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[TheRan]

Yeah direct drive isn't always best, otherwise every Zero would be geared 1:1 and Energicas wouldn't have their gearboxes.

[DonTom]

Although that would be a major drawback if touring in a remote part of the world and trying to change it by the side of the road.

Have you tried to do that in the last few years with the new tires?  I don't think it is even possible these days. It is actually easier to change a truck tire than a motorcycle tire on the side of the road when you have the proper hand tools.


I tried to change a tire (which I have done countless times in the distant past) on my little Suzuki DR200SE with large, long tire irons. I gave up and brought the wheel to a shop for them to change it with their shop tools. Took them a few minutes or so. And even on this bike, I have changed the tires before. The tires have changed in the last few years. Much more difficult to remove. I couldn't even do it.


-Don-  Reno, NV

[princec]

I keep reading this nonsense about shaft drive efficiency being ludicrously low and it's repeated about on the internet, the same set of figures, parrot-like, but I have a feeling it's ... bullshit. Or BMWs would be slow as hell (they are not), and their shaft housings would be rather hot to the touch after a 100mph blast down the motorway (they are not, they barely get warm). I've had 5 shaft-drive BMWs. They were all noted for being surprisingly fuel efficient.

I bet the losses are large just in relative terms to a chain or belt. That is if a chain is losing 3% to friction then ooh maybe the shaft loses twice as much! Or ... 6%. I'd still take the shaft drive even if it meant I could only go 94 miles instead of 97.

Cas

[DonTom]

I keep reading this nonsense about shaft drive efficiency being ludicrously low and it's repeated about on the internet, the same set of figures, parrot-like, but I have a feeling it's ... bullshit. Or BMWs would be slow as hell (they are not), and their shaft housings would be rather hot to the touch after a 100mph blast down the motorway (they are not, they barely get warm). I've had 5 shaft-drive BMWs. They were all noted for being surprisingly fuel efficient.

I bet the losses are large just in relative terms to a chain or belt. That is if a chain is losing 3% to friction then ooh maybe the shaft loses twice as much! Or ... 6%. I'd still take the shaft drive even if it meant I could only go 94 miles instead of 97.

Cas

I think you will find BMW's fastest bikes to be using a chain drive. The ICE bikes for touring are the ones with the shafts. FWIW, my 1,000 lbs Harley uses a belt and usually gets better than 50 MPG. However, my TTSE is shaft driven and gets around the same MPG but it is a lot lighter.


My MotoGuzzi only gets around 42 MPG, Shaft drive but also uses TBI instead of the true EFI. Kinda difficult to compare. But I heard about the power  loss of driveshafts long before the internet existed. BTW, shaft drives can give some real serious problems, they are not 100% reliable either and when they give problems, there's no fixing on the side of the road.


Power loss in a motorcycle chain is around 3%. A drive belt is about 10%. Power loss of a motorcycle drive shaft is often above 20%.


The one I cannot figure out is why the big difference between the chain and belt.


-Don-  Reno, NV

[TheRan]

With bicycles the difference in efficiency is very minimal (a percent or two) and mainly comes from the higher tension of the belt, and the difference is greatest at lower power levels for some reason. A motorcycle belt is at an even higher tension so that's probably why. It could also be due to the generally lower gearing than a bicycle, you've got many more teeth engaged on the larger rear sprocket with a belt where as with a chain drive not every roller on the sprocket is actually applying force.

[SBK74]

There are two main reasons the shaft is not preferred and that is cost and weight. 

[Specter]

The one I cannot figure out is why the big difference between the chain and belt.


-Don-  Reno, NV

I would say friction losses but THAT much you'd think it'd burn up the belt in short order.  Maybe, because it's friction drive, the metal holding the belt at either end is greater to transfer that friction...without burning up the belt, and the extra weight of all that metal spinning round is eating efficiency... but 3 percent??   You'd probably lose a bit of energy at the start up due to slippage but what overall amount?  it can't be THAT terrible.

Is the 3 percent .vs. 6 percent a stat that is still valid with today's tech, or is it one of those things where they figured it out in 1953 and just ran with it to this day and nobody every questioned it because the 'experts' said it is that??

Aaron

[JaimeC]

You would make far more impact on range by designing a proper fairing in a wind tunnel than you would with ANY final drive system.

[Fran K]

There are two main reasons the shaft is not preferred and that is cost and weight.

How about chasis jacking?  apply power rear swingarm pivots up, do a downshift  swingarm squats.  Or use something like BMW paralever set up.

The shaft itself probably isn't where the losses are it is in the 90 degree turns and the reduction gearing in those turns,

When you have to buy chain and sprockets retail the shaft most likely is more economical for the user in the long term.

[princec]

I think you will find BMW's fastest bikes to be using a chain drive.

Tell that to my K1300S!

My GSes regularly got over 55mpg (UKmpg too - which I think is about the equivalent of 45 USmpg) and that simply doesn't strike me as inefficient as it's about the same as most bikes get when ridden at around the same speeds. If 20% of the energy is being lost by the shaft then it's being lost as heat, and if we're doing 70mph then we need about 11kW to reach the rear wheel, and you're saying that's only 80% of the energy output by the gearbox output shaft? So there's another 2.5kW of waste heat blasting out of the shaft drive? There's no cooling whatsoever - it'd be red hot after a few miles!

The one I cannot figure out is why the big difference between the chain and belt.

Because, once again ... it is probably not true. Some internet nerd will have quoted some figure years ago and it'll have been Googled and parroted ever since. Here's the reality: https://www.cyclingabout.com/belt-drivetrain-efficiency-lab-testing/

Cas