Look no chain!

[Jonah]

Saw (what I presume is) the new cycle hire bike scheme in Reading on our way through last week. The bikes have the Nexus 3-speed hub gear and no chain. I know it's not a new idea, but do you think chainless bikes will ever catch on? We didn't see many being used while we were there.

 

[flecc]

Yes, there's been a few shaft drives over time and this one is the current one. Not too long ago we had the Chinese Zero bike shaft drives, with an outlet in Birmingham, but that's failed.

The limitation is that they suit just one hub gear usually, the Zero used the 7 speed Nexus, and most don't have sealed rear bevel gears. They do seem to work quite well though with acceptably low loss of efficiency, but the public don't seem to want the concept. Toothed belt drive is better for a clean transmission.
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[KirstinS]

It's a real shame in my book
If I could buy a shaft driven , alfine 8 hub hybrid bike I would snap it up

Unless it looked like that monstrosity !

 

[flecc]

Here you are KirstinS, they are already in the USA with shaft drive Shimano 8 speed hub gears. Link

And here's a kit shaft drive for those hubs too. Link

 

[neptune]

These look like the hire bikes available in Lincoln, and other towns. I have ridden one for about five miles. I think they are basically designed for reliability, and proof against vandalism. All bolts are security type, including wheel nuts. The bike is somewhat heavy, but the design is a good alround compromise.

 

[KirstinS]

Here you are KirstinS, they are already in the USA with shaft drive Shimano 8 speed hub gears. Link

And here's a kit shaft drive for those hubs too. Link

Ooo ! Thanks flecc

Shame you have to order 8 of those kits as a minimum. I really want one ! Must be a uk supplier somewhere - I try to find out when I have time and post back here

 

[KirstinS]

I've emailed dynamic cycles uk to see if they'll sell me a kit - they just sell complete bikes on their website

Not sure this drive will fit a 68mm bb with English thread

Bb terminology is all Greek to me

 

[RobF]

Dynamic say on their website they do not do kits.

Weight and efficiency was always a problem with shaft drives.

If you believe Dynamic's website, their drives are just as efficient as a chain and only weigh about a pound more.

 

[flecc]

If you believe Dynamic's website, their drives are just as efficient as a chain and only weigh about a pound more.

Impossible, two bevel gear drives could never match chain and sprockets which are as close to 100% when new as matters.

Bicycle component makers play fast and loose with efficiency figures, Rohloff's 99% and similar from NuVinci for example are ludicrous. Toothed belt makers also claim to exceed the efficiency of chain, again impossible.
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[RobF]

Impossible, two bevel gear drives could never match chain and sprockets which are as close to 100% when new as matters.

Bicycle component makers play fast and loose with efficiency figures, Rohloff's 99% and similar from NuVinci for example are ludicrous. Toothed belt makers also claim to exceed the efficiency of chain, again impossible.
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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.

 

[KirstinS]

Dynamic say on their website they do not do kits

e.

Really ? I can't find that anywhere - are you looking at the uk site ?

 

[flecc]

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

The new generation of toothed belt drives have certainly improved, but they have a fundamental efficiency flaw. They are made as perfect circles, meaning that when on the toothed wheels on a bike they describe smaller circles, especially at the rear. This means the rubber on the inside of the unstretchable cords has to compress and on the outside stretch on a continuous basis. This is draining energy in a way that a chain doesn't, and cannot compare to the new chain's circa 99% efficiency.

The newer belts have the rubber thickness minimised to reduce the losses, but they are still present.

Then there's also the rubbing of the rubber coated teeth as they enter and leave the toothed apertures, again comparing very unfavourably with chain rollers over sprocket teeth. That's been alleviated by making the latest belt teeth very shallow, but again some disadvantage will still be present.

Having said this, toothed belt is certainly acceptable on a utility or e-bike since the losses are not great, but I can never see them being on fast road bikes.
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[RobF]

Really ? I can't find that anywhere - are you looking at the uk site ?

From the 'common questions' section:

Can existing bikes be retrofitted with a shaft drive?
No. The shaft drive requires a specially designed frame. All of our bicycle frames were designed specifically for use with the shaft drive, ensuring the highest levels of performance and reliability.

