What is the optimum number of gears?

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As many as necessary, but as few as possible

For decades there has been a shift towards bikes having an ever-greater number of gears. Not long ago 5-speed derailleurs were the norm, with the total of 10 gears they afforded seeming almost excessive. Nowadays 27-speed bikes are commonplace, and 10- and even 11-speed cassettes are becoming more popular, providing 30 gears or more.

 

However, many of the gears on a modern derailleur-equipped bike are either duplicates or unusable combinations, so in fact a so-called 24-speed bike probably has at most 13 usable ratios. In contrast, a 10-speed bike has no unusable combinations, and with careful choice of chainring sizes will have no duplicate ratios either, so in reality is only 2 or 3 gears different to a 24-speed bike.

 

Some professional road racers may need specific and close-set gear ratios, but the vast majority of cyclists in fact don't use all available gears, and often shift two or three at once. A wide range of gears is certainly of great benefit to most commuters, cycle tourists, mountain bikers, and especially novices and leisure cyclists, but very rarely do they require so many increments within that range. And not only is having too many gears fairly pointless; there are also several downsides.

 

Chain wear is significantly accelerated on modern bikes with so many gears thanks to the narrowness of the chain and sprockets, reduced height of the teeth, higher chain tensions due to the advent of compact chainsets, and probably also because of the disappearance of the true sleeved-bush chain in the quest for one with less lateral stiffness. We are now at the point where chains must be replaced every few hundred miles on a modern mountain bike if sprocket wear is to be avoided. Gone are the days when a chain would last for years or even decades. See my article on drivetrain wear for more information.

 

Gear shifting is also more problematic with a larger number of derailleur gears, assuming all else is equal. Although technology has been developed to alleviate the situation, such as indexed shifters and special teeth profiles, the root of the problem is that more gears have been crammed into the same small space, so tolerances are much tighter. This is why old 5- and 6-speed gears with friction shifters are easy to set up, rarely require adjustment, and are very tolerant of worn derailleurs, dirty cables and other wear and tear. In contrast, modern 9-, 10- and 11-speed systems require complex and delicate gear shifters, high quality cables, and very accurate setup. They also require frequent readjustment, and will not tolerate any significant amount of dirt ingress, corrosion, or wear.

 

Another problem with multi-speed derailleur gearing is that it has led to weaker rear wheels. To create space for the ever-larger number of gears on the cassette, the rear wheel has become increasingly asymmetrically dished, with shorter, tighter spokes on the right and longer, slacker ones on the left. Ultimately this leads to broken spokes and can contribute to cracked hub flanges or rims. In the most extreme situation (an 11-speed road bike with its relatively narrow 130mm hub), it can be difficult even to achieve a balance between over-tension on the right spokes and under-tension on the left.

 

What does all this mean for our choice of gears in the real world?

 

Modern hub gears are now available with up to 14 speeds and a range as wide as even a touring bike derailleur system, so it has become an increasingly viable option to use a hub gear to provide the desired level of reliability and longevity for commuting, touring and even some mountain bikes. However, this is currently still an expensive and relatively heavy option, and is inherently a few percent less efficient compared to a derailleur system thanks to the internal friction of the hub gear. It also seems a shame to write off derailleurs altogether, simply for want of a less unreliable implementation. Surely it must be possible to design a system which combines the low weight, large range, and inherent efficiency of the derailleur system with the cleanliness, reliability and longevity of the hub gear?

 

It is easy to think that a large number of gears allows a higher top speed, or makes it possible to climb a steeper hill, but this need not be true. I once took apart an 8-speed cassette, removed half the intermediate sprockets, and installed it on a mountain bike. This 4-speed setup worked flawlessly without reducing my gear range at all, and was lighter and narrower than the original 8-speed system. Thus it would be entirely possible to replace the 27 gears on a typical modern mountain bike and achieve exactly the same overall gear range with only 8 well-spaced gears, e.g. with a 13- to 36-tooth wide-range 4-speed cassette and a 28/48-tooth wide-range double chainset. In theory this should allow for a stronger rear wheel and possibly the fitment of a full chaincase enclosing the entire cassette and derailleur. In reality the current lack of a suitably narrow freehub body and suitably wide chain and sprockets prevents this from being a sensible option for mountain bikers and cycle tourists looking for longer chain life and a strong, symmetrical rear wheel. And a derailleur-compatible full chaincase for commuter and utility applications does not (yet) exist as far as I know. Although there is no reason why this system could not be put into production, there seems to be little incentive for manufacturers to market such an 8-speed bike - probably because the average consumer assumes a 27-speed bike must be better, and because manufacturers have no direct incentive to produce a bike which wears out less quickly.

 

So using standard, widely-available components, what is the next-best option? Derailleur systems designed for wide 1/8" chains are long gone, as are sleeved-bush chains. Good quality 5- and 6-speed freewheels are no longer available (and in any case for unrelated reasons of axle breakage it is highly desirable to have a cassette rather than a freewheel hub). We are therefore left with 7- or 8-speed cassettes as the only reasonably practicable option. I have 'downgraded' (I would argue upgraded) several of my own bikes from 27-speed to 24 or 21 when the original drivetrain has worn out. Whenever we build a tough touring or expedition bike for a customer we specify an 8-speed cassette and chain in preference to 9-speed: drivetrain wear is a little slower; gear shifts and indexing will remain reliable for a little longer; and the wider chain is stronger and, unlike a 9-speed chain, can be repaired if it breaks. When available, we use 7-speed cassettes because the narrower freehub allows for a stronger wheel with less asymmetry.

 

Meanwhile the marketing machine continues in its apparently unstoppable pursuit of ridiculous numbers of gears with 10-speed cassettes now appearing for mountain bikes and 11-speed road systems becoming increasingly common. A tiny minority of cyclists who are professional athletes may benefit; unfortunately the general public also lap it all up, only to discover that the penalty is poor long-term reliability and drastically reduced longevity.




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