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Old 03-19-09, 01:57 AM   #1
Lewis Butler
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Brompton Modification Questions

Hi all,

I am looking at seriously modding a Brompton in the style of LittlePixel's fixie conversion, I have learnt a lot from reading over the posts here but still have a couple of things that aren't clear in my mind:

1. Does anyone know a place I can source an aluminium alloy chain tensioner as available on the Merc / Flamingo bike? I've looked for the eBay ID '123maddy' mentioned in LittlePixel's post and cannot find anything for sale

2. Can Birdy size (ETRTO 355) wheels be made to fit the Brompton rear triangle & fork if slicks such as Schwalbe Stelvios are used?

3. If I did make the above modification would I mess up the handling of the bike or the fold? Am I limiting the tyre choice I have available to me in comparison to 349? The benefit I can see is that I can use shorter drop brake callipers resulting in better braking.

Many thanks for your time
L
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Old 03-19-09, 05:40 AM   #2
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Hi Lewis; Nice to hear my bike is an inspiration...

I can answer most of these questions - so here goes...
1) I think Merc have stopped trading on the UK ebay for the time being - hence your lack of luck finding parts (I think EvilV bought them all! ). She's still registered as a seller so this might change - you could try contacting her directly - she may still have one lying around.

However - an alloy tensioner isn't necessarily mandatory. After having more than my share of chaindrops I took mine off and switched it out for a Brompton 2-speed derailleur (thanks somnatash!) that has deliberate side-to-side play on the jockey wheels that better works with the not-quite-100%-accurate chainline I was running. I say 'was' as I've recently upgraded to a shorter-axle bottom-bracket that fixes the chainline.

I think the main reasoning behind getting the alloy one is that the Merc plastic one is pretty cheap; the Brompton ones however are pretty well engineered and not something you should automatically disclude as a parts option on your bike.

Are you planning to ride fixed?

2) Yes I do understand that 355 wheels can be used - there's a white japanese one in a thread entitled 'best looking brompton' that I think has them. found it here. I don't recall whether the rear triangle needed any mods to make it fit but the front should take them with skinnys with no mods at all. Discount any ideas about fitting any mudguards though It has been reported that Moulton so-called 17" wheels (ISO 369) can be fitted with a little persuasion. I think that this must be with the ultra skinny panaracer tyre (and ultra hard to find)

3) it shouldn't mess up the handling. It'll feel a teeny bit more long legged with bigger wheels, though this will be a negligible effect; The fold should be fine too as we're only really talking about an increase of 6 mm to the wheel (that's only 3mm on either side of the axle).

Re better braking - I recently made some pretty unobtrusive drop-bolts so I could fit some rather elegant Campag Centaur skeleton calipers on the front - I must post some pix at some point; They work very well - if your bigger wheel choice is primarily about fitting shorter reach brakes, then don't rule out drop brackets/bolts.

Good luck with your build - I'm very interested to see / read more about it once you get it off the ground...

Huw

[edit] here's another thread with a cool B with ISO 355 wheels:
Terrific 18-speed brompton MOD

Last edited by LittlePixel; 03-19-09 at 05:48 AM. Reason: additional link to add
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Old 03-20-09, 05:08 PM   #3
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Thanks for the advice on the tensioner, I'm converting a single-speed Brompton that should come with the plastic derailleur you mention. Yes - I'm planning to ride fixed.

After a bit more reading on these forums I can see that the ETRTO 369 Moulton might be so large that it interferes with the seatpost when the bike is folded, does anyone know for sure?

355 might be a more sensible option, what rims are available in that size? The Alex DA-16 is fitted to some Birdy's, is that any good in comparison to the Velocity Aerohead's that I can get in 349?

The most concerning thing before I take the plunge is will a certain tyre size continue to be available for some time. I don't want to be stuck with some size that I have to eBay from the US.

Currently there are 369 Stelvio's available from SJS cycles, and there seems to be no issue getting the 355 or 349 size from many sources on the web.

But Schwalbe seem to have discontinued the Stelvio, it's not in the 2009 catalogue from memory (but it still seems to be available from Brompton's distributors). The replacement is the Kojak, which is a little wide for my liking.
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Old 03-20-09, 08:34 PM   #4
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I do not know for certain that the 369 tires will fit on a Brompton, but you may want to refer to the following site that gives diameters of various size tires:

http://www.ctc.org.uk/DesktopDefault.aspx?TabID=3802

Based on the information on that site, the 32-369 (Moulton) and 40-355 (Birdy) tires have an outer diameter very close to the 37-349 Brompton tires.
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Old 03-20-09, 09:40 PM   #5
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Quote:
Originally Posted by Lewis Butler View Post
Hi all,

I am looking at seriously modding a Brompton in the style of LittlePixel's fixie conversion, I have learnt a lot from reading over the posts here but still have a couple of things that aren't clear in my mind:

1. Does anyone know a place I can source an aluminium alloy chain tensioner as available on the Merc / Flamingo bike? I've looked for the eBay ID '123maddy' mentioned in LittlePixel's post and cannot find anything for sale

2. Can Birdy size (ETRTO 355) wheels be made to fit the Brompton rear triangle & fork if slicks such as Schwalbe Stelvios are used?

3. If I did make the above modification would I mess up the handling of the bike or the fold? Am I limiting the tyre choice I have available to me in comparison to 349? The benefit I can see is that I can use shorter drop brake callipers resulting in better braking.

Many thanks for your time
L
Check Brompton Talk for a table that discusses different wheel/tire combinations that fit the Brompton. Although I don't think that the mod is worth it.
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Old 03-31-09, 03:19 PM   #6
Lewis Butler
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Thank you everyone for their input on wheel size, I'm sticking with the real 16" (349) in the shape of 28 hole Velocity Aerohead rims. Seems to be more sensible as I at least know the tyre choices from almost 7 years of owning a Brompton.

Pixel/Huw - one