You need easier gearing — why and how-to

20 October 2023
I. Why

I’m a believer in that most of road bikes are way overgeared. The standard combinations are:
• 53—39 (“standard”) or 52—36 (semi-compact) or 50—34 (compact) double chainrings with
• 10- or 11-tooth smallest sprocket on a cassette.
Even with the easiest combination — 50—34 / 11 — the top gear allows you to keep pedalling till 70 km/h (with a reasonably high cadence of 120 rpm). However, such speed can only be achieved on a slope of 5 % — if you can hold about 500 watts for that — or steeper.

On such a grade and speed, it is more effective to stop pedalling and tuck into an aero position, which is a well established fact. Depending on a lot of individual factors, the speed at which aero-tucked coasting beats power spinning vary, but I’m confident to cite a 60–65 km/h figure.
Thus, there are only two scenarios where you actually need the tallest gear on a typical road bike:
• you are riding a long-ish and not very steep downhill with a strong backwind — and want to avoid coasting not to cool down, regardless of how high the speed is, or
• you are racing, and need to stay in a group where people push gazillion of watts on a descend.

The first one is a rather specific and rare scenario (I personally encountered that once, when intentionally went “sailing” strong tail wind on a non-flat route), and the second — a niche one, as not everyone races competitively.
Now, there is nothing bad in having some extra room on the top end of gearing per se (especially if you still have a room for improvement in training your high cadence), but on the other end of the spectrum, I think that most of road — and even gravel — bikes do not have low enough gears. And how low we can go is limited by the top gear.

Where I ride, from time to time I find myself at a 20+ % uphill of considerable length. If I push some 300 watts (4 w/kg), I’d climb at the speed of 6 km/h. But, with a compact 50—34, I would need a 44-tooth cassette sprocket to do that at a reasonably low cadence of 60 rpm.

However, there is no out-of-the-box road rear derailleur on the market with a capacity of more than 39 teeth — which means that the largest cassette you can normally fit with a 50—34 compact is 11–34. Ten teeth shy of what I’d want not to suffer on occasional steep uphills.
<capacity explanation>

A front derailleur has one function — to shift chain from one chainring to the other. A rear derailleur in fact has two functions — the additional one is to make sure the chain is always in tension, regardless of whether its effective length is short (when on smallest chainring/sprocket) or long (when on largest chainring/sprocket).

For that purpose the rear derailleur not only shifts sideways between sprockets, but also moves its cage and cogs front-and-back, thus tightening and loosening the chain by “folding” its excessive length when not needed. The length of the chain “fold” could be measured in chainlinks, but it’s the same as teeth, and so the capacity is measured in teeth for convenience.

A derailleur capacity depends chiefly on its cage length, and can be found in the fact-sheet. The calculation of the capacity required by your drivetrain, on the example of 50—34 crankset & 11–32 cassette, is:
• crankset — 50 minus 34 = 16
• cassette — 32 minus 11 = 21
• 16 plus 21 = 37-tooth capacity — the derailleur must have no less than that (a bit of wiggle-room usually exists in practice).

</capacity explanation>
In fact, with the largest 11–34 cassette that fits a 50—34 compact, and at the quoted 4 w/kg, one could only do 14 % seated climbs before the cadence is too low — meaning the torque is too high — and muscles cannot produce the required power if it is anywhere close to the rider’s sustained limit (ftp).

While on a road you can normally ride up such grades out of the saddle with a lower cadence, on gravel climbs — whether you ride them on a road or gravel bike — it is not always feasible, as loose terrain, such as sand or fine gravel, requires the bike to be steady and not swing as it happens when standing on the pedals.

Consider that 4 w/kg is more or less the upper limit for an amateur who is not sacrificing other things in life to train on her bicycle, rest, eat, sleep, repeat. If instead of the more forgiving 50—34 / 11–34 we would take a classical 53—39 / 11–28, the max comfortable grade even for the rather high 4 w/kg would be just 10 %.
II. How-to

Luckily, the pinnacle of innovation is always just today. But let’s begin with simple solutions and build up on technological advancements from there.

