Brompton S2E
 

Hello!I am planning to go with S2E. They adviced me to upgrade to 18T cog and 58T chain ring. I would like to know, what would be the resulting gear ratio compared to the standard stock S2E specs. Gear inches at Brompton, says a
standard S2E gearing goes, 1st gear- 56.0"= 4.47m 2nd gear- 74.7"= 5.97m.
If I may ask, what would be the result now with an 18t cog and 58t chain ring?
I hope this is not too much of a question. Thanks
REPLY

Thread moved from Introductions to Folding Bikes.

Sheldon Brown's Bicycle Gear Calculator is a very useful tool for your purposes and yields for 18/54 51.8 gear inches. However, you have another sprocket so plug that in as well and you will get the other gear inch number. What's best for you will depend on your strength, the hills you will encounter and the headwinds typical to your location. I switch from a single with 54/12 ( 74.9 GI) to a standard three speed with 50, 67 and 89 GI which are both just fine for my location.

the 12~16 is stock , I found (older MK2) a 16t cog hits the end of the frame tube, 18t may not even rotate or let you put the wheel in at all.

I have a 15:54 (M3L) .. order your bike with the 54t crank , if that's not high enough, then you can shop for a bigger chainring..




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That was I was thinking. The 18t cog is perhaps a little too big and with 58T, the purpose of going faster is being negated. Pardon my English, not my first language. So you think guys, that I should leave as it is the stock sprockets but replace the chain ring with just a 54t? :foo: :twitchy:

Thanks for this info. I tried searching it, but I got too confused. The 2speeds Brompton seems yo be not listed there, or how do I put the info in there. Lol! :crash:

NB: You can order the bike with 3 choices of crank/chainring combinations, One of the Options is a 54t,,
so you don't have to change it, it's an order choice..

the 50 is their medium size, 44 their lower gear option.. they use a minus for the 44 and a + for the 54.

for non mechanical customers that don't use tooth counts in their choosing..

Simply go here - it is made for Brompton gearing: Hub Gear Calculator

With 75 GI you should be able to do some small grades and deal with 15-20 mph headwinds although both at the same time might be tough. That 56 GI option would bail you out. Bromptons have a lot of wind resistance due to the upright seating. As said before, the terrain/wind conditions where you are would make a big difference. With the new crank setup you can add a chain ring for greasy finger shifting ( I can't find any 130 BCD chain rings with less than 38 teeth), but still it's an inexpensive option which weighs very little more than the 2 speed Brompton.

that's because its mechanically , physically impossible, to bolt a chain ring on that ts smaller than the bolt circle to mount it..





[tripleizers are specially made as middle chainrings for a second chainring to be bolted to its inner circle.. to have 3 on double cranks..

so have both a 130 and a 74 bolt circle ..]





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Sorry for my understanding of " That 56 GI option would bail you out." meaning, I will have more hard time pedalling? As I've said, English is not my first language. The Brompton is shipped already and will wait 2-3 das eta. The stock 54T ring is in the box including the Brompton stock kevlar tires. I had it replaced with sleek Kojaks for less rolling resistance so more speed hopefully.

My Brompton 2-speed has 12T/17T cog with 54T chainring. It does need some extra step to make it work. I suggest you to keep your Kevlar tires for a while. They are not that bad.