Back end hopping on launch
03-23-2006, 04:02 PM
#33
Three Wheelin'
Originally Posted by Alexander Stemer
Jeff,
I think there is more to it, but essentially it's a matter of design and grip. The twisting forces due to power applied to the rear axles will either cause the tire to spin or the spring to wind up. When the traction is enough to make the spring wind, it compresses until it's force exceeds that applied, then it expands, causing that wheel to hop. Solid axle cars can do this too, but are more resistant.
My old Olds 442 just burned rubber until I put on race tires for gymkhana's (now called autocross), then it had hop.
My Lola would do it (mildly)on cold rain tires, but cold slicks just spun.
My 1990 C4 did it in dry conditions but not snow and ice. I won't even try it in my tt.
I think you can avoid it by clutch slipping, but then you are brutalizing the clutch. Fastest standing starts typically require some wheelspin to keep the engine in the power band.
The factory testers were quoted on the 993 tt as saying the ideal launch involved the right number of revs(about 4000 by recollection), and sidestepping the clutch. Then, if you do it right, the whole car shudders for a moment, then takes off. But even they admit they don't get it right each time. There are only a limited number of such launches the driveline will tolerate. Do it enough, and you will be able to inspect your differential by examining the pieces you pick off the asphalt.
BTW, my 1991 C2 cab tip did not do this, nor will a Boxster tip, since the torque converter absorbs the shock, and neither can spin the tires from a standing start.
I'm not an engineer, but I think I got the basics right. AS
I think there is more to it, but essentially it's a matter of design and grip. The twisting forces due to power applied to the rear axles will either cause the tire to spin or the spring to wind up. When the traction is enough to make the spring wind, it compresses until it's force exceeds that applied, then it expands, causing that wheel to hop. Solid axle cars can do this too, but are more resistant.
My old Olds 442 just burned rubber until I put on race tires for gymkhana's (now called autocross), then it had hop.
My Lola would do it (mildly)on cold rain tires, but cold slicks just spun.
My 1990 C4 did it in dry conditions but not snow and ice. I won't even try it in my tt.
I think you can avoid it by clutch slipping, but then you are brutalizing the clutch. Fastest standing starts typically require some wheelspin to keep the engine in the power band.
The factory testers were quoted on the 993 tt as saying the ideal launch involved the right number of revs(about 4000 by recollection), and sidestepping the clutch. Then, if you do it right, the whole car shudders for a moment, then takes off. But even they admit they don't get it right each time. There are only a limited number of such launches the driveline will tolerate. Do it enough, and you will be able to inspect your differential by examining the pieces you pick off the asphalt.
BTW, my 1991 C2 cab tip did not do this, nor will a Boxster tip, since the torque converter absorbs the shock, and neither can spin the tires from a standing start.
I'm not an engineer, but I think I got the basics right. AS
i know you have a lot more experience than myself.
mine was more of a semi-educated guess!
no problems with the light weight elise hopping?
how much hp is it making?
03-23-2006, 06:31 PM
#34
I had an early 80's Camaro with supposedly 150 hp V8 (felt more like 400 hp). Even though it was quite nose heavy it was easy to induce axle tramp by heavy application of the throttle (once it as so bad and the car shook so much it really scared me). I would love to be able to race this car against my 997. Just old tech overhead valve, 4 barrel carb.
03-23-2006, 07:51 PM
#35
cgng30 re wheelhop My E46M3 would not come off the line w/o wheel hop The only way to launch and avoid hop is to slip the clutch and balance engine speed and wheel spin until it hooks up This places the stress on the clutch Whether this is "better" is questionable I think in the R&T review which got under 4 secs 0-60 they mentioned that they did not experience hop This leads me to believe that the surface they launched on allowed wheelspin off the line ie was a little "slippery" and worked to the P's advantage
03-23-2006, 08:16 PM
#36
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Thanks to Coochas, here's the latest C&D short take on the C4S (they comment directly on this topic):
http://coochas.com/porsche/Resources...CandDmay06.jpg
I had a 997 C2S and I too experienced severe rear axle tramp on hard standing start acceleration runs (and these were NOT 4K RPM drop clutch moves).
This has been a characteristic of 2WD 911's for years.
I am looking forward to my upcoming C4S order since up to 40% of the power can be sent forward.
