Brompton gearing & speed

Gearing

When considering Brompton gearing, the options are a minefield. You can choose from 6-speed, 3-speed, 2-speed, or 1-speed … and then fine-tune your choice with +% or -% options. How do you reach a suitably-informed decision?

Personally, the advantage of additional gears offered by 6-speed over all of the other variants trumps any additional weight, or any potential cabling complexity (it’s not that complex). Yes, it is a more expensive option but, in the context of the overall cost of a Brompton, it is not that much more expensive.

Switching the front chain ring for one more or less teeth is an easy way to change a Brompton’s gear ratios and range

I came across a great thread on Bike Forums some time ago, in which a number of contributors offered their own take on the question of “What gearing?”. One contributor posted the following table of gearing statistics, for which I’m eternally grateful (thank you DoubleDiamonDog):

The numbers below reflect the range of speeds when pedalling at a cadence of 60 rpm in the lowest gear to 90 rpm in the highest gear. The table is ordered as follows, with speeds in mph:
/ Gearing option /
/ Lowest Gear Inches – Speed /
/ Highest Gear Inches – Speed /

6 sp +8% / 35.7 – 6.4 / 108.0 – 28.9
6 sp std / 33.1 – 5.9 / 100.0 – 26.8
6 sp -12% / 29.1 – 5.2 / 88.0 – 23.6
3 sp +8% / 51.7 – 9.3 / 91.7 – 24.6
3 sp std / 47.9 – 8.6 / 84.9 – 22.8
3 sp -12% /42.1 – 7.6 / 74.7 – 20.0
3 sp -18% /39.1 – 7.0 / 69.4 – 18.6
2 sp std / 56.0 – 10.1 / 74.7 – 20.0
2 sp -7% / 51.9 – 9.3 / 69.2 – 18.5
2 sp -19 % / 45.7 – 8.2 / 60.9 – 16.3
1 sp std / 74.7 – 13.4 / 74.7 – 20.0
1 sp -7% / 69.2 – 12.4 / 69.2 – 18.5
1 sp -19 % / 60.9 – 10.9 / 60.9 – 16.3

I opted for the 6-speed standard gearing when I purchased my Brompton. In the two thousand or so miles that I have pedalled since then (at the time of writing), this choice has proven to be right for me. And that is my point, it is right for me. I’m fit, but not that fit, and may carry a load on my Brompton, but not a truly excessive load (circa 20kg at most). I pedal up every hill, even if I have to stop en route (Gold Hill in Shaftesbury excepted, but I think that was a reasonable cop out), and I cruise fairly comfortably at 15mph on the flat (when there is no headwind).

However, were I fitter (or not), or carrying a greater load (or not), or determined to climb any gradient (or not), or want to fly along the flats (or not), my personal choice of gearing would need to reflect my own unique combination of those variables.

To date, the standard 6-speed gearing has provided me with a sufficiently low lowest gear to climb quite severe gradients. Indeed, my lungs have usually given out before my legs. I stop, I catch my breath, and then I continue to climb. Actually, the limiting factor isn’t so much my choice of gearing, as the geometry of a Brompton, which means that, beyond a certain gradient, the sit-up-and-beg riding position naturally limits pedalling efficiency. Different gearing would not do much to improve this shortcoming (Bromptons offer many, many advantages, but this is one of the disadvantages).

In due course, I plan to upgrade my front hub to one incorporating a SON dynamo. I’m led to believe that these can reduce pedalling efficiency by 2-3% (quoting from a great article at Cycling About), so when I do so, I may then upgrade my gearing at the same time, opting for a front chain ring with 44 teeth (and switching to a shorter chain), so that my gearing is 6-speed -12%. This should more than compensate for the efficiency limitations of the dynamo, such that I can still pedal with a similar cadence to that I achieve currently, and give me a better lowest gear for winding up those steepest gradients, especially when fully loaded for a camping-based bicycle tour.

Speed

No one pedalling a Brompton is going to break any speed records (except for those specific to Bromptons, of course). However, just because they have small wheels, do not underestimate a Brompton’s ability to be ridden at a reasonable speed.

I have topped out at over 30mph, riding downhill (31.6mph, descending Bulbarrow Hill, in Dorset), and my touring speed is an average of 11mph, when cycling in landscapes such as rural Dorset (not renowned for being flat). These statistics are not too shabby, given that we are talking about a bicycle designed for urban commuting, not for fully-fledged bicycle touring (or any sort of touring, to be honest).

At 11mph, I can travel 60 miles in about 5.5 hours. Add 50% to that time for stops – taking photographs, making a hot drink, having lunch, ‘seeing the sights’, chatting to people, shopping for food – and you have a touring day of 8.25 hours. Even allowing for a longer stop – if I’m exploring a town, or a sight of specific interest (e.g. a National Trust property) – I’m only looking at a 9-hour bicycle touring day, and only actually pedalling for less than two-thirds of that.

And that’s if I’m travelling 60 miles. My bicycle touring is about exploring the world in which I live, not covering a set number of miles each day. So if I plan to explore somewhere during a specific day, and expect to take a while doing so, I would plan to cover less distance that day. I’m still going to get/stay fit on a lower mileage, and I’m going to enjoy my exploration without the self-imposed pressure of a high-mileage schedule.