In Reply to: "Jerk" posted by Bob ///M3 on June 21, 2000 at 11:13:37:
: Jerk! No, not you...
: I have driven many different cars of the years, many of them high performance cars with various engines; normally aspirated, turbocharged and supercharged with 4, 6 and 8 cylinders. Some with lightweight racing flywheels, some with up to 16 to 1 compression ratio, super raunchy high lift cams, 5:12 to 1 rear-end gearing, etc, etc. Some of these cars were very hard to drive on the street and in normal traffic.
: The really rather docile I6 M3 engine and its drive-train is for some reason rather hard to learn not to be jerky when driven normally, especially taking off and in the lower gears. I can't put my finger on exactly why this is! The lighter flywheel, the DME electronics and sensors doing their thing...I don't know. When driving the car in a spirited fashion it is actually easier. Any jerkiness only becomes a problem when driving easily.
: Here are a few things that may help make your "normal" or easy driving style less jerky:
: Increase the rpm a little higher than normal or more than you have been when pulling away from a dead stop and try to maintain this rpm until the clutch is completely out. Let the clutch pedal out until your feel the friction or foward movement and "leave your foot" at exactly the same clutch level until the clutch and flywheel lock-up. (This is not considered riding the clutch since first gear is so low that an increased rpm will not allow the car to be traveling very fast and your foot will only be left on the clutch a few seconds.) The pull away from a dead start will be very smooth and not jerky.
: When upshifting to second and the higher gears notice that the rpm "hangs" for a half second or slightly more at the last rpm level. (Try it-rev the engine up in neutral to maybe 3,000 rpms and leave it there for a second or so and then lift off. The rpms will hang at the 3,000 rpms for a fraction of a second even after you have lifted.)
: A smooth transition between gears, especially from first to second, is dependent on good timing when shifting into the next higher gear and catching the rpms in the "hang" period. One way is to upshift slightly quicker than what would be considered normal thereby hitting the next higher gear just right when the rpms are matched (before the rpms fall from this "hang"). In other words, you engage the next higher gear quickly enough that the rpms have not dropped too low. Just because you shift quicker doesn't mean you have to go faster or apply the gas heavier.
: In normal or easy driving you won't even have to feed the engine any gas or be concerned about letting the clutch out too quickly when the rpms are matching for the higher gear. There will be no jerkiness...it will be very smooth and sound better too! Right after the clutch is back out you can apply gas and pick up the speed until the next upshift.
: It's hard to explain but the key is in the timing of the shifts (quicker the better) and using this natural "hang" of the rpm to your advantage.
: Bob ///M3
: : What I mean is when i shift, the car 'jerks'. I tried putting more throttle but that doens't seem to help...sometimes i can drive it smooth but most of the time it's just horrible and the temp aroudn LA is goin up...ne1 think it's a mechanical problem?