Myth: Belt drive has poor efficiency

[baru]

Mark Sanders says,

"I recently met the guy from Gates.com who developed the belt for Strida (and car camshafts and motorcycles).  He reminded me that belt toothed belt drives (like Strida's) are used to replace chain and V belt drives as part of government energy efficiency schemes.  He explained that motorcycle manufacturers (like Harley Davidson and Kawasaki) have been using belts for years for the best life long efficiency and to be clean and maintenance-free
(chain wear on a motorbike is a real pain and uses a lot of energy).

There are more losses by using hub gears, and tensioners/idlers on bike chain drives than when using a belt. Allow the chain to get dirty, or use a non-aligned derailleur gear ratio and the belt wins hands down on efficiency."

[awcute]

Um.. does that mean we burn less calory due to better efficiency? hehehe

Thanks, nice article baru.
Another advantage of the belt other than clean (no grease required) is safety.
Imagine getting a finger in the chain & its gearing-mechanism compared to belt.

My grandfather told me that during Japanese occupation in Indonesia, Kempetai (Japanese secret police service in WW2) used bicycle chain + gears as one of their torture equipment. Just place the hand between the gear and the chain, and kick the bike pedal. It could crush fingers.

[cyclistjohn]

Mark Sanders says,

"I recently met the guy from Gates.com who developed the belt for Strida (and car camshafts and motorcycles).  He reminded me that belt toothed belt drives (like Strida's) are used to replace chain and V belt drives as part of government energy efficiency schemes.  He explained that motorcycle manufacturers (like Harley Davidson and Kawasaki) have been using belts for years for the best life long efficiency and to be clean and maintenance-free
(chain wear on a motorbike is a real pain and uses a lot of energy).

There are more losses by using hub gears, and tensioners/idlers on bike chain drives than when using a belt. Allow the chain to get dirty, or use a non-aligned derailleur gear ratio and the belt wins hands down on efficiency."

Interesting, thanks baru.

We only have 1 gear ratio on the Strida, & the nearest chain driven bikes to ours would be single speed upright bikes. Since they only have 1 chain ring & 1 rear sprocket, there would not be any misalignment unless the frame became damaged.

I have a friend who is a good mechanical engineer, & he wonders why the "snubber" bearing is placed effectively at the centre of the rear sprocket rather than at the point where the belt starts to wrap around the sprocket?

If you get a chance to ask Mark, that would be interesting to know, thanks.

My grandfather told me that during Japanese occupation in Indonesia, Kempetai (Japanese secret police service in WW2) used bicycle chain + gears as one of their torture equipment. Just place the hand between the gear and the chain, and kick the bike pedal. It could crush fingers.

Ouch - that's a very "creative" method awcute!

Luckily, I had already eaten when I saw your post ;-)

I have read of cases on bikeforum.net where riders have suffered quite bad injuries from the sharp chainwheels & sprockets, so you're right, the belt is much safer.

My wife prefers her Strida too over other bikes, as it keeps her dress clean :-)

[baru]

Interesting, thanks baru.

We only have 1 gear ratio on the Strida, & the nearest chain driven bikes to ours would be single speed upright bikes. Since they only have 1 chain ring & 1 rear sprocket, there would not be any misalignment unless the frame became damaged.

I have a friend who is a good mechanical engineer, & he wonders why the "snubber" bearing is placed effectively at the centre of the rear sprocket rather than at the point where the belt starts to wrap around the sprocket?

If you get a chance to ask Mark, that would be interesting to know, thanks.

Hi CyclistJohn,

Here's Mark's reply:

"The mechanical engineer is theoretically correct   - the ideal theoretical position for the snubber would be at the at the start of the belt wrap. But this would restrict the bottom tube movement when folding, (ie when lowering bottom tube to the ground). Also I did some testing and found the position of the snubber around the rear pulley made marginal difference, to the effectiveness of the snubber - I think this is because when belt teeth jump, they ALL rise up over the pulley teeth together, so a snubber position is less critical than theory suggests.  It certainly works 100% on Strida :-) ..

