Is it possible to build an inexpensive belt drive?

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azad   1 W

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Is it possible to build an inexpensive belt drive?

Post by azad » Aug 23 2020 11:50pm

Hi,

I'm interested in converting my chained mid drive into a belt drive but the cost of this setup seems a major obstacle. The Gates carbon drive pulleys and the belt cost more than 300Euros easily which is ridiculously high. So, I would like to know an inexpensive solution for this. I have a Shimano Nexus Inter-7 with bafang front sprocket. Please also advise which belt sprocket would fit with this hub.

Balmorhea   1 MW

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Re: Is it possible to build an inexpensive belt drive?

Post by Balmorhea » Aug 24 2020 2:30am

Belt drives are damaging to internal gear hubs because of their high minimum operating tension. That’s one if the reasons they have been used for decades, but have never become popular.

Does your frame have a split that can be opened to admit the belt?
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azad   1 W

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Re: Is it possible to build an inexpensive belt drive?

Post by azad » Aug 24 2020 2:51am

Balmorhea wrote:
Aug 24 2020 2:30am

Does your frame have a split that can be opened to admit the belt?
I don't know what do you mean exactly, this is how the rear end of the frame looks. (I have yet to install Nexus though)
bike_rear.jpg
bike_rear.jpg (71.74 KiB) Viewed 244 times

AHicks   1 kW

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Re: Is it possible to build an inexpensive belt drive?

Post by AHicks » Aug 24 2020 7:58am

To remove a chain from the bike completely, generally you would remove a master link. As there is no master link in a belt, you have to have another way to install remove it.

azad   1 W

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Re: Is it possible to build an inexpensive belt drive?

Post by azad » Aug 24 2020 8:56am

AHicks wrote:
Aug 24 2020 7:58am
To remove a chain from the bike completely, generally you would remove a master link. As there is no master link in a belt, you have to have another way to install remove it.
Ah I get it now, I was too deep into finding a solution for belt drive that I didn't think about this earlier. Too bad, It would've been nice to have a belt drive. I shall have to buy a better bicycle then I guess, which is even more expensive!

2old   100 kW

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Re: Is it possible to build an inexpensive belt drive?

Post by 2old » Aug 24 2020 10:32am

Not so much better, but with a "split" or some other method to allow a belt conversion. Possibly less expensive to purchase a bike that's been designed for one.

qwerkus   10 kW

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Re: Is it possible to build an inexpensive belt drive?

Post by qwerkus » Aug 24 2020 1:35pm

azad wrote:
Aug 23 2020 11:50pm
Hi,

I'm interested in converting my chained mid drive into a belt drive but the cost of this setup seems a major obstacle. The Gates carbon drive pulleys and the belt cost more than 300Euros easily which is ridiculously high. So, I would like to know an inexpensive solution for this. I have a Shimano Nexus Inter-7 with bafang front sprocket. Please also advise which belt sprocket would fit with this hub.
There is no way around Gates stuff for a clean belt drive setup. There are alternatives using industrial belts, but none will be as good as Gates, because you'd need wider belts/pulleys to reach the same strength. This monopolistic situation is probably the main reason for the absurd pricing.

Now as others pointed it, I'd think twice before going that road. Even in the best setup, a Cdx Gates drive will be 3 to 5% less efficient than a well lubed chain. Why? Because the belt has an internal elastic friction which you have to overcome when pedaling and "forcing" the teeth around the pulley. An IGH has already non negligible friction losses, which can push the total to 12-13% in case of your Inter-7. human power is the tighter resource on a bike/ebike: don't waste it to pure friction losses.

On top of that, as you can't split open a belt, you need some sort of bolted opening of the right chainstay. Easy enough to weld on steel frames, but it will create an additional weak point. On alloy frames you can forget about it.

So save yourself some troubles and keep your chain. With the extra money, ditch that garbage Inter-7 and get an alfine, or an Inter-8 premium (not the classic). Worlds of difference.

Balmorhea   1 MW

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Re: Is it possible to build an inexpensive belt drive?

Post by Balmorhea » Aug 24 2020 2:08pm

Bicycle drive belts and sprockets also cost more and wear out faster than chains, in my obsevation. The non-Gates options don't cost as much (though still more than chain drives), but wear out especially quickly.

If this stuff were anywhere near as good as chains, it would be on entire categories of bikes. The fact that it isn’t should tell you something.
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AHicks   1 kW

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Re: Is it possible to build an inexpensive belt drive?

Post by AHicks » Aug 24 2020 2:20pm

Balmorhea wrote:
Aug 24 2020 2:08pm
Bicycle drive belts and sprockets also cost more and wear out faster than chains, in my obsevation. The non-Gates options don't cost as much (though still more than chain drives), but wear out especially quickly.

If this stuff were anywhere near as good as chains, it would be on entire categories of bikes. The fact that it isn’t should tell you something.
I'm thinking, and I beleive a lot of others do as well, that a belt will hold up MUCH better than a chain in the case of a 1000w+ mid drive.

Balmorhea   1 MW

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Re: Is it possible to build an inexpensive belt drive?

Post by Balmorhea » Aug 24 2020 2:40pm

AHicks wrote:
Aug 24 2020 2:20pm
Balmorhea wrote:
Aug 24 2020 2:08pm
Bicycle drive belts and sprockets also cost more and wear out faster than chains, in my obsevation. The non-Gates options don't cost as much (though still more than chain drives), but wear out especially quickly.

