms" or other suspension mod's to eliminate it.

[Mark_T]

I had bad wheel hop until I changed my front motor mount. Now I get none regardless of how hard I launch it

[jsceash]

Originally Posted by Mark_T

I had bad wheel hop until I changed my front motor mount. Now I get none regardless of how hard I launch it

Hey thank you, this is a good confirmation of something I was starting to feel the last several week ends I had the car out in the morning when it was cold.

[Topless]

Originally Posted by blue2000s

+1 and it's very hard on your drivetrain. The impact of the little jumps in traction can break joints and gears. It's very common on Porsches in general from what I understand.

Yes. Wheel hop/axle tramp are one of the best ways to murder your transmission (ask me how I know. A gentle right foot that can ride that fine line between max acceleration and spinning the inside wheel is to be found on a very skilled driver indeed.