rear suspension rise

[yadada]

Just about got the XJ back on the road. All I have let to do is change the engine oil, grease the brake pedal shaft, get new tires, and fix whatever it is that makes the rear of the bike rise up when I accelerate. I have spun both wheels on the center stand and they are pretty well free, within reason. It seems to move through its travel okay while riding and bouncing up and down. Is it just the nature of the beast to do this? Should I grease something?

[Jerry]

Due to the shaft drive and the "backward" rotation of the XS 11 engine, it is the nature of the beast to have the back end rise under acceleration. This design is one reason the XS11 was the fastest 1/4 mile production bike when it was introduced; the dynamics puts more power to the ground instead of raising the rear end and smoking off usable horse power.

And yes, it is possible to do a wheelie on and XS or XJ 1100......

[scoobes]

for me its one of the best bits about riding the xs1100

[TopCatGr58]

Hey there Yadada,

The bucking bronco style of ride experience is normal for the XS11, but more so with worn shocks!!! I know my OEM shocks didn't have enough damping affect, and I got that rising feeling everytime I got on the throttle. Then after 20yrs, I got a new set of el cheapo shocks, but the damping works very well, and I don't experience that rise anymore! SO....you may be in need of some new rear shocks, especially IF you're actually bouncing a fair amount when running over bumps and such!
T.C.

[pggg]

Having trouble understanding this 'more power to the ground' thing. I've read it on the merriam cycle pages, and don't beleive any of their B.S. !! Power is going to ground on all shaft drives is it not? What would the reverse engine have to do with any of this, as the gearbox and drive unit rotate forwards as per usual. Front drive bevel spins forward. Second front bevel along with the shaft spin left to right. (facing forward) Shaft is trying to climb upwards. Rear pinion has reversed teeth to spin the wheel forwards off the same shaft rotation. No different from a billion other shaft drive vehicles is it? Reverse engine means diddly squat. Convince me otherwise with facts.

[stevo]

have you ever watched the torque reaction of a motor (any motor) even in nuetral.if hanging on soft mounts you will see one side of motor rise.if you suddenly accelerate it ..the back of an xs motor trys to lift...on other bikes that motor spins forward... the front of the motor trys to lift...thats why xs doesn't wheelie as quick as forward(motor) turning motorcycles...for every action there is a reaction...go look under the hood of your car and have someone jam throttle breifly (in neutral) and watch the motor rise. on drag cars we used to chain torque side down..just an observation...went riding sunday.. ya gotta love the south

[yadada]

Sweet Glad it's supposed to be like that. I kinda like it too. I'll get a picture of my "inaugural everything is fixed for the first time ride" and get it posted eventually. Time to order new tires....gonna try the elite 3's.

[pggg]

O.K. if the XS motor tends to lift at the rear, we're LOSING power to the ground on the back wheel? I'd have thought the backward running crank would lift the front. But if the XS motor is lifting at the rear, the heavy gearbox will be counterbalancing that centrifugal force once the bikes' moving?

I figure the XS shaft drive is really well designed for the bike. I know there's a horizontal right to left centrifugal force on the countershaft(driveshaft) coming from the 90 deg bevels. I'm assuming, without delving too deep into it, that the rear 90 deg bevel is also creating a right to left centrifugal force, not a right to left force, as the pinion angle is reversed to rotate the back wheel FORWARD.

But, not being a rocket scientist to really know, I'm also thinking the rear horizontal centrifugal force may still be actually running from left to right, therefore cancelling out the front sideways torque action to make the spinning shaft neutral. Either that or the engineers have the system nicely designed to be inline with the whole bikes' centre of gravity.

So no tendency for the bike to tip sideways under power. All in all, the XS11's shaft system is nicely neutral. I've never noticed any undue horizontal torque re-action on an XS11 when on the power out of a corner. I'm picking if the bike was say, 100lbs lighter, or the centre of gravity was changed with lighter components eg.. magnesium wheels or other lightweight stuff, then some sort of handling quirk from shaft re-action would start to be noticible.

[Pat Kelly]

The torque of the motor tries to 'plant' the front wheel. The driveshaft (pinion gear) tries to 'climb' the ring gear in the rear drive causing the back end of the bike to rise. This further helps in keeping the front wheel down allowing more power to be used (as opposed to letting-off the throttle to bring the front wheel down).
The front wheel being 'planted' along with the weight transfer to the rear aids in 'putting the power to the ground'.
Yes the front wheel can come off the ground with enough power and/or the back wheel can spin. Tire compound has a lot to do with this.
The inherent charictaristics of the XS design helped with it attaining the title of "Worlds fastest production motorcycle" when it was introduced. That technology is now a quarter-centry old and other designs are faster.

[xs650mike]

Excellent analysis Pat.

[GNEPIG]

.. i can see where pggg is coming from but i think the drive shaft and the gear that spins it would have to weigh alot more than it does and be bigger around in diameter before we would feel the effects he is describing ,like a bmw, cx500 or a moto guzzi the side to side torque action
.. if the engine rotated the other direction the back end of our bikes would want to squat on excelleration, the geometry of the whole bike would change in the oposit direction ,the drive shaft would try to lift the rear wheel up changing the rake of the front end, shifting the weight more towards the rear and the front of the bike would get to light to easy.. on heavy excelleration this would cause a really nifty tank slapper reaction like on the KH500s and 750s when you forgot to tighten up the steering stabilizer
.. if you put the front end of just about any chain drive bike built before 1986 up against a wall [running]and release the clutch slowly you will notice the rear of the bike start to squat, i think Yamaha was trying to counter this action

[xs650mike]

IMHO the rotation of the crank doesn't have near as much effect on raising the rear during acceleration as the shaft jacking (pinion climbing the ring gear). My XJ750 and XZ550s all had the rear jacking effect and older BMWs and Guzzis I have ridden also exhibited this characteristic. The XS11 just does it even more than those bikes did probably more due to the higher torque on the bevel gears than the reverse rotation of the crank.

[Pat Kelly]

Right Mike.
The engine rotational torque pushes the front down (however slightly ).
The shaft drive causes the rear to 'rise'.
Actually, after I thought about it some more, the rear drive raises the front of the swingarm, at the swingarm pivot. Cars do this too. That's why racers use traction bars (either slapper or ladder bars). Our swingarms are like ladderbars.

Now I'm wondering about a 4-link rear suspension for a motorcycle.................

[xs650mike]

Well BMW uses their "Paralever" rear suspension just to prevent jacking.

[xs650mike]

Just remembered ex-racer Mert Lawill's double swing-arm suspension that he has used for years on mountain bikes (human powered) and also on his new Harley based street tracker. This system allows the suspension to work entirely free from the effects of drive torque and braking forces which are transferred to the frame. I don't have a picture of his tracker in front of me right now so I can't visualize if this system would work equally as well with a shaft drive instead of chain but it might.