A comment on belt drives

Inspired by a question from Rachel's dad, done as a separate post following a suggestion from my dad. 

We have belt drives on the tandem rather than the usual chains. There are a few reasons for this hopefully I can go through these in this post.

Firstly though; a bit about chains. Chains are used on the vast majority of bikes because they are pretty efficient and relatively cheap. Because of small amounts of play between the links they can move across sprockets on a geared bike with relative ease. In addition, when they move from bigger to smaller sprockets (and vice versa), rear derailleurs work effectively to take up the slack.

On the tandem there are two separate drive trains. One connects my pedals to Rachel's meaning that when one person is peddaling, the other has to as well.

The other connects Rachel's pedals to the back wheel. On tandems with chains, the one connecting both sets of pedals wears over time and stretches meaning regular adjustments are needed to take up the slack. Our belt drives contain carbon fibres and have no moving parts meaning they don't stretch. Thus, once this belt is set at the right tension it does not need any adjusting.

Because belts have no moving parts (unlike chains that have hundreds of parts that move over one another), they don't need lubrication. A huge advantage of this is that they don't get dirty so we don't end up with oily chain marks on our legs. Another advantage of this is that they are dry so dust and sand does not stick to them. They are not made of metal so they cope well with rain and water. A consequence of all this is that they last a lot longer than chains.

Because they are a single loop of material, it is essential to have a frame that splits near the rear wheel so the belt can be fitted into the frame. 

Thus you need to a frame that has been designed for this. Because they are a fixed length and can't move across sprockets they can't be used with traditional gears. Unless you want to ride a bike with only 1 gear then having internal hub gears if essential. We have a Rohloff hub that has 14 internal gears. A bonus of this is that there is no rear derailleur to snag on things or get bent.

For us, belts are a great choice. Not needing to keep a chain oiled, not needing to take up the slack up on the timing belt, no oil to get on our legs and longevity are real bonuses. Belts are kept in place by a ridge and groove system so they don't come off which can happen with chains especially when changing gear with two sets of legs applying pressure.

The downsides are the needing a frame that can split to fit the belt, needing to use hub gears, the cost (they are more expensive than chains even factoring in their longer life) and their availability (they are a specialist item that is not stocked in most bike shops)

All in all, we are super happy with our belt drives but they are a niche solution for specific needs and are not going to replace chains on bikes anytime soon.