Belt drive. What do you reckon?

by TRs Blurb n Blog   March 12, 2010  

Is this the future? How much extra would you be prepared to pay? What do you think are the major down falls of using a belt drive?

27 user comments

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I'd like to try it on my Rohloff hub commuter, but I'd have to take a saw to the frame!

I think it is a great idea, but you do need a frame which separates at the dropout to get the belt in. The chainline has to be perfect too, so crankset choice will be limited. And if you change the number of teeth on your chainring or sprocket then you need a new belt of the correct length. And it does not work with derailleurs.

Otherwise it is supposed to be silent and oil and maintenance free.

Does anyone know how efficiency compares to a roller chain?

two wheels good; four wheels bad

posted by cat1commuter [1370 posts]
12th March 2010 - 11:18

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retrofitting is always an issue with new ideas (take the ugly fittings required to fit a rohloof to a standard frame) but sawing your frame in half is a bit of a show stopper! ;0)

I dont think its an issue at all for new bikes tho, there are so many designs of split dropout or chain/seat stay that have proved soild, reliable and easy to use/maintain. A few quick examples off the top of my head...

Alu road frame with carbon stays, 90% of these are actually bolted/rivited at the dropout already!
Many MTB frames have dropouts that hold together the chain/seat stays, example - SantaCruz blur.
Every 4/faux bar full susser by Specialized/Kona/Trek has a split dropout. If fact Kona makes Bass/Cowan frames which have a pivot around the bb so are ripe for a belt conversion!

Efficiency wise i cant see it being worse than a chain, tho you do have to run a belt very tight which might have an impact on bearing wear/resistance, but that would depend on your hub.

STATO's picture

posted by STATO [420 posts]
12th March 2010 - 11:47

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I'm not sure what problem a belt drive is the cure for?

Is there a real advantage to a belt drive? It will still suffer from wear, is at present a bit of a pain when removing the back wheel, and have heard that getting the belt to run true can cause issues too.

A chain is cheap, simple and robust. A belt isn't a radical departure, it seems to me to be just another way of doing the same thing.

I'm sure in the future I will eat those words, when bowling down the road on my belt drive road bike, but it seems a bit pointless to me at present.

Complicating matters since 1965

DaSy's picture

posted by DaSy [649 posts]
12th March 2010 - 12:43

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hmmm.. im kinda with DaSy on this one, but hey you cant stop innovation and progress.. and i spose if i had the funds i would certainly like one fitted to a 'town' bike, with mudguards and dynamo..

Fringe's picture

posted by Fringe [1083 posts]
12th March 2010 - 13:31

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I think that's where the belt drive's niche is - maintenance free town bikes. There are an awful lot of cyclists round Cambridge who never oil their chains. And a belt drive is supposed to last longer than a chain (even if you oil the chain).

two wheels good; four wheels bad

posted by cat1commuter [1370 posts]
12th March 2010 - 14:45

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But with the tight tolerances required to make the system work properly, I wonder how long a neglected belt drive would actually work for?

A chain seems to manage to keep going through some amazing neglect, if the chav's I see round this way are anything to go by!

Complicating matters since 1965

DaSy's picture

posted by DaSy [649 posts]
12th March 2010 - 14:50

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DaSy wrote:
But with the tight tolerances required to make the system work properly, I wonder how long a neglected belt drive would actually work for?

a fair distance it would seem....

http://www.cyclingweekly.co.uk/news/latest/444118/james-bowthorpe-s-roun...

4500miles before he changed belt, but no obvious wear anyway.

STATO's picture

posted by STATO [420 posts]
12th March 2010 - 15:02

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with an enclosed braking system and mudguard, belt drive makes a great commuter and doesn't everyone commute? Low maintaince joy. Fit reliable tyres and it'll be my perfect all weather machine. I'll pay an extra £100 but ideally lower since it's a gearless system so I'll expect it be an extra £40.

posted by Alankk [121 posts]
12th March 2010 - 15:10

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belt's aren't a good idea for suspension bikes though, as most use chain growth in the design for anti-squat. The round-the-bb bikes would work but they tend to pedal poorly due to having no anti-squat, fine set up stiff for jumps but not good for plusher bikes that need to climb.

it's a hub gear/town/commute/fixie type bike only option at the moment, and i'm still not convinced that the cost-to-benefit ratio works out. for a one-use, low-maintenance bike it's interesting but changing ratios is a faff.

