Gearbox systems are becoming more and more popular on touring bikes. The most common form of gearbox is the internally geared rear hub, which has actually been available since the late-1800s. The earlier ones were a two-speed design, but these days we have the 14-speed Rohloff hub as our benchmark.
While there is often a weight penalty to gearbox systems over derailleurs, this is negated by how easy they are to maintain, especially in poor cycling conditions. But let’s put the pros and cons of gearboxes aside for a second.
What I want to know is the difference in drivetrain efficiency between gearbox systems. With this data, I can then analyse the speed differences between different gearboxes.
Andreas Oehler from online magazine FahrradZukunft conducted his own testing to find out the drivetrain efficiency between gearboxes, using a singlespeed drivetrain as a benchmark. You can read the full internal hub test HERE and the internal crank test HERE.
Two different test rigs were setup to measure both internally geared hubs and internal crank gearboxes. The pedalling rate was setup at 60 RPM which provided the most consistent data (despite most cyclists pedalling 20%+ faster). A low-tension lubed chain was used to drive the wheel and the same front chainring was used for each test.
Two different power rates were tested, 50 watts and 200 watts; the former used to get a sense for the idle losses at the gearbox.
While the data from the graph indicates the drivetrain efficiency for each gear, I’ve averaged out the drivetrain efficiency across each gear range to come up with the following numbers:
Singlespeed: 97% efficient (Drivetrain loss of 6w @ 200w).
Rohloff : 94.5% efficient on average across 14 gears (Drivetrain loss of 11w @ 200w)
Pinion: 90.5% efficient on average across 18 gears (Drivetrain loss of 19w @ 200w).
Shimano Alfine 11: 90.5% efficient on average across 11 gears (Drivetrain loss of 19w @ 200w).
Shimano Nexus 8: 90% efficient on average across 8 gears (Drivetrain loss of 20w @ 200w).
Nuvinci 360: 83.5% efficient on average across the gear range (Drivetrain loss of 33w @ 200w).
You can see the Nuvinci 360 testing on this graph.
For this article, I will focus on the power rate of 200 watts as it’s in line with my other testing.
At a power rate of 200 watts, there was less than 10 watts difference between the most common gearbox systems (Rohloff, Pinion and Shimano). While seemingly insignificant, this is a similar difference in resistance between a set of touring tyres with an off-road tread (Schwalbe Marathon Mondial) and a set of road touring slicks (Schwalbe Marathon).
The Rohloff hub came out on top, as it’s more efficient in almost every gear than the other gearboxes. Two things are surprising, however; in the direct drive gear (number 11) it’s less efficient than gear 8 despite it engaging more moving parts, and the noisiest gear (number 7) isn’t actually the least efficient. I’m not exactly sure why these may be.
The Pinion P1.18 is the most consistent throughout its gear range. It slightly underperforms when compared the Alfine 11 in the low gears, but has the edge in the higher gears. These two gearboxes average out to have a similar efficiency.
The Shimano Alfine 11 gets less efficient as the gears get higher. That means that in the top gear, you’re losing ~15w through drivetrain inefficiencies when compared to the Rohloff. If you do the bulk of your riding in the higher gears (ie. on the flat) you will have the most to lose.
The Shimano Nexus 8 (practically the same as the Alfine 8) has an interesting efficiency graph. It’s quite obvious that gear 5 is the direct drive gear, using 20 watts less than the 4th gear. Given the way the efficiency gradually reduces in two sections, it’s clear the hub engages more internal parts the closer you get to gear 4 and 8.
Pinion P1.18 vs. Rohloff Speedhub Gearbox Systems
There are a few reasons why the Pinion P1.18 is less efficient than a Rohloff hub. Firstly, the chain runs 50% faster in the equivalent gear, so this results in more losses at the chain itself. Secondly, as the gears get higher on the Pinion it engages faster rotating internal cogs, potentially resulting in additional losses. And lastly, the large seals at the crankshaft may also contribute to the losses.
What Is The Speed Difference Between Gearboxes?
When comparing the most and least efficient gearbox systems there’s a 22-watt difference in resistance. This translates to about 1.44km/h (0.89mph) slower travelling speeds using the Nuvinci 360 rather than the Rohloff hub, with all things being equal (200w, 85kg total weight, flat road). Knowing the speed difference, we can determine the time differences over the course of a typical touring day using Bike Calculator*.
On A Flat 100km Route (0% Gradient)
Over 100km, the 1.44km/h drop in speed from the Rohloff to the Nuvinci will add 9 minutes and 30 seconds to your cycling time (4.9% slower). To put that into perspective, carrying 30kg (66lb) extra on your touring bike would add 5 minutes to your ride time (2.6% slower) on the same route.
Over 100km, the 0.51km/h drop in speed from the Rohloff to the Pinion P1.18 will add 3 minutes and 15 seconds to your cycling time (1.7% slower). To put that into perspective, carrying 20kg extra on your touring bike would add 3 minutes to your ride time (1.6% slower) on the same route.
On A Hilly 100km Route (10km up, 10km down x5 @ 2% Gradient)
Assuming it’s hilly, gearbox resistance plays an even greater role because of the lower travelling speeds. The less efficient Nuvinci 360 adds 13 minutes and 20 seconds to your cycling time (5.9% slower) when compared to the Rohloff. To put that in perspective, carrying 15kg (33lb) extra on your touring bike would add 15 minutes and 30 seconds to your ride time (6.9% slower) on the same route.
Over 100km, the less efficient Pinion P1.18 adds 4 minutes and 31 seconds to your cycling time (2.1% slower) when compared to the Rohloff. To put that into perspective, carrying 5kg extra on your touring bike would add 5 minutes to your ride time (2.3% slower) on the same route.
How Does Gearbox Efficiency Compare To Derailleurs?
A pretty common derailleur drivetrain efficiency number that’s thrown around is 95%, and this seems about right to me. The reason a derailleur system is less efficient than a singlespeed is due to (a) the derailleur jockey wheels and (b) the chain line; in other words, the angle at which a chain has to run from the front chainrings to the rear cogs.
A slightly worn chain tensioner was fitted to the above testing rig and it was determined it lost 2-3 watts using a gear with a straight chain line (resulting in 94-95% efficiency). This rate of efficiency is the same as the Rohloff hub when fitted without a chain tensioner. In fact, if you use a derailleur gear with a bad chain line (eg. a large front chainring and a large rear cog) it may actually be quite a bit less efficient than the Rohloff.
Does Gearbox Efficiency Really Matter?
I’ve now looked at the speed difference of gearboxes, gear weight, aerodynamics, tyres and dynamo hubs. Gearbox efficiency can make a significant difference at the extremes (comparing the best and worst performer) but is much more negligible in the scheme of resistance.
At most, a Pinion gearbox or Shimano Alfine 11 hub will cost you five minutes per 100km (2.1% slower) when compared to a Rohloff or derailleur drivetrain. This is similar to the effect of a dynamo hub generator (1-3% slower) when compared to a regular hub.
The biggest speed differences come from tyre rolling resistance and aerodynamics. When comparing fast and slow rolling tyres on flat and hilly 100km courses, we can add between 12 and 17 minutes (5-7% slower) to our ride time. The aerodynamic testing yielded similar results with panniers adding 12 to 18 minutes over 100km when compared to bikepacking bags.
So with this in mind, you’re best to pick one of the gearbox systems based on your budget and whether the gear range offered is suitable for the terrain you ride.