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Hi Folks.... I have the std. rear link arm...... 385mm. I have read on here that to shorten this to the GS version or the replica length is the best mod you can do (other than a Y piece).

My style of riding does not necessarily need quick steering....but I have noticed that when the bike is off the c/stand there is a definite angle created by the final drive to the line of the shaft drive. Presumably getting the shorter arm levels this whole lot out and makes for better/smoother drive

Any comments by you the experts... you know who you are?

Cheers

Stuart

error in posting sorry

Please disregard the above... this was suppose to be undera separate heading.... However if you can help here also that would be great.

It's been a hard day!!

stuart

To ride, the bike does feel better with the 365mm (ie GS) arm. Sure it steers quicker/lighter but whether you like or want a bike to do that is totally subjective. I'll always trade a bit of light steering for better stability.

The downsides?

The shaft angles you mention. A UJ needs to have the same angle of input to that of output to work correctly. By fitting the shorter arm the output angle (ie the one which is at the rear diff) is not the same as the one at the input (ie the one which comes out of the gearbox to the driveshaft). This does put extra strain on the transmission - that's a physical and unarguable fact. Just Google 'universal joint' and the info is freely available.

As Bailey rightly once said on this very topic, it's far better to have an adjustable length shock as it maintains the same angle between the two UJ's. The shorter arm doesn't.

Gromit.... I thought by using the shorter arm, that would line up the angles as it were. I.e. the angle of the final Uj would be level with the actual swinging arm shaft. Perhaps I am not explaining this well... see below



Although on the c/stand.. you can see the angles set up... surely by shortening the arm, you pull in the final drive lnk and line up the final UJ... does that make sense?

stuart

I guess the line of the final drive is in line with the output of the gearboxbut say 1 inch, maybe more lower... surely that's putting strain on the Uj's???
stuart

Stuart - have a read of this which will explain what I mean.

That's to say...

If the input velocity of a UJ is A the output velocity also needs to be A. By keeping the input and output velocities of the same (by keeping the input and output angles the same) there is balance in the system. Introduce the shorter arm (therefore making the output angle unequal to the input) causes the output velocity to change. That's bad for UJ's - the joints will probably last for ages (20k+) but it is, by the laws of physics, putting extra strain into the system. Have a good read of the link - it's extremely well-written (and backed up by a mate of mine who's a tecchie on Chinook helicopters).

Cheers Gromit.. I am all "read up" now.

I will keep it standard then Cheers

Stuart

I have found a couple of pics of my bike, before and after. I've found that the torque arm certainly makes the bike a more lively, sporty ride. It also seems to have smoothed out some vibes in the 70-95mph zone. It is hard for me to attribute performace to torque arm alone though; I did other stuff at the same time.