February 23, 2012 cburnham

Gear Questions Continued…Mountain Bikes

Yesterday I went over the gearing options for road and triathlon bikes.  Today we will tackle mountain bike gearing which can actually be a little more complicated due to the option of having two different wheel sizes.   

Mountain bike gearing has become increasing complicated over the last couple of years with the rise of the 29er wheel and new 2 x 10 drive-trains.  First off, the double crankset coming to mountain bikes is one of the best things to happen to mountain bikes since the suspension fork.  Triple cranksets were plagued with slower shifting, redundant gears, and wide q-factors.  Besides, double cranks just look sweeter.  Since most of the questions I have been receiving lately have been on purchasing new equipment, I am going concentrate on the double crankset options.

Crank options
Just like in road, there are several gearing options for mountain bike cranks.  In a double ring setup you have a 22-36, 24-38, 26-39,  28 -42,  28-40, 30-42, 30-44.  For triple cranks you basically have a 24-32-42 (Shimano), or a 22-33-44 (SRAM) option (as I noted above, these are slowly going the way of the Doo-Doo bird).

Cassette Options
Specific mountain bike cassettes tend to be either a 11-32, 11-34, or 11-36.  For the sake of this article and not getting too complicated, I am going to ignore the fact that you can run a 10-speed road cassette on your mountain bike.

OK, so my head just exploded.  That is a total of 36 different drive-train options, 72 if you factor in 29 versus 26 inch wheels.  So what are the best options?  That really depends on your riding style, are you racing, cross-country or downhill, 26 or 29er, just trail riding.  For this article I am going to stay primarily focused on cross-country riders but these basic guidelines will apply to trail riders as well.

Twenty Niners
The bigger 29 inch wheel essentially increases the distance the bike will travel with each rotation of the crank.  A 29er wheel will basically go faster than a 26inch wheel being pedaled at the same speed in the same gear. This is important because the low gear you have on your 26inch wheel bike will be approximately 15% lower than the same gear in a 29er.  That is the difference between clearing that steep climb or having to get off and walk it.  So we basically need smaller gears, but how small?

The Gary Fisher Team has been exclusively on 29ers for a few years now.

For cross-country type riding, I am going to ignore the triple cranksets for the reasons I noted above.  In double cranksets we will have to look at what will give us the best range while not sacrificing the minimal gear we will need for climbing.  Obviously this will depend on the trails you are riding and racing, and your overall strength.  For most riders, being able to climb at a minimum of ~6MPH while spinning at 90RPM is plenty low enough for most trails (at 60RPM that would be about 4MPH).  Any slower than that and it is probably faster to walk the climb.  A 26 x 34 gear ratio will give us a riding speed of 5.9MPH at 90RPM.  You could also run a 28 x 36 and get almost the identical speed (6MPH).

What about the top end speed?  We typically don’t have high-speed sprint finishes in mountain biking, and while there can be super fast descents at 35+ MPH, most of those aren’t sections that we will be pedaling down.  The bigger issue with the big ring size is to find a gear that would allow you to stay in that gear as long as possible while climbing without sacrificing too much top end speed.  This would allow you to minimize front shifting that can sap momentum from having to back off on the pedals slightly to allow the shift.  This is minor, but can add up over the course of a two-hour race.  When looking at the current options a 39 or 40 tooth big ring will allow you to ride at 9MPH at 90RPM when in the 34tooth cog; while the 11tooth cog at 100RPM would give you 30.5MPH.  That is a pretty good for most cross-country situations.

For 29ers, my recommendation would be to go with a 26 – 39 with a 11 – 34 cassette, or a 28-40 crankset with a 11 – 36, or a 11 – 34 if you’re a good climber or don’t have very steep climbs in your neck of the woods.

For the 26 inch wheel folks
All of the same issues we talked about for the 29ers apply to the small wheeled bikes but the gear ratios have to be bigger since the wheel is a little smaller.  When looking at the climbing gears and that ideal 6MPH at 90RPM, a 28 x 34 gear gets us pretty close at 5.7MPH.  A 30 x 34 could be a good option too since that will give us 6.1MPH.  For the big ring we would like to be close to that 30MPH at 100RPM I noted above with the 29ers.  A 42 x 11 would get us 29.2MPH while still offering a good climbing speed in the 42 x 34 of 9.5MPH.