"I'll pay an extra £100"
so would i! belts add a lot more than that sorry..

give me a wax-lubed chain instead - fairly clean and a lot more adaptable. but for non-mechanically minded or mainteance-shy it's interesting - it does pedal very smoothly indeed.

posted by james-o [208 posts]
12th March 2010 - 16:09

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Belt drives are used successfully in some motorcycles, most particularly models from BMW and Harley Davidson. In a motorcycle using a belt drive instead of a chain helps cut vibration, an important factor with the big V-twins built by Harley Davidson or BMW's parallel twin and single cylinder models. I have heard of belt drives on these motorcycles failing when stones have been trapped between the belt. And I also assume the belt is mechanically less efficient than a chain due to elasticity. Hub gears could be used on a bicycle too and would offer the rider a choice of ratios.

OldRidgeback

posted by OldRidgeback [2288 posts]
12th March 2010 - 16:10

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james-o wrote:
.

give me a wax-lubed chain instead - fairly clean and a lot more adaptable.

so i take it Genesis wont be heading out on the commuter-belt-drive-bike way for a bit. Big Grin

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posted by Fringe [1083 posts]
12th March 2010 - 16:26

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we don't just make what i want though.. Wink as long as it rides nicely and works, i'm happy. I just don't want to do it 'just because', we need to be sure it offers something for the rider's benefit. smooth and clean is enough, but it's a hgh price for that alone.

"And I also assume the belt is mechanically less efficient than a chain due to elasticity"
- it should be more efficient as there's no stretch in a good belt (Gates for ex) and the drive force transmission is smoother/more direct/less 'stepped' - anyone know the proper term for this...

posted by james-o [208 posts]
12th March 2010 - 16:52

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Analogue?

Complicating matters since 1965

DaSy's picture

posted by DaSy [649 posts]
12th March 2010 - 16:53

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Mechanically I am led to believe its a lot more direct than a chain - in fact the torque transfer has created new problems for frame manufacturers. I have not seen the end results however a certain manufacturer has hinted at frames twisting/tubes crushing due to the change in characteristics that a belt brings - its not just them either!
something along the lines of - in a car or a motor bike the drive (front ) sprocket is smaller than the rear sprocket ( I know a car does not quite fit description but its idea ) on a bike the reverse is the case - thus the way torque is transferred some how affects the distribution of load on the frame?

posted by rustyrider [5 posts]
13th March 2010 - 21:52

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Is that not just due to the necessary tension required to keep the belt in place puts a new load on the chainstay that a chain doesn't?

There can be only a pretty small difference in the power transfer between a chain and a belt, power put in at the pedals either turns up as power at the rear wheel or lost as heat, and a chain doesn't seem to get hot.

Complicating matters since 1965

DaSy's picture

posted by DaSy [649 posts]
14th March 2010 - 7:38

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the extra tension and the fact that you need a demountable dropout of some kind to get the chain on are the main problems from an engineering point of view.

in terms of efficiency it's pretty hard to beat a direct drive chain, they normally run at 98% efficiency or above. a belt *can* be more efficient than that but the gains are tiny. I expect we'll see belt drive coming to track bikes very soon, as tiny gains mean something in that arena. for the average rider the main benefits are longevity and low maintenance, but for me the benefits come at too great a cost. if the price of the technology starts to come down then we'll see more belt drive commuter bikes too.

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posted by purplecup [232 posts]
14th March 2010 - 8:14

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On doing a bit of research on the net (mainly looking at motorcycles, as they have already done a lot of this research) it appears that a well lubricated chain drive system is as much as 98% efficient, and a well tensioned belt system is a similar figure, mostly quoted as slightly lower.

The main thing here is the 'well lubricated' part, chain efficiency drops off very quickly if not well maintained, whereas a belt drive system needs much less attention to stay efficient. But still, a poorly tensioned belt (either too tight or too loose) loses efficiency quickly too.

All power loses manifest as heat ultimately as the power has to go somewhere.

The belt tension does look like it will necessitate a beefier chainstay to cope with the constant belt tension too, is that right James-O?

Complicating matters since 1965

DaSy's picture

posted by DaSy [649 posts]
14th March 2010 - 8:15

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Beat me to it Purplecup...

Complicating matters since 1965

DaSy's picture

posted by DaSy [649 posts]
14th March 2010 - 8:17

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I wouldn't expect you to need a stronger chainstay for a belt. The belt needs a higher tension than a chain, but it is not so high that it will start deforming the chainstay. The chainstay is only being compressed, and you're not going to put so much force through it from the screw which tensions the belt that it buckles!

two wheels good; four wheels bad

posted by cat1commuter [1370 posts]
15th March 2010 - 11:17

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As I said Dasy - a belt is slightly less mechanically efficient than a well-maintained chain. This has been quoted by Both harley Davidson and BMW, which is why I knoew my facts were correct.

