# Bicycle Mechanics - Gearing Decision - Need Advice

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View Full Version : Gearing Decision - Need Advice

Beck
09-15-09, 08:24 PM
I'm converting to 10 speed and trying to decide what cassette to use. I'm working with Shimano 105 components and would like to use a compact crankset (50/34). I live in a relatively flat area, with the occasional long, moderate hill.

Warning: here comes the math...
I've done the number crunching on the gears based on my comfortable cadence. I spin between 94 - 112 rpm which are typically my comfortable shift points (i.e. once my cadence drops below 94 I look for the next lowest gear, etc.). With an 11-23 cassette and 50/34 crank, my lowest possible speed at 92 rpm is 10.8 mph. Is that low enough? I'd hate to get towards the end of a century on a long hill and have to mash the pedals at 70 rpm. Due to the cost of 10 speed cassettes, I'd like to get one that works for everything. Should I get a cassette with a 25T gear?

Thoughts?

FYI, I use this calculator http://www.panix.com/~jbarrm/cycal/cycal.30f.html plus my own program.

joejack951
09-15-09, 08:36 PM
You are the only one who can decide the answer to whether 10.8mph is low enough. I'm assuming you are already cycling in the area you plan to ride. Do you ever dip below 11mph on your current routes? Do you have plans to ride in more hilly areas? Personally, I find the jumps between gears on a 12-27 cassette close enough that I don't see why you'd bother with a more narrow range cassette. Might as well carry some extra gearing if there is basically no penalty.

AEO
09-15-09, 08:46 PM
what are you using now and has it worked for you on the steepest hill you could find?

I use a 11-25 and 12-27 with 34/50 and this gets me up short 19% grades.
I wouldn't be able to do it for hours, but I'm not you, and you're not me.

Beck
09-16-09, 09:10 AM
Right now I'm on a 50/39, 12-21 7 speed and I can just about get up the steepest hill I normally ride at an acceptable cadence. I'm just not sure if I want a lower fall-back gear incase I find myself a steeper, longer hill one day. I used to have an 11-28 7 speed on this bike and never needed the 28 and only rarely the 24. I think I'll put that one back on my 7 speed for centuries...

Homebrew01
09-16-09, 10:30 AM
Right now I'm on a 50/39, 12-21 7 speed and I can just about get up the steepest hill I normally ride at an acceptable cadence. I'm just not sure if I want a lower fall-back gear incase I find myself a steeper, longer hill one day. I used to have an 11-28 7 speed on this bike and never needed the 28 and only rarely the 24. I think I'll put that one back on my 7 speed for centuries...

If you're going to a 34, then you only need an 18 in back to replicate your current 39-21. So get an 11-21 and you'll be fine.