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Chainring Logic?(11 posts)

Chainring Logic?Hap
Mar 19, 2001 5:59 AM
Not to long ago the standard set-up for road bikes was a 52t/42t chainring configuration. Now the standard seems to be 53t/39t. What was the logic behind this change?

Thanks, Hap.
Gear Inchesgrz mnky
Mar 19, 2001 1:23 PM
Well, if you sit down and do the math you'll see that when we were limited to 5 and 6 cog freewheels the 52/42 chanrings worked out to reasonable steps between gears. Now with 8, 9, and 10 cog cassettes you're left with a lot of redundancy in terms of overlap between gears. Going to a 39 up front gives you a wider range yet still maintains reasonable jumps. BTW the 42 is still used on the middle CR for Shimano road tripples. Some road racers will actually run a 42 with a "straight block" cogset, depending on the terrain.

Gear Inches = front # teeth/rear # of teeth x 27"

Work this out for each combo and then compare the deltas. There is a book currently available on bicycle gearing that goes in depth on the subject.
Doing the mathErik W
Mar 19, 2001 4:41 PM
As I'm deciding on what components to put on my new bike I'm enjoying playing with the "gear inches" formula. I'm not sure if I'm going to get a double or triple crankset so I've figured out what the comperable gearing is on my MTB of say a 39 or 30 tooth ring and a 23, 25, 27 or 29 tooth cog on a Road bike. I've then ridden in the hills. I do realize it's a bit different on fat tires but it gives me a general idea of the gearing I can comfortably ride. I live in Boulder CO so their are some pretty steep roads west of here. A couple ideas I've had are a triple with 52/42/30 crank and 12/25 cassette or a 53/39 crank with a 13/29 cassette (Campy only). I'm not sure if the 53 and 13 combination isn't too small for the biggest gear though.
Doing the mathgrz mnky
Mar 20, 2001 8:11 AM
A 13 tooth does top out kind of quickly when you've got big hills to fly down. I sometimes would use an 11-28 with my 39/53, but this is a Shimano XT MTB cassette only available in 8 sp. since Campy doesn't do MTB this option isn't available to you. Currently I run a 9 sp. 12-27 for hill climbing - we also have lots of steep hills out here in the SF Bay Area.

Be careful when comparing MTB gearing to road bike since the effective wheel diameters are usually different. A 26" wheel with 2.1" tires comes close to the diameter of a 700C w/23 mm tires, but it's not quite the same. Slicks vs. knobbies changes everything. It would be worth your while to be a bit more careful with the gear inches formula and use the correct diameters.
Good pointErik W
Mar 20, 2001 2:00 PM
Yeah, I wasn't sure how accurate figuring out what would be similar gearing on an MTB would be. I realize the tire size/drag and other factors change things but who knows for sure how much.
Boulder, COTJeanloz
Mar 20, 2001 9:01 AM
I too live in Boulder, and assuming you're pretty fit, a triple shouldn't really be necessary. There are really only 3 steep hills; Old Stage, Lee Hill, Magnolia, the very tippity top of Left Hand Canyon (@ Ward)- I'm not sure if it's that steep, but it feels like it after climbing for 15 miles. Most of our climbs are long grinds that can easily be done in a 39/23. Granted, Magnolia is worthy of a triple unless you want to put out a lot of effort. What it really comes down to is how fit you are, and how easy you want to ride the hills. And the question remains, with a low enough gear, are hills the challenge that they might otherwise be?
Boulder, COgrz mnky
Mar 20, 2001 9:36 AM
Yeah, it all comes down to what your idea of fun is and how you define pain. Some people ride tripples and don't need to and others don't, but should. If you're "calorically challenged" then you might need the tripple in the beginning, but not later. "Spiiners" and "mashers" have different needs.

The important thing is that you get out, ride, and enjoy yourself.
Boulder, COErik W
Mar 20, 2001 2:37 PM
Thanks for the input. It's good hearing from someone who knows the area. I'm new to long rides on the road. I'm not sure what my fitness/endurance level is for the sport. My rides (on my MTB until I get a road bike) have been getting longer and steeper. In general I'm fit. I hike a couple of times a week, do some mountaineering, snowshoe and backpack, when it's the season. My friends seem evenly split on whether to have a double or triple. Some have a triple and say they would never have anything else, the others have a double and love it. One friend has a triple but wishes he'd gotten a double instead. I guess, like you said, it depends on how fit you are and how much of a challenge you want. I'm leaning towards a double. I just don't want to get in a situaion where that's not enough. But I'd rather raise my fitness level then cater to a lower fitness level.
Boulder, COdoug in co
Mar 22, 2001 9:42 AM
glad to hear Old Stage qualifies as a steep hill.. I've done it in a race with 38x21, wasn't pretty but got up it eventually. Haven't found anything I couldn't climb with this gearing in/around Denver, and I'm not any kind of fast/experienced cyclist. Having said that, admittedly I'm getting a 13-26 for my first century, but will probably go back to the 13-21 for any shorter races.
Cassette sizeErik W
Mar 22, 2001 2:50 PM
I've been thinking of getting a 13/26 or 13/29 cassette. You said you run a 13/23 usually? Do you feel you have a big enough gear with the (I assume) 53-13 combo? Thanks.
I don't know why they changed ...bianchi boy
Mar 19, 2001 7:11 PM
But I can't push a 53 x 12, 13 or 14 unless I'm going down a long or steep hill. I'm thinking about changing my big chainring to a 50 for that reason. On my old bike with a 52, I used my big chainring a lot more. I do like the 39 small ring, though. I guess this shows how strong my legs are.