- TL Smith
http://coochas.com/porsche/Resources...CandDmay06.jpg
I had a 997 C2S and I too experienced severe rear axle tramp on hard standing start acceleration runs (and these were NOT 4K RPM drop clutch moves).
This has been a characteristic of 2WD 911's for years.
I am looking forward to my upcoming C4S order since up to 40% of the power can be sent forward.
- TL Smith
03-23-2006, 08:50 PM
#37
I hope you enjoy your car. I do not feel, however, that wheel hop or the lack of it should be the sole determining factor of whether you go rwd or 4wd. There are well documented advantages and disadvantages to both systems. At PDE I was able to get my 2C off the line w/o hop by using a little clutch slip. While the instructor cringed I was real fast in dragstrip mode
03-23-2006, 09:58 PM
#38
Rennlist Member
Hey Jeff,
The Elise has the power upgrade to it's Rover engine. There were some reports that early models didn't make the advertised 190hp. Mine is a later one, so I don't know that. The moded ECU and exhaust offered by Lotus was said to add 15, and seems to.
Yes it will burn rubber if laucnched with about 4000 revs (redline is 7800). It is about as fast as a Ferrari 355 up to about 100, when the gearing just doesn't work for it.
The car that really burns rubber is my Kurtis. Actually, you can't launch it without breaking traction, so turning out of the driveway is always sideways. And no axle tramp. Seems it's torsion bars are immune. But Porsche handling and Kurtis handling can't be compared, tho mine will beat most of the DE cars around gingerman. AS
The Elise has the power upgrade to it's Rover engine. There were some reports that early models didn't make the advertised 190hp. Mine is a later one, so I don't know that. The moded ECU and exhaust offered by Lotus was said to add 15, and seems to.
Yes it will burn rubber if laucnched with about 4000 revs (redline is 7800). It is about as fast as a Ferrari 355 up to about 100, when the gearing just doesn't work for it.
The car that really burns rubber is my Kurtis. Actually, you can't launch it without breaking traction, so turning out of the driveway is always sideways. And no axle tramp. Seems it's torsion bars are immune. But Porsche handling and Kurtis handling can't be compared, tho mine will beat most of the DE cars around gingerman. AS
03-24-2006, 09:30 AM
#39
Three Wheelin'
Originally Posted by Alexander Stemer
Hey Jeff,
The Elise has the power upgrade to it's Rover engine. There were some reports that early models didn't make the advertised 190hp. Mine is a later one, so I don't know that. The moded ECU and exhaust offered by Lotus was said to add 15, and seems to.
Yes it will burn rubber if laucnched with about 4000 revs (redline is 7800). It is about as fast as a Ferrari 355 up to about 100, when the gearing just doesn't work for it.
The car that really burns rubber is my Kurtis. Actually, you can't launch it without breaking traction, so turning out of the driveway is always sideways. And no axle tramp. Seems it's torsion bars are immune. But Porsche handling and Kurtis handling can't be compared, tho mine will beat most of the DE cars around gingerman. AS
The Elise has the power upgrade to it's Rover engine. There were some reports that early models didn't make the advertised 190hp. Mine is a later one, so I don't know that. The moded ECU and exhaust offered by Lotus was said to add 15, and seems to.
Yes it will burn rubber if laucnched with about 4000 revs (redline is 7800). It is about as fast as a Ferrari 355 up to about 100, when the gearing just doesn't work for it.
The car that really burns rubber is my Kurtis. Actually, you can't launch it without breaking traction, so turning out of the driveway is always sideways. And no axle tramp. Seems it's torsion bars are immune. But Porsche handling and Kurtis handling can't be compared, tho mine will beat most of the DE cars around gingerman. AS
03-24-2006, 10:24 AM
#40
You either need more throttle to get the tires to spin more (which will slow you down), or a little less throttle to get them to grip continuously. The hop means that you are just at the point where the wheels spin/grip - you need to get off that balancing act. That point will be influenced by the tire temp (tire grip) to a small extent, as well as the surface you're driving on.
Launching a C2 well requires more skill than a C4. That's true of basically everything, except drifting and inducing oversteer, which is easier in a C2. Hence, the C4 is easier to drive, less prone to oversteer, more prone to understeer, and probably safer than a C2. On the other hand, the steering is less communicative, it weighs more, and in experienced hands, it's probably a little less fun to drive.
