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I am now in training for cycling. Long time didn't got into bike. I am using a 21 gear mountain bike with highest gear, and around 70 - 80rpm. What's surprise me is my average speed only 12km/h(recorded from strava) and 14km/h(recorded from mapmyride).

I was wondering whether i am using the wrong gear? I thought that the higher with the same rpm will move faster than a lower gear with same rpm.

12km/h is much slower than my expectation. I expect 70rpm would be 20km/h or more.

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  • It is slow, but everyone moves at their own pace. Select your gear based on the effort required to maintain a decent cadence (70-80 is good). If you feel you can put out more effort (over the distance you're doing) then use a higher gear. (Your highest gear would be the largest front sprocket and the smallest rear sprocket.) If the highest gear is not satisfactory, you can probably get the rear cluster changed for one with smaller cogs. – Daniel R Hicks May 2 '15 at 12:02
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    Plugging typical tooth counts for entry-level hard tail mtbs into sheldonbrown.com/gears I doubt the gears themselves are the problem if you're really doing 70+ rpm (I'm assuming 28-38-48 chain rings, the smallest sprocket might be 12 to 15 teeth) – Chris H May 2 '15 at 12:34
  • @DanielRHicks i tested all the gear and pretty sure that left 3 right 7 is the hardest to pedal. Yup. I am able to maintain 70-80 rpm per hour for more than an hour but what i am uncertain that it is 12km/h a normal speed for full 21 gear for 70-80 rpm. Wondering if that is my cycling problem, or is it a problem with the bike or the app i use – vincentsty May 2 '15 at 12:37
  • Get a stopwatch and measure yourself riding a mile or something, without traffic lights and stop signs. Then, calculate it out by hand if you think its the gps. But I doubt it is, and your cadence is lower than you think it is. – Batman May 2 '15 at 12:38
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    @vincentsty strava and mapmyride will be using the same underlying gps data, so you can't dismiss that. Both will cheat you (possibly by different amounts) in tight turns, so try a straight line with a clear view of the sky (then it's easy to grab the distance of google or a map and time with a stopwatch). All that said though, I doubt the GPS is making that much difference. – Chris H May 2 '15 at 13:01
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You can calculate your speed vs cadence using this online calculator. You want your cadence to be roughly 80 rpm (60 being the lower bound).

With a 42t chainring and 14t cog in the back (not uncommon for a 26" mtb -- this is big ring in front, small in back), you should be doing around 31 kph at 80 RPM, so chances are you're either spinning too fast in a too low gear or spinning too slow in a too high gear.

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You say the highest gear on a 21 speed mtb bike. This would be the largest chain-wheel & the smallest cog. The largest chain-wheel is most likely a 48t. The smallest cog could be in the range of 11t to 14t. Let's say it's a 14t. At 70-80 rpm with a 48t x 14t, your speed would be somewhere around 30kph to 34kph. (any cog smaller than 14t would produce and even faster speed) If you are truly turning 70-80 rpms (how are you checking this?) and if your speed is only 12 to 14kph then you are not in the highest gear. Shift to the highest gear. Now LOOK at the position of the chain. Is the chain on the outside/largest chain-ring and the smallest rear cog?

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  • I think this would be the case. Either they aren't actually in the highest gear, or they aren't measuring cadence properly. Even if you had a very small highest gear like 30-14, you'd still be getting 24 km/h at 80 rpm. – Kibbee May 4 '15 at 12:36

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