Michael Hanslip Coaching

If you want to go faster, you have to pedal harder

Belt drives don't like rocks

I can still remember back in 2006 when Stromlo got what would become the 2009 World Championships XC course. For 2006-8, portions of that course were used for competition at Stromlo as they dialled in the details for the big show. In 2006 it might well have been National Championships that ran on these trails. In 2008 there was a World Cup round held on virtually the same course as Worlds would be the next year.
If you have ridden a mountain bike at Stromlo, you've probably ridden up the front-side climb to the summit. Beginning from the parking lot you hit Cockatoo Switchbacks. At the top of this trail you turn left onto a firetrail and head back into the singletrack at Blue Gums. This is where the competition course begins. There is a trail on the uphill (right) side of Blue Gums called Cardiac Arrest (the earlier Nationals course used a climb called Heartbreaker - so this one is a bit of a pun, a bit of a continuation of the naming convention, and a LOT more difficult). Near the top of Cardiac, one has to ride over a small boulder. I can't remember how many people I knew who took a tooth of two off their big chainring (back then, everyone had front derailleurs and multiple chainrings) on that rock. The rock is still there, sporting the scars from all these hits. The only way to protect the teeth was to have the chain on that chainring - hard to use the big one when you're climbing a technical trail.

It was about that same year that I got my first single speed bike (a Gary Fisher Rig). It had a single mid-sized chainring (32T) and sprocket (18T). Being single speed, the chain is always on that chainring. Which meant if I happened to drop the chainring on a rock during a ride, the chainring teeth were protected and usually no bad happened. Fast forward to single speed #3 for me (Spot Rocker SS). This one has very little in common with that Gary Fisher from nearly 20 years ago. Where the Fisher was aluminium, the Spot is carbon fibre. The Fisher had a chain, the Spot a belt (Spot brand was instrumental in the development of the Gates belt drive system). They did share some traits too. Both had Fox forks. Both were 29ers.
I've long wanted to go to a belt drive on my single speed. Belts are quiet (but not silent I've learned), and light and they last a much longer time than a steel chain does. What I didn't think about was rocks. Even taking two teeth off a 40T chainring leaves you with a working bike. Touching the chain against the rock leaves a mark on the chain, a mark that might impact shifting on a geared bike but nothing that will impede a single speed. That same touch against the rock with a belt drive could well leave you stranded at the trail side. The belts are carbon fibre, which is why they have so many restrictive handling rules (don't bend them, don't fold them, don't roll them up tight, don't turn them inside out and so on); if you break the carbon fibres then the belt will fall apart quickly. Just an innocent tap of the belt against a rock (between the chainring (beltring?) and the rock) can slice the belt in half. I touched something once, don't even remember what, and lifted up a tiny piece of the protective rubber covering and one fibre sticks out. I was initially worried, but it is holding up fine after a year or more.

My intention was to equip the bike with something to protect the belt from touching down ever again. But what?
My first thought was a bashring. These are larger in diameter than the chainring and chain combo and several millmetres thick to ward off any impacts. Except that they are all designed to replace the outer chainring when the middle chainring is the in-use chainring. And the beltring on the Spot is in the outer position on the spider AND the belt is really wide compared to a chain. No easy mounting solution for a bashring.
Another tricky part is that the belt has to go on quite large sprockets at the hub, so the chainring also has to be quite large to get the desired gearing (which for a 29er bike is usually around a 50" gear). This makes it more likely to hit a rock and also harder to protect.
I found a Shimano Saint DH bashguard device that might fit. There weren't any in Australia, but Shimano kindly brought one in for me. That took ages. The Saint device only protects 1/4 of the circle. Which is OK.
Divide the circle into four pieces and two of those pieces are protected by the crank arms themselves. And most people ride one foot forwards preferentially most of the time. That means protecting only 1/4 might be enough.
Again, the thickness and outboard position of the belt were problems. The Saint device is meant to attach to the outer position of a Saint crank with the chainring in the inner position.
I succeeded in installing it in the correct position with some chainring spacers and much longer bolts. Long enough that there would be a huge leverage on the protection device if it hit a rock.
Then I found a bottom bracket mounted ISCG device. By removing the 5 mm spacer which usually sits between the drive side cup and the frame, this space can be devoted to an ISCG mounting bracket. Which in turn can hold any ISCG mounted chain device. I found a tiny chain protector of the correct size to sit outside the belt. I have similar bash guards on my DH and enduro bikes. The belt is sandwiched between the inside positioned fixed protection mounted to the bottom bracket and the 1/4 circle outside protection mounted to the crank spider.
Being mounted on a hardtail means that the bottom bracket doesn't change height quite so much as a full suspension bike and therefore the belt doesn't touch down quite so often on things. It also means I'm probably travelling a little slower on rough terrain where the probability of a strike increases.
Inside and outside protection is probably overkill, but the belts are quite expensive and I'd hate to cut it on a trail simply for misjudging a rock's position. I have some good piece of mind that my belt will last a while.

There are numerous places where you could ride a belt-drive bike without any protection. Sparrow Hill is one such place. With a little bit of experimenting and a build-your-own-adventure result, I can ride my belt bike anywhere and not fear for the life of the belt.