 

[RobF]

The new generation of toothed belt drives have certainly improved, but they have a fundamental efficiency flaw. They are made as perfect circles, meaning that when on the toothed wheels on a bike they describe smaller circles, especially at the rear. This means the rubber on the inside of the unstretchable cords has to compress and on the outside stretch on a continuous basis. This is draining energy in a way that a chain doesn't, and cannot compare to the new chain's circa 99% efficiency.

The newer belts have the rubber thickness minimised to reduce the losses, but they are still present.

Then there's also the rubbing of the rubber coated teeth as they enter and leave the toothed apertures, again comparing very unfavourably with chain rollers over sprocket teeth. That's been alleviated by making the latest belt teeth very shallow, but again some disadvantage will still be present.
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Makes sense.

Another thing that puts me off is belt life.

Gates - the maker - claim life to be 'about twice that of a chain'.

Not good when you consider spare belts are £80-£100 - if you can get one.

The belt also seems very sensitive to tension and alignment.

A break may be unlikely, but if it happened you would be immobilised so I think a wise rider would carry a spare.

I don't carry spare stuff for a chain, but a break can often be bodged and you would only need to push to any bike shop to get it sorted.

 

[axolotl]

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

Very close. Toothed belts are capable of 98% efficiency (http://en.wikipedia.org/wiki/Belt_(mechanical)). Can't find good figures for a chain but by the laws of physics it must be less than 100%, so they're extremely close. Compared to other losses, I think you could consider them to be identical.

However...this is when considering a brand new, perfectly clean and properly lubricated chain. Whilst a toothed belt is practically maintenance-free, if the chain isn't well maintained (and most aren't) then efficiency will fall off over time.

So, a toothed belt might well be more efficient in practice, most of the time, depending on your usage levels and maintenance intervals. For applications like commuter bikes (my main area of interest) I'd like to see some toothed belt drives coupled with hub gears and have the whole lot fully-enclosed from the elements. Such a system could be close to zero maintenance, which is ideal from my point of view.

Going back to the thread topic though, I'd have to give shaft drive a thumbs down. I just don't see the advantage for any type of cyclist.

 

[flecc]

The belt also seems very sensitive to tension and alignment.

Alignment is extremely critical, the slightest error and the belt quickly destroys itself. At one time I used to work on equipment that relied on a number of these belts, hence my knowledge of them. One place where they work well and where alignment is ensured is the timing drive for car camshaft, though their life is 40,000 miles while an internal timing chain lasts practically for ever.
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[JohnCade]

I like the idea of belt drive too but the figure above for replacement cost is a bit daunting. Belts must wear and break easier than chains too. When belts mostly replaced chains as cam drives in engines failures became common. Some have to be replaced in only 30,000 miles and failure to do so will result in a meeting of valves and pistons eventually.

Seem to have crossed with the above a little bit...

 

[RobF]

Very close. Toothed belts are capable of 98% efficiency (http://en.wikipedia.org/wiki/Belt_(mechanical)). Can't find good figures for a chain but by the laws of physics it must be less than 100%, so they're extremely close. Compared to other losses, I think you could consider them to be identical.

However...this is when considering a brand new, perfectly clean and properly lubricated chain. Whilst a toothed belt is practically maintenance-free, if the chain isn't well maintained (and most aren't) then efficiency will fall off over time.

So, a toothed belt might well be more efficient in practice, most of the time, depending on your usage levels and maintenance intervals. For applications like commuter bikes (my main area of interest) I'd like to see some toothed belt drives coupled with hub gears and have the whole lot fully-enclosed from the elements. Such a system could be close to zero maintenance, which is ideal from my point of view.

Going back to the thread topic though, I'd have to give shaft drive a thumbs down. I just don't see the advantage for any type of cyclist.

Your ideal drive train appeals to me, although I would still carry a spare belt.

As flecc said, a belt is a pretty good prospect on an ebike or for most ordinary users.

Pro racers will continue to use chains because in their environment a fraction of a percent could make a difference of a few inches in a sprint finish which could mean a win rather than second.

 

[KirstinS]

From the 'common questions' section:

Can existing bikes be retrofitted with a shaft drive?
No. The shaft drive requires a specially designed frame. All of our bicycle frames were designed specifically for use with the shaft drive, ensuring the highest levels of performance and reliability.

Ahh that's the US website - not on the uk's FAQ section

But I guess same applies . Boo

 

[flecc]

Very close. Toothed belts are capable of 98% efficiency (http://en.wikipedia.org/wiki/Belt_(mechanical)).

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.

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