OldRidgeback

posted by OldRidgeback [2288 posts]
16th March 2010 - 11:16

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I've been riding a Strida 5.2 folder since last July. Despite appearances, it's a really practical and fun bike to ride, folds in 5 seconds and rolls on its own wheels when folded.

It's belt driven. The belt weighs only 130 grams compared with a chain's 250-300 g. The manufacturer rates longevity at 60,000 - 80,000 km. There's no discernible stretch. The belt doesn't need to be tight - the frame has a "snubber", a small roller beneath the rear sprocket, normally about 1 mm away from the belt, which stops the belt riding up out of the sprocket and jumping. The belt and snubber only touch if the belt begins to ride up. Result - the belt never jumps.

The frame already separates (to fold the bike) so replacing the belt is easy. No lubricant means an easy-to-clean bike. My experience of it has been totally positive.

stridart

posted by nightoil [2 posts]
23rd March 2010 - 23:02

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Great on a folder too, since there isn't a chain to get your clothes oily when you're carrying it.

two wheels good; four wheels bad

posted by cat1commuter [1370 posts]
24th March 2010 - 15:03

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"The belt tension does look like it will necessitate a beefier chainstay to cope with the constant belt tension too, is that right James-O?"

sorry, late reply -

the current Gates belt isn't under enough tension to affect frame design and tension under drive is same as a chain if the cogs have the same radius, but what does necessitate a stiff chainstay is the fact that the belt can 'ratchet' or slip by one tooth if there is any flex that leads to slack in the belt run under the chainstay / onto the rear sprocket. Gates now use an 11mm pitch belt to avoid this (previously it was avoided in part by tension, the snubber mentioned above can do the same thing too), other 8mm pitch set-ups without the carbon layer to the belt slip much more easily ime.

the detachable / split dropout's not an isse to a frame designer, there are many ways to do it that don't affect frame durability or add excess weight.

posted by james-o [208 posts]
23rd April 2010 - 14:54

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Interesting to compare the Fixie Peacemaker on this and the Trek District Carbon - the Fixie's belt was running at about the same tension as a chain - there was some give and in fact we were told not to over tension it, the Trek by comparison is under much more tension - it's practically rigid.

Would I be right in saying too that the belt is much stronger than a chain James? It certainly felt that way on the Fixie - the riding sensation when putting pushing it was that there was a lot less lateral flex in the belt than there was in the frame - not that the latter was more flexy than you'd expect of a good steel frame, just that it was more flexy than the belt attached to it. I'm not saying that was a problem, the Fixie was a very pleasant bike to ride, but it was a very noticeable sensation in the ride.

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posted by Tony Farrelly [4154 posts]
23rd April 2010 - 17:38

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i'm not sure of the UTS of the Gates belt tbh - chains can vary quite a bit but i'd expect the carbon belt to be stronger than a basic 9-speed chain. I'll ask..

I'd guess the Gates 11mm pitch on the Fixie Inc is different to the Trek, is the Trek 8mm pitch? I've ridden 8mm that wasn't too well tensioned / set up and it slipped so easily that it made the bike a bit of a joke to ride. Gates say the 11mm pitch avoids this, it's more set-up friendly and it needs far less tension than other systems. They even have a neat pocket tensiometer that 'pops' a bit like a torque wrench when the tension is correct.

The sensation you describe is what i noticed on Gates belt/steel frame combos, the smooth transmission of power and zero stretch / high tolerances made frame movement more noticable. Yet a chain doesn't flex either, so it must be the 'smooth transmission' i mentioned above, that i still don't know the proper term for.. feels good to me, smooth with the noticable feeling of spring in the frame. Also stiffer/smoother feeling due to the stiffer 'chainring' i think, it's like having a much stiffer crank / bb combo.

posted by james-o [208 posts]
30th April 2010 - 15:52

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As long as it is cheap to replace the belts.

I wouldn't want to break one miles from home-its a long walk... but with a chain a powerlink will get you home.

Also I wouldn't use a fix I'd like gears and hub gears can add up the price.

On a SS or Fixie I think it Belt drive would be great.

Less muck or oil lube.

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posted by Zaskar [137 posts]
1st May 2010 - 20:51

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less muck / oil is a good argument in favour of belts, but all my SS / Alfine-d bikes use a few drops of wax lube and run clean anyway. to me cleanliness isn't as big an advantage of the belt as you may think - non-derailleur chains can run clean enough to be busy-train-carriage friendly anyway.

posted by james-o [208 posts]
5th May 2010 - 14:06

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