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Deep thoughts…on low gears

Our sales history speaks for itself -- 10-speed is the hot ticket. Since SRAM debuted their XX group, it’s been present on our high-end mountain bike builds like marshmallows at a campfire. And with Shimano’s release of their new XT 10-speed Dyna-Sys drivetrain, our curiosity was sparked. What would be the ideal setup for my bike… or yours for that matter.

It’s a question worth discussion for sure, and in my book, worth an investigation into the subtleties (like a splinter stuck in your finger or a big stick to the head) between what we’re used to and what we’re looking at when shopping for new parts for our new bikes.

So when a co-worker and I were discussing his sweet new Mojo HD, I asked about his new XT 10-speed drivetrain. He loves it of course, but we focused on our original question -- Why would Shimano do 10-speed with a triple chainring? Was that their best response to SRAM’s 10-speed (see our video review) with double chainrings? Why not fight fire with fire? Or is it better to bring something different to the table?

Any of you who’ve tried various suspension designs know that different is usually at least that, different. Sometimes one design is better for one person or particular terrain, but as consumers (and ultimately, we all are) I think we can all appreciate having choices. And as the drivetrain is concerned, we’ve all had easy access to what I’d like to call ‘traditional’ 3 x 9-speed from all makers, and now we’ve ridden the relatively new 2 x 10-speed and really new 3 x 10-speed groups from SRAM and Shimano respectively.

Each has its pro’s and con’s, but my recent discussion with the co-worker centered on the low gear.

The way I see it, most of us are middle packers. By that, I mean I’m a competent bike handler and have an expert (oops, sorry… I mean Cat 1… Damn USAC) license, but I’m a bit removed from the rider I was when I got my original 1#### five digit NORBA number. These days I enjoy the competition, though I spend my race days aboard a single-speed, honestly, so I can do the shorter Cat 2 distance. I like to think that I followed some good advice I once got from a veteran roadie friend. ‘You should try racing smarter,’ he said. Yeah, shorter is probably smarter. But, in reality, I’m just a middle packer in the grand scheme of things, and I refuse to believe that I’m alone.

I also have a confession to make -- I use the little chainring. Sometimes. But hey when I need it, I need it. So for me, the low gear discussion has merit. The way I see it, most folks spend a lot of their time in middle-of-the-range gears. That much is certain based on what we’ve seen on repair bikes. But of the two opposite ends of the gear spectrum on either side of middle, which one could you sacrifice? Which one is more important to you, the granny gear or the leg shredding top gear?

As I began looking into total gear inches for a few basic bike configurations, I expanded my investigation into the differences between 26′ and 29er wheels as well as a switch to either of the new 10-speed Shimano or SRAM shift systems from what we’ll define as a ‘traditional’ 3 x 9 gear setup and how all this affects the low gear.

Here’s what I found:

Low gear difference from 26′ wheels to 29er wheels:

Assuming comparable drivetrains from one bike to the next, this yields a final drive increase of anywhere from 11.2 to 11.9%, depending on your component configuration. This much should be fairly obvious since 29er wheels are bigger -- 3′ nominal diameter increase. 29er riders will always suffer with taller low gears than an equally equipped 26” bike. In real terms, an 11-12% jump in gear inches equates roughly to a 4 tooth difference on the big side of the cassette.

Low gear difference from an “old” 3×9 group to a new 10-speed group:

26′ bike assuming 11/34 and 11/36 cassettes respectively

Group

Chainrings

Increase

3×9 to 2×10 26/39 11.9%
3×9 to 2×10 28/42 20.2%
3×9 to 3×10 24/32/42 3.0%
 
29er bike assuming 11/34 and 11/36 cassettes respectively

Group

Chainrings

Increase

3×9 to 2×10 26/39 11.2%
3×9 to 2×10 28/42 20.2%
3×9 to 3×10 24/32/42 2.7%

As strange as it may seem, even with a “revolutionary” 11/36 cassette, all the new 10-speed groups suffer with a gear inch increase in comparison to a typical 3×9 setup with a standard 11/34 cassette. This is because they all have larger small rings in front. Most significant is the difference in the jump from 3×9 to a 2×10 with 28/42 chainrings. The 20% increase in gear inches would be nearly be equivalent to a 7 tooth difference in the low gear!

 

Low Gear difference from old 26” 3×9 bike to a new 29er bike with 10-speed group:

26′ bike assuming 11/34 and 11/36 cassettes respectively

Group

Chainrings

Increase

26” 3×9 to 29er 2×10 26/39 24.4%
26” 3×9 to 29er 2×10 28/42 34.5%
26” 3×9 to 29er 3×10  24/32/42 14.9%

It’s obvious that 29er bikes will always have a larger final drive. What you might never have imagined is this -- the switch from a 26” bike with an 3×9 group to a 29er with a 28/42 2×10 would net a low gear increase of 34.5%, roughly equivalent to a 10 tooth difference!

For what it’s worth, I think the new XT 10-speed group with the triple crank would be a good component choice for the 29er rider, especially if they’re not an expert level racer. True, it gives up a bit on the low side to a 3×9 crankset with a 22t inner ring, but it’s very close. And the fact that the tooth range between the small and big rings is now 18t as opposed to 22t on a typical 3×9 triple crankset makes the shifting a little slicker and more trouble-free.  

Another interesting thing to note (and I would consider it an improvement) is the total chainwrap difference between an old 3×9 (45 teeth) and the new 3×10 XT 9 (43 teeth) – while two teeth may not sound like much, it will be easier for the rear derailleur to take up this difference in chain tension. From a practical standpoint, better derailleur tension means the chain is more likely to be where you want it and you’ll get less slap on the chainstays (less noise and less mangling of the finish).

I don’t often worry about gears since I ride a single-speed a good bit, but when I ride in terrain that is more enjoyable on my Santa Cruz Heckler with its 150mm of glorious travel, I certainly appreciate the gear options, especially on extended or technical climbs. So my perspective for priority is skewed towards the low side of middle. And if the trail dips down away from my handlebars, sure I’ll slam it into the big ring and hammer, but I won’t fret about spinning out. That’s geography and gravity letting me know that, ‘we got this.’ So I just ease back, hang on and enjoy the ride.