1. A super-compact crankset

The 46—30 super-compact chainrings combined with an 11-something cassette allow pedalling till 65 km/h with the 120 rpm cadence — and as you remember from above, that is about the speed where you should really stop doing that and just tuck.

I can do 1,500 watts at a sprint and am a fast descender — not in comparison to Mohoric or Pidcock, but I ride with strong people all the time so I know my strengths and weaknesses — and the said gearing is exactly what I ride on my road bike. I wouldn’t want to go lower, but that’s just enough for everything outside of racing.

Admittedly, I also have a more aerodynamic position than most, so for me the terminal pedalling speed is likely lower — but I normally stop pedalling at about 60 km/h, so there is still enough margin to recommend the super-compact to amateur cyclists in general. You could push it a bit further with a 10–XX cassette which would add 6.5 km/h to the top pedalling speed.

From the technical point of view, you need to know that:
• depending on the frame mount, a front derailleur may not be able to go low enough for a 46—30, which may or may not be solved by an adaptor (e.g. I use one by FSA),
• a 10-sprocket cassette, of whatever manufacturer apart from Sram AXS, can work perfectly well with any non-AXS chain (both 11- and 12-speed) and the rest of the drivetrain, but you need a freehub body other than HG — meaning Shimano Micro Spline, Sram XDR, or Campagnolo.

The super-compact with a 10–34 cassette gives you a 520 % range — compared to 450 % with the abovementioned 50—34 compact & 11–34 cassette. (Technically, the former would require a 40-tooth capacity derailleur, but a 39-tooth one will do just fine, trust me.)
<range explanation>

The range is the difference in gear ratio between the lowest gear (smaller chainring / largest sprocket) — which is considered a hundred percent — and the tallest (larger chainring / smallest sprocket).

Now, for a 42—30 super-compact with a 10–30 cassette the calculation would be:
• 30 chainring / 30 sprocket = 1 = 100 %
• 42 chainring / 10 sprocket = 4.2 = 420 %

In the above comparison of super-compact vs compact, 520 % are perceived as way more than 450 %. Like, seventy percent more, right? However, this number is a bit misleading.

What really matters is the percent increase between individual sprockets. For example, the difference between the two smallest sprockets in a 10–XX cassette — 10 & 12 teeth — is 20 %. This is the biggest difference you want, as it represents jumping between the cadence of 80 rpm & 100 rpm when shifting between those sprockets.

(I will add to that that road cyclists tend to prefer much smaller jumps between gears, such as circa 10 % in classical road cassettes. When riding in a group, you do not chose your speed but try to match the others’ speed. Thus, it is easer to find a comfortable cadence with smaller gear jumps. That said, the comfortable cadence range is a trainable metric, and if you do not ride at your limit in groups — i.e. not racing — 15–20 % jumps should be just fine.)

Now, on the larger end of the cassette, to add same 20 % to a 42-tooth sprocket, you need the next sprocket to be 50-tooth. So, the difference, in this example, between 420 % and 500 % is only one “extra” gear, and not the impressive almost-one-fifth as one could imagine.

</range explanation>
So, while super-compact is indeed helpful and I do recommend it (or at least a sub-compact 48—32) as the simplest gearing upgrade, it only gives one “extra” lower gear. To get more, we need to go deeper.

2. Custom rear derailleur

A derailleur is not that complicated of a device, and we can gerry-rig with it in all sorts of ways. However, I’ll just mention plug-and-play solutions that only require the ability to turn bolts.

The geometry is simple — the longer the cage, the greater the amount of chain “fold” (as explained above), and thus the more the derailleur capacity. Considering the predominant shift to a single chainring (or one-by) drivetrains on mtb and then gravel bikes (and which is even finding its way to road bikes), the latest mtb & gravel groupsets have really long cages.

