Steve’s Bike Tech: Gearing Options

By Steve Bowen

Most LA Wheelman riders have either a road bike (drop handlebars) or a hybrid bike (geometry like a non-suspension mountain bike with straight handlebars.)  Let’s break it down by each type so we can examine the various common gearing concerns and complaints for each type, and options for each.

Hybrid bikes

The biggest complaint heard from hybrid bike riders who do longer rides is that they don’t have high enough gears for long, straight sections of road, gradual downhills or riding with a good tailwind. This forces the rider to pedal at an uncomfortably high cadence to keep up on these types of terrain.

Almost all hybrid bikes have three chainrings on the front crank, where the pedals attach to the bike. The typical size of the three chainrings is 44, 34 and 24 teeth. The largest available big chainring on a typical 4-arm crankset found on a hybrid bike is 48 teeth. Compare that to a typical road bike big chainring with 52 or 53 teeth, and you can see how it is hard for a hybrid bike to keep up with a road bike on a long ride. As mentioned above, for the typical 4-arm crankset found on most hybrid bikes, 48 teeth is the largest chainring that will fit. Another option is to replace the complete crankset. You can get one where the teeth sizes are 48-38-28, and for many people this will be enough of an improvement. In that case, you probably won’t have to replace any other components.

Another option is to replace the front crankset with a road triple; these typically have 5 arms for added strength with the larger big ring. These come in configurations of 52-42-30 teeth, 53-39-30 teeth, 52-39-30 teeth, or 50-39-30 teeth. If you change to a road crankset on a hybrid bike, you will most likely have to replace the front derailleur and possibly the bottom bracket also. If the 30 tooth small ring is too big for long climbs, you can replace it with a 28 tooth one.

Use caution when replacing a hybrid crankset with a road one – most hybrids have 24- or 27-speed drive trains with 8 or 9 cogs in the back. Almost all the newer road cranksets are made for a 10-speed rear cluster, which uses a narrower chain. You can run a 9-speed rear cluster and chain with most 10 speed cranksets, but the chain will be a little noisy.

Road bikes

The biggest complaint from road bike riders is that they don’t have low enough gears for long rides with lots of climbing, or very steep hills. Older road bikes often have 2 front chainrings, with 52 and 42 teeth. Combined with a 7 or 8 speed rear where the largest rear cog is often no bigger than 25 or 26 teeth, this is simply too high a gear to comfortably ride long or hilly courses.

Newer road bikes, starting from about 12 to 15 years ago, have front chainrings of 53 and 39 teeth. 39 by 25 or 26 is an acceptably low gear for a lot of riding, but it really is more efficient and less tiring to use lower gears than that. For road bikes with 9 or 10 rear cogs, you can get a cassette with a 27 tooth large cog, and the gear ratio at 39 front and 27 rear is pretty low. I’ve gotten up the steep section of Potrero several times with this gearing, although I now prefer a slightly lower gear than that.

Road triple front cranksets are an option found on many bikes, with the teeth sizes mentioned in the paragraph about putting a road crank on a hybrid bike. However, if your bike is currently set up for a front double, you will have to change a lot of parts to get a triple: crankset, bottom bracket, left shifter, front and rear derailleur – too expensive to make sense for most people with older bikes. A newer, and better option if you already have a double chainring crankset, is to replace it with a compact double. This will have a big ring of 50 and a small ring of 34. With a 12-27 cassette, you will have the gears you need for the majority of rides, with less weight, less chain wear and fewer derailleur adjustments.

Carrying heavy gear

If you are touring, or carrying a lot of gear on your road bike, the above options will probably still not give you low enough gears for every situation. In this case, it gets a bit more complicated. First, you are going to need a triple crankset, so it’s better to start with a bike that already has one. Then, you are going to need mountain bike gearing in either the front or rear of the bike. For a road bike with an 8 or 9 speed rear, the easiest solution is to replace the rear derailleur with a mountain bike one – it will have a longer cage than a road derailleur. Then you can put on a mountain bike cassette with a 11-32 or 11-34 gear spread. The shifters, crankset, front derailleur, and bottom bracket do not need to be changed.

If you have a newer bike with a 10 speed rear, it gets more complicated still because Shimano doesn’t make 10 speed mountain bike cassettes. However, you can get an aftermarket 10 speed Shimano compatible cassette that will give you a 12-34 gear range in the back. Then you can put on a mountain bike rear derailleur as before; even though mountain bikes top out at 9 speeds, an XT or XTR rear derailleur will shift 10 speeds just fine (the indexing, clicking precisely from one gear to the next, is built into the shifters, not the rear derailleur.)

If you want to stick to Shimano, get an LX front crankset with 48-36-26 rings. These are a little hard to find, but they are available. Then you can probably get away without changing any other components, although the front chainrings might shift a little more smoothly with mountain bike front derailleur. However, unless you have long chainstays that allow an inch or more between the rear tire and the seat tube, you may not have enough clearance for a mountain bike rear derailleur.

Confused? Well, you can always get a single-speed bike and forget about all the gearing complications...