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Changing Brompton rear sprockets

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Changing Brompton rear sprockets

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Old 04-15-18, 11:50 AM
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Joost
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Changing Brompton rear sprockets

Hi all,

First, let me introduce myself as I'm new on the forum. My name is Joost (almost 40) and I'm from The Netherlands. My daily driver is a (also almost 40 years) old Sparta city bike which I love. Besides that I have classic racing bike from the eighties.

I'm thinking of buying a Brompton. Thanks to the internet and this forum in particular, I'm pretty sure I will order the 2 speed with mudguards and M type steer (M2L).

However, I'm a little stuck on which gear ratio to get. Having looked at the gear ratio table on the Brompton site and the hub gear calculator, I will probably end up with the 50t or the 44t chainring (-7% or -19% ratio). That's because I prefer a lighter and faster cadence, and also because my house is on top of the only hill in our kingdom.

Now for the question: If I go for the 44t chainring, the second gear will have 60,9 gear inches. If I go for the 50t chainring, that will be 69,2. My ideal cruise ratio (based on my beloved city bike) is around 64. I could get that by having the 50t chainring and exchanging the smallest rear sprocket (12t) to a 13t. Is it possible to change the rear sprocket to a 13t or 14t? If so, are these standard parts? Brompton only sells the 12t ad 16t.
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Old 04-15-18, 01:24 PM
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2 speed is a narrow cassette like freehub, and the cogs are retained by a steel wire snap ring..

B considers 50t the 1, 44t the minus 54t the +

they adopted the Shimano BMX splined pattern.. a 1 speed uses an 1/8" thick cog, 2 uses 3/32"..

You may find cogs 12 to 17t, via Sun Race , TW parent company supplying some Brompton parts to the factory in UK

though a 17t may hit the frame tube ends of the rear, for the 14 15, 16.. you can use other 130 bcd chainrings too, like a 39t
but they won't have the trouser cuff guard.

I have the 3 speed BSR, I use a 15:54..

FWIW ..I'm a Pootler not rushing, in a not flat * but by the riverbank town. (& 30 years older than you)
*.. So I added a geared crankset..



....
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Old 04-15-18, 01:32 PM
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Originally Posted by Joost View Post
because my house is on top of the only hill in our kingdom.
This is what I call bad luck. Must be the famous "dutch mountains"...

Originally Posted by Joost View Post
Is it possible to change the rear sprocket to a 13t or 14t? If so, are these standard parts? Brompton only sells the 12t ad 16t.
You can use any Shimano compatible sprocket. Brompton also sells a 13t which is intended for the BWR and should be a fit (did not try it but I think it should fit on the 2-speed, too).
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Old 04-15-18, 01:48 PM
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"dutch mountains"

Amstel Gold race route go somewhere around your town?

as I recall Maastricht, is near the northern end of some of the Belgian Ardennes, just down the Maas a ways from Liege BE.

Even Sittard, not that far north, I don't recall being hilly when I rode thru, Lo these many years ago..




...
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Old 04-15-18, 02:08 PM
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Originally Posted by fietsbob View Post
"dutch mountains"

Amstel Gold race route go somewhere around your town?

as I recall Maastricht, is near the northern end of some of the Belgian Ardennes, just down the Maas a ways from Liege BE.

Even Sittard, not that far north, I don't recall being hilly when I rode thru, Lo these many years ago..

...
The places you mention are all in the most southern part of the Netherlands, called Limburg (it's a province). That's is quite a hilly area (at least for the Dutch it is) and that's where the Amstel Gold race is held. The rest of the Netherlands is almost completely flat (really, really flat), except for a small ridge in the middle called the 'Utrechtse heuvelrug'. That's where I live. So I'm lucky.
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Old 04-15-18, 02:11 PM
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Originally Posted by fietsbob View Post
"dutch mountains"

Amstel Gold race route go somewhere around your town?
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Old 04-15-18, 02:17 PM
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Originally Posted by fietsbob View Post
they adopted the Shimano BMX splined pattern.. a 1 speed uses an 1/8" thick cog, 2 uses 3/32"..

You may find cogs 12 to 17t, via Sun Race , TW parent company supplying some Brompton parts to the factory in UK
....
Originally Posted by berlinonaut
You can use any Shimano compatible sprocket. Brompton also sells a 13t which is intended for the BWR and should be a fit (did not try it but I think it should fit on the 2-speed, too).

Thanks, that's useful info!
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Old 04-16-18, 07:23 AM
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I would suggset you ride a Brompton before ordering. 70 gear inches on a 25 lb bike may feel different than on your city bike which may weigh more. The 16 inch wheels accelerate from a stop faster than 28 inch wheels. I would also try a 3 speed with a 13/50 combination. That gives you 46, 62 and 82. The high and low would be nice if going with and against the wind.
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Old 04-16-18, 09:59 AM
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The three speed Bike is not much more £ than the single speed when buying new - conversion to 2 speed is easy and not expensive and you may think about keeping the 3 speed kit if you ride outside Holland.

