Folding Bikes - Kevlar belt/chain

I did a search and found nothing on the Folding Bikes thread so...

During the Five Boro Ride on May 3rd I saw a gentleman on a folder with a kevlar belt instead of a chain. He was moving pretty well but I wasn't able to talk with him very long as the traffic and steady rain wasn't real conducive to conversation.

Does anyone know what brand that type of bike might be? Does the kevlar last? How are they to ride?

It sure was interesting to look at.

The 3 folding bikes with belt drives that I am aware of are:

Strida (http://www.strida.com/)
ixi (http://www.ixibike.com/index2.htm)
and of course...
Abio Verdion (http://abiobikes.com/)

If 'kevlar' is mentioned, it is likely a Strida as they may have kevlar in their belts. I was chatting with the founder & patent owner of Gates' CarbonDrive and he told me that Gates at one point in history, used kevlar but he they no longer do that for I think cost reasons (?). So maybe Strida figured a way to do it more cost effectively.

Having said that though, with or without kevlar, the belts are still very strong and are generally made for heavy machinery so high mileage is not a concern.

So was it a Strida by any chance?

TC

The Dahon Mu frame can be converted for belt drive. It is quite an effort though. And $300-$400. If interested, here is the thread: http://www.dahon.com/forum/index.php?showtopic=6872

One of the drawbacks to belt drive is that since you can't take the belt apart like a chain you have to have a gap in the frame to put it on/off. Easy if the bike was designed that way, but, like pibach said, sort of a big deal to retrofit.

The upside is that they don't require lubrication.

Similar setups are common on mid-size motorcycles.

One of the drawbacks to belt drive is that since you can't take the belt apart like a chain you have to have a gap in the frame to put it on/off. Easy if the bike was designed that way, but, like pibach said, sort of a big deal to retrofit.

The upside is that they don't require lubrication.

Similar setups are common on mid-size motorcycles.


Additionally, I don't think a belt is the way to go for a bike.. limited sprockets, limited belt lengths.. the need for an extremely stiff frame/bb assembly as any flex in the area affects belt tension negatively (belt slips/jumps cog teeth).. cogs need 'shoulders' to keep the belt from working off the cogs .. belt needs a perfectly straight run and the cog axles exactly parallel, or it will fall hard against the cog shoulders in an effort to derail .. belt needs a tensioner, or at the very least a snubber to keep the belt from jumping at the wheel under high torque conditions... a belt can still get dirty (used in trail conditions) and will leave marks on clothing etc. .. a belt is not very tolerant when debris like rocks or twigs get caught between the belt and cog teeth .. a belt does run quiet.. and that can be nice .. a chain drive system can run pretty clean also, if waxed and not oiled .. and chains are reasonably quiet when in alignment .. having ridden a belt drive bike for a few months, I can't see any significant advantages over a chain .. other than the slight reduction of drivetrain noise .

I can't see any significant advantages over a chain .. other than the slight reduction of drivetrain noise .

Hey Bruce, how bout not needing to lube the belt, that seems like a pretty big + to me

Hey Bruce, how bout not needing to lube the belt, that seems like a pretty big + to me

You can use silicon based chain fluid. For example, this 105 (http://www.fullcycles.com/product_info.php/products_id/688)
Keeps the chain smooth, dry, and clean. Pretty much maintenance free.

I think Bruce has made a lot of good points there. He and I have Strida copies and although the belt is silent and pretty clean by comparison to a chain, they can be a bit finicky about adjustment. I really like being able to go down to the pub on my belt drive bike in a pair of fawn chinos without clips, something I'd never do on my other folder because the legs would be plastered with oily grime, but there are serious disadvantages of the belt drive, mainly the limited alternatives you have in terms of pulley sizes and belt lengths. It is so easy to alter the gear ratio of a traditional chain dive system by swapping front rings and if using a hub gear, altering the chain length to suit. You can't do that with a belt drive.

I don't ride that bike on rough trails so the debris problem isn't really applicable to me, but Bruce is right about the belt / pulley system's intolerance to twigs and stones. People say the belt breaks.

I'm not sure how long a belt would last in normal use. One poster on the Strida Forum said his rear pulley and belt wore out pretty quick when riding on wet grimy winter roads.

There are also serious disadvantages to wearing fawn chinos! LOL! :lol: :roflmao2: :eek:

There are also serious disadvantages to wearing fawn chinos! LOL! :lol: :roflmao2: :eek:

You just have no taste.

:)

Hey Bruce, how bout not needing to lube the belt, that seems like a pretty big + to me

Honestly, I've spent way more time cleaning the belt of dirt and making sure there isn't something in the cogs than I ever spent worrying about or lubricating a chain.. as EvilV I think pointed out, rainy condtions are not that great for a belt either as the dirt turns to mud and the mud cakes in the cogs and all that smoothness disappears until you clean it.. not that big a deal of course, but a chain can run basically trouble free for years with a minimum of maintenance .. and chains are extremely cheap to replace if the need arises..

