
Originally Posted by
magicmonkey
I assume it's a downwards change of revs we're talking about here when shifting up, are you talking about completely closing the throttle and then re-opening it is just lowering the rev count briefly?
I wouldn't worry about clutchless shifting just yet.
But if you insist, this is how/why it works...
When you are rolling, there are 3 types of throttle setting. Closed = decelerating. Part-open = maintain speed. Open = accelerating. However, even part-open is still a mild state of acceleration - to offset the friction forces that are trying to slow you down. Your gearbox is in constant-mesh, meaning whatever the throttle does, there is pressure on the face of one gear cog teeth against the teeth of the one it is touching. There is a small amount of play in the mesh, so if you change from accel to decel, the pressure on the geartooth faces changes from one side to the other. Momentary backing off the throttle, or pulling in the clutch, achieves this 'unloading', and allows the cogs to move into the next gear up.
Most people don't clutchless downshift, but it is a reverse of the above...if you are slowing down, your throttle will be closed, but you need to apply a momentary slight acceleration to unload the gearbox...etc.
Do you realise how many holes there could be if people would just take the time to take the dirt out of them?
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