For 26inch wheeled bikes, my recommendation would be to go with a 28 x 42 crankset and a 11- 34 cassette.  That gives you the widest usable range.  A close second to that would be the 30 x 42 crankset with the 11 – 34 cassette.

One last note on mountain bike gearing
I know a lot of riders get caught up in finding the ideal setup, with perfect gear ratios, so they can be the most efficient rider possible.  That is all good but keep in mind there are a lot of guys crushing the trails on single-speeds. Just check out the results of any cross-country race these days and you will see single-speed guys finishing at about the same time as the geared guys.  Gearing is important, but it is still 95% rider at the end of the day.  In other words, don’t use your gearing as an excuse.

**As I noted in the road article, you can play around with all the gearing options here.

Comments (22)

  1. Tom from spokane WA

    “For 29ers, my recommendation would be to go with a 26 – 39 with a 11 – 34 cassette”.

    I do not get why everyone is trying to push such big gears now days. My old ‘trail’ oriented FS 26er had a shimano 3×9 front (smallest = 22) and a 11-34 cassette. In gear inches, my lowest climbing gear (22/34) = 16.82.

    Doing the same gear inch calculations for the lowest climbing gear on a 29er using (26/34) = 22.18.

    That difference is equivalent to taking the two lowest gears off my 26er and not using them at all!

    where I ride, in mountains, with extended climbs that go on mile after mile, for 1500 to 3000 feet, I must resort to those low 2 gears frequently! I’m not a young pup, but I ride usually 3 times a week, seem to be in the top 1/3 of riders in my age group and often find myself passing riders on the trail that appear much younger than me.

    I did get a 29er, and it had shimano 3×10 with a lowest climbing gear of (24/36) = 19.33 gear inches. This was STILL like throwing away the lowest gear of my 26er. It was too painful and not any fun for me to climb the endless climbs in the mountains. I swapped the 24 for a 22 and now have a 22/36 = 17.72 on my 29er. Still not quite as low as I had on the 26, but good enough and I’m happy now.

    Yes super fit, high end riders could ride a 29er with “26– 39 with a 11 – 34 cassette”, or riders that don’t ride for hours in the mountains. But for the normal ones of us (even folks like me that are far above average fitness for my age), why would we want to put ourselves through that pain? It is so much more enjoyable to gear down and spin up the climb. And believe me, after climbing 3000feet for many miles, I’m still exhausted, even with my low climbing gears.

    • You definitely need to figure out what gearing works the best for your fitness level and terrain you ride. This article was written primarily for athletes that are racing where their needs may be different than yours. Efficiency and performance can deviate at the higher intensity levels of riding or racing.
      Your old lowest gearing of a 22 x 34 at 80rpm, which would be fairly fast for climbing, is only 4.2mph. At more typical climbing cadence of 60RPM that is only 3.1MPH. At that point it may be faster to run than to ride up something that steep and is something that should be considered for anyone concerned with finishing a ride/race as quickly as possible.

      • Thank you for the informative article. I’ve gotta go with Tom from Spokane here. My 29er is geared WAY too high for long backcountry climbs. Some of the “trails” in the Cascade Range hold a 10-15% grade for 2000 feet of continuous elevation gain over just a couple of miles. Sometimes more. The problem with getting off a bike to walk it on those grades is that if the trail doesn’t let up, you’re not getting back on the bike until you get to the top. Maybe it would be easier if I lived in a part of the country where there are more trails with reasonable grades. I think if I were racing and able to stay in that kind of shape, I would think about this differently.

        • Tom From Spokane

          Here is my comment on riding speed up a mountain vs walking. I will preface it by saying, remember I am a fit 50 + year old that can out ride many younger riders, and ride in at least the top 1/3 (more like 1/4) of peers in my age group who also ride 3-4 times a week.

          When I ride up mountains, mile after mile of relentless climbing, I’m not sure, but I bet I’m not even doing 60 rpm when it gets real steep. On the steeps, I’m going only 3mph or less. Could someone walk (or run) faster? Well yes in some cases, but I guarantee you that everyone in my group is so tired by that point that few if any have the energy to walk up the same hill at that point in time any faster! There is one steep trail in particular where I occasionally encounter hikers. Once some runners did pass me (they were in great shape obviously – but I passed them as soon as the grade dropped to a more manageable 6-8% – where I no longer am in low granny) but I’ve yet to have a walker pass me.

