Components: Gears

Count the number of teeth on your smallest crankset chainring (the front set of gears on your bike). If it's more than 24, the online community says we may have a problem. Combined with the largest chainring on the cassette (the back set of gears), which results in your smallest gear possible, it's suggested we have a ratio of 24/25T (24 teeth on the front, 25 on the back). See Figures. This actually means that in this gear one complete revolution of the pedals does not even make a full rotation of the rear tyre. This would be stupidly slow. We're talking 3-4 mph. We may as well walk up the mountain.

Bear in mind that some of the people that go touring are in the 70 + age group and would be lucky to go 15 mph even if they were late for bingo. I hope we can do a little better than that. We better, because these are the gears I have:

Triple Crankset



10-Speed Cassette

Fortunately, as I have a beginner road bike, I have a triple crankset (3 chainrings). Most race bikes have either a compact or just 2 (the compact has a slightly lower gear ratio, or no. of teeth). My gear ratio of the crankset is 50/39/30T, with the 50 being the crainring the chain is actually on in the top figure. My cassette is 10-speed, meaning 10 gears; 12T through 25T (some teeth are left out). 

So after all that my lowest possible gear ratio is 30/25T. So what you say?

Well it means my minimum, or critical speed is not nearly as low. This is the speed you can barely stay up on your bike, often when climbing hills and your cadence or rpm drops to below 60. And we are going to be climbing some hills on the tour.

Thanks to Sheldon Brown, we can calculate my exact critical speed, and produce a printout:



Yellow boxes are gear size in teeth (Cassette as a column, Crankset as a row). White boxes are speeds in mph, assuming 60 rpm.

So the slowest speed for me is 5.8 mph (in my smallest 30/25T gear). Problem? That's what I've got to decide. I went up Lemmon around 9-10 mph, and that's between 5-7% grade. One climb on the proposed route is steeper than that (9%), and with the additional weight, I'm not sure how fast I'll be able to go. That particular climb is short though. The issue increases with the nicer race bikes (where a 39T crankset chainring is often the lowest). This would put critical speed at a decent pace of 7.5 mph. There may be sometimes where walking is the only option...

So do people think this is an issue, or is it a case of HTFU (Harden the F up)? A simple swap-out of the bottom chainring to a 24T or less can be done for $10 and around 10 minutes of labour. It's really easy work to perform, and might make the difference. Alternatively if you're looking for a commuter-style road bike for this tour, then check the gear ratios! It's geeky, but it's worth it.

Normally this wouldn't be an issue. I can climb a hill at more than 6 mph thank you very much. It's just with this extra ~40 lbs that we'll be likely carrying. Thoughts anyone?