Tom's Road Gears for 8-speed Doubles

Road Gears for 8/9-speed
This listing is gear-inches based on 26.4 inch wheel diameter (2107mm rollout)
Formula: Gear-Inches = (Front Teeth x 26.4") / (Freewheel Teeth)

Summer Strength
freewheel	40	53
11	*	127
12	88	117
14	75.4	100
15	70.4	93.3
16	66	87.5
17	62.1	82.3
19	55.6	73.6
21	50.3	66.6
23	45.9	60.8
25	42.2	*

Touring Double
freewheel	39	52
11	*	125
12	86	114
14	73.5	98.1
15	68.6	91.5
16	64.4	85.8
18	57.2	76.3
21	49.0	65.4
24	42.9	57.2
28	36.8	49.0
32	32.2	*

Of course everyone's legs are different, the idea is leaving out the 13 for an 11-23 cluster to give as many of the right gears as possible with the total range desired for typical road work (for an 8-speed). Going to a 25 is easy, drop the 16, or the reverse, drop the 23 and fill the 13 for flatter terrain (Seattle has lots of steep climbs). The 53-11 is good for dropping off the mountain passes, and the 23/25 for the walls around town, Dravus West up to Magnolia being a classic.

Knowing the exact rollout for your gear mechanical advantage is actually quite important, but hard to find without a heart-rate monitor and a track. A two gear-inch difference in your main "flat" gear can feel like one gear is too big and the other too small.

I can't live without something near 54 gear-inches, or a 2:1 mechanical advantage; the rythmn of it climbing is noticeable to me, so I must have one. These special gear numbers include something around 88 gear-inches for my flat gear for spinning at speed; for time-trials I use whatever can squeeze over 28mph going out, usually around 106 gear-inches (better have that 13). To really learn gears, my own opinion is that track riding is the best way, it's also a blast and definitely a little scary at first.

If all this is new to you and you would like to learn more about gearing, the first thing to do is count the number of teeth on every cog. Then measure the rollout of your wheel by marking a spot with the valve stem on the pavement, roll a straight line for 2-3 revolutions with your weight on the bike. Divide the result by the number of revolutions to get the circumference of the wheel. If you measure in metric units, convert to gear-inches by dividing by pi(3.14156) and by 2.54. If you measured in inches, just divide by pi.

You will probably have mainly repeated gears from most "standard" freewheel/chainring combos. The 52/42 especially has few distinct gears, but it is used because about ten teeth is right to go from standing to sitting or the reverse. So, the gears weren't chosen for variety in front, but for racing convenience to not have to double shift very often. With our fancy shifters now, you can forget that problem. So having more distinct gears is more of an advantage, when you learn them, you can apply the right gear to the situation more often. This means you get more speed/distance for the same heart-rate (effort).

There are many good books on gearing, for every tour it seems I've made a new chart and used different gearing. From all that, and track riding, you learn what the numbers mean. I prefer cross-over gearing. This means you ride in the little ring until you're on the truly level or downhill. Less double shifting, therefore lazier. Yes.