Evolution of transmissions and tires: how to calculate your gears?

Gear ratios have always been a hotly debated topic among cyclists. With 12-speed cassettes becoming almost universal on most recent drivetrains, you might think things would be even simpler. But that’s without considering the paradigm shift of two of the three major groupsets now offering cranksets with smaller chainrings, and the increase in tire size on modern bikes. To help you find your way around, here's how to calculate and choose the range of developments that suits you..

By Guillaume Peephole – Photos: ©Cervélo / depositphotos.com

In less than 40 years, we've gone from five to 12 rear sprockets on most transmissions.. Talking about "speeds" as we all do is also an abuse of language, since the number of sprockets on the wheel is associated with the number of chainrings on the crankset. The six-sprocket freewheel dates back to the early 80s, then we moved on to seven sprockets before the 90s, to eight sprockets around 1992-1993, to nine sprockets in 1996-1997, to ten sprockets in the early 2000s, and to 11 sprockets just before 2010. And it was a little less than ten years later that 12-sprocket transmissions (more often called "12 speeds") appeared, before gradually becoming widespread at almost all levels of the range. Two single-chainring groupsets are even available today with 13 sprockets (Rotor and Campagnolo Ekar), but more for Gravel use.

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Until the end of the 2000s, the three main transmission brands (Shimano, Campagnolo and Sram – on the market route since the mid-2000s only) offered many cassette options, several chainring options (even if the concept of compact chainrings only dates back a good twenty years), and above all, there were many equipment manufacturers who offered compatible chainrings, so that a combination of developments could be created tailored to the terrain, habits or level of each person.

With 11- and even more so 12-sprocket cassettes, manufacturers have primarily sought to make transmissions more and more versatile., capable of driving you both on the flat and in high mountains.tagne. Adding additional sprockets has allowed for a wider range of gears on a single cassette, but at the expense of some comfort for those who ride year-round in a specific region and never use all the available sprockets. By optimizing the speed of gear changes across their entire drivetrain, manufacturers have also progressively limited the number of compatible third-party chainrings, locking users into a sort of ecosystem that is difficult to escape.

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At Shimano, for example, there is no 12-speed cassette with a large sprocket smaller than 30 teeth. Anyone who lives in the plains and is properly trained therefore never uses the last two or even three sprockets on their 12-speed cassette, or they keep the large chainring all the time and never shift to the small one.

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At Sram, we do find a cassette with a large 26-tooth sprocket (in addition to cassettes with 28, 30, 33 or 36 teeth maximum), but this is necessarily associated like all Sram cassettes with a small 10-tooth sprocket and smaller chainrings than at Shimano. The 10-tooth sprocket allows you to extend the gear range, but the difference in development with the 11-tooth sprocket is such that changing from one to the other is not always very comfortable. Depending on the size of the chainring at the front, the difference in gear is about one meter per crank revolution between 11 and 10., while it is only about 80 centimeters between 12 and 11. Such a development gap between two sprockets is comparable to that felt when going from 15 to 17 teeth or from 17 to 15 on the cassette with the large chainring.

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Finally, Campagnolo with its new Super Record WRL groupset offers a well-equipped cassettetagée from 10 to 25 teeth (in addition to 10-27 and 10-29), but again with a 10 sprocket and smaller chainrings than what we knew until then.

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obviously, For most novice or recreational cyclists, this increased versatility is a boon.tage. We are satisfied with the transmission offered on the bike at the time of purchase, and we do not ask ourselves any questions. The bike is suitable for Sunday outings, and also for a possible escapade in montagonce a year, without changing anything. For those who aim for performance, sometimes you have to adapt. But The most frustrating thing is probably having so many possibilities with increasingly efficient transmissions, without using all the gears available..

Bigger and bigger tires

Added to this are the changes in habits regarding tire sizes. Here again, a brief flashback is necessary. In the 80s, we rode with 19 or 20 mm section tubulars. The 23 became established from the mid-90s, to remain the reference for a very long time, at least until the beginning of the 2010s. Then the 25 appeared first for a question of comfort, then of efficiency at the same time as the phenomenal evolution that we have seen in a few years in terms of efficiency for tires, then tubeless, which have almost completely dethroned tubulars, even among professional riders. The 28 section ended up becoming the standard since the generalization of disc brakes, to offer more support on the route when braking. But we also see 30, 32 or even 35 among those looking for endurance and comfort, with tires that allow you to escape from time to time outside the routes bitumen.

What are the consequences in terms of gear ratio? If modern rims for the route always have the same circumference (700c or 28”), their widening allows the use of larger tires, which increases the circumference of the total wheel, and therefore the development. For every pedal revolution in a set gear, you go further with bigger tires.

Calculate the equivalence of the gears

It is therefore possible to easily compare gears with each other, whatever the cassette used, and whatever the chainrings, provided that it is done with the same tire size. To do this, simply divide the number of teeth on the chainring by the number of teeth on the cassette. This gives us a ratio, which then allows us to compare the different combinations with each other.

Example: 50/10 (at Sram or Campagnolo) = 5:1. To have the same ratio of 5:1 at Shimano, you need a 55/11. At the other end of a development scale, a 36/36, a 34/34 or a 30/30 are always equivalent to a ratio of 1:1. Which means in this case that one crank revolution is equivalent to one rear wheel revolution.

These are extreme developments, but you can apply these calculations to the entire range of gears offered by your transmission, which can be useful for example if you switch from the chainring combinations offered by Shimano to those of Sram or Campagnolo, or vice versa.

To compare the influence of tire sizes

If you want to compare developments with different tire sizes, however, you must perform a more complex calculation that takes into account the circumference of the complete wheel. And there you can have surprises.

To calculate an exact development, you must therefore repeat the same operation as before by dividing the number of teeth on the crankset by the number of teeth on the sprocket, but multiplying by the circumference of the complete wheel. For a 53/11 gear ratio for example, the development is 10,28 m – (53/11)x2,135 – per crankset revolution with a 25 tire, and 10,45 m with a 32 tire. This is approximately the same as if you were switching to a 54/11 (to within 3 cm) with your 25 tire. And this obviously applies to the entire range of gear ratios. Fortunately, the smaller the ratio, the less influence the wheel circumference has. For the famous 1:1 ratio which allows one revolution of the pedals for one revolution of the rear wheel and which is dear to cycle tourists in the high mountains.tagor those who do Gravel, the real difference in development between a 25 mm section tire and a 40 mm tire is only 6,5 cm.

The overall increase in the size of tires used on modern bikes therefore has less influence on our habits than the evolution of the combinations of teeth offered. But it is still easy to compare the ranges of developments to choose the one that suits you best.

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