-B
Launching a C2 well requires more skill than a C4. That's true of basically everything, except drifting and inducing oversteer, which is easier in a C2. Hence, the C4 is easier to drive, less prone to oversteer, more prone to understeer, and probably safer than a C2. On the other hand, the steering is less communicative, it weighs more, and in experienced hands, it's probably a little less fun to drive.
-B
03-24-2006, 10:30 AM
#41
Rennlist Member
Hi Jeff,
Before the OT monitors hit, my Kurtis is the Ward Kurtis that Jon Ward built to win the La Carrera Panamericana in 1990 (and it did win). Therefore it is a 2 passenger car with front cycle fenders. It is a factory built Kurtis frame (built in the Kurtis plan in Bakersfield) but built with modern steel alloy, and has a factory number plate. However, it has several racing upgrades including Nascar style power steering, radiators, coolers, Jericho trans,... and almost forgot 405 inch all aluminum chevrolet dyno'ed at 570 (I left the compression at 9.0 for pump gas). Technically, it's a continuation car, since no bolt existed before 1990, tho the title and number plate say 1953, and the LaCarrera accepted it.
If you read Autoweek, Car and Driver or Road and Track in the 90's, you've seen the car. It's still Mclaren orange, but the cage is off. The street plate is "1Mexico"
But, back on topic- with Hoosiers, just endless burning rubber- no hop. And, whatever you say about the ZO6- it doesn't hop either. That's why a ZO6 will more consistently smoke your self-owned Porsches. He can launch without traumna, and we can't. The magazines don't care, so they beat the test Porsches up. AS
Before the OT monitors hit, my Kurtis is the Ward Kurtis that Jon Ward built to win the La Carrera Panamericana in 1990 (and it did win). Therefore it is a 2 passenger car with front cycle fenders. It is a factory built Kurtis frame (built in the Kurtis plan in Bakersfield) but built with modern steel alloy, and has a factory number plate. However, it has several racing upgrades including Nascar style power steering, radiators, coolers, Jericho trans,... and almost forgot 405 inch all aluminum chevrolet dyno'ed at 570 (I left the compression at 9.0 for pump gas). Technically, it's a continuation car, since no bolt existed before 1990, tho the title and number plate say 1953, and the LaCarrera accepted it.
If you read Autoweek, Car and Driver or Road and Track in the 90's, you've seen the car. It's still Mclaren orange, but the cage is off. The street plate is "1Mexico"
But, back on topic- with Hoosiers, just endless burning rubber- no hop. And, whatever you say about the ZO6- it doesn't hop either. That's why a ZO6 will more consistently smoke your self-owned Porsches. He can launch without traumna, and we can't. The magazines don't care, so they beat the test Porsches up. AS
03-31-2006, 11:18 PM
#42
Instructor
I swear my '99 996 with TC and Limited Slip Differential (not available on later 996s) rarely hopped. My '05 997 definitely hops and requires me to modulate the throttle a bit more. I'm wondering if having a LSD makes a difference since it doesn't rely on the braking system (PSM and TC) to minimize wheel spin?
03-31-2006, 11:42 PM
#43
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It's easy - on a front engined rear wheel drive car - you would just spin the rear tires - but the 911 with the weight on the rear is hooking up then bouncing from all the force.
"Ladder bars" like on a dragster would fix this but screw up your handling.
Like some one said before - this is a sports car - not a dragster!!!!
"Ladder bars" like on a dragster would fix this but screw up your handling.
Like some one said before - this is a sports car - not a dragster!!!!
04-01-2006, 10:56 AM
#44
Fully realizing the 911 isn't a muscle car, there will be times when i would want to launch hard at a stop light, e.g. those times when there's some idiot in his Nissan Maxima staring me down...and this axle hop would bother me...it's enough to help me make my decision that I would want the 4S...i was on the fence b/w the S and 4S previously, but leaning towards the 4S, now i've fully decided.
04-01-2006, 06:42 PM
#45
Three Wheelin'
Go look at the May 2006 Car & Driver and they mention that the 4s doesn't have the hop on lauch due the power distribution to the front wheels.
The 4S rules baby!
The 4S rules baby!