I would be concerned what effect the constant spring pressure might have on the clutch life and if any high torque situations could result in slippage.
I am with you on this. It was the reason I built this prototype the way I did.
There is a 6mm threaded rod connecting the spring. I can count the tightening nut turns to gauge the relative tension of the assisting spring.
I tweaked the design so that I can tighten it till it opens the clutch, or loosen it till it has no tension at all on the system.
This is what my testing of different setting has yielded:
- At low RPM I find that the adding more tension to the spring is tolerated. I cannot notice any slippage even if I jerk the throttle open and closed in first and second gears. The reactions between accelerating and decelerating is sharp and crisp. It is the same as with no spring tension at all.
At a functional tension for this low RPM range, the clutch is significantly lighter than stock. My guess is >50% lighter.
I played the spring tension all the way till I could feel the slip when doing this. The clutch is feathery light and I could play it even with my pinky. But this is a useless setting because at any higher speed, there is significant slip.
- At the other end of the spectrum, I can make the clutch slip even at relative low tension setting. This would be in an overtaking case. Say 80kph (45mph) and knocking it back to 5th and opening up to overtake. In 5th it still feels OK, but in the upchange back to 6th on an open throttle, there is a second or so of slip till the bike catches up.
I guess this is due to the higher HP and torque at the higher RPMs. (see image)
Because of the way this prototype is setup, I can easily adjust with an 8mm wrench.
- I have no idea yet on the effect this is having on longevity of the clutch, but I am sure it is wearing it out faster than without the mod. (obvious)
- If I detect no clutch slip, then it does not necessarily mean there is no slipping, but I am assuming it to be minimal and probably nothing to worry about.
- I have yet to do a temp test of the clutch cover, aside from using my hand which is not very scientific. At least it is not burning the skin off!
- I am also working with the assumption that motorcycle clutches are not overly difficult to replace and not very expensive.
- I am wondering about shortening the spring and bridging the gap with a fixed section to magnify the spring effect and see how it changes the behaviour.
- Using a compression spring setup may yield better results, but would require a different setup all together. Maybe if I am bored one day.
- I have used it with a pillion (a realistic simulation of a packed bike I'd say). There was a difference but it was not as large as I imagined. That surprised me.
How I can see it being used:
- I would imagine that dropping the tension right off for highway or mainly tarmac riding
- Rise the tension for off-road conditions. Especially long days off-road where the wrist may get tired and painful.
I will be doing an off-road tour around Sardinia, Italy in about a month so will have a good chance to test.
This is the real test for me will be the off-road, because road use is not the problem for me. The wrist is slowly getting better, but it is the 8h off-road riding, day after day, that will really be the test of this device.
I am a furniture designer and I can imagine a fully developed product. It would be a simple bolt on thing, which even a novice mech could install. It would be adjustable from zero to full slipping, and could be a useful add on for cable clutched bike that are a bit heavy on clutch tension (BMW GS800 for example), or female riders who find the clutch work a bit much for their left forearms.
n.b. I done some off-road tours with the africa before my injury, and did not even think of this idea.
This innovation is born basically from my ill timed injury i.e. right at the start of the riding season here in Europe.