Diaphragm vs. Borg and Beck.............

I agree with YR that too much clamp pressure is counter productive and kills parts. But there are other ways to dial in appropriate clutch clamp pressure during critical parts of the run, ways that he appears to have no experience with. If he does have experience with them, he should be able to point out specific differences as to what makes his way better.

Probably the biggest reason we differ in our points of view is likely because YR may be looking at things strictly from a traditional bias slick perspective, where it's important to hit the slicks just hard enough with the clutch to get them to spin, without spinning them too much. Because the engine does not typically make enough torque to break the tires loose on it’s own, it needs help from the clutch to release additional inertia energy from the engine’s rotating assy, which helps get the tires turning. It's the release of that extra energy that causes the engine to lose rpm just before the tires begin to spin. When the tires begin to spin the clutch no longer has to slip, basically trading less wear/tear on the clutch for more wear/tear on the tires. The benefit of an adjustable clutch is that it can adapt to different track conditions, enabling you to dial in just enough initial hit to get the tires turning, balancing that against centrifugal assist keeps the clutch from slipping too much down the track. It’s been that way for a long time now, but that’s beginning to change.

We now have radials which are a much more efficient tire. Just switching from slicks to radials will gain you some mph, that fact alone tells you the slicks consume more power. Problem is, you can’t just bolt a set of radials on a traditional stick/slick setup and get all the benefits. Radials just won’t tolerate the violent hit or the wheel spin that the slicks needed to work effectively with a manual transmission. When you eliminate the overly violent hit and wheel spin, it becomes much easier to reap the benefits of radials. Temporarily holding back some clutch clamp pressure is that key to making radials work. The basic difference is that for slicks you match the clutch to track conditions to get the tire slip you need, for radials it's more about matching the clutch to the engine's power to minimize engine rpm loss on launch and after the shifts. This is where the adjustable clutch with centrifugal assist falls short with radials, as the centrifugal assist causes the clutch to hit radials way too hard after a flat foot WOT shift.

The most overlooked part of a manual car getting off the line with radials is in controlling the clutch. To be more specific, it's about using the clutch to control the flow of inertia energy out of the rotating assy. Good tires can probably handle the power of the engine in 1st gear if you were doing a rolling start, it's the dump of the clutch that usually knocks them loose. The reason the dump of the clutch knocks them loose is that when the clutch grabs, it causes the engine to lose rpm. You have to look at the entire rotating assy as one LARGE flywheel...crankshaft/flywheel/pressure plate/engine pulleys/etc. Flywheels are an inertia energy storage device. When you put energy into one, it speeds up. When energy flows out of a flywheel, it slows down. The engine losing rpm when you dump the clutch is an indicator of inertia energy, stored within the rotating assy, being dumped into your input shaft. Radials can probably handle engine power alone, but engine power + inertia energy can easily put them over the edge. If your engine loses rpm when you dump the clutch, you probably need to work on fixing that if you want to run radials successfully. You might not need to completely eliminate all the rpm loss to get the tires to stick, just slowing down loss of rpm will minimize the effect and might be enough to get by.

A well trained foot can get the job done, but you may need to master several different launch scenarios (in my case- NA vs nitrous). Instead, i found the solution of installing a small adjustable hyd cylinder onto the clutch pedal to be much easier. It’s purpose is to slow down the clutch pedal's return stroke as needed, for instance making it easy to switch between the setups required for launch NA without bog, to what's required for a nitrous launch without bog. Laying down a quick pass on radials with a clutch is no longer “hit and miss” like it used to be.