# Gates belt drive: installing larger front sprocket

I ordered a Cube Hyde Race bike with Gates belt drive. I live in an area where it rains a lot, and I use my bike year round, so I was sold on the promise of virtually maintenance-free drivetrain.

The bike has a 46 teeth front sprocket (Gates S150 CDN 46T), 22 teeth rear (Gates CDN 22T) and Shimano Alfine 8 hub. If I understand correctly, the maximum gear ratio is 46 / 22 * 1.61 ≈ 3.37, compared to 48 / 11 ≈ 4.36 on my current bike. Probably enough for daily commute, but not for faster rides (I ride with my friends outside of town every now and then).

I tried to find belt drive bikes with higher maximum ratio, but 46/22 (or similar ratio) seems to be the most common. However, it is possible to order front sprockets with higher teeth count: 50, 55, ..., 70, which I will probably end up doing.

Will I need to order a longer belt as well in this case? If so, how do I calculate the correct belt length? There also seem to be 3 different types of belts/sprockets: CDX, CDN and CDC. CDC is obviously different mechanically (does not have the center track), but are CDX and CDN compatible? Can I use CDX front sprocket instead of CDN? Any other things to consider?

• Calculating the correct length is at most high school level math, but we'll need the exact distance between the centers of the sprockets to give an exact answer.
– ojs
Dec 30, 2017 at 15:51
• @ojs Can I calculate the correct belt length based on the stock belt? The stock belt is Gates CDN 111T (111 teeth, I suppose). If the new front sprocket has 60 teeth, the count increases by 60 - 46 = 14, and the new belt will need to have 14 more teeth, that is 125, is that correct? Dec 30, 2017 at 15:58
• You can, but the math gets more complicated than that. The belt wraps around slightly more than half of the front cog. How much exactly depends on the size difference and distance between the cogs. Dividing the difference by two is close but not exact.
– ojs
Dec 30, 2017 at 16:19
• @ojs Oh, right, not all front sprocket teeth are in contact with belt :) The bike hasn't been delivered yet, so I can't measure the distance between sprocket centers. Anyway, when I do the measurement, how do I use it? Is there some kind of formula or compatibility table? Dec 30, 2017 at 16:34
• You should be able to derive the formula with high school level math. But since you don't have ridden the bike yet, I'd recommend trying it first to see if it needs any modification at all. And no, I have no idea what CDX and CDN sprockets are.
– ojs
Dec 30, 2017 at 16:39