Road gearing

24/09/22 15:19 Filed in: Gear

If you begin looking at road bike gearing in the 1960s, everyone had a 144 mm spider that would accept a 42T small ring. Not surprisingly, that happened to be the standard at the time. By the late 1980s the spider has shrunken to 130 mm (135 mm for Campagnolo), with a small chainring standard of 39T (the 130 mm will accept a 38, just as the 144 mm will accept a 41 - but neither was common).
Both of these small ring sizes were usually accompanied by a 53T big ring.
By the mid-1990s, the triple chainring option (which was usually 74 mm for the granny and 110 mm for the two outer rings) was losing favour to the better shifting "compact" crank option of two rings on a 110 mm spider. Standard rings for the compact are 34T for the inner ring and 50T for the outer ring. I remember when this 16T jump taxed the ability of front derailleurs, but they have improved considerably since then.

Over the same period of time, the set of sprockets on the hub have added more choices and a bigger range. In the early 1980s most bikes had 5 sprockets on the freewheel. By the early 1990s the sprockets were now a cassette (the freewheel mechanism became part of the hub) with 7 gear choices. My 1992 road bike had the brand-new 8-spd gearing from Shimano.
Serious riders would pick their 5 options from a larger range to suit the course they were riding. A 12-16 had five one-tooth jumps for flat courses. A 12-24 had huge jumps between gears, but provided a more hill-friendly option. With 8 choices, there was far less need to swap cassettes between rides. A 12-24 with 8 sprockets has comfortably small jumps so it is suitable for both flat and hilly rides.
The low gear on that 8-spd road bike was 2:1 (42/21), a relatively high gear choice. I attended a road race in Buderim Queensland in approximately 2000. I was still on 8-spd and I brought my 12-23 cassette with me just in case the course was hilly. It was actually pretty flat except for one climb which was incredibly steep. I could barely make it up there in a 42/23! Someone from Canberra leant me their lower geared 8-spd cassette and I removed my 16T and added in the largest sprocket from their cassette just in case the state of wear was different between my chain and their cassette. I didn't want the chain to skip and I didn't have time for testing. I got terrible shifts across the gap where the 16 was meant to be and then into and out of low gear, but I managed to get over the climb multiple times in a many lap race.
This trend continued until now, all high-end road bikes have 12 sprockets on the hub. My current race bike still has a 39/53 up front, but now it has a 11-29 range at the rear. My commuting bike runs a compact up front (34/50) with the same 11-29 at the rear.
I read somewhere that most pros choose to ride most races solely in the big ring, using the wide range of modern cassettes to avoid the use of the front derailleur as much as possible. I note that the lowest gear in my big ring (53/29) is considerably lower than the lowest possible gear on my old 8-spd bike (42/21). In fact, almost 10% shorter gearing. That is why I can ride a lot of places around Canberra only in the big ring if my fitness is OK and I am going swiftly.
The lowest gear on my commuting bike is a whopping 71% lower than my old 8-spd road bike. But! The top gear is also 3% larger.

The trend has been towards smaller chainrings and more range in the sprockets (smaller = higher high gears and larger = lower low gears). Where 8-spd sprockets started at 12T (and freewheels could go down to 13T, but usually started at 14T), now all 12-spd cassettes start at 11T, except SRAM (which uses a different style of freehub) which uses a 10T high gear.
The only drawbacks to smaller sprockets are higher wear due to the fewer teeth to share the chain load and chordal action, which happens noticeably with bike chain on sprockets 14T and smaller - this phenomenon is of low importance on a bike but not of no importance (it causes vibrations and fluttering in the drivetrain).

In the days of 8-spd cassettes I was routinely able to get over 20,000 km out of one chain and cassette. Now with 12-spd cassettes, despite much better metallurgy and surface treatment, I believe my commuting bike won't make 6,000 km on a chain and cassette. Despite the 12-spd one being markedly more expensive too.
Modern stuff is super-effective and easy to ride along with being incredibly reliable, but it just can't last the way older stuff did. I have often opined that an 8-spd system made using 12-spd material science might last the life of the bike. I don't know if many would be willing to go back to 8 sprocket cassettes - I don't think I would do it.

Michael Hanslip Coaching

If you want to go faster, you have to pedal harder

Road gearing