Crossover gear lever physics

chrisk

chrisk

Hero member
Location
Brisbane, Australia
I am no expert in physics, so need some help.

On my crossover linkage, left foot change. I have at the left lever similar length lever arms. On the right I have a short lever at crossover shaft and a longer lever at the gear lever shaft.

Logic (mine) says this is arse about.

My problem is, the force required to change gears is monumental.

What would be ideal?
 
Make sure that there is almost a 90? angle between levers and linkage joints at point of engagement. Given your description, this probably isn't the case at right hand side due to the different lever lengths, but at least you should try to get as close as possible to the 90?.
 
Try going to basic principals, if the one on the left of the crossover is 50mm long and the one on the right side of the bike is 100mm long it's twice the length of the leverage available. Just to complicate this on my bike with right side gear change rear sets fitted for the gears no crossover the front lever has 2 holes, bolted to the lower hole reduces the gear lever throw a hell of a lot.
I have NOT mentioned force at all, my bike doesn't require much foot force at all to change gear, brakes yes, gears no. The only difference changing lengths to any gear links was to the length of the throw. I remember seating at Bunnings while you bought that bolt after the links slipped at The Not The Barry, there is something not right going on here with that kind of force required to change gears. Try doing a sketch of the lengths of links to compare to what others have, but I think its something else binding, BTW the levers all need to be as close to 90 degrees to work correctly.
 
Chris,

The easiest method is to ascertain the stock ratio between shift lever length and internal length of the shift mechanism.  With all the levers involved, you need to try to stay close to this ratio overall to keep both lever force and travel within bounds.  Previous comments about the included angles are also very important, these should be as close to 90? as possible at rest to give maximum mechanical advantage in both directions.

So, basically, it's  only mathematics... :D

piet


 
rowdypat said:
What would be ideal? Fuck off the crossover :-)
Click to expand...

As much as it pains me, I've thought about this since reading your post Pat ..... I think you are right, I'm onto it!
I'm sure it'll seem like eating porridge with my left hand, for a while though. But, if I can do it with a beer, anything is possible.
 
chrisk said:
On the right I have a short lever at crossover shaft and a longer lever at the gear lever shaft.
Click to expand...

Hi Chris

It sounds as if you have a lifetime habit of using your right foot for braking and left for gear changing.
So without wishing to heap shit on Pat's suggestion to fuck the crossover off, I don't think that's necessarily the right answer for you.

Also, with the lever arm lengths you describe, the crossover linkage should actually be giving you extra leverage (with greater movement at the pedal) than the standard setup. So pissing the linkage off and going for right side gearshift will in theory make the gearshift heavier.

The above assumes that the heaviness of the gearshift is in the selector mechanism, such as a too heavy return spring. In that case you'll need to open up the selector cover and have a look inside.

If there's a problem with your crossover linkage that's making it heavy, such as inefficient angles between links and levers, it can be fixed. Post photos of both sides of the crossover setup and we'll be able to assess it better.

The Laverda gearshift crossover works very well when set up properly. It's a perfectly adequate solution to those who prefer a left foot gearshift.


 
OK, so here's what has convinced me to change:
Peg height is too high, and find my hips can't handle the squatting position, looking at other SFC pictures, seemes, almost inline with swingarm pivot is the norm.
Left foot from previous break, isn't happy.
Rear master cylinder on right side sticks out too far, and annoys me.
Crossover spline is buggered.
Current rear sets aren't adjustable, in regard to lever vs pedal.

So I'm off to pick up a set Tarozzi adjustable pegs today, make a new set of mounts and see how that goes. If then I need to dive into side cover, then so be it.
 
Thats the reason why I lowered my pegs 30mm, its so much more comfortable on 400k plus days. But getting a comfortable hip and knee bend with good ground clearance and not ending up with a too tall seat height isn't easy.I can raise and lower mine this 30mm in about half an hour on the spanners, handy if the apparent  Eastern Creek Track day happens. Fitting into my leathers is another thing though
 
You'll still have a linkage system with the Tarozzi rearsets, but that'll give you some flexibility with mechanical advantage which might be helpful if it's a heavy selector mechanism. While you're changing habits of a lifetime, you may as well set it up for a race pattern shift - 1 up 4 down. That'll challenge your brain  :D
 
I'll have to look at mine ...... I have the original style crossover on the 3C and the later style with factory rearsets on the Formula. I think the shift lever itself is longer on the crossover models than the shift lever that is on the RHS. Perhaps it has to do with the leverage that the longer crossover type shift lever allows.

 
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