GPL: 'Drive Line Snatch'

Something I noticed in GPL; probably already been said, but I'll say it again, anyway. If you down-shift too quickly, the rear end will break away from you! This is caused by drive line snatch, where the wheels, being driven by the engine (now, this is where I loose my understanding...) are unable to match the speed of the engine, and therefore, lock up... right? Whatever, I know I've experienced it in my road car, in my race car and now in GPL... it's the reason why drivers blip. Rob "...and I've got to stop, because I've got a lump in my throat!" ~Murray Walker "82.4% of statistics are made up on the spot" ~Vic Reeves "When the segulls follow the trawler, it is because the expect fish to be thrown for them." ~Eric Cantona

If you are describing a downshift under braking then the engine is being driven by the wheels. This is compression braking which you can use to your advantage, just downshift a bit later. If you try to engage the engine at too high of an rpm it will lock the wheels, so match the speed a little better and use the force luke. JM

Quoted text (14 lines)

> Something I noticed in GPL; probably already been said, but I'll say it again, > anyway. If you down-shift too quickly, the rear end will break away from you! > This is caused by drive line snatch, where the wheels, being driven by the > engine (now, this is where I loose my understanding...) are unable to match the > speed of the engine, and therefore, lock up... right? > Whatever, I know I've experienced it in my road car, in my race car and now in > GPL... it's the reason why drivers blip. > Rob > "...and I've got to stop, because I've got a lump in my throat!" ~Murray Walker > "82.4% of statistics are made up on the spot" ~Vic Reeves > "When the segulls follow the trawler, it is because the expect fish to be > thrown for them." ~Eric Cantona

Not only that, but if you do it just right, you can get the diff to try to spin you INTO the corner at the same rate your car is travelling through the corner. Great help for Zandvoort! I discovered this half by accident and half by thinking "If I step on the gas and the car spins..." Av/Mikey |If you are describing a downshift under braking then the engine is being driven by |the wheels. This is compression braking which you can use to your advantage, just |downshift a bit later. If you try to engage the engine at too high of an rpm it |will lock the wheels, so match the speed a little better and use the force luke. |JM | | |> Something I noticed in GPL; probably already been said, but I'll say it again, |> anyway. If you down-shift too quickly, the rear end will break away from you! |> This is caused by drive line snatch, where the wheels, being driven by the |> engine (now, this is where I loose my understanding...) are unable to match the |> speed of the engine, and therefore, lock up... right? |> |> Whatever, I know I've experienced it in my road car, in my race car and now in |> GPL... it's the reason why drivers blip. |> |> Rob |> "...and I've got to stop, because I've got a lump in my throat!" ~Murray Walker |> "82.4% of statistics are made up on the spot" ~Vic Reeves |> "When the segulls follow the trawler, it is because the expect fish to be |> thrown for them." ~Eric Cantona |

>Something I noticed in GPL; probably already been said, but I'll say it again, >anyway. If you down-shift too quickly, the rear end will break away from you! >This is caused by drive line snatch, where the wheels, being driven by the >engine (now, this is where I loose my understanding...) are unable to match the >speed of the engine, and therefore, lock up... right? Almost. It's really quite simple to understand. Imagine this: You're driving on a straight at constanbt velocity in 4th gear and shift down quickly to 3rd. In 4th gear, the speed you are going at the moment equals 6000rpm. In 3rd gear, the same speed equals 8000rpm. Given that you shift down very effectively (and the rpm doesn't drop at all in the interval, which it will usually do unless you blip the throttle), your engine will still be doing 6000rpm - whereas your rear wheels "expect" 8000 rpm. What happens? The rear wheels will turn more slowly than necessary for this speed. They will not lock, but they will break traction anyway. While braking for a corner and downshifting, essentially the same thing happens. It's just a bit more complicated since the speed you're travelling at also changes. In GPL (and real racecars, I presume), the ramp angles of the diff also play a role - but don't ask me what role that is. This is where I lose my understanding. :) What you do by blipping is simply this: you shift out of 4th, blip the throttle to bring it to the 8000rpm needed in 3rd at this speed, then shift into 3rd. In Real Life, I need this skill usually not while braking but while going uphill in underpowered cars and trucks, though. -- Wolfgang Preiss \ E-mail copies of replies to this posting are welcome.