Have you also compared Euro prices in NL with £ prices in the UK - maybe because of the fall in the £ you could save money by buying in the UK if you ever visit

Holland - one of my favourite countries, we lived there for 3 years from 1979 - in Amstelveen and we have visited quite a lot with good friend there
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Old 04-16-18, 02:19 PM
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The 3-speed is much heavier than a 2-speed and does - at least in my opinion - not offer a relevant advantage for most riders but the disadvantage of the weight. Thus I'd stay away from it - either 2-speed or 6-speed. In flat areas the 2-speed would be (and is) my favorite. Buying a 3-speed with the plan to convert it to a two speed sounds a bit silly to me. Including the conversion cost you could easily buy a six-speed instead and still have money left on the bank. The better choice is to go for the two-speed and - if it turns out to be necessary - add a BWR wheel later to switch for longer tours. This way you can have a two speed and you can switch to six when you need it (though I highly doubt you will ever do that).

Personally I consider the OP's choice of 50/13 for the two-speed really shortish, but erveryone to his own taste.

Regarding the 3-speed: Stock it comes with 13/50 which is unfavorably long in 3rd in practice - as an average rider you only rarely will use the 3rd happily wheras the 2nd is too short quite often. Going for 14/50 is much better in practice.
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Old 04-16-18, 03:16 PM
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Real hill climbing , for the less gram conscious , was a benefit of the swiss mountain drive.. a fast gear change at any speed
from a 50t to a '20t', and back up again.. via heel tapped button in the crank center.

with the BSR the double shift between 3rd & 4th , * works a lot better with newer shifter on my Mk4, than it did with the steel trigger, on the Mk2..

* high in low range to low in high range, double epicyclic gears shifted at the same time..

really useful when bogged on a hill and needing to do the double downshift. badda bing..




but yea, now buying a couple cogs and a different chainring is no problem afterwards, If you change your mind..
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Old 04-20-18, 03:49 PM
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Yesterday I made a three hour test drive on the standard geared 3 speed. I found the third speed to be very high and only useful when going downhill. Personally I would never use this gear on the flat. Just to heavy. The second speed however felt good for me. A little short on speed when going downhill or when having the wind from behind, but not so heavy that there’s a need to downshift when going slightly uphill. The second gear never becomes uncomfortable to my taste and capability.

Based on the test drive I today ordered a 2 speed with a -19% (44t) gearing ratio. I think this is closest to the second gear of the default 3 speed. This also means that the first gear is very low and more useful for climbing the steep hill to my house than the first gear on the 50t chainring version.

In case I eventually find the gears to low I can always buy a 50t chainring and go experiment with the rear cogs. We’ll see. I’m happy for now. Now I just need to wait 5 weeks for the bike to be build. 😩
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Old 04-21-18, 10:49 AM
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15t on my BSR, any larger cogs are dished.. 16t+
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Old 07-14-18, 05:00 PM
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Originally Posted by berlinonaut View Post
You can use any Shimano compatible sprocket.
The "Brompton Sprocket/Disc set 13/16T BWR 6-spd , wide ratio" retails for €14, and a no-brand chain is €10.

Considering I need to replace the chain + sprockets about every 3,000km, would I save money by buying Shimano-compatible sprockets from someone else, or is the price difference too small to bother?

Thank you.
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Old 07-15-18, 01:44 AM
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Originally Posted by Winfried View Post
The "Brompton Sprocket/Disc set 13/16T BWR 6-spd , wide ratio" retails for €14, and a no-brand chain is €10.

Considering I need to replace the chain + sprockets about every 3,000km, would I save money by buying Shimano-compatible sprockets from someone else, or is the price difference too small to bother?
I'd stick to the original in this case - the Shimano compatibility comes into play it you want to use different sprocket sizes than offered by the factory. In most cases you'd need to buy whole Shimano cassette and then take it to parts, so the Brompton ones will probably cheaper (ans less effort) most of the time as long as you stick to the original sprocket-sizes. Regarding the chain I'd go for an 8-speed chain and not necessarily buy the cheapest one (depending from your usage of the bike). SRAM and Wippermann/Connex have both proven to be a good choice in terms of quality and lifespan. Maybe a tad more than 10€, but still way below 20€.
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Old 07-15-18, 04:27 AM
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Until now, I actually used SRAM PC870, and I was wondering if I could use something lighter.
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Old 07-15-18, 07:36 AM
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Until now I was too lazy to bother with saving weight via the chain, but I'd assume it would be possible. Unfortunately SRAM seems not to publish the weight of their chains - the 890 seems to be next in the range and possibly of a bit higher quality than the 870 (that I am using most of the time as well). You could also look at the connex range of chains. They outline the weight and at 114 links (which is a couple more links than used on a Brompton) you'd save about 40g when going top notch instead of entry level (~280g vs. ~320g). There are brands like Yaban that market "titanium chains" but I have no personal experience with them. They seem to be lighter (possibly around the 210g mark) but the price seems very prohibitive, at least for me and not worth the extra money.
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Old 07-15-18, 09:25 AM
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Ok, it doesn't like it's worth it. Thanks.
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Old 07-15-18, 11:55 AM
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I happened to find a couple NOS full bushing 3/32" wide Whipperman .. they have proven to offer a longer wear life
than the bushingless 5~8 speed derailleur chains..

next AW cog 1/8" so an easier to find full bushing in that width will be a bit better..
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