          But this is the most interesting thing: I’ve found from experience that unless the trail is really technical, I use far less energy riding up a steep section than walking. So, no matter how tired I am, or how slow I go, my goal is to RIDE up the hill. And that is what my low gearing helps me with.

          I just can’t help believing that the masses of riders, no where near riding 3-4 days a week, and also riding hilly terrain would want these low gears too.

    • Dan Heiser

      Please let us know what 22 ring you purchased for your 3×10 XT crank (Manufacturer/model). I have delayed the build up of a new bike until we can solve the the low gearing problem for a 29er (for TransAlp ride).

        • Tom From Spokane

          I don’t see a comment here that I posted so here goes again: on my 3×10 XT crankset with a 24 low ring, I replace the 24 with a 22 tooth ring from a 3×9 crankset. Not sure if it was even an xt crankset or not. Does shimano ‘sanction’ it in their literature? NO But does it work? YES! I have this same setup on both my 29ers (tallboy carbon with 120mm front) and Trek HiFly with 100mm front fork and I guarantee it works.

          • Dan Heiser

            Tom, thank you for prompt response. I was worried the 9sp 22T would not work on a 10sp Triple and 10sp chain. I bought a Race Face 22T 10sp ring to try but wanted to get some sort of answer before I put it together.

            If you did not need to add or remove links in chain than no further response is requested. I will be using the XT long cage SGS rear derailer 24->22T/32/42T Xt Triple (180mm, I’m 6’5″) with 11-36 rear. If I need to lose higher gears to make this work, that is fine. Thx again…Dan, Santa Cruz

    • clepak

      After recently reading your comment, I could not agree more. I recently finally bought a new bike, a Scott genius 29″ wheel that came with a triple. 24t was my lowest in front with a 36t in back. I live in Boise, ID where we have endless climbs for 3000ft. I have been finding that I struggle on climbs I could previously spin up. After having several knee surgeries on each knee, I just don’t have the tolerance for the high compression forces in my knees that pushes high gears does to you. I am a physical therapist and know it is better to spin than grind with your knees. Hence, I recently ordered a 22t M770 Shimano XT. Hope this works!

      • I am not a real huge fan of 175 cranks. Especially for long drawn out climbs. Think steps, If you want to run up steps with a high cadence then you can take them 3 at a time. Plus your momentum will cover 1 1/2 of the 3 steps. but if you are walking then you can’t take steps 3 at a time and not expect your knees to blow out.
        Are crank arms any different? at 5’8″ it hurts to push a 175 slow or fast. plus I have no power out there regardless of gear ratio.

        • Theoretically, longer cranks should give you a bigger leverage arm to create more torque which we see more often in the dirt than on the road. That is typically why mountain bikes are speced with 175mm cranks, however we often go to shorter crank arms for people that have hip flexion limitations without any issues. You shouldn’t see any decrease in performance going to a shorter crank arm (you probably won’t see an increase in performance either), and if it makes you more comfortable on the bike than I don’t see any reason to not switch.

      • Tom From Spokane

        Just saw your comment in your email. FYI this may be helpful for you. ON my 29er I bought a 22/30/40 xt front crank and bought a 21 tooth custom front ring for my crank off EBAY (not sure if they are still there or now). It works great and now my lowest gear is 21 with 36 in back.
        I love it for spinning up long steep climbs. You may too.

        I’m also able to stay in the 30 middle ring up front for much more of my ride now.

  2. Jd

    Great conversation, especially considering that this is the 15th plus site/blog/forum I have read his morning. Actually, so surprised that I haven’t yet come across any statements aligned with my thoughts about gearing. I am quite fit and ride very fast for a 55 year old ( road, cross-country, and trail). I race my buddies often and “red line” rocky, steep, and 20 to 30 mile loops and out-n-backs, both ascents and descents. The issue (competition) is often not how fast a section is done, but whether or not you can actually ride it without putting your foot down, truly, no dabs and ” no touch” . Often, one of us looks at a side trail while zipping along at 20 mph and slams on the brakes while shouting, “meet me up there”. My Santa Cruz Superlight (26) enjoyed the 2.2 mph crawl, sure —slower than walking, but we are on a bike ride, and will only “hike a bike” after we crash multiple times. Apparently, my Superlight (22/32) has the same low end as my new stumpy 29er (22/36), but it doesn’t seem that way, so considering a lower gear on stumpy. I realize that the geometry of the 29er does not encourage a very up front of seat- upright riding style in order to keep wheels from spinning, so it is a disadvantage at less than 2 mph when climbing super steep rocky technical climbs when your buddies who have crashed are now hiking their bikes past you :). But cheering you on! Any ideas are welcome since my statement of a style of riding is not commonly referenced in the forums. Happy riding, and remember, ” no touch”! Cheers.

