Brompton folding bikes come in 4 gearing options, including the single speed, 2 speeds, 3 speeds, and 6 speeds. Specifically, the standard single speed has 12T rear sprocket and 54T front chainring; the 2-speed version has 12T/16T rear sprocket and 54T front chainring; the 3-speed version has 13T rear sprocket and 50T front chainring; the 6-speed version has 13T/16T rear sprocket and 50T front chainring.
Apart from the standard versions, the Bromptons are also available in reduced or raised gearing variations. So, you will have more choices to pick your suitable gear inches. You might want to choose a lowered gear to pedal easier on hillier roads or a raised gear to go faster on flatter conditions. Keep in mind that the gear range on a Brompton will feel a little different as compared to the range of road bikes.
Now, let’s check out the gear inches (the diameter of the hypothetical wheel each gear creates) and meters of development (the distance the bicycle travels for one crank revolution) of all the Bromptons.
| 1st | 2nd | 3rd | 4th | 5th | 6th | |
| 6 speed standard | 33.1” 2.64m | 40.7” 3.25m | 51.9” 4.14m | 63.8” 5.09m | 81.3” 6.49m | 100” 7.98m |
| 6 speed -12% | 29.1” 2.32m | 35.8” 2.86m | 45.6” 3.64m | 56.2” 4.48m | 71.5” 5.71m | 88.0” 7.03m |
| 6 speed +8% | 35.7” 2.85m | 44.0” 3.51m | 56.0” 4.47m | 68.9” 5.50m | 87.8” 7.01m | 108.0” 8.62m |
| 3 speed standard | 47.9” 3.82m | 63.8” 5.09m | 84.9” 6.78m | |||
| 3 speed -12% | 42.1” 3.36m | 56.2” 4.48m | 74.7” 5.96m | |||
| 3 speed -18% | 39.1” 3.12m | 52.2” 4.16m | 69.4” 5.54m | |||
| 3 speed +8% | 51.7” 4.13m | 69.0” 5.50m | 91.7” 7.32m | |||
| 2 speed standard | 56.0” 4.47m | 74.7” 5.96m | ||||
| 2 speed -7% | 51.9” 4.14m | 69.2” 5.52m | ||||
| 2 speed -19% | 45.7” 3.64m | 60.9” 4.86m | ||||
| 1 speed standard | 74.7” 5.96m | |||||
| 1 speed -7% | 69.2” 5.52m | |||||
| 1 speed -19% | 60.9” 4.86m |
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Hello. I use my 2 speed Brompton for my daily commute, but find that on medium inclines the low gear is a bit too slow but the top gear is quite hard work. Currently I have a 54t front and 12/16 rear sprocket. If I decide to change the front chainring, what would you recommend – I don’t want to lose too much top speed, but want a bit more speed on the inclines.
thank you
David
50 inch
Hi I have the opposite question of the original poster, I have a 2 speed but would like to increase the gear inches to get somewhere near to the top gear on the 6 speed. Is there any way to do this but still keeping the 2 speed?
Hello Ricky.
I’m confused by the gear inches and metres travelled table at the link above. The inch and metres measurements are not equivalents. For example, with the Brompton 6 speed standard and 1st gear, 33.1 inches equals 0.84 metres, not 2.64m. This is way out, across the whole table. What am I not understanding?
Regards
Hi,
Gear inches and meters of development are equivalent terms used in America and Europe respectively. In the calculations, gear inches use drive wheel diameter instead of circumference.
Thanks for explanation – ie, multiply the gear inches by 0.0254 to convert to metric, then by π to go from diameter to circumference 🙂
Hi I wonder if you can help me out here. I have a new P line. 50 chainring with 11/13/15/18 cassette. Please advise have I calculate the gear inches?
Kind regards
Chainset teeth / cassette teeth x wheel diameter” = length of gear in inches
50/11*16=72.7
50/13*16=61.5
50/15*16=53,3
50/18*16=44.4
This is quite a narrow span. 44.4″ is quite long for climbing. 72.7″ is quite short for flats and downhills.
pi is missing.
50/11*16*3.14=72.7*3.14=228.39 in
50/13*16*3.14=61.5*3.14=193.20 in
50/15*16*3.14=53,3*3.14=167.44 in
50/18*16*3.14=44.4*3.14=139.48 in
The formula for gear inches calculations does not include pi:
(Chainring Teeth / Cog Teeth) x Rear Wheel Diameter (wheel & tire) = gear inches
Hi, What are the corresponding number of cassette tooth that you used for the Stormy Archer 6 speed/-12%? I’d like to figure out what my gear inches using a different chainring. Thank you!
re 3 speed
54 teeth = +8%
50 teeth = standard
44 teeth = -12%
I think?
But what combination creates -18% please?
Hi. 33.1 inches on a tape measure lines up with 0.84 metres on the metric side of the tape. However, the 33.1 inches refers to the equivalent size (diameter) of the front wheel of a penny farthing. If you pedalled that penny farthing for one complete turn of the front wheel, it would travel 2.64 metres. This is the continental way of measuring the size of a gear.