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Cycling and Gears – Everything the Noob Needs to Know about Road and Mountain Bike Gearing

The inspiration for this post was a mountain bike ride that I took on Wednesday.  A little more than 17 miles on Wednesday, on dirt roads.  I have a nice mountain bike but it’s not like my road bike.  It’s a heavy, hulk of a thing and it’s an 8 speed drivetrain rather than the 10 speed on my road bike.  Shifting, of course, is just as easy on either bike.  For the road bike, a flick of the wrist against the brake lever (or middle a finger for a harder gear) and I’m in a new gear.  A flick of my thumb on the mountain bike (I have the under/under shifters rather than the older over/under shifters).


The 20 speed Double Road Bike or the 24 speed Triple Mountain bike?

Where this gets interesting is the 8 and 10 speed drivetrain and how the number of gears help (or hurt) speed.  For we older folk, who grew up with ten speeds, where the total number of gears were ten, or maybe fifteen if you had a triple crank up front, you might think the 24 gears of an 8 speed triple on the mountain bike would trump the 20 of the 10 speed double on the road bike, for building and maintaining speed – and you would be wrong.  Never mind the differences between the two bikes that make the road bike vastly faster anyway.  Even if we were to take into account that the mountain bike is 5 mph slower, on average, there is a huge problem built into the 8 speed transmission of the mountain bike that makes maintaining speed miserable and that makes those 10 and now 11 speed cassettes awesome.

My Rockhopper has an 11 tooth to 34 tooth 8 speed cassette (the size of the gear is measured in the number of teeth)  That means you’ve got 8 gears to span a difference of 23 teeth.  On my Venge I’ve got an 11t to 27t (it came with a 28 originally)…  So I’ve got ten gears to span a difference of just 16 teeth…  Do the math, and the average jump from gear to gear on the mountain bike is just shy of 3 teeth.  On the road bike it’s only 1.6

Here’s the gears on the 8 sp.:  11,13,15,18,21,24,28,34
And on the 10 sp.:  11,12,13,15,17,19,21,23,25,27

Down at the small end of the cassette, there is a difference of two teeth for the first three gears on the 8 speed, while the first three gears on the 10 speed road cassette only go up by one…  After that, there’s a difference of three teeth for the next three, four on the fourth and six on the fifth to get you to 34.  On the road cassette, it’s a jump of two all the way till the largest cog.  11 speed cassettes are even better, giving the cyclist an extra gear at the hard end with a difference of only one tooth.  Why is this important?  First, the gears are closer the smaller they get because the smaller cogs are harder to pedal.  As you get easier, the jump gets bigger, especially on the mountain bikes.  Got that?

Okay.  Maintaining speed on the road (dirt or paved) is all about maintaining a cadence.  With a jump of three teeth or more into a harder gear (smaller), there’s a huge leap in the power required to maintain speed.  This doesn’t matter so much on a slower single-track, where there are often intense changes in elevation so you rarely have long stretches where you’re pounding down the trail, trying to pick the perfect gear.  You’re often up and back down the cassette in the space of a few hundred yards.  Conversely, on the road, hills are usually less sharp and the bikes are much lighter so you don’t need quite the range on the cassette and with the extra two gears and only a two teeth jump, it’s a lot easier to pick a gear to match a desired speed and cadence.  In short, the closer you can get the gears (especially as they get smaller on the cassette), the easier it is to find a desirable gear to match your cadence and the amount of force you can put on the pedals.

Now, with that out of the way, I wanted to get into a little bit about how to use the gears.  We have 20 to 33 gears on a bike for a reason – to use them.  They’re not there to look cool (in fact, some would argue that having more than 22 is useless my Trek is a triple and I do love it down south in the mountains).  Most people, if you really pay attention, don’t shift near enough.  I use every gear on my 10 speed cassette (except the 27 tooth cog to prevent cross-chaining) and it has been successfully argued that we don’t even have hills on that 3o mile route.  We do, of course.  They’re just not all that big.  In any event, it’s a rare day that I’ll ever use the baby chain ring, but I do use all of the gears on the cassette, multiple times.  I shift constantly as the elevation changes…  As soon as my cadence starts to slow or when it gets harder to maintain, I shift.  There are times when it makes sense to try to muscle through a gear (if my breathing is too fast or heart rate is too high, for example or if the top of the hill is within a few dozen meters) but they are few and far between.  It’s almost always better to shift and maintain a high cadence while maintaining the speed to keep up.

We can use weight lifting as the example here.  Most people, especially men though, if you put a five-pound weight in their hand, will be able to do curls all day long.  Up that to 30 pounds and you won’t be able to do as many reps.  Well, pedaling in a hard gear works on the same principle.

As President Clinton used to say:  Shift early and shift often.  Err, wait…