Gates Carbon Drive Belts

[Cardigan]

Hi Everybody,
Has anyone specified/asked for a Gates carbon drive belt on a Nomad Mk2? If so, what was the outcome?

[julk]

How would you fit one?
They need a removeable rear dropout or a split seat stay, neither of which are on the Nomad Mk2...

[tandemman]

I believe thorn are not fond of the belt drive system for a number of reasons, one of which being the thicker seat stays neede give a compromised ride and the thicker chainstays needed make the rear end too stiff. I  don't believe they have any plans to make a belts drive frame available in the near future.

[Cardigan]

Thanks Tandemman,
A well balanced informative reply that didn't make me feel at all stupid.
Julk, Sr. Member. Nuf said.

[julk]

Cardigan,
sorry if I came across a bit abrupt, didn't mean to.

The problem with the belt drive is the belt is a loop with no way of splitting it like a chain - makes fitting it a real challenge for the frame builder.

You can get a seatstay fixed to have an removeable insert, Shand Cycles can do it to your Nomad Mk2, then a respray is needed.
You would also need a belt, a new sprocket on the Rohloff and a chainring - both suitable for the belt drive.

All in all it comes out a bit expensive and you would lose your Thorn lifetime frame warranty.

[il padrone]

How would you fit one?
They need a removeable rear dropout or a split seat stay, neither of which are on the Nomad Mk2...

S&S do a coupling specifically for this purpose, to fit in the seat-stay. As they say the coupling is stronger than the tubing I don't see why a heavier seat stay would be required.

[Hamish]

I understood that stiffer chain/seat stays were required to reduce flex/twisting under heavy loads and so maintain perfect alignment of the belt.  If the alignment is incorrect the belt will drift off the 'sprocket'.

[Cardigan]

Hi Julk,
Thank you, I should also apologise!
The S&S coupling sounds interesting.
Thanks for all the advice/opinions on this. Keep them coming.

[sloe]

Surely it cant be beyond the wit of wo/man to split the belt.

[Danneaux]

A small question wrt the Gates carbon belt drive:

Are the chainring and cog grooves for  the Gilmer belt ribs placed on a 1/2" pitch, as with a chain?

If so, it would make it far easier to calculate gearing and make direct comparisons to a conventional chain drive.

The information available at Gates' website ( http://www.carbondrivesystems.com/installation.php?lang=us ) is not clear as to effective pitch of the Gilmer ribs.  Or, perhaps I missed it...?

Thanks,

Dan.

[in4]

Sarah Outen has a Santos complete with rohloff and belt drive. She's currently resting in Japan after a leisurely ride across Eastern Europe etc.

http://www.sarahouten.com/the-mission/boats-and-bike/

Seems like the combination is eminently doable!

[pdamm]

Dan

I had this concern too when I was investigating a Rohloff / belt drive equipped Van Nicholas Pioneer.  Then I realized that the pitch doesn’t really matter, what matters is the ratio of the number of teeth in the front and rear rings and the size of the driven wheel.  The bike ended up having 22 teeth on the rear sprocket and 55 teeth on the front ring.  The belt has 122 teeth on it.  The pitch looks similar to the 1/2 inch pitch of a chain but I haven’t measured it or investigated it to find out what it is exactly.  This combination of gears on the 26 inch wheels gives the bike much the same range as my Raven Tour with a 40 teeth on the front chain ring and 17 teeth on the rear sprocket.  The Van Nicholas is for my better half and being titanium her new bike is about 3kg lighter than her old steel frame steed.

Peter

[Danneaux]

Thanks, Peter, that helps a lot.

If you ever get curious and decide to measure the pitch of the ribs, center-to-center, would you mind telling me?   

I'm burning with curiosity now.  I'll head back to the Rohloff support page and take another look at their charts.

All the best,

Dan.

[Andre Jute]

I believe the Gates Carbon Drive tooth pitch is 14mm. There was no reason for them to stick with half an inch because, as you say, what matters is the ratio of teeth between the chain wheel and the cog. -- Andre Jute

[Danneaux]

In4, Peter, Andre --

All good information and I am getting a handle on it.  Also helpful is Santos' belt-dedicated website, in the original Dutch here...
http://www.beltdrivebicycles.com/
...and Google's English translation here...
http://translate.google.com/translate?sl=nl&tl=en&js=n&prev=_t&hl=en&ie=UTF-8&layout=2&eotf=1&u=http%3A%2F%2Fwww.beltdrivebicycles.com%2F&act=url

Helpful diagrams, pics and their own FAQ proved helpful to my understanding.  I now see the chainring pulley is completely open, which means no possibility for mud-clogging.  Gates' ladder-concept drive pulley is brilliant.  The photos also show some mud tolerance on the rear drive pulley.  It cannot be open like the chianring (too little space), but still allows some self-clearing action in use.

In4, what a wonderful journey Sarah's taking. Thanks for posting the link.

I would love to see pics of a really worn, weathered Gates Carbon Drive belt at the point of failure to see just how it appears.  I have seen automotive low-load Gilmer timing and accessory drive belts with sheared ribs, and GMC 6-71 supercharger belts that went on and on, despite the tremendous instantaneous torque generated by a 1000+HP drag race engine.  Looking at Gates' own website for the Carbon Drive, it seems the real achilles heel of the system is the need for a good baseline alignment, as it is for all Gilmer drives.  Noise is one indication of trouble (though it may quieten with water) and is brought on or hastened by misalignment, as in a skewed or loose BB eccentric.  Still, overall life should be quite good.

Best,

Dan.