<snip>Dry clutches can not take lots of slipping,..... If one owns a bike with a dry clutch they may want to modify their riding technique so as not to abuse it by lots of slipping.
Rotating speed (differential) of the clutch is the critical component (whatever type). When the clutch is spinning too fast to rid itself of the energy differential (much horsepower applied to get vehicle to move from stationary, for example) causing the heat -- it can have detrimental effects. Oil bath clutches may benefit from the cooling effect of oil (in some cases)? They can just as well be handicapped by the 200+ degrees oil temp. environment.
While there can certainly be differences in engineering and design -- it's the speed differential between the clutch friction material and the fast moving metal piece/s (flywheel or clutch outer basket) and slow or non-moving piece/s (pressure plate face or clutch inner hub) that is at issue. Crankshaft mounted clutches (BMW single plate, dry, is an example) by definintion operate at engine speed -- and therefore are at a somewhat disadvantage for getting rid of speed-generated heat. The FJRs (and many other motorcycles) have a reduction (usually, gear-set nowadays) from the crankshaft to the clutch making the clutch (and transmission) operate at a lower speed than engine speed -- that can often be a big plus.
Friction materials in a clutch are not unlike the friction materials used in brakes (in early vehicles, material used to re-line clutches and brakes were often the same) -- and so is the heat generated (in normal use, and when abused, brakes get hot). Clutches will take slipping for very long periods of time (depending on.....?, of course) if the speed differential is kept low (usually meaning slipping at idle (or, just above) -- it's the high engine speed slipping that becomes detrimental.
Clutch longevity is, in many cases, as much an 'operator issue' as a mechanical design issue.
'Fred W': Once it overheats, it's a goner.
Not necessarily. With many clutch materials, once they cool, they can regain much of their original abilities. Although.... too much abuse, too much heat, can warp components -- and that will not 'heal'.
'Fred W': ....slipping, as is taught in MSF courses to maximize control at slow speeds (or so I have heard).
MSF begins with 'friction zone' clutch lessons -- which
are necessary (and, which everyone must use). It's part of the method of m/c control -- and, necessary. 'Friction Zone' at high engine speeds (and low vehicle speeds) is not taught, initially. (Actually.... high speed anything doesn't often happen at MSF courses -- students usually need much encouragement to get both/either engine speed and/or vehicle speed 'up') There is a lesson taught, wherein close manuevering is often aided by clutch slipping -- no problem..... up to a point (as described above).
Lots of words in an attempt to try to shed some light on something that is, often, a bit hard to visualize.....
