Internally geared hub for downhill?

Hi Lee,
I have a question for you. I really want to get a speed hub for my downhill race bike.
I am running an external derailleur on my rocky mountain RMX and i was looking at rohloff speed hubs, but they are slightly out of my price range. Could something like a Sram S7 work for downhill racing?
thanks,
wes

Hey Wes,

The rear derailleur is the bane of downhilling. Why does your bike’s most delicate part have to hang down by the rocks and roots? Many smart people have tried to solve this problem, but — aside from the new gearboxes — few solutions have worked better than rear derailleurs.

Disadvantages of internally geared hubs
– Loss of power. External setups are up to 99 percent efficient. Internal hubs are up to about 92 percent efficient. Seven points might seem like a lot, but whey you’re sprinting at 1,000 watts, that’s less than one percent difference at the pedals.

– Weight. Internally geared hubs are heavier than derailleurs and such.

– Cost. A Rohloff is supposed to be awesome, but it costs about $1,200. Wow. The SRAM S7 … $200. OK, that is less than one X.0 rear derailleur. So cost isn’t necessarily a big factor.

– It’s unknown whether the S7 can handle Awesome Power(tm) and the rigors of downhill. But: Most of us mortals don’t make a ton of power, and I’ll guess SRAM tested the heck out of that system.

– Limited rear axle options. 2006 and 2007 RMXes haves a 20mm rear axle. There’s no way the S7’s 10×1 will fit. Older RMXes, I don’t know.

How about this Madness? Check out The Shaft.

Advantages of internally geared hubs

– No dangling derailleur. If you ride very tight, very raw trails, your rear derailleur and your hangers are temporary. I spent a three weeks in Whistler when they first opened the Garbanzo, and I trashed three derailleurs in that time. You’re welcome for clearing the trail!

– Quieter. I don’t care how trick your bike is. Chain slap makes any bike feel terrible. An internal hub and properly fitted chain should be silent.

– You can shift without pedaling. This could be a significant time saver. Imagine pedaling all the way to a turn, shifting while you rail, then being in the perfect gear.

Considerations

– Your chain length changes as your RMX goes through its travel. You need a chain tensioner to adjust for this change. You can order a Rohloff DH chain tensioner for about $80. Who knows how that mates to the S7.

This just in: Eric Sovern at Surly Bikes says a Singleator chain tensioner ($40) will probably work.

– Brakes! You don’t want to race DH with the coaster brake S7. The freewheel S7 won’t accept disc brakes. So you’re left with the drum brake model. Will this drum brake handle DH?

– You gotta build a wheel, install a shifter, mess and fiddle and deal with who knows what.

– What about a single speed? Do have have awesome low-end torque? Can you spin like a CR125? Are you a citizen of Pump Track Nation? Pick a gear and do some timed runs. If you’re just as fast without shifting, you know what to do.

Are you ready for some Madness?
Check out The Shaft. My buddy Jon Heim, a genious inventor guy at Stanford, was sick of losing derailleurs at Northstar. Here’s his solution.