SRAM DualDrive X 2?
Hi all. First post, be gentle. Let me get this out of the way. I've been lurking this forum on and off for years and want to thank all involved for a great resource.
I picked up a used '06 Cannondale Prophet a few months ago. I really like it. I don't do any serious trail riding but wanted something that was capable of anything city and park riding could dish out. The Prophet is certainly that and more. I'm finding that 27 speeds is way overkill for my style of riding. I've always hated rear deraileurs. I've been lusting after a Rohloff ever since I found out about them in '00, but have lately come to the conclusion that it's too expensive and heavy. After searching the forums I've read about the SRAM dualdrive disc. What I'd like to do is use a single cog in the back, with spacers to get the correct chain line, and a chain tensioner, which I'd need anyway because of the rear suspension, and use a dual chain ring setup up front. The Paul Melvin chain tensioner is said to have the facility to be able to do this. This would give me 6, widely space, useable gears, well 5 really, because of redundentcy, after playing around with Sheldon Brown's gear calculator. My question is, what is the widest range of front chain rings allowable that will work smoothly? The Melvin is said to have a 20 tooth range, but is there a front deraileur that will work smoothly with, say, a 22x42 combo? Or tell me about something I haven't thought of that makes this unworkable.Thanks in advance.
You are combining the worst of all worlds:
Heavy, expensive geared hub
Flopping chain due to Melvin (same as rear derailleur)
Wide-range chainrings that are hard to shift
As you say, Prophet requires chain tensioner, so you may as well use a derailleur for the job and eliminate the Melvin and front derailleur.
Personally, I would remove 2 chainrings and shifter, and use 11-34 cassette for lighter weight, easy-to-find parts. See 1x9 thread for MANY examples. You can try it for free by just staying in your middle ring for a week or two. if you're dying to upgrade soemthing and riding parks mostly, you can probably run a 34-40t singlespeed ring in front.
Or, buy the SRAM 7-speed or new 9-speed geared hub. They weigh about the same as 3-speed, give you about the wide range of the setup you describe, but eliminate one chainring and the front derailleur. But you're still stuck with Melvin and chain slap.
That said, it's your bike, so I'll play along.
22/42 is going to be very difficult to shift. You could add more pins to the 42, but I think you'll still have problems under any load.
34/50 has become common on road bikes and shifts OK. The Shimano R700 cranks with 34/50 shift as well as Dura-Ace or XTR (perfect).
I ran 32/48 in the past and it did not shift well under load. But, it was OK for my touring bike.
Thanks for pointing out the obvious, and I am NOT being sarcastic! Until you mentioned it I had not plugged in the values for a 1X9 gear inch table. What I got, for a 34 tooth chainring, was a range from 24.9 gear inches on the 34 tooth cog to 76.9 on the 11tooth cog. Using a 38 tooth chainring would give a 27.8 to 85.9 range. Plugging in your example of the 34/50 yeilds a 32.5 to 89 range, with a 19 tooth cog on the dualdrive setup. Plugging in the 32/48 yeilds a 30.6 to 85.4 range with dualdrive.
In my desire to eliminate the rear deraileur I had not considered just going with the 1X9. I appreciate your explanation and its exactly what I was looking for. I had a feeling that a 20 tooth jump would not be practical.
In defense of the dualdrive disc though, its relatively light, for internal gear hubs, at 985g. and it would result in a better chainline with just 2 chain rings and 1 cog in back. Its not that expensive either. I've seen prices fom $180-280. And the Melvin is much less complicated, and costly, compaired to a rear deraileur. As you so rightly point out, chain slap would be the same with either setup.