New Brompton owner - gearing question

[Bugsbunny]

Hi there folks...

I've just bought my first (second hand) 2016 Brompton which is a S6 - without the rear rack. Believe that makes it an "L"? It came with the standard 50T with 6 speed wide gear hub.

I'm planning on taking my Brompton touring and I like climbing. My passion is to do big climbs (like I normally do with my road bike).

I've searched long and hard about Brompton gearing and tried to use Sheldon Browns gear ratio calculator but I've not figured things out.

Basically the standard 50T will not be enough for my fitness for climbing. I'm talking 1000m elevation, circa 8-10% avg gradient climbs.

I want to do a modification without breaking the bank, and it seems that the easiest and lowest cost way is to swap the chain ring to a 39T (or 38T). I can understand that top speed will be sacrificed, but I believe for touring - my avg speed will be about 22km/h so top speed is not my priority.

My question is, if I swap to a 39T chain ring combined with my 6 speed hub, at say 85 cadence what will be my speed be in first gear and sixth gear?

I generally prefer climbing at around 85-93 cadence so I'm trying to get that sort of gearing for climbs.

Bugs

[iow]

see HERE
c. 6.5 & 20 mph

[Brucey]

yup, that range of gears would be OK for touring on I reckon; I'd use 5th quite a lot on the flat and bottom gear would quite good on the long climbs.

cheers

[Bugsbunny]

Thanks Mark. That is bloody brilliant! I've probably spent 10+ hours scouring the internet and trying to figure it all out. What confused the hell out of me was the two rear derailleur gears on the Brompton and how to factor that into traditional gearing apps.

From the chart, a 38T might be the way to go.

Bugs

[Brucey]

FWIW that gear calculator is very useful; I have recommended it many times. Dirk recently changed it and there may yet be some bugs in the current version; I found one recently and he soon fixed it. There may be a small change to it before too long; I have suggested an additional feature that he may incorporate at some stage.

cheers

[mercalia]

please report back how you get one touring on a Brompton that has a modest range of gears

[iow]

Thanks Mark. That is bloody brilliant! I've probably spent 10+ hours scouring the internet and trying to figure it all out. What confused the hell out of me was the two rear derailleur gears on the Brompton and how to factor that into traditional gearing apps.

From the chart, a 38T might be the way to go.

Bugs

yes. the lower the better I think, if my S6 is anything to go by - unfortunately, it's totally out of it's depth in the climbs (noodle) and too twitchy coming down the other side...
it will be interesting to hear how you get on with it.

[Barks]

Brompton offer smaller chain rings to reduce the gearing by 12% and possibly 18% - i’m Not sure of the tooth count. I have the 12% version on my three speed but they do the same for 6 speed. You can get all the information you need from the Brompton website ‘support’ section. I have seen some blogs of people who use Bromptons for touring and most seem to have the reduced gearing.

[softlips]

I rode the Flanders sportive and Tour de Yorkshire sportive earlier this year.

On both I saw people on Brompton’s. All were 6 speed and all but one were standard gearing (the othe, at Flanders, was -12%). This helped me decision to get a six speed standard ratio.

[Bugsbunny]

I've placed an order for a 38T on CRC. Fingers crossed no issues with compatibility or chain dropping etc. Will try and re-use the existing chain if I can too. Should arrive in a week or so and will update you guys on how it rides. There is a 140m elevation climb behind my house which avg about 7-8% - with a pitch of 11% so that should be a good test bed.

I find the Bromptons quite a bit harder to climb with mainly due to their weight. I only weigh 62kg, so the overall weight increase vs my regular road bike is quite substantial.

Bugs

[mercalia]

I've placed an order for a 38T on CRC. Fingers crossed no issues with compatibility or chain dropping etc. Will try and re-use the existing chain if I can too. Should arrive in a week or so and will update you guys on how it rides. There is a 140m elevation climb behind my house which avg about 7-8% - with a pitch of 11% so that should be a good test bed.

I find the Bromptons quite a bit harder to climb with mainly due to their weight. I only weigh 62kg, so the overall weight increase vs my regular road bike is quite substantial.

Bugs

lucky lucky you

[rmurphy195]

I've placed an order for a 38T on CRC. Fingers crossed no issues with compatibility or chain dropping etc. Will try and re-use the existing chain if I can too. Should arrive in a week or so and will update you guys on how it rides. There is a 140m elevation climb behind my house which avg about 7-8% - with a pitch of 11% so that should be a good test bed.

I find the Bromptons quite a bit harder to climb with mainly due to their weight. I only weigh 62kg, so the overall weight increase vs my regular road bike is quite substantial.

Bugs

Let us know how you get on, I might try this myself. And as for chain length - a nice rule of thumb is that if you are dropping 6 teeth, then shorten the chain by 6 links (or is it 3 pairs of links?)

[Bugsbunny]

Will update you guys how it goes - no problemo.

As for chain links to remove - I'm not 100% sure but I believe 1 chain link for every 2 teeth reduction on the chain ring. So 50 - 38 = 12, so in theory 6 links. However, I might err on the side of caution and go with 5 link removal in the first instance.

[Brucey]

Will update you guys how it goes - no problemo.

As for chain links to remove - I'm not 100% sure but I believe 1 chain link for every 2 teeth reduction on the chain ring. So 50 - 38 = 12, so in theory 6 links. However, I might err on the side of caution and go with 5 link removal in the first instance.

yup, six (half) links will have to come out.

NB, unless you have half-links to install/remove, you are bound to remove an even number of chain links, rather than an odd number

cheers

[Bugsbunny]

Thanks Brucey!

The chain ring arrived today. Can't wait to install it!

Going off tangent here - but as I'm gonna take it to Japan in August for rides out in the country side, what do you guys do for puncture prevention? Frankly, whilst I've seen on YouTube how to do a tube replacement - I'm 90% sure I'm screwed if there is a puncture roadside and I'm riding solo too. I have the original Brompton Kevlar tires.