Look no chain!

[KirstinS]

Another thought occurs

With a chain and alfine setup you might need to go to a larger chainring after adding a front electric hub

But I guess your stuck if you've got a shaft drive - you can't adjust for electrification

 

[flecc]

Yes, they are completely inflexible, locked with regard to ratios and often locked to specific hub gears.
.

 

[axolotl]

Sorry, but I can't agree with this for our application. The Wikipedia article says that those with chevron teeth are more efficient than straight teeth and can have efficiency up to 98%.

"Up to" whenever we see it is meaningless, and bikes do not use the progressive entry chevron teeth designs. They probably couldn't since alignment is even more critical with those.

The same article also states that 95% efficiency is typical for belts in general.

In any case they are speaking of car camshaft drive where alignment is perfect, something not guaranteed by any means on bikes.
.

Why not? I'm envisaging a system where the belt is completely enclosed and alignment is ensured by the manufacturer in the design of the frame and choice of components. Whilst I can imagine that in a home-built bike this could well be a problem, I don't see why it should be an issue for a decent manufacturer.

 

[axolotl]

Yes, they are completely inflexible, locked with regard to ratios and often locked to specific hub gears.
.

This is undoubtedly a limitation. Given the requirement for accurate alignment and setup, belt drive is never going to be ideal for those who like to fiddle with their bikes and experiment with different ratios. For me, however, it's a non-issue. I just want to buy the bike and ride it.

 

[flecc]

The same article also states that 95% efficiency is typical for belts in general.

Still well short of chain though and very unspecific. This issue reminds me of hub gears, where makers similarly claim efficiencies around 98/99% without verification, but independent labs show they virtually all fall short of 90%, most being in the mid 80% region. Beware manufacturer's figures.

Why not? I'm envisaging a system where the belt is completely enclosed and alignment is ensured by the manufacturer in the design of the frame and choice of components. Whilst I can imagine that in a home-built bike this could well be a problem, I don't see why it should be an issue for a decent manufacturer.

The problem is that a completely different design of bicycle wheel hub and mounting would be needed to have such a comparable perfect alignment, and that would be small scale production and costly. And can the comparatively frail bicycle frame guarantee maintaining that alignment, especially when it has to be a separating frame to fit the belt? As for chaincases, we haven't even got decent ones today, though very good ones existed over seventy years ago. It's the mass market that's helped to kill them, the same mass market that prevents concepts like the one you suggest.

A pity I agree, but it's the world we live in.
.

 

[axolotl]

Still well short of chain though and very unspecific. This issue reminds me of hub gears, where makers similarly claim efficiencies around 98/99% without verification, but independent labs show they virtually all fall short of 90%, most being in the mid 80% region. Beware manufacturer's figures.

I'd be very wary of manufacturer's figures but wiki is generally quite reliable on things like this because manufacturer's statements can be easily challenged. In any case, I doubt that there's a big difference between a good belt and a chain. Certainly, after some use in the field, it wouldn't surprise me of the belt was better.

The problem is that a completely different design of bicycle wheel hub and mounting would be needed to have such a comparable perfect alignment, and that would be small scale production and costly. And can the comparatively frail bicycle frame guarantee maintaining that alignment, especially when it has to be a separating frame to fit the belt?

Whether or not the frame is rigid enough to maintain alignment may well be an issue. However, you could have a separate tensioner wheel, avoiding the need to separate the frame for belt changes.

As for chaincases, we haven't even got decent ones today, though very good ones existed over seventy years ago. It's the mass market that's helped to kill them, the same mass market that prevents concepts like the one you suggest.

A pity I agree, but it's the world we live in.
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To a degree. The UK/US market is particularly bad in this respect though, because the marketing people tend to assume that nobody in the US/UK wants to use a bike for commuting. In the rest of Europe, concealed drive trains are commonplace. Ditto hub gears. I've even seen a shaft-drive bike on the streets of Amsterdam. Here, on the other hand, sport dominates and with it, the obsession with weight reduction and absolute performance, even thought this isn't really relevant to most riders.

 

[flecc]

However, you could have a separate tensioner wheel, avoiding the need to separate the frame for belt changes.

I'm not quite sure I know what you mean by this, a tensioning wheel makes no difference to fitting a belt unless the lower frame strut is bent to a very different lower path, making the frame even weaker. In any case a tensioning wheel adds even more to the inefficiency. Or do you mean a two stage drive which would be even less efficient?

The belt or chain is inside the frame struts at the rear and outside at the front, so a split is necessary to fit the belt, which with most frames can be in the seat stay only. Chains are joined after being inside the rear frame of course, another advantage.
.

 

[RobF]

There are various solutions to getting the belt inside the triangle.

This is from Trek, although I'm not entirely sure how it comes to bits.

 

[flecc]

Indeed Rob, all existing ones entailing the frame parting, which of necessity compromises the integrity and adds weight.
.

 

[Deus]

How efficent will this one be ? and how old do you think it is ?

 

[Croxden]

How efficent will this one be ? and how old do you think it is ?

Wouldn't the bike be going backwards with that set-up?

 

[Deus]

Nope take another look and imagine the rotation and you will see it will be taking you forward

 

[flecc]

How efficent will this one be ? and how old do you think it is ?

It's an early one but I can't date it. Bicycle shaft drives go back to early in the last century. The efficiency will suffer a little from the unprofiled gear "teeth" though the contact friction area is low. I couldn't guess at a figure.
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[Croxden]

Nope take another look and imagine the rotation and you will see it will be taking you forward

Ah, I have had a whisky and can see it now.

 

[Deus]

Flecc
It was made by Quadrant in 1899 !!! i saw it at the transport museum at Hull

 

[flecc]

Thanks Deus, I'm not surprised. Oddly enough shaft drive was one of the first "improvements" pursued in the safety bicycle history.

Every one of the modern so called new ideas in bike design can be found long ago in bike history.
.

 

[axolotl]

I'm not quite sure I know what you mean by this, a tensioning wheel makes no difference to fitting a belt unless the lower frame strut is bent to a very different lower path, making the frame even weaker. In any case a tensioning wheel adds even more to the inefficiency. Or do you mean a two stage drive which would be even less efficient?

The belt or chain is inside the frame struts at the rear and outside at the front, so a split is necessary to fit the belt, which with most frames can be in the seat stay only. Chains are joined after being inside the rear frame of course, another advantage.
.

Ahh, I see what you mean now. My bad.

 

[VictoryV]

Tend to agree.

Bike chains have lasted so long because their efficiency cannot be beaten.

Properly set up, they produce next to no heat, noise or friction, so all the pedal energy is transferred to where you want it - the rear sprocket.

Motorcyclists will tell you shaft drive motorbikes are flat compared to their chain drive counterparts.

Having said that, I think a belt must come close to a chain in terms of efficiency.

At one time the RAF used to issue bicycles on loan, to be returned on posting off the unit. They were usually huge machines, no gears and rod operated brakes. I was riding by a colleague one day and heard this crackling noise coming from the bike. It was his chain, it was a deep rust colour and bone dry with a covering of mud. I said to him he needed to oil and clean the chain since that would make the bike easier to ride. His reply was that the bike was too efficient and he needed the grotty chain condition to give him some exercise whilst riding.