...as the dirt turns to mud and the mud cakes in the cogs..
Bruce, I generally agree. But I think the cogs with holes plus the gates belts are a lot better than those things on the Strida.

http://www.simpel.ch/typo3temp/pics/e3419694ab.jpg

Also frame design can be adopted for certain belt drive specifics:

http://phil.veloblog.ch/gallery/7/previews-med/spannsystem_2.jpg

I am glad to see this kind of innovations going on.

I did the belt drive conversion mentioned in the Dahon forum.

Still testing, but so far so good. Smooth silent and light, what's not to like (except the cost)? I haven't managed to make it skip despite not having tensioners on the axle - just used the lever the wheel back system.

The whole job was done with basic handyman tools.

I can't look at a bike now without checking to see if it is "eligible" for a conversion.

I did the belt drive conversion mentioned in the Dahon forum.

Still testing, but so far so good. Smooth silent and light, what's not to like (except the cost)? I haven't managed to make it skip despite not having tensioners on the axle - just used the lever the wheel back system.

The whole job was done with basic handyman tools.

I can't look at a bike now without checking to see if it is "eligible" for a conversion.

Nice!! ... any pics? did you use composite pulleys or metal? what belt width? single speed or hub gear? any pics? :)

I used the Gates Carbon Drive system, so it's an 11mm pitch belt, almost the same as a chain.

The belt is 10mm wide and the sprockets are slightly wider. The sprockets and belts come in a limited range of sizes at present, and unfortunately this can make it difficult to get the gear ratios right on single speed setups, although a hub gear gives you more latitude.

To quickly summarise, the first step is to make sure you can get a set of ratios that will allow you to fit within your existing chainstay length with the range of belts, next step ensure you have physical room for the sprockets, and last step is will they line up (alignment is critical). It's best to work all this out before buying any parts :)

Details of how I did it are here in the SS section of MTBR -belt drive conversion (http://forums.mtbr.com/showthread.php?t=518332).

Scroll down a bit to see the pics.

I used the Gates Carbon Drive system, so it's an 11mm pitch belt, almost the same as a chain.

The belt is 10mm wide and the sprockets are slightly wider. The sprockets and belts come in a limited range of sizes at present, and unfortunately this can make it difficult to get the gear ratios right on single speed setups, although a hub gear gives you more latitude.

To quickly summarise, the first step is to make sure you can get a set of ratios that will allow you to fit within your existing chainstay length with the range of belts, next step ensure you have physical room for the sprockets, and last step is will they line up (alignment is critical). It's best to work all this out before buying any parts :)

Details of how I did it are here in the SS section of MTBR -belt drive conversion (http://forums.mtbr.com/showthread.php?t=518332).

Scroll down a bit to see the pics.

Thanks!.. nice looking setup.. I like the kit.. reminds me of how belt driven OHC engines went from barely functional to totally reliable.. or in this case, the Strida approach vs your project bike (albeit, at a bit higher price tag).. :thumb:

I was reading the other day about a conversion of the top end of a motorcycle engine. The writer suggested that ten percent of the 70hp engine's power was used in turning over the valves. Factoring in the increased size of a car engine's components, we are probably talking about around ten horse power being used by a four cylinder car's valve train - all transmitted through a toothed belt. Since these are changed about every 1200 hours, the comparatively feeble power of a bicycle rider pedaling a strida or other belt driven bike, ought to mean the belt would last more or less forever. This doesn't seem to be the case though, since people do break the belts. Is this just because of the debris and dirty environment on a bike; is there a quality issue with the bike belts, or have I made some fundamental miscalculation here?

I used the Gates Carbon Drive system, so it's an 11mm pitch belt, almost the same as a chain.

The belt is 10mm wide and the sprockets are slightly wider. The sprockets and belts come in a limited range of sizes at present, and unfortunately this can make it difficult to get the gear ratios right on single speed setups, although a hub gear gives you more latitude.

To quickly summarise, the first step is to make sure you can get a set of ratios that will allow you to fit within your existing chainstay length with the range of belts, next step ensure you have physical room for the sprockets, and last step is will they line up (alignment is critical). It's best to work all this out before buying any parts :)

Details of how I did it are here in the SS section of MTBR -belt drive conversion (http://forums.mtbr.com/showthread.php?t=518332).

Scroll down a bit to see the pics.

Very nice Datako & great instructions! That's the first convert I've seen so far!

I was reading the other day about a conversion of the top end of a motorcycle engine. The writer suggested that ten percent of the 70hp engine's power was used in turning over the valves. Factoring in the increased size of a car engine's components, we are probably talking about around ten horse power being used by a four cylinder car's valve train - all transmitted through a toothed belt. Since these are changed about every 1200 hours, the comparatively feeble power of a bicycle rider pedaling a strida or other belt driven bike, ought to mean the belt would last more or less forever. This doesn't seem to be the case though, since people do break the belts. Is this just because of the debris and dirty environment on a bike; is there a quality issue with the bike belts, or have I made some fundamental miscalculation here?

EvilV, you are right about the durability - one of the folks from Gates explained to me that their belts are built for heavy machinery equipment so based on his calculations, the belt will actually last longer than the other parts and maybe the frame also.

BUT from the sounds of it, I think Strida has a special line of belts that are made for their bikes so maybe it's made differently (?).