The 2023 mtb cassettes reach the range of 10–52, which is the same 520 % as in the example of a 46—30 super-compact with a 10–34 cassette given above. Here, however, it is achieved with a single chainring, which doesn’t affect the range, so all of it is in the cassette.

But why we are even talking mtb here? Gravel bikes have been unofficially, and now with wireless electronic connections, officially supporting “mullet” setups where an mtb cassette and rear derailleur are combined with drop bar dual-control shifters.

(While wireless works out of the box, the mechanical mullet needs a modification of either derailleur or shifter — as they have different pull-ratios, i.e. the amount of cable that is pulled per one shift. Actually, it is a pretty simple mod for the derailleur — a required small piece could be 3d-printed or bought cheaply.)
Now, the minimum capacity of a rear derailleur for the large mtb cassette is 52 minus 10 = 42. Which is not that much more than 39 max for road derailleurs. What gives?

See, as elaborated in the <range explanation> section above, the size of sprockets increases exponentially. To add just one gear (+20 %) to the allready-huge 52-tooth sprocket, we’d need 62 teeth. The half-circumference of the largest sprocket — and the extra chain length to be “folded” — thus, would increase by almost 6.2 cm!

A cage that could accommodate that, would have to near-touch the ground, especially on a 650b wheel. So, 52 teeth is near the limit of what is physically possible for a cassette.

However, if we’d combined two-by chainrings with a reasonably large cassette, we could get more range than 520 %. But why don’t we have suitable rear derailleurs? Well, because the cycling industry doesn’t think anyone really needs more than 520 %.

And while they are probably right (if you know me, you didn’t expect that, huh?), I can tell you from experience that I could utilise up to around 740 % of range just fine: from the fastest ~ ×4 gear ratio that I ever need (and already have with 46/11 road & 40/10 gravel), to ~ ×0.5 for the hardest of ascends (that’s actually what they have in mtb with a 28t chainring & 52t sprocket — sacrificing top pedalling speed, of course).

What we can do to try and approach that, is fit either an mtb cage (e.g. sourced from a broken derailleur — could buy one for peanuts) to a road derailleur, or an aftermarket cage to a compatible derailleur (I use Garbaruk cage on my gravel bike). That way, we could combine the 46—30 super-compact with a 10–42 cassette, resulting in 590 % range. Another “extra” gear compared to a super-compact with a normal cassette, or a mullet, but still not enough.
3. Internal gearing + derailleur

You didn’t think I would just let the 740 % figure be, did you?

You could hear something about Classified hub recently. That is a rear hub that have two internal gears — a 1:1 (effectively being a regular hub) and 0.7 (where the hub rotates slower than the cassette).

To put simply, you could say that the Classified hub adds a virtual smaller chainring, while not adding extra slack in the chain that would otherwise need to be “folded” by a too-long derailleur cage.

And it so happens that with my best gravel setup of 40t chainring & 10–52 cassette, the size of the virtual chainring would be exactly 28 teeth, resulting in the range of — you guessed it — 740 %!

The downsides are the hub weight, expensiveness, and the fact that on the 0.7 gear the Classified loses some mechanical efficiency (they claim the efficiency of 99 % — which is comparable to ~ 1 % loss between 10t vs 11t sprocket — and mechanical engineers agree that, yeah, sure, the figure most likely starts with “9” indeed :)
While this sounds great already, I would like to also mention the Pinion gearbox that can be integrated into the bottom bracket area of the frame. Yes, it is even heavier and also expensive (hard to compare with the Classified as it is built into premium wheels, and the Pinion is integrated into premium frames). But on its own it provides a 600 % range — so more than any derailleur combo — with a belt instead of a chain. That means no fragile derailleur occasionally going out of alignment, no lubing and cleaning — just hassle-free riding.

Or, if to combine the Pinion, just for laughs, with a derailleur and a 10–52 cassette, we could get a total range of 3,120 %. Not that it was not enough still, but we could actually add the Classified hub to that combo as well, so that we’d have 4,460 % range. I have no better way to end the post other than with this video: