Brompton Gear Ratios

Other bike manufacturers migrated to the similar sram 5 speed but the brompton frame is unusually narrow and it was not until may 2002 that the company came up with its own solution the 6 speed more correctly 2 3 speed sram brompton derailleur hub gear. The 2 speed version has 12t 16t rear sprocket and 54t front chainring.

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This acts like an internal hub gear but for the front chainring.

Brompton gear ratios. All three chainrings are interchangeable having a 130mm bcd so some experimenting is available for the more adventurous. It has two options a 1 1 ratio and a 2 5 1 downshift. What speeds will your brompton do in its lowest gear at a 70rpm cadence and in its highest gear at a 90rpm cadence.

As i have kept the schlumpf mountain drive from my old brompton i have no need of any lower gears. It turns out that the 44t brompton will let you crawl up a hill at just 6mph in first gear at 70rpm while the 54t brompton will get you up to 28 8mph in 6th gear at 90rpm. Brompton folding bikes come in 4 gearing options including the single speed 2 speeds 3 speeds and 6 speeds.

Long term readers may recall that the bankruptcy of hub gear manufacturer sturmey archer in the summer of 2000 left brompton short of a suitable 5 speed hub. Three speed brompton standard ratio 13t rear sprocket. We can now refine the question.

1 sp 19 60 9 10 9 60 9 16 3. Six speed brompton wide ratio 13t 16t rear sprockets. 2 sp 19 45 7 8 2 60 9 16 3.

The 3 speed version has 13t rear sprocket and 50t front chainring. In all cases the chain length will need to be adjusted to accommodate the new chairing size. Having given up hope of getting my brompton t5 gears fixed i decided to upgrade to a new six speed version.

Brompton bikes can also be fitted with a 44t chainring reducing the ratios by 18 for very hilly conditions. It would be brilliant except that it costs 275. This would replace all the current rear gearing on the brompton and give 14 internal hub gears.

In fact the transition between schlumpf top and brompton bottom is perfect but i find the brompton derailleur. 1 sp 7 69 2 12 4 69 2 18 5. Another option is to use a rohloff speed hub.

54 tooth front chain ring. 50 tooth front chain ring. I opted for the 6 speed standard gearing when i purchased my brompton.

1 sp std 74 7 13 4 74 7 20 0. Specifically the standard single speed has 12t rear sprocket and 54t front chainring. 50 tooth front chain ring.

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