If this stuff were anywhere near as good as chains, it would be on entire categories of bikes. The fact that it isn’t should tell you something.
I'm thinking, and I beleive a lot of others do as well, that a belt will hold up MUCH better than a chain in the case of a 1000w+ mid drive.
Some kind of belt, sure. But there isn’t room for that. If you put a big ol’ motorcycle chain on it, that will hold up better too (and it stands a better chance of fitting in there). What I see in terms of stuff that comes into the shop is that belts and belt sprockets wear out much faster than chains when loaded only with pedal power and their operating tension, no motor. That certainly doesn’t bode well for their prospects with a mid drive.
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AHicks   1 kW

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Re: Is it possible to build an inexpensive belt drive?

Post by AHicks » Aug 24 2020 6:19pm

If what you say is true, that idea doesn't bode well for some of the high end belt drive bikes available, with internal geared hubs that cost more than my bike did, either....

Balmorhea   1 MW

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Re: Is it possible to build an inexpensive belt drive?

Post by Balmorhea » Aug 24 2020 11:58pm

AHicks wrote:
Aug 24 2020 6:19pm
If what you say is true, that idea doesn't bode well for some of the high end belt drive bikes available, with internal geared hubs that cost more than my bike did, either....
Just because they’re high end does not mean they’re worth a damn. Or in this case, worth as much as a comparable bike with a chain.

Gimmicks sell. Mostly to ignorant fools.
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azad   1 W

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Re: Is it possible to build an inexpensive belt drive?

Post by azad » Aug 25 2020 5:36am

qwerkus wrote:
Aug 24 2020 1:35pm

An IGH has already non negligible friction losses, which can push the total to 12-13% in case of your Inter-7. human power is the tighter resource on a bike/ebike: don't waste it to pure friction losses.

So save yourself some troubles and keep your chain. With the extra money, ditch that garbage Inter-7 and get an alfine, or an Inter-8 premium (not the classic). Worlds of difference.
Does that mean IGH is less efficient than an external freewheel/cassette hub? I haven't replaced the external hub wheel yet and was infact hoping to get better performance with Inter-7 but if it is even going to be worse then I guess I made a mistake for buying a new wheel with nexus 7.

qwerkus   10 kW

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Re: Is it possible to build an inexpensive belt drive?

Post by qwerkus » Aug 25 2020 6:24am

azad wrote:
Aug 25 2020 5:36am
qwerkus wrote:
Aug 24 2020 1:35pm

An IGH has already non negligible friction losses, which can push the total to 12-13% in case of your Inter-7. human power is the tighter resource on a bike/ebike: don't waste it to pure friction losses.

So save yourself some troubles and keep your chain. With the extra money, ditch that garbage Inter-7 and get an alfine, or an Inter-8 premium (not the classic). Worlds of difference.
Does that mean IGH is less efficient than an external freewheel/cassette hub? I haven't replaced the external hub wheel yet and was infact hoping to get better performance with Inter-7 but if it is even going to be worse then I guess I made a mistake for buying a new wheel with nexus 7.
This is an ongoing debate. A good start is this article: https://www.sheldonbrown.com/internal-gear-theory.html See the two last sections.

The usual statement is: a clean and well lubed chain with optimal tension will reach an efficiency up to 98%-99% on a derailleur. Nothing else will ever beat this because of the simplicity of the setup. Now that's under lab settings.

Real life is a different story. Of 100 bikes I might encounter during a trip, ONE might show signs of a perfectly maintained derailleur transmission. All other ones are rusty, filthy, bent, under-tensioned or worse. In those case I doubt they reach 90% efficiency, and those people would be better off using an IGH.

So my bottom line is: if you count not only pure mechanical efficiency, but also time and energy of maintenance, cleaning and swears lost over chain drops, a good IGH beats hands down any derailleur. That's why I switched to IGHs on most of my bikes. Best choices are nexus inter-3 disc, newer nexus inter-5, alfine 8 and of course the paramount rohloff. On e-bikes, enviolo shine too because of their ability to switch gears under load, although 1kg heavier than the competition.

The inter-7 you mention is a swampy piece of hardware if you ask me. You can literally feel the drag when pedaling, that's why I would never recommend it. Best 7 speed was the now discontinued sachs 7 but it would not last one trip with a bafang mid drive.

AHicks   1 kW

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Re: Is it possible to build an inexpensive belt drive?

Post by AHicks » Aug 25 2020 7:30am

Balmorhea wrote:
Aug 24 2020 11:58pm
AHicks wrote:
Aug 24 2020 6:19pm
If what you say is true, that idea doesn't bode well for some of the high end belt drive bikes available, with internal geared hubs that cost more than my bike did, either....
Just because they’re high end does not mean they’re worth a damn. Or in this case, worth as much as a comparable bike with a chain.

Gimmicks sell. Mostly to ignorant fools.
and every ignorant fool is allowed an opinion......

Balmorhea   1 MW

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Re: Is it possible to build an inexpensive belt drive?

Post by Balmorhea » Aug 25 2020 12:52pm

azad wrote:
Aug 25 2020 5:36am
Does that mean IGH is less efficient than an external freewheel/cassette hub?
Almost any internal gear hub is slightly less efficient than derailleur gearing. The best measured efficiency among gearhubs is Rohloff, which is almost equal to derailleur gearing in most ratios, and the worst is NuVinci N171, which can lose as much as 20% of input power in the lowest ratios.

The Nexus 7's efficiency is worse than average compared to other gearhubs, but most pedal cyclists find it acceptable. The main advantages it has are cleanliness, relatively low wear and maintenance, a stronger wheel, and the ability to shift to any gear at any time.
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