Originally Posted by BoostedBMW
I've only skimmed the first few posts because I have been driving a MT for a few years and don't think I need to learn at this point, but why would you need to push in the clutch twice to revmatch a downshift? That just seems like it would take waaaaay to long to do smoothly.
Just put the clutch in, select the lower gear, and as you are letting the clutch back out blip the throttle right before the engagement point. I guess I don't see the point of double clutching then.
It is important to match revs on a downshift. If you do not match revs when you engage the lower gear the car will slow down. This will transfer weight to the front wheels, enlarge the size of the front contact patches and reduce the size of the rear contact patches. If you are at or near the limits of adhesion this can cause Trailing Clutch Oversteer (TCO) which can cause the car to spin out.
To properly execute a downshift while braking:
1. Apply the brakes smoothly with the left side of your right foot..
2. Depress the clutch with your left foot
3. While braking rock your right foot and "blip" the accelerator.
4; Shift into the next lower gear.
6. Release the clutch.
If this is done properly the car will not slow down/
On cars without synchomesh transmissions it is necessary to "Double Clutch"
1, Apply the brakes with the left side of your right foot.
2. Depress the Clutch with your left foot.
3. Shift into neutral
4. Release the Clutch
5.While still braking smoothly rock your right foot and "blip" the accelerator
8, Depress the clucth with your left foot.
9. Shift into the next lower gear.
10. Release the Clutch.
Once you get the hang of it this can be accomplished very quickly and very smoothly.
Many race cars have "Straight Cut" gears and non-synchomesh transmissions.
Most modern MT cars (such as BMWs) have bevel cut gears and sychomesh transmissions. Although "Double Clutching" will work it is not necessary.
I got into the habit of double clutching when I started learnig how to drive race cars. I had 130,000 miles on my Lexus SC300 when I got rid of it and I was still on the original clutch and brakes.
"Coasting" is not a good practice. To keep a car properly balanced you should either be accelerating or braking or applying "maintenance throttle". This is not usually citical whe driving on the road well below the limits of the car but when driving a race car at or close to the limits "coasting" can upset the cars balance. The brakes and accelerator are as much for keeping the car balanced as they are for speeding up and slowing it down.