Wednesday, February 23, 2011

SRAM Dual Drive

During my research for more options on getting lower gears in prep for climbing hills, I discovered the SRAM Dual Drive system. Utah Trike sells it and it happens to fall in between the two prices of my other options:

1. Add a 3 chainring setup at the front boom - $250
2. SRAM Dual Drive - $400
3. Schlumpf Mountain Drive - $700+50 (shipping/tax/blah)

Q: So what's the SRAM Dual Drive?

A: It combines a 3-speed hub with a 9-speed cassette. So what does that mean? It's a single unit that replaces the front chain ring as well as the rear cassette or in my case, a freewheel. It basically relocates the front would-be chain rings to the rear in the form of an internal hub. The cassette is added on. If installed, I'll get 3x9 = 27 gears instead of my current 7.

The cassette is actually a 9-speed with the following cogs:
11, 13, 15, 17, 20, 23, 26, 30, 34

This is how the gear chart looks like. The middle column shows my current range. It's not completely accurate b/c my current freewheel is only 7 speeds while the new cassette will be a 9-speed.Looking across the chart, I see that I'll be getting 3 lower gears! It's significantly lower - 16.1GI's instead of 22GI's.

Another effect of going from a 7-speed to a 9-speed is that the transitions between the gears will be a lot smoother. There's no jump from second lowest gear to lowest gear like there is now.

In addition to the lower granny gear, I get two higher gears for downhill speed! 78.3GI and 92.5GI is a big enough hop from the existing 67.9GI's. That gives me a 36% jump!

In my previous posts, I noted that 88GI's would be my ideal high end. Having a gear higher would be even better. What I'm most excited about though is the 16.1 lower gear.

Another advantage to this system is that less can go wrong. The system is definitely more complex, but there's less to mess around with. Everything is internal and gear changing is all done from the rear. Nothing happens up front.

The kit comes with a wheel! Since I need a back rear wheel anyway for backup, I won't have to buy an extra. The kit also comes w/the shifter, derailleur, cable, hardware, grips. Sounds really good! Hmmm.


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