My last post I talked about the idea of putting a Rohloff in my Santa Cruz Nomad. That idea has stalled because of the performance issues associated with adding a significant amount of unsprung weight to the rear wheel. Another thought is to add a Hammerschmidt 2 speed BB to the Nomad and swap in a short cage rear derailleur.
The Hamerschmidt is a 2 speed BB made by Truvativ. It gives you a direct drive lower range and an over drive range that is 1.6 times the lower range. The All Mountain version I’d be interested in would be like having a 24T granny and a 38T middle ring. Shifting is instantaneous and can happen at any time – under load or while coasting. I often find myself jumping back and forth between my two front rings [big ring replaced by a bash guard] as I go from steep uphill to steep downhill.
This has the following benefits:
- no extra weight at the rear wheel
- shorter derailleur and less chain to slap and move around
- impossible to throw chain on front rings
- instant front gear changes when coasting or under load
- no extra drag in low range when climbing [BB running at 1:1]
- weatherproof front shifts
- access to all 9 cogs at rear all the time due to better chain line
- very good clearance for obstacles
- small amount of extra weight [200grams or so] is sprung on main frame of bike
The downsides are:
- not cheap @ $900cdn+ for the All Mountain version
- Nomad not optimized for running in 24T ring all the time
- still have a rear derailleur
- rear end of drivetrain not weatherproof
- requires ISCG 03 or 05 tabs to mount HS
I tried out a Santa Cruz Driver 8 with Hammerschmidt at Bow Cycle and I was impressed. It shifts so fast you can respond to whatever the trail throws at you without having to pedal or wait for the chain to get sorted.