X-Class 3 chain ring setup with SRAM Dual Drive

It turns out the X-Class had two styles. One had two chain rings, 22/42 and the other had three, 22/32/42.

This is how the gear chart would look like. However, it would never be possible. The SRAM has a 30T limit. It doesn't support chain rings smaller. It's interesting to see the combination though.

SRAM Dual Drive a failure?

I've heard horror stories of the unreliability of SRAM's Dual Drive product. This scares me b/c one guy completely lost all his low end gears midway through a ride:

http://www.bentrideronline.com/messageboard/showthread.php?t=60147&highlight=sram+dual+drive

I can't imagine what I'd do if that happened. That would be horrific. Stuck at the bottom of a mountain with failed gear unable to get up the hill with 6 more days of 100mile/day rides would be a huge disappointment if not impossible mission.

The unit is probably much harder to fix. The mechanics on the ALC ride wouldn't want to touch it. Perhaps the standard 22/42 compact double that the KMX X-Class offers would be the way to go.

Reading through the forums further, I found that the SRAM Dual Drive has a limit of 30T chain ring. That means I cannot combine it with the 22T from the X-Class setup. Let's see how the gear chart would look with a 30T ring up front.

Low gear is still 12GI's. That's far from the 8GI's I originally found with a 22T chain ring up front, but that's not so bad. 8GI's is ridiculously low. The lowest GI I've ever heard recommended anywhere was 10, but mostly 12. 8 is unnecessary so I'm not really disappointed.

Gear range with this setup is 12.1 - 92.5

After tinkering around with the charts, I found a new configuration that might work better. I used the smallest and largest chain rings available from Sinz (cheap chain ring supplier) and picked the exact middle number for the center chain ring and the chart came out like this.

GI range is 13.7-111. I can comfortably start in 2nd or 3rd gear w/o engaging the SRAM Dual Drive using the 41T chain ring. I expect to do most of my triking in this setup which would be ideal since the efficiency should be best for the SRAM Dual Drive in this configuration. It's very similar to my existing 7-speed setup.

I would engage the SRAM's high gear for fast flat land and switch to the 48T chain ring while in SRAM's high for down hills rides. As I'm walking myself through this, I find that there will be a lot of double shifting. Engaging the Dual Drive while in the 41T chain ring pops the GI's up by 36%. To get a smoother transition, I will have to downshift my cogs by one gear every time I engage the Dual Drive to a higher gear effectively going from 69.6GI to 80GI's. That's much better than going from 69.6GI's to 94.8GI's.

This gets really complicated! Let's see how a compact double crankset would work. The chart is the same minus the 41T chain ring.


The jump from engaging the SRAM Dual Drive is still extreme but that's because it's governed by the ratio of the internal gears. There's nothing I can do about that. As expected the GI range has also remained unchanged. It's easier to think about though. I'll spend most of my time with the 48T chain ring which would be used for flats and minor slopes both up and down with the Dual Drive disengaged.

The Dual Drive would only be put into high gear for extreme down hills. I will only pop the Dual Drive into low and bring the chain ring down to 34T during extreme climbs. There we have it.

No rear brakes!

The Catrikes don't have rear brakes and neither do many of the other models. Having one is what makes the KMX stand out. I just realized though that I'd have to sacrifice the rear brake in order to install the SRAM Dual Drive. I don't believe a disk brake can be installed on it. I'll have to call Ashley over at Utah Trikes to find out.

I got an email back from them and apparently there's an option to add a rear disk brake. The option costs $80 though!

Conclusion for gear design

It's been almost a year since I've started analyzing gear options. I need to make a decision by the end of next month in order to give myself ample time to practice, get used to the system and other preparation for the ALC ride.

The Schlumpf is too expensive and weighs too much. It's no wonder most people don't have it. The system is pretty cool though and doesn't give you any gears you won't use. There's good points and bad points, but overall for my particular situation, the Schlump comes to the bottom of my preferred list.

1.
2.
3.
4. Schlumpf Mountain Drive

So now the choice is between the SRAM Dual Drive and the X-Class setup. I feel like I would eventually want both, but which one would help me on the Aids Life Cycle ride? This has to be an objective question and the answer is?

1. SRAM Dual Drive and X-Class combination
2.
3.
4. Schlumpf Mountain Drive

Well, the X-Class setup is way cheap compared to the other options. It's almost 1/4 the cost of the Schlumpf. Big plus on that! It also provides me lower gear inch for hill climbing than the Dual Drive would - at least with a 40T front chain ring.

Final decision?

1. SRAM Dual Drive and X-Class combination
2. X-Class stock setup
3. SRAM Dual Drive
4. Schlumpf Mountain Drive

Test riding Catrikes

I scheduled with CVC San Francisco, a local recumbent trike dealer to test ride 4 of their models.

Option #1: X-Class setup

I might have posted this before, I'm curious how my new options compare against the stock X-Class gear range. My cheapest option of getting lower gears would cost me $250 and these are the results. The chart looks like this:

This mod would give me one higher gear and three lower gears. The gears are significantly lower than my current setup and still even better than using the SRAM Dual Drive.

I can't help but to think what would happen if I combined the two. Hmmm, now that would be interesting. Best of two worlds? Let's see.

Combining both systems would give me a range of 8.9 - 97.1! That's insane! I could probably climb a wall with that setup! That would be pretty ideal, but it would cost me $650+ to get there. That's still less than the installed cost of the Schlumpf drive and would weigh less overall. Two points against getting the Schlumpf. I understand the Schlumpf drives weigh in excess of 10 extra lbs! Do I really want to carry around a 52lb trike? Uh, no!

38T chain ring on an SRAM Dual Drive?

I'm curious how swapping the 40T chain ring for a 38T would effect the lowest gear. How much lower gear inches will I get from the replacement? Would it be worth it? Let's take a look.

I saw the preliminary gear chart and thought, "Why stop here?" So I decided to tap on another couple chain ring sizes to see how low I could go and what the effects would be on the high end Here's the side by side comparison of a 36T, 38T and 40T chain ring on the SRAM Dual Drive setup.

Tough choice. I love the idea of being able to go under 15GI's, but that comes at the expense of one less high gear than my stock setup. I'm liking the 38T chainring.