And now something completely different from BMW

[Eddieb]

F800 based 2 wheel drive hillclimb bike.

The bike is powered by the engine from an F800, in a custom frame with an extended swingarm, dirtbike ergonomics, and a paddle-style rear tyre. The front wheel is driven from the countershaft sprocket, and it’s unclear exactly how this is managed.The bike saw its first taste of competition at the recent Obersaxen round of the European Hillclimb Championships in Switzerland, attacking the famous Karitscha Hill. The course is only 235 metres long, but in this distance it climbs a massive 115 metres, and has sections so steep it would be extremely difficult on your hands and knees, let alone on a 100+ horsepower motorcycle.

http://www.thebikergene.com/dirtbikes/bmw-races-a-2-wheel-drive-f800-in-european-hill-climb-championship/#more-89

[MisterD]

Seems blindingly obvious that the front wheel is driven hydraulically...

[Skunk]

Seems blindingly obvious that the front wheel is driven hydraulically...
Yep. But how is the power to the front wheel managed?

[xwhatsit]

Yep. But how is the power to the front wheel managed?
Heheh, hydraulically?

Countershaft to hydraulic pump, hoses to front wheel, hoses to hydralic pump connected to the hub.

Wait, what do you mean?

[_intense_]

Not sure why, but thats a strangely erotic bike. Does it come in purple?

[LBD]

Yep. But how is the power to the front wheel managed?

Nothing to manage, a fixed displacement pump turning at a fixed ratio to the countershaft driving through fluid power to a fixed displacment hydraulic motor on the front hub.

The motor to pump displacment ratio would be the same as counter shaft, to rear sprocket ratio ( if the counter shaft to pump is 1;1)

Then if the rear looses traction, more power to the front and vickey verka...

[Starky307]

Nothing to manage, a fixed displacement pump turning at a fixed ratio to the countershaft driving through fluid power to a fixed displacment hydraulic motor on the front hub.

The motor to pump displacment ratio would be the same as counter shaft, to rear sprocket ratio ( if the counter shaft to pump is 1;1)

Then if the rear looses traction, more power to the front and vickey verka...

Exactly how the yamaha 2 trac worked.

Would be a good idea for a hill climb bike as the spinning rear wheel would increase the front's speed and in turn the gyroscopic effect would help bring the front end down, and keep it there helping pull its way up the hill.

This effect was one of the disadvantages of the wr450 2trac, it would dive down in the whoops. When the rear wheel is trying to skip from whoop to whoop it brakes free and spins, this then speeds up the front making it dive the front end and made it very hard to ride on top of the whoops.

[xwhatsit]

This effect was one of the disadvantages of the wr450 2trac, it would dive down in the whoops. When the rear wheel is trying to skip from whoop to whoop it brakes free and spins, this then speeds up the front making it dive the front end and made it very hard to ride on top of the whoops.
I reckon all you would need -- and it wouldn't be hard, considering it's hydraulics -- is a little button you press with your thumb which cuts hydraulic pressure and turns it back into a 1WD momentarily. Hold it down when you need it?

[Starky307]

I reckon all you would need -- and it wouldn't be hard, considering it's hydraulics -- is a little button you press with your thumb which cuts hydraulic pressure and turns it back into a 1WD momentarily. Hold it down when you need it?

The idea is good but I think it would be extremely hard to actually do that while flying through a set of rough whoops.

[Conquiztador]

U ever heard about the "Christini" ?

http://www.sep.benfranklin.org/news/071100-christini.pdf

And many moons ago there was a guy who used a JAP in motocross where he had the front wheel also doing the driving in similar fashion. This was (from memory) in the 1940's or 50's? The diff was that he used chains and sprockets from the motor to get the power to the frontwheel!! Sadly I can not find any articles on it. Think it was in Sweden.

[lankyman]

Nothing to manage, a fixed displacement pump turning at a fixed ratio to the countershaft driving through fluid power to a fixed displacment hydraulic motor on the front hub.

The motor to pump displacment ratio would be the same as counter shaft, to rear sprocket ratio ( if the counter shaft to pump is 1;1)

Then if the rear looses traction, more power to the front and vickey verka...

Wouldn't there be quite a lot of energy loss in this system?

[Motu]

The hydrostatic drives I've dealt with had speed control,obviously some sort of flow valve.You could give the rider control of this valve with a lever or twist grip.Trouble is most of these extreme hill climb bikes end their run with the front wheel in the air and eventually looping out.Traction and control are not usually a problem at the bottom of the run.Maybe another metre in the swing arm would keep the front wheel on the ground to gain extra traction.

[Starky307]

U ever heard about the "Christini" ?

http://www.sep.benfranklin.org/news/071100-christini.pdf

And many moons ago there was a guy who used a JAP in motocross where he had the front wheel also doing the driving in similar fashion. This was (from memory) in the 1940's or 50's? The diff was that he used chains and sprockets from the motor to get the power to the frontwheel!! Sadly I can not find any articles on it. Think it was in Sweden.

Yip, and seen one too, a crf 250 with it fitted.

[Bass]

The hydrostatic drives I've dealt with had speed control,obviously some sort of flow valve.You could give the rider control of this valve with a lever or twist grip.Trouble is most of these extreme hill climb bikes end their run with the front wheel in the air and eventually looping out.Traction and control are not usually a problem at the bottom of the run.Maybe another metre in the swing arm would keep the front wheel on the ground to gain extra traction.

Hydrostatic drives commonly use(d) either variable displacement pumps or variable displacement motors to achieve speed control. That way everything is still positive displacement.

[BMWST?]

Hydrostatic drives commonly use(d) either variable displacement pumps or variable displacement motors to achieve speed control. That way everything is still positive displacement.

maybe the control is via computer.BMW arent afraid to use em....