    • Absolutely, if your primary goal is to clear a section without putting a foot down than gearing will become a limiter. If we define performance as how fast can you get from point A to point B, than gearing typically isn’t a factor.

    • Tom From Spokane

      Yes this sounds exactly like the kind of riding me and my buddies do. Sometimes we are ‘crawling’ up the steep section, but the goal is to ride the whole thing and not walk! And those guys who don’t make it, fall off and stop walking, NEVER are walking fast enough to stay out of the way of the guys still riding!

      so much for walking faster than riding………

  3. jd

    Thanks C. Burnham. Do you agree with my statement (jd here again) of the 26er super light (22-32) and the new stumpjumper 29 (22-36) have equal low gears for 2.5 mph tech climbing / crawling speed? And, maybe the same of different question— at crawling speed, do these gears require the same amount of physical effort to perform equally? Because, if they are equal, I am trying to understand why the 29er seems to require more effort on a very steep half mile climb in first gear only (I seem to be able to spin the 26er with a slightly higher cadence which makes me a little faster and less fatigued when having to sprint upon reaching the plateau).

    Also, funny that in both pics at the front of this forum, both riders are standing (maybe sprinting up a steep smooth climb at about 6 – 10 mph to reach a summit). Or, is standing a technique to be considered at crawling speed? It seems to create easier tire spin for me when I try it (poor technique or my 6’2″ 215 lbs probably doesn’t help)

    Also, are my thoughts correct that the other disadvantage of the crawling speed of the 29er on super steep tech terrain is that the riding style using a rider’s perineum on the nose of the seat (which works great on the 26er) causes the rear tire to spin more easily on the 29er due to not having enough weight on the rear tire….. maybe due to the thought (or rumor) that you sit “on” a 26er and “in” a 29er??

    If I opt for lower gear on 29er, hearsay implies that I need to exchange the entire cluster, therefore sacrificing the high gear that lets me power by buddies when finishing the ride on undulating level terrain….. oh well, give and take – smiles

    Thanks, always trying to learn 🙂 cheers.

    • A 29 inch wheel in a 22 x 36 gear is 17.8 gear inches and a 26 inch wheel in a 22 x 32 is 15.9 gear inches, so the 26″ wheel is still 10% lower.

      I would disagree that a 29er has less traction for climbing on steep terrain. Fore-aft weight distribution is a function of bike fit on a mountain bike and overall contact points shouldn’t be different between a 26 to a 29 inch wheeled bike. Also, a 29er typically has more traction at the wheels due to the bigger diameter allowing more tire to make contact with the ground.

      Hope that helps and definitely let me know if you have any other questions!

      • Tom From Spokane

        I hate to be a dissenter, but are you sure those numbers are correct? Using this equation:

        (wheel diameter in inches) * (number of front ring teeth / number of back ring teeth)

        I get the following results:

        29er 22 x 36 = 17.72 (both My 29er’s have this)
        26in 22 x 32 = 17.88

        Which back to JD’s question would mean that yes, his two bikes are essentially equal gearing.

        I have this on my 26er:
        26in 22 x 34 = 16.82 ( My 26er has this)

        and when I am climbing a 10% grade or more, I can tell you for absolute certainty that I feel the difference between 17.72 and 16.82.

  4. Leonard

    I think, there’s something missed here. At which grade is the climb being performed and for how long? (5.9mph @ 90RPM)

    • The grade is somewhat irrelevant since we are talking about mechanical gear inches. But grade will change power outputs at given speeds, and the length of the climb will matter as to how it fits with in your own power/duration curve. Depending on your weight, 250 watts may be enough for you to go up a 7% grade at 5.9mph. If that is below threshold then you should be able to do a climb at that grade for over an hour. If your threshold 220 though, you may only be able to maintain it for a few minutes.

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