- Hi, welcome to 128.bike
- In my post about belt drive systems I have explored the pros and cons of belt drive.
- One of the important points mentioned was the necessity of exact belt line for the system to be efficient and long lasting. Perfectly the belt line tolerance would be up to 0.5mm which is not easy to achieve.
- To overcome this issue Gates has teamed up with Thun to provide a perfect bottom bracket which will provide exact belt lines every single time and named it Zumba.
- As you will see in the technical documents Gates has provided the belt line for all available rear hubs and belt lines that they would need. Then for these belt lines there are specially made bottom bracket sizes of spindles made by Thun and marked in a very clear understandable way
- For example for belt line 43.7mm appropriate model would be GBL440 which is in the 0.5mm tolerance.
- Second very important thing to remember here is that for a long lasting system like Gates belt drive it is sensible to have a long lasting bottom bracket. What would be the sense of long lasting drivetrain with bottom bracket lasting one third of its lifetime.
- That’s why Zumba is made with very high quality 2RS bearings with rubber seals which are set on perfectly machined spindle to make them last even longer. Spindle has extra thick Zinc plating to make it rust proof for a really long time in all weather conditions.
- Because belt drive tension is a bit higher than with chain systems, strength is also important, so Zumba has a profiled steel sleeve which provides extra strength while making internal routing easier.
- That’s all topped with composite cups with two shoulder system to make them strong and yet easily serviceable.
- If you need help with choosing the right size of your Zumba for the belt drive feel free to write me email or send me a message on LinkedIn, I will be happy to help
- Ride safe and long with Thun and Gates !
This sounds very good.
Thun also has Belt and Chain ring / crank adaptor for 104 BCD rings, called “Greenwich”
My question is, if Rohloff recommends a chain-line of 57mm how do I adapt to 54.7mm CDX belt-line? It appears I need spacers?
Hello
Thank you for your comment and interest in this article.
Greenwich is still not in the serial production but should be available in 2022. It is more made for e-bikes and double sided torque sensor measurements so Thun didn’t release it until they finish the sensor. Now with electronics delivery times serial production had to be postponed.
As far as your question for belt line goes I think a 2mm spacer under the right cup will do the trick. You can either buy it in the aftermarket.
If it is not available you can find a standard 35mm inner diameter steel pipe and cut a 2 mm ring… it is a DIY but it works 🙂
I recommend not to go over 2mm, but as you described it does the trick for you as you will be in 0.5 mm belt line tolerance Gates recommends.
The bearing on my bike broke (STEVENS CITY FLIGHT LUXE) so I disassembled the gates (Thun Zumba GBL 460), but now I can’t buy the same one in a shop. So than I have decided to replace the bearings. I don’t remember what of sides of the shaft was longer. Please tell where the left and right sides of the shaft are. How to properly assemble the details together.