I’ve long been in the habit of doing mathematical equations in my head while riding; this came about involuntarily but quickly became a way to pass the time doing long road miles. While mountain biking primarily keeps my brain occupied with technical trail features rather than algebra, I can’t help but fall back into old habits.

The single ring revolution is a common subject while I’m turning the pedals lately. The majority of mountain bikers – or, rather, the product managers who spec the bikes the majority of riders buy – are in the process of accepting single ring drivetrains, but this new reality doesn’t come without its misconceptions.

I have two points to make about single ring drivetrains and they relate to common complaints that I hear in conversation. My first point relates to the jumps between gears, while the second speaks to the overall gear range of a system. Unsurprisingly, both points are related to numbers and the answers are actually quite simple.

Bigger Jumps

Traditionally, bicycle cogsets have aimed for an approximately 12-13% jump between gears. With appropriately chosen gears, you feel a similar change in perceived difficulty when you drop a cog anywhere on the cassette. Wide range mountain bike cassettes make the 13% ideal a bit more challenging to attain, and numbers as high as 17% and can be found between the largest cogs – but for the most part you’ll find averages around that traditional ideal. (This is part of the reason we benefit from more gears on our cogsets.)

“The jumps between gears on an 11-speed cogset are bigger.”

I’ve heard this stated more than once while out on the trails – particularly by riders using an 11-speed system for the first time. Is a rider really able to discern a difference in the spacing between gears?

In thinking about the second cog on a 42 tooth cogset, which is a 36, I had a bit of a eureka moment. That cog is the same size as the largest cog on a 10-speed cogset. And it’s got one more gear. The 10-speed cassette starts at 11 teeth and the 11-speed starts at 10 teeth. They’ve got to be damn close. Here’s the proof:

10-speed 11-36: 11-13-15-17-19-21-24-28-32-36 (Shimano)

10-speed 11-36: 11-12-14-16-18-21-24-28-32-36 (SRAM)

11-speed 10-42: 10-12-14-16-18-21-24-28-32-36-42

There’s your answer, fishbulb. SRAM’s numbers are exactly the same apart from the bottom cog, which rarely sees use under most riders. The notable difference between the manufacturers is an extra 3 tooth jump mid-cogset on the SRAM cassette. That itself is potentially discernible, but at 16.7% it’s not a bigger jump than other gears on the cogset. The bottom line is the jumps between gears on an 11-speed cogset are very close to those of the 10-speed one.

Overall Gear Range

“Why do we need more gears? I was doing just fine with 9 (and 8, and 7 before that).” OR “11-speed doesn’t give me enough range.”

When discussing gear range, percentage is again the traditional way to compare systems: what is the difference between the lowest and the highest gear? To work this out, we divide the largest cog by the smallest (eg. 36 / 11 = 3.27) and the largest front ring by the smallest (eg. 36 / 24 = 1.50). Then, multiply those numbers: 3.27 x 1.5 = 4.91 or 491%. For single ring systems, just divide the largest by the smallest cog (so a 10-42 has a 420% range).

The average mountain biker uses a fairly wide range of gears, but mostly on the low end of the spectrum. If we can agree (and I think this is quite reasonable) that a 24/36 double chainring setup with an 11-36 10-speed cogset provides adequate gear range for the average rider, we have the basis for an educated discussion of overall gear range.

The 10-speed double setup with its 491% gear range has the 11-speed single beat by 71%. This is the reason it’s still important to choose the right front ring with the single ring system: you can achieve the same top gear or the same bottom gear – but you can’t have both. Most riders choose based on what they think they’ll need for a bailout climbing gear.

I’ve often wondered at what point rear gears will cease to become any larger. Will the dinner plates on our rear wheels be limited by overall size, the derailleur’s capability to control a long chain, or perhaps by sheer weight? I got to thinking about the simplest logical step beyond current 11-speed systems.

The Answer

With just one more gear, a 49 tooth cog, the single ring system will no longer be at a gearing range disadvantage. Is 12-speed the answer? The end of the gear wars? The percentage jump from a 42 to a 49 is the same as that from 36 to 42: 16.7%. Plausible. Obviously innovation will continue but it seems as though the front derailleur could truly be pronounced dead with just one more cog out back.

Top level racing pushes development in bicycle technology. Elite racers are the measurable determinant of what companies need to provide. At the current moment, the 420% range provided by SRAM’s 11-speed system has been on plenty of winning bikes in both XC and Enduro. However, these racers are still carefully choosing a chainring depending on the course. It would certainly be simpler if we just had a bit more gear range…

Want to nerd out on gearing? Start with the late, great Sheldon Brown’s calculator.