May 6, 2006 4:40:25 AM
- U Boat Commander
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Board: Porsche - 911 - 997
Language: English
Region: Worldwide
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May 6, 2006 11:15:23 AM
- robbo
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Nov 13, 2007 7:08:04 PM
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John H
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Re: Is Wheelhop Bad?
Quote:
U Boat Commander said:
This is something I've wondered about for years but never really knew the answer. I mean, it can't be good to violently shake the engine compartment on launch. Right?
Thanks Rennteamers.
Sorry to rake up this old post, but I hadn't experienced 'Wheel Hop' or 'Axle Tramp' or whatever it's called until yesterday.
I was launching from traffic lights on a damp but level surface when the whole car shuddered instead of accelerating.
Is this Wheelhop?
What causes it? I've just had new front tyres fitted - rears okay for few more months. Could this have anything to do with it?Thanks guys....
Nov 13, 2007 7:34:10 PM
- 69bossnine
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Re: Is Wheelhop Bad?
It's bad, the forces and stresses involved have little relation to driving on a rough road, or shifting hard... It's a "bind" where your entire driveline is fighting the road, the tires and the chassis links, and they're kicking back at each other in an escalating fashion, until something screams "mercy", or a variable such as weight transfer forces the equation toward stability (i.e. transferring weight enough to plant the rear tires with enough force to stem the harmonic action...). That's why wheel hop is typically momentary... eventually the forces pressing downward on the rear suspension overpower the chassis's tendency to flop around like a fish...
I realize that a drag-race 3600-rpm launch will create some hop, and you've just gotta "do it" to get a good 1/4-mile e.t... But repeated launches like that would eventually wind up with catastrophic failure, typically at the half-shaft joints or the shafts themselves...
I've seen wheel hop break many a Corvette and Viper at the drag-strip... Those cars could drive on rough roads for a 1/4 million miles without breakage, but one-to-many drag launches..... and every so often you'll see a wheel come loose in the wheelhouse and wreak havoc...
I realize that a drag-race 3600-rpm launch will create some hop, and you've just gotta "do it" to get a good 1/4-mile e.t... But repeated launches like that would eventually wind up with catastrophic failure, typically at the half-shaft joints or the shafts themselves...
I've seen wheel hop break many a Corvette and Viper at the drag-strip... Those cars could drive on rough roads for a 1/4 million miles without breakage, but one-to-many drag launches..... and every so often you'll see a wheel come loose in the wheelhouse and wreak havoc...
Nov 13, 2007 9:00:04 PM
- Greentree
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Nov 13, 2007 10:16:34 PM
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Carlos from Spain
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Re: Is Wheelhop Bad?
I believe in this case its also due to the PSM and not the traditional wheelhop that 69bossnine very well explained.
If find that if you turn on the sport chorno button (hence lowering the PSM activation threshold), or directly turning off the PSM, that it doesn't happen, and you get a smotyh slide or traction transsition. But if you do it with PSM it then appears, right when the PSM kicks in. ANd it can happen not only on straight line launching but also in attempting a powerslide or similar.
If find that if you turn on the sport chorno button (hence lowering the PSM activation threshold), or directly turning off the PSM, that it doesn't happen, and you get a smotyh slide or traction transsition. But if you do it with PSM it then appears, right when the PSM kicks in. ANd it can happen not only on straight line launching but also in attempting a powerslide or similar.
Nov 14, 2007 4:25:26 AM
- Heist
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Reply to:
Carlos from Spain
Nov 14, 2007 2:37:18 PM
- Leawood911
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Reply to:
Carlos from Spain
Re: Is Wheelhop Bad?
Quote:
Carlos from Spain said:
I believe in this case its also due to the PSM and not the traditional wheelhop that 69bossnine very well explained.
If find that if you turn on the sport chorno button (hence lowering the PSM activation threshold), or directly turning off the PSM, that it doesn't happen, and you get a smotyh slide or traction transsition. But if you do it with PSM it then appears, right when the PSM kicks in. ANd it can happen not only on straight line launching but also in attempting a powerslide or similar.
PSM has nothing to do with wheelhop. All 911 (or cars with independent rear suspensions) have issues with wheelhop. Especially 911s when you drop the clutch at 4k or above. Every one of my old 911s also did it and they never had PSM. I do not ever try to do this on purpose but accelerating too quickly from a stop on wet pavement can also cause this. Just ease off the second you feel it, as you are not going anywhere at that point and tearing up the driveline in a major way.
Peace.
Nov 14, 2007 6:52:29 PM
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Carlos from Spain
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Re: Is Wheelhop Bad?
Again, yes thats true, but what I'm trying to say is that this case may not be the same wheelhop, since there is one type that appears on the 997/996 that is caused when PSM engages that dissapears on the same situations when its OFF or in sport chrono. That doesn't mean that the traditional wheelhop all cars get (not only cars with independant rear suspension but also front wheel drives, etc) does not happen too.
Nov 14, 2007 11:37:27 PM
- Weasel
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Reply to:
Carlos from Spain
Re: Is Wheelhop Bad?
It happened to me on wet pavement. I turned left onto the street and goosed the accelerator. It feels like a bump-bump-bump-bump. I got off the accelerator right away wondering, "What was that"? Apparently one of the rear tires was slipping. The PSM works to control the slippage by applying the brake to that wheel.
I notice the Carrera 4 has what's called "Intelligent All Wheel Drive" and "PSM Plus". I suppose this sort of wheel slip happens much less frequently in that case.
I notice the Carrera 4 has what's called "Intelligent All Wheel Drive" and "PSM Plus". I suppose this sort of wheel slip happens much less frequently in that case.
Nov 19, 2007 3:44:53 AM
- Puffy911
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Reply to:
Carlos from Spain
Re: Is Wheelhop Bad?
The subject has been described by 69 above already, it is, to my knowledge, primarily caused by the number of flexible joints between engine&drivetrain and the chassis. Haven't been able to urgently launch a 997 without some axle tramp, some people told me that it occurs less on the aircooled 911 variants.
You could reduce/eliminate it by installing stiffer engine mounts which would, in return, transfer more noise and vibration into the cabin. The fact that PSM (and its correspondent dashlight) kicks in might be the outcome of this phenomoenom.
You could reduce/eliminate it by installing stiffer engine mounts which would, in return, transfer more noise and vibration into the cabin. The fact that PSM (and its correspondent dashlight) kicks in might be the outcome of this phenomoenom.
Re: Is Wheelhop Bad?
Wheel hop, or "axle tramp', is caused by a compliant suspension with high tire traction. The Carrera has 62% of its weight on the rear, combined with foot wide, high traction tires. The hooked up tire loads the compliant suspension, compressing it, it then breaks the tire loose, allowing the wheel to rebound. The process then repeats itself. This behavior is common with clutch drops. You can get the suspension to hit the stops both top & bottom. It is true that the drivetrain components will take a beating, but the real victim is often the clutch. It is said that you should put $100 in the kitty for a new clutch every time you rev up the car & dump it from a standing start.
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