Belt drive. What do you reckon?

less muck / oil is a good
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.

i’m not sure of the UTS of
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.

“The belt tension does look
“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.

I’ve been riding a Strida 5.2
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.

I wouldn’t expect you to need
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!

On doing a bit of research on
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?

Is that not just due to the
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.

Analogue?
Analogue?