Interesting factoids ..
Strida (and  car cam shaft belts) are reinforced with Kevlar for super strength.
However kevlar is a weird material with a reverse co-efficient of thermal expansion (ie unlike most materials, it gets longer as it gets colder and vice versa).

In the early days of the Strida I didn't realise this  -  so in the winter when I was testing early belt systems I'd set up the tension perfectly (in the warm workshop), BUT when testing it seemed to get loose, back in workshop it was OK ....  It took a lot of head scratching to work this out :-).

Lotus cars 1st introduced snubber in the 1970's when they were developing their 1st belt drive cam shaft engines ... which used to jump in cold Canadian mornings - and wreck the engines ... but their snubber where crude - did not have bearings and just forced the belt to stay engaged.  Snubbers, especially with bearings are very neat because they do not touch the belt in normal use, only when the belt is about to slip -  they allow the belt tension to be reduced and so improve efficiency and wear."

[cyclistjohn]

baru, I'm impressed, that's a very fast response, thank you, & could you kindly thank Mark for his very interesting reply?

It looks like this forum will be by far the most useful Strida resource :-)

[coolthought]

Actually, I know nuts about a snubber till this thread started. CyclistJohn, your friend post a pretty good question. And I kind of try to look for a picture of it. Think it will be helpful to the rest who might not know. Please let me know if I got it wrong.

[cyclistjohn]

Actually, I know nuts about a snubber till this thread started. CyclistJohn, your friend post a pretty good question. And I kind of try to look for a picture of it. Think it will be helpful to the rest who might not know. Please let me know if I got it wrong.

Coolthought, your picture does indeed show a "snubber" bearing. When I bought the Strida, I wondered about the position of that bearing myself, & although I am an engineer (not mechanical - which would actually be more useful these days) I wasn't sure If I totally understood why it was in that position, so I asked my friend when we went to visit him, & he was surprised at its location, hence the question.

Apparently, it's not present on earlier versions of the bike, & owners who have (had) earlier bikes & the Strida 3, report that belt slippage is much less on the 3, so a big improvement.

BTW, it's worth checking every few months that the bearing is turning freely. It's not supposed to touch the belt normally, only when the belt is under very heavy load (up a hill effectively) but if you regularly ride along canal towpaths (are there canals in Singapore - please excuse my ignorance ?) like I do, dirt can build up on that bearing & stop it working properly.

It's easy to clean it, & of course the whole bike is easy to maintain - one of the Strida's many strengths :-)

[beachboyz27]

Just how is the life span of the belt drive on a strida?
Any bad experience when it broke?

[davidtch]

Just how is the life span of the belt drive on a strida?

Pls. check Strida FAQ. 

Any bad experience when it broke?

Well, i don't think we hav any bad experience wif belt snapped on us yet.

[coolthought]

Just how is the life span of the belt drive on a strida?
Any bad experience when it broke?

Last I heard if I remember correctly is that it is good for 50,000 km before a change is needed. Err... anyone gone even beyond 10k km? If I'm not wrong, it is the common timing belt used in most car engines. (different belt specs on different engine lah) And it is made of kevlar. Same material used in a bullet proof vest. unless you managed to cut it, it shouldn't break at all. If not, there will be lots of car breaking down on the road and lots of officers killed when their bulletproof vest failed to stop the flying bullet. (minus the armour piercing one lah)

Hope this will cure your worries.

PS. To get you into perspective. The circumference of the earth is about 40,000km. The kelvar belt should be good for going round the earth once with lots of spares for your daily commute to work and home plus weekend shopping and exercise.
PPS. It is about cycling the length of Singapore for about 1190 times. (length of Singapore is about 42km)
PPPS. Or do a 390 times round island trip of Singapore. (one round is about 128km (for the coming NTU round island ride))