I was hoping to change my Pugsley over to an IGH (probably an Alfine 8 or 11) next spring, but this thread on forums.mtbr.com may have changed my mind! The info presented there is bad news for IGH fans.
According to Aaron Goss of Aaron’s Bicycle Repair, and I’m paraphrasing here, IGH’s are best used sitting down, on relatively flat roads. If you exceed a certain torque, whether by standing on the pedals, riding up steep hills, using an innapropriately low front chainwheel – back sprocket ratio, or a combination of the preceding, you risk stripping the pawls inside the hub.
According to Shimano, none of their hubs are suitable for off road use. Short steep grades increase the torque, as does standing on the pedals. Shimano IGH hubs fatal flaw is that they use a single (or in some gears just 2) pawls to transfer all the load. Modern Sturmey-Archer hubs have the same problem. SRAM hubs have 2 points on a sliding key which are designed to fail. Hubs we have found very durable are the SRAM P5. It uses 6 fixing points on the axle for the sun gear.
Now this is obviously bad news for someone who wants to use an IGH for off-road touring. My current low gear on my Pugsley is a 20/34, which works out to 17.4 gear inches. You read that right! I hate getting off to push!
If I follow the recommendations in the spreadsheet of IGH gear ratios provided by Aaron, these are the lowest gear ratios I can achieve on various IGH’s (assuming a 29.5″ diameter for a Pugsley wheel and choosing the sprocket ratio for horizontal dropouts when that option is available):
|IGH||Min gear ratio||Min sprocket ratio||Min gear inches|
|SRAM i-Motion 9||0.54||1.73||27.6|
|Shimano Alfine 11||0.527||1.7||26.4|
|Rohloff Speedhub 14||0.28||2.35||19.4|
(Interesting to note that the internal minimum gear ratio of the two Alfines is identical, but the recommended minimum sprocket ratio is so different.)
Even with a Rohloff, the lowest gear recommended is 19.4. That’s not too bad. Moving to more affordable choices, the lowest recommended gear for the Alfine 8 is 22.2. That’s a 28% jump over my current 17.4 gear inches. That’s a BIG difference.
Aaron specifically singled out the SRAM P5 as being very durable, which means perhaps it could be run at higher torque than is recommended. Unfortunately, this hub has only a 250% gear ratio spread, which would not provide a high enough gear. Also, the SRAM does not take a disc brake.
So, I’m kind of bummed about this.
Update: Here’s a nice comparison of many IGH’s.