Paging Greg Masters - wot you torqueing about?

Lou Can

Lou Can

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Greg posted recently on a thread about clutch slip and stated that a bike always shows clutch slip first in a high gear sue to max torque in that gear.

I was trying to look clever and thre this into a conversation with a mate and we both scratched our heads for a bit. I appreciate that its true (had it happen to me) - but why is it true? Intuitively it seems wrong.

Give us an idiots explanation!

LC
 
The higher the gear the more force required to propell the bike

(if this was not the case the bike would accelerate at the same rate in 5th as 1st.nor would need more than one gear)

so when you accelertae in 5th you exerte a greater force on the clutch than

in 1st hence clutch always starts in the higher gears :D :D

Probably not as clear as Mr Masters would have been but hope this helps. :)
 
yeahbutnobutyeahbut.........

If the inertial mass of you and the bike remains the same (which it should do) and discounting aerodynamics and stuff, the engine produces a constant maximum bhp (i.e. force) then the resistance to that bhp is the thing that varies. BUT the resistance to accelerating really fast (in a low gear) i.e. significantly changing the momentum of the vehicle in a short space of time (e.g. 250kg from rest to 40kph in 2 secs) must surely be greater than chaging the momentum over a longer period of time (250kg from 100 to 140 kph in 20 secs, say). Isn't the instantaneous load on the clutch (necesseary to overcome the static friction of the plates) gong to be greater in the first scenario??

This is going to be something to do with i/2mvsquared innit, where the speed is the critical factor?

Oooh I love ignorance

LC
 
Yes, Matt's on the money!

In low gears there's what's referred to as 'mechanical advantage' - simply put, it means that the gear ratios impose less load on the clutch. In the highest gears that's not the case.

If your bike was on a static rig with the rear wheel locked solid, the performance of the clutch wouldn't be different whatever gear was being used. Either it would slip or it wouldn't and the engine would stall.

But on the road it's different. In low gears it's relatively easy to accelerate the bike. There's no great requirement to transmit a resisted accelerating (ie torque) force.

But in high gears at higher speeds, you need all the torque that you can muster to accelerate the bike. The clutch has to transmit all of this.

On a GS the most demanding test you could make is at, say 100 mph in top gear (ie 6th or 5th on older models), apply FULL throttle and, without releasing the throttle - assuming you have a rev limiter - quickly pull and then release the clutch lever. If your clutch is working well, it will bite instantly and carry all the power. If it's at all weak it will slip momentarily or, if really on its way out, for a fair while. NB Clutch slip accelerates its wear, so don't do this test too often!

Greg
 
Lou Can said:
yeahbutnobutyeahbut.........

If the inertial mass of you and the bike remains the same (which it should do) and discounting aerodynamics and stuff, the engine produces a constant maximum bhp (i.e. force) then the resistance to that bhp is the thing that varies. BUT the resistance to accelerating really fast (in a low gear) i.e. significantly changing the momentum of the vehicle in a short space of time (e.g. 250kg from rest to 40kph in 2 secs) must surely be greater than chaging the momentum over a longer period of time (250kg from 100 to 140 kph in 20 secs, say). Isn't the instantaneous load on the clutch (necesseary to overcome the static friction of the plates) gong to be greater in the first scenario??

This is going to be something to do with i/2mvsquared innit, where the speed is the critical factor?

Oooh I love ignorance

LC
Click to expand...

The energy that you have to apply to accelerate increases with the square of the speed.

Ie to accelerate from 100mph to 101 mph requires a hundred-fold more energy than to accelerate from 10 to 11 mph.

e=mv²

Greg
 
Nippy Normans supply Touratech, Wunderlich, Desert Fox and many other makes of accessories.
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