|[ Main index » Bicycle components tests » Transmission types and number of gears » Gears: How much do gears (number and gear step size) influence your speed, and what is optimal?||]|
This is not a test of specific bike parts, but a general test of different setups using the same bicycle. This is the bicycle I usually use for tests of components and for this too:
I used this for years and I ride very fast with it. By fast I mean that people on road bikes never pass me, instead I regularly pass them (i.e. on the flats I usually ride about 33 km/h and more unless there's reasonably strong headwind or very strong side wind). And this is with all the panniers you see in the picture. These panniers + small stuff such as the mudguards cost about 3 km/h compared to a road bike, which I tested and later I calculated it from wind resistance which gave the same result: 37 km/h on the road bike = 34 km/h on the touring bike. The rides to test this were using a heart rate monitor to pedal just as fast, while riding under exactly the same conditions on the same 7 km route, using this touring bike and a road bike. When I'm not going all-out, my average is about 26-27 km/h on a slightly longer route that I often ride. It is the same route as in the test but with additionally about 3 km in a small city on roads where you cannot go fast due to some bad roads and many traffic lights, which mean that an average of 30km/h on that section is very difficult to achieve.
The reason I did this was really out of necessity: The gear changer (for the rear derailleur) broke, and so I fixed the derailleur to be in a specific gear... I had already removed the front derailleur some time ago as I was planning to change to a geared hub. The resulting speed using about the same effort (i.e. pedalling faster takes more effort than slower pedalling with a higher ratio) as with the derailleur fully working, on that 10 km route, was about 20-21 km/h. Here I was naturally getting passed a lot by road bikes...
I couldn't use a higher ratio because I use that bike a lot for e.g. groceries, and need to get up to some hills with it... Suppose I were to change the gears to a higher ratio in case of a bike that's not ever used for transporting heavy stuff, this would definitely give me a little more speed on long stretches of flat road, but a lot less in the city/village, and as you can see with the Sturmey Archer 3 speed hub, it will never come close to a 3x7 derailleur system.
View of what I had to do to make an old Sturmey-Archer 3 speed hub fit:
As the axle wasn't long enough I had to mount the cable stop with a rack mounting bolt. Also note that I use the derailleur only as a chain tensioner and I had to use longer bolts for the derailleur wheels, with spacers, to make room for the wider chain...
I used the single speed setup for quite a while, which resulted in pedalling at higher cadence than before. But as the chain kept getting worse (btw, 7-8 speed chains only last a maximum of 2000 km on my bikes, independent of good or bad weather) and often fell off, after a few months I installed a new single speed chain + old wheel with Sturmey Archer 3 speed hub. The difference was immediately obvious. Using the same effort again on that same 10 km route, the average speed went up to 23-24 km/h.
I don't get close to the derailleur system because I always have to adjust my speed to give a comfortable pedalling speed. When you look at the Sturmey Archer 3 speed hub specifications (the normal version, not the close ratio that was also available long ago), it's apparent why: its ratios are too big (a factor 1.33 between gears).
With this setup I did on various occasions pass road bikes, but only under good conditions, i.e. I had to be able to cycle comfortably at a high speed. With the setup as above, for me comfortable pedalling speeds are when I cycle at ca. 26 km/h in 2nd gear (cadence 90 rpm), and ca. 36 km/h in 3rd (95 rpm) although if necessary I can go higher (e.g. 30 km/h in 2nd gear means 104 rpm and is still ok, but I prefer lower). If the wind is such that regarding required power I feel like riding at say 32 km/h, then I have to use 3rd gear with a low cadence (84 rpm), which doesn't feel right (although it could be better in aerobic efficiency, but with low rpm there is more stress on the joints which I don't like) and isn't optimal for me.
I mention 'same effort' which is a bit vague, and deliberately so. Power use will not be as high with a single speed with low ratio as with a 3x7 derailleur system but it's uncomfortable to pedal very fast at relatively high power output with that single speed setup. Therefore, 'same effort' means that when I get to my destination, in both cases the exertion I may feel is both due to actual energy spent and other factors, and this will feel the same. I hope that makes it clear.
From these experiences it was pretty obvious what a large influence available gear ratios have on one's average speed. If you like to cycle quickly, then a single speed bike makes no sense whatsoever. The required difference in ratios is an interesting problem. For me, a 3x7 speed derailleur system is nearly perfect. 3x8 or 3x9 don't add anything that really improves this. On a 2x10 speed road bike the steps between successive gears were so small (about a factor 1.08) I often wondered if I had switched gears at all. This is probably partly due to me being accustomed to the 3x7 ratios (using 28,38,48 in front, and 12-18 or 13-28 in the rear) which means I knew exactly when to switch to what gear and possibly adjust my pedalling to the gear a little when needed, instead of always choosing the gear that's 'perfect' for the given situation. This won't matter much in efficiency (changing your pedalling speed changes efficiency, but the change is very little in this case), so I really doubt the necessity (for giving a higher efficiency) of more than a 3x7 system (which using a 12-28 or 13-28 cassette gives about a 1.15 factor between gears).
