If the tire slips, than the clutch cannot be the only thing in the system that gives. Once the tire is letting go, there is no more strain on the clutch, or the rest of the system. If tires provided more traction when they were sliding than rolling, there would be no point in ABS.JBaz said:yes, but with clutchless shifting from higher gear to a lower gear may slip the rear tire. It's worse for the transmission, but it also adds more wear and tear on the clutch than normal use. That jumpiness or shakiness when you loose traction is slipping the clutch just a bit because the transmission is providing too much power and breaking the static coefficient of friction. That force of friction is also providing a large resistance to the transmission, which is then transferred back to the clutch. The clutch then slips a bit because it's the only thing in the system that will allow to "give" to the stress. The transmission is pretty much fixed in transferring energy from the engine to the wheel, or vice versa. If the transmission does give, something usually breaks or grinds. (a bad sound that you shouldn't hear is usually associated with it though)
Unless you have a slipper clutch, when you break traction from speed shifting down, it adds a lot more strain/pressure on the clutch and transmission system compared to normal use. This is really debatable because you hear people say that it's better to clutchless shift than to use the clutch when shifting gears. I'm only taking about high revs, which multiplies the forces involved and increases the wear and tear on the parts (all parts involved), and that generally involves the slip of the rear (the point of where it turns into excessive power transfer).