Tuesday, March 30, 2010

Thoughts on 29er Gearing

Several of my fellow Fitzy teammates are considering racing a 29er this season and our team has some excellent options. In addition to frame options, the drive train is a major consideration. If I were building a 29er race bike today, I am not 100% sure what drivetrain I would choose so I decided to do a little math.

Before I geek-out to much, I have to come clean. I use my 22F/34R combo. There, I said it. I would like to think that I am getting stronger and could live with a 32 in the rear instead of the 34 but to this day I am clinging to the safety of my 34. And now that the sexy SRAM XX 2x10 speed is here, and other 2x9 drive trains are trying to compete, do they offer comparable gearing AND the advantage of crisp front shifting?

I plugged four current drivetrain options into the Sheldon Brown Gear Calculator and used my trusty 22F/34R combo as the baseline. Here is what I learned:

The numbers circled in red in the lower left corner represent gear inches in the "easiest" gear combo. The bigger the number, the harder the gear.

The 22F/34R combo is my baseline at 18.8 Gear Inches

The 22F/32R combo is 5.85% harder at 19.9 Gear Inches

The smallest front chainring you can get with SRAM XX is 26 and the largest available cog is a 36. The 26F/36R combo is 11.1% harder at 20.9 Gear Inches

The top-of-the-line Jamis 29er comes with a 2x9 drivetrain; FSA 27/42 crankset and a Shimano 12-36 cassette which results in a stout 15.95% increase over a traditional 22F/34R at 21.8 Gear Inches

The Felt Nine Team comes with traditional 22/32/44 in the front and an 11-34 in the rear

The Jamis Dakota D29 Team comes with a 2x9 drivetrain and is for fit riders who can push the 27F/36R up the steep hills

The Jamis Dakota D29 Pro offers a drivetrain with a larger-than-normal safety net; a 22/32/44 in the front and a 12-36 in the rear

The biggest eye opener of this exercise was the 11.1% difference of SRAM XX vs. my current gearing. When I am 9 hours into a 12 hour Cream Puff 100 race, could I really push a gear that is 11.1% harder? Some will argue that you will simply adapt, and therefore go faster, and that having the 22F/34R is a crutch. What do you think?

EDIT 3/31/2010: I am not building a new geared bike but I have been curious about the new SRAM XX. For now, I will stick with my 22/32/44 and my 11-34 in the back.


HarmonyCreekBrewery said...

what about an Actiontec 20 tooth chainring? Will that fit on your crankset?

Ken Hurd said...

That's a tough call – I know that I much prefer to spin an easier gear at a higher cadence than grunt through a tougher option (esp. on the climbs).

With that said, from what I understand one of the main benefits of running a 29er set up is the momentum and ability to simply 'roll' over things... Wouldn't the opposite be true when you're at super low speeds (ie. climbing)? Not only would you be pushing a harder gear (up to 11%), but you would be fighting against a set up that is inherently more difficult to spin up?

That said, switching to a 29er is also on my radar (though not for this season) – I'll be interested in what you find out.

Gabe said...

I ran a 22F/32R on my 29er for the past 3 seasons and only once did I ever want a 34R. That was at the Puff and Im sure you remember the heat.

Although, my new F-Nine does have a 34 and I plan on keeping it set up that way for a while.

I don't think I could turn a 2x9 in a 100 mile race.

Ed said...

My brain just exploded, please don't do that again!



brandon said...

This post makes the 29er thing look a little weak next to the
26er. We all know the 29er rolls downhill faster but the engine always has to work harder to keep that big hoop and rubber moving. Seems to me like XX was designed to be used on the XC World Cup race bikes which are almost all

I think you've made a strong case against XX being a poor choice for the endurance rider/racer. Way to geek out! Who knew blogs were such a huge wealth of info. Thanks again Dave.

By the way...do you have any pictures of a new bike?

Dave said...

Ed - I forgot to add the disclaimer at the top of the post that says "If you ride a rigid singlespeed, stop reading right now. :)"

Dave Harris said...

I'm with Ed.

But seriously, XX gear ratios just don't cut it for enduro racing. XC perhaps, depending on the course and rider.

I did CTR on a 1x9. It really sucked a lot (front ring was a 34) and I did a lot of walking, but one interesting note is that I never spun out, even coming into BV on slightly downhill pavement with a tailwind. ScottM runs a 20x32 front ring setup with a bash guard instead of a big ring. That's the money setup for multi-day enduro riding.

On a 29er I wouldn't go any larger than 22 teeth on the small ring. And, if I do CTR again there will be a 20x36 available!!!

Hamilton said...

yeah, pictures of your 34/20 please!!!

Chris E. said...

Yeah but 22 X 32 on a twenty six inch wheel is 17.9 gear inches. There ain't nothin' wrong or wimpy about a 34 on a 29er...

T-Race said...

Well it just so happens I am looking into these Jamis 29ers you are comparing...thank you for the info.