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Lowering Your Gearing

By Jim Langley 

Road bike rider logoThis time of year, depending on your location, you’re either preparing for the big spring and summer events to come, or already rolling up the miles. Either way, one of the most important things is having easy-enough gearing on your road bike for the shape you’re in and the terrain you ride.

Figuring out what’s right

You probably already know if your gearing is low enough for where you ride because if it isn’t, you likely have trouble on the tougher climbs. Maybe you have to stand and muscle your way over the top, or push so hard your knees hurt. Or maybe on the steeps you have to zig zag across the road. Those are all signs that you’d avoid injury, be more efficient and even enjoy riding more if you lowered your gearing.

Another reason to go lower is to be ready for a big ride, like a mountainous century. Don’t be like me, and assume that because you can make it up even your steepest local climbs on an 11-21 cassette that it’ll work for a true alpine event like the Fresno Cycling Club’s Climb to Kaiser. Oh, I covered the155 miles and crawled over the 13,000-plus vertical feet that come in the first 65 or so miles. But it about put me in the hospital.

In comparison, my RBR teammate Scott Martin almost made last summer’s 2-day Everest Challenge, with its 29,035 feet of climbing, look easy.

The difference was that before Everest, Scott had me significantly lower his gearing. This let him spin up the climbs, while I essentially leg-pressed my way up Kaiser’s steeps burning up my reserves and bonking badly.

Tip: Maybe it’s obvious, but since I made this mistake, you might too. Don’t let your fitness and confidence (or maybe it’s hubris?) trick you into riding gearing that’s too hard for a tough climbing ride. If the event flier doesn’t have recommended gearing, consider calling the organizer, or Google the name of the event plus “ride report” to find an online account with gearing tips.

Doing the math

When considering gearing changes it’s helpful to understand how much you gain with the different options. To do this you need to know a number called “gear inches.” To find it, count the number of teeth on the smallest chainring (on the crankset) and on the largest cassette cog (on the rear wheel) and use this formula: chainring/cog x 27 = X (where X is your gear inches).

For example, for a 34-tooth smallest chainring and a 25-tooth largest cassette cog: 34/25 x 27 = 36.72 gear inches. Once you have that number, you know what your lowest gear is, and can compare it with the gearing changes you’re planning.

In Scott’s case, he read up on the Everest climbs and learned his 34/25 low gear wasn’t going to cut it. So, I put on a cassette with a 32-tooth cog, dropping his low to 28.68 gear inches (keep reading).

Tip: To make calculating your gearing easy, I have a simple Excel gearing chart with instructions on my website:  Feel free to download it and use it.

Before I get into the options for lowering your gearing, note that I’m not covering triple-chainring cranksets here because I’m assuming you prefer the lighter, less complicated-shifting double. If you already have a triple, you know how nicely they flatten the ups.

Option 1: Get a larger cassette

In most cases, the least expensive way to lower your gearing is going to a larger cassette. It’s cheapest because you usually don’t need a longer chain. You can just swap out the cassette and be good to go. For perfect shifting it’s best to go with the same brand you have, but it’s fine to get a less expensive model if you want.

For 10-speed cassettes, you can go as low as 28 teeth. For 11, a cassette with a 29 is available. Going from a 34/25 or 39/25 lowest gear to a 28 makes a 4-gear-inch difference, which may not seem like much, but it’s significant and can save you over a long day of climbs.

Tip: Someone may tell you that if you get a new cassette you need to buy a new chain. This is only true if your chain is worn out, so make sure you check it before replacing it.

Option 2: Get a compact crank

If you have a 39/53 (standard) crankset, a nice way to lower your gearing is to replace it with a compact 34/50 (compact) crankset. If you have a 25 on your cassette, the 34-tooth chainring drops your lowest gear almost 6 gear inches. And, if you need lower, you can still go to a larger cassette. Compact cranksets have come down in price, yet it’ll still cost more than a new cassette.

Tip: With a few basic bike tools it’s easy to swap cassettes and cranksets. So if you only do one or two epic rides a year, you might want to get a compact crankset and climbing cassette and just install them when needed.

Option 3: Go super low with mountain-bike equipment

This is what I did for Scott’s bike. He had a compact crankset but changing to a 28-tooth cassette didn’t get him a low-enough low. So, I installed a mountain-bike cassette with a 32-tooth large cog.

A cog that large exceeds the capacity of a standard road derailleur, so I had to change Scott’s to a mountain-bike derailleur. And, the larger cog and longer-cage rear derailleur meant installing a new, longer chain too. But the new super low made all the difference.

Tip:For Scott’s bike I replaced his 10-speed cassette and rear derailleur with the 9-speed cassette and derailleur off his mountain bike, and they worked fine with his 10-speed Shimano Dura-Ace STI shifters (not perfect, but good enough). But, now that Shimano and SRAM are offering 10-speed mountain-bike cassettes with giant 34 and even 36-tooth cogs it should be easier to make this type of conversion.

Jim Langley has been a pro mechanic and cycling writer for 38 years. At RBR he’s the author of Your Home Bicycle Workshop and moderator of the technical forums on the Premium Site . Check his “cycling aficionado” website at http://www.jimlangley.net , his Q&A blog and updates at Twitter.


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