Brompton ~ gearing / some hills

Nasqueron

Just pondering a Brompton for work travel due to change in circumstances (would be for railway in the morning, 6 mile ride home). I have spoken to people on a Facebook bike group so I am confident the riding distance is ok.

I think the single speed 54/12 would be unsuitable, top end is fine, hills less so, ditto the 54 12/16 two speed but I can't seem to find the teeth count for three or six speed (though I think the 6 speed is a bit excessive for what I need!) - any ideas what the actual number of teeth are and how they are for riding away from flat city roads?

somersethillbilly

Take a look here....

https://brompton.zendesk.com/hc/en-us/articles/203295861-What-are-the-Brompton-gear-ranges-and-ratios-

Nasqueron

somersethillbilly wrote: »

Take a look here....

https://brompton.zendesk.com/hc/en-us/articles/203295861-What-are-the-Brompton-gear-ranges-and-ratios-

Yeah I have already seen that

I asked about teeth count as I need to know that, I don't need gear ratios cheers

surreysaver

Is this any help?:

http://www.foldabikes.com/Talk/gear/gear20.php

WobblyDog

I've got a 20 year-old 3-speed standard that I used to ride in hilly North Devon. It's worth noting that you can't efficiently "come out of the saddle" on a Brompton to help on steep hills, it's too wobbly for that. So you might want slightly lower gearing than you would have on a conventional bike. I used to plan routes to avoid any gradients steeper than 10% (I was pretty fit at the time).

Nasqueron

WobblyDog wrote: »

I've got a 20 year-old 3-speed standard that I used to ride in hilly North Devon. It's worth noting that you can't efficiently "come out of the saddle" on a Brompton to help on steep hills, it's too wobbly for that. So you might want slightly lower gearing than you would have on a conventional bike. I used to plan routes to avoid any gradients steeper than 10% (I was pretty fit at the time).

Cheers, fortunately my route home only has a very small couple of hills and I've ridden it on normal bike now and I'm happy enough doing that so I think so long as there is possibility of spinning up, I should be ok. I ride a 52/36 11-32 on my best and 50/39/30 11-28 on my commuter / 46/36 11-28 on winter commuter/CX so going up hills are ok with the gear ratios I have, so it's just trying to match that

Nasqueron

surreysaver wrote: »

Is this any help?:

http://www.foldabikes.com/Talk/gear/gear20.php

Yeah I've seen that side, the problem is they don't have the teeth count or ratios for all the gears unless I am missing something obvious (though that might be down to the 3 speed internal hub gears which I don't known much about)

Single speed is 54/12 which is fine for flat but pain for any sort of hill
Two speed is 54 12/16 which even on the bigger one gives a ratio of 3.375 which is the sort of top end racing gear ratio, not for hills (obviously they have the reduced gearing like the 50T/44T)

Three speed is 50 on the front (with 44/54 options available) but no idea what the rear gives you

Brompton themselves say the 6 speed is the one for any sort of tough / touring hills, which I am not going to face, so the three speed sounded ok but the problem is getting the T count for the rear cassette as if the ratios are all similar. I might as well get the two (for the familiar derailler) and just mash it up hills with clipless pedals!

The other problem I have is the Brompton bike builder seems to be unavailable (components and Next Step are greyed out) which means I can't see stuff so I have to use the "help me choose" which builds it with stuff like a light (I have them, no need) and mudguards but no rack (pointless for me) and it defaults to 3 speed -12% gearing as I choose middle hills or 2 speed with -7% gearing if I choose not very hilly

I'd probably do best going off and chatting to a shop and testing them as it's not massively urgent!

WobblyDog

According to my calculations, a standard 3-speed Brompton (16" wheels) has these gear ratios:
45.7" (0.7419 x 16" x 50 / 13)
61.5" (1 x 16" x 50 / 13)
81.4" (1.3226 x 16" x 50 / 13)

Your 52/36 11-32 bike (assuming 26" wheels) has a minimum gear of 29.3" and a maximum of 122.9".

Apologies for the units, bike gears are one of the few things I still think of in terms of inches. In practice, I think 81.4" is plenty large enough for typical Brompton use, but 45.7" might be a bit limiting in hilly areas.

Richard53

WobblyDog wrote: »

Apologies for the units, bike gears are one of the few things I still think of in terms of inches.

Me too. 52/13 means nothing to me except it sounds big, and a 'developpement' of 8.8m is meaningless. 108" tells me exactly what it is.


Gear inches, being the diameter of the equivalent wheel on an Ordinary Bicycle which will travel the same distance for one turn of the pedals, are completely illogical, of course. But, like much in the Imperial system, they make sense in human terms which other systems do not.