Regarding gear hubs: 8 speed hubs can have issues with shifters getting out of synch with the hub, and for this reason I would think a simple 5 speed gear hub could be nice for in particular nearly maintenance free city bikes. 3 speed is just too limited, and with 5 you could get a decent range while not having too large steps, that the 3 speed hubs do have (their ratios are usually: x1.33 x1.33). Sturmey's 5 speed hub is one that is not set up right in this respect as the ratios are largest from 2-3 and 3-4 (ratios: x1.20, x1.33, x1.33, x1.20). So in the very low and very high ratio there is a smaller jump. Basically it's a 3 speed hub with its too large ratio between gears, to which are added a very low and very high gear. Why? You only need the very low ratio in case of hills or starting after a traffic light, and the very high gear for a tailwind or down a hill and there having a close other gear is not so important. The ratios should have been: x1.33, x1.20, x1.20, x1.33, which would give 3 gears in the middle not too far away from each other for normal use, and a traffic light/hill gear + tailwind gear. I suggested this to Sturmey a few years ago...
I had a similar bike to the one shown above that I did all my tests with, bought in 1992, which came with a 12-28 cassette (ratios between gears ca. 1.15x) but when that was worn I tried a 12-21 cassette (ratios between gears ca. 1.10x) to give me close ratios. I didn't like it. I needed to use the front derailleur a lot (esp. for use within the city, as I used that bike as I use all my bikes, as transport, and parts of my rides are always within the city, and within the city I also ride fast, so I want to be able to choose the most suitable gear ratio. I also didn't get a feeling of improvement from being able to better fine tune the appropriate gear on long stretches of road.
This is on bike 2 with which I tested the NuVinci N360 hub, and the interesting effect was going back from NuVinci to the derailleur system (because I want a different test bike). I felt the change in effort in thinking. Suddenly I had to think about shifting, about using the front derailleur. Just not having the front derailleur takes away a lot of decisions that must be, can be made. Also I had to fiddle and adjust the derailleur on the first rides to make it ride smoothly again, and this is something you will never have with the NuVinci, I mean no missed gear switches. It gives a much freer feeling...
Addition 2021-8-26: The Nuvinci (renamed Enviolo some time ago) has a bit higher losses in power than a derailleur or other internal gear hubs (ca. 84%, measurements can be found in Fahrradzukunft, which confirms what I estimated already long ago from the ranges of vehicles using an electric motor that used gear hubs as a transmission), but it's not that much of an influence. A statement that I read on a Dutch site (I will see if I can find it again) that bikes with these hubs didn't sell well and that this was caused by the low efficiency and that people felt this immediately is just nonsense. As I tested, I didn't notice it and a weak rider whom I let ride with the bike for a few days, didn't notice it either. You do not notice 10% loss of power, it simply means you ride a little bit slower, and how do you know that you ride slower unless you keep track of that with a bike computer while at the same keeping track of the wind speeds/direction at each ride? Or unless you do a statistical analysis (average speed over rides)? Well, you don't. The main issue I felt was that the infinite variability is not so infinite because of stiction (static friction), i.e. you can't change the gear slightly, you will overshoot a small change because of needing a larger force to move the gear changer. In practice I felt that though the idea is good, it is no better than good internally geared hubs (with actual gears).
2015-2-5: I had a look at Sturmey's website and a lot of their new hubs now have equally distanced gears (factor 1.25x between all gears). This is better than the original version, but I still think it would be better to have the gears in the region where one rides most to be closer together, as per my original suggestion. But I may try out one of these hubs...
I watched a video recently on youtube about the perfect number of gears for urban cycling which was stated to be 3. This is of course not true, it depends on how you use the bike and how you ride, see my tests above if you like to ride fast, then a 3x7 system is far better than a 3 speed hub or single speed. If you like to ride fast, and especially if you ride longer distances (say 10 km and more) then you need far more gears for the optimal cadence so you can ride fast and go comfortably up hills, esp. with loads or with a trailer, without stressing your joints too much. This means:
From this you see where the number of gears of the Rohloff comes and why that makes sense...
[ See the new section about cadence and optimal gear step size for a deduction from a few principles in a far more strict derivation. ]
For just city cycling, not carrying much but mainly transportation of yourself, and not caring about speed, then 3 gears is enough. If you like to ride fast, and if you carry stuff such a groceries over hills or steep bridges, 11 equally spaced gears are good, and 14 such gears are better. The longer the distances are that you ride and/or the more you like to ride fast, the more these extra gears matter.
|To email me go to the email page|
Last modified: 2023-3-27