Wednesday, July 31, 2013

Belt Drive MTBs are they ready for PRIME TIME?

Recently I purchased a new mountain bike for 2 reasons.  One, the frame design was old school and evoked a feeling of nostalgia, that I don't often feel. Two, the frame had split stays which would allow the bike to be easily converted to Belt Drive.

The bike is a 2011 Trek- Gary Fisher Sawyer and had some of the worst paint I have seen on a MTB.  The paint was a non-descript sad grey and although the bike had seen no dirt, just shop wear, and hanging the bike on bike racks had taken a toll.

Step one was to add a real durable finish and 1 Off Powdercoating came to the rescue.  Dale did his typical excellent job, even though with all the curved tubes and strange shapes.  I selected Grabber Orange, which is closer to Yellow than Orange.  The color reminded me of my first bike which also had curved top tubes and it also reminded me of a original 1970s Honda ATV that used the same color.

Unfortunately, selection of the belt drive components wasn't as smooth.  As an experience mechanic I expected very few issues. 1 belt and 2 sprockets.  DONE!

Well there are several iterations of Gates Carbon Drive components available.  They are not compatible with each other. The naming conventions does allow for clear distinctions when parts shopping, so I don't think DIY applications were a high priority for Gates.

In my quest for components the first thing I noticed is how pricey they are.  Plan on spending at least double, what you would for a chain drive equivalent.  The online calculators are very useful once you have the chainstay length of the frame you will be using.

One thing that is important but hard to uncover is that most of the current applications are really for a specific marketing segment.  Based on the Carbon Drive home page that segment is urban hipsters who wear white and are deathly afraid of chain oil.  I am not sure what they use for lubricating their hubs, bottom brackets, and headsets, but I am guessing it is a synthetic version of their own smugness.  So if you ride in the city, work in a loft and have a monochromatic lifestyle a belt drive bike is for you!

You will discover in reading the Tech bulletin that if you are riding a Mountain bike or Fixed Gear you will need nearly double the belt tension for proper performance. Okay, no problem, probably a bit more resistance too, but wearing white pants is probably worth it.  Wait.  Doubling the tension is when you are going from city cruiser with internal hub to the Mountain or Fixed Gear application and are a Lightweight Speedster.  If you can figure out what a lightweight speedster is, then good for you.  I think that means God gave you thighs that don't generate enough watts to impress anyone... ever.  So for normal riders that HAMMER, SPRINT, CLIMB, GENERATE 1000 WATTS, and KICK ASS and ride MTB or FIXED GEARS triple the belt tension.  nearly TRIPLE, really. From 35kg to 85kg.

Now your frame flex is coming into play and Gates has a program for OEMs to analyze their rear ends.  I am not making that up.  It also matters how much belt wrap you have.  My selected gear was 39x22 yielding a ratio 1.75, which I though would be perfect for my 29ER SS.  I was warned that more belt wrap is required for this application. That means jumping up to 46x26 and a 118 tooth belt instead of 113. Don't worry though because there is an app for that.

Sounds to me like I am back to chain drive for the epic ride this weekend, because I have a lot of belt drive components to sell and then re-buy.  So it will be a while before you see me trying to BELT ONE OUT, but I think I might have also avoided an on-trail disaster, on a ride that means so much to me.


Eric Brandt said...

It took me a while of messing with the high tension required by the belt drive, to realize that running belt drive was not for me. I struggled with the belt drive tension messing with the disc brake alignment.
When I got the tension correct the brake would not work. Dialing down the tension allowed the brake to work but drivetrain was not right. I am guessing that the same frame would not be sold with a factory belt drive using the Cog and ring size I tried. Switching back to chain drive took all of 15 minutes, and I am happy to say worked immediately. YEAH METAL!

metag3 said...

I am running a 39x22 center track belt on a Fisher Sawyer for over 2 years with no issues. Good gearing for single track in Colorado and Alaska. I don't tighten the belt too much and have rarely had it skip. It is a bad sound when it does skip, but nothing compared to gears constantly chunking. Personally, I think the belt skips when it is too tight...