Traditionally bike gears have been expressed in Gear Inches.

‘Gear inches’ is actually the diameter in inches of the drive wheel of an Ordinary Bicycle (penny-farthing) with equivalent gearing. Although this is a rather old fashioned way of looking at gears, it makes it very easy to see the relative gears from different set-ups. Road bikes run on 700c wheels, by the time there is a tyre this is as near 27” as makes no difference, so a 27” bottom gear is like having a 27” front wheel  on the Ordinary Bike (More Penny Penny) – very low in deed.

Gear Tables allow you to see the gears you get from different cassette and chainring combinations.

The tables below show the current 11 speed Shimano cassettes and compact and semi compact chain sets. Campagnolo cassettes are different. Other chain sets are available.

If you want a copy of the Gear Table so you can change the sprockets and chain ring sizes to get the gear combination you want, e-mail membersfirst@hafren.cc

What the gear table shows is that the move to Semi Compact (52/36) effectively replaces a low gear with a high gear and spreads the middle of the cassette (where most of us ride) out a little.

If you pedal a 123” gear (that’s the top gear that comes with a standard Shimano Compact setup) at 100 RPM (Cadence) the resulting road speed is 35 mph. Of course if you can pedal at a high cadence of 130 the speed rises to 46 mph. See the speed table at the bottom of this page.

Strong legs or flat roads or both to be able to push the 128 inch gear at that cadence. On a decent a good descending position will probably be faster as over 30mph the additional aero drag created by pedalling takes some over coming.

You can also see from this why TT bikes often come with even larger chain rings, 54 or 56 not being uncommon.

You see a lot of 11-32 cassettes at sportives, giving a 29” (almost 1:1) bottom gear.

What gears have I got?

The sprockets will be stamped, you might need to remove the wheel and clean. You only need the biggest and smallest – Shimano doesn’t do a lot of variations. If you can’t read the stamp just count the smallest and largest Sprockets. Much easier with the wheel off.

Compact
Chain rings	50	34		Chain rings	50	34		Chain rings	50	34		Chain rings	50	34
11-23 Cassette	Resulting Gears			11-25 Cassette	Resulting Gears			11-28 Cassette	Resulting Gears			11-32 Cassette	Resulting Gears
11	123	83		11	123	83		11	123	83		11	123	83
12	113	77		12	113	77		12	113	77		12	113	77
13	104	71		13	104	71		13	104	71		13	104	71
14	96	66		14	96	66		14	96	66		14	96	66
15	90	61		15	90	61		15	90	61		16	84	57
16	84	57		16	84	57		17	79	54		18	75	51
17	79	54		17	79	54		19	71	48		20	68	46
18	75	51		19	71	48		21	64	44		22	61	42
19	71	48		21	64	44		23	59	40		25	54	37
21	64	44		23	59	40		25	54	37		28	48	33
23	59	40		25	54	37		28	48	33		32	42	29
Semi Compact
Chain rings	52	36		Chain rings	52	36		Chain rings	52	36		Chain rings	52	36
11-23 Cassette	Resulting Gears			11-25 Cassette	Resulting Gears			11-28 Cassette	Resulting Gears			11-32 Cassette	Resulting Gears
11	128	88		11	128	88		11	128	88		11	128	88
12	117	81		12	117	81		12	117	81		12	117	81
13	108	75		13	108	75		13	108	75		13	108	75
14	100	69		14	100	69		14	100	69		14	100	69
15	94	65		15	94	65		15	94	65		16	88	61
16	88	61		16	88	61		17	83	57		18	78	54
17	83	57		17	83	57		19	74	51		20	70	49
18	78	54		19	74	51		21	67	46		22	64	44
19	74	51		21	67	46		23	61	42		25	56	39
21	67	46		23	61	42		25	56	39		28	50	35
23	61	42		25	56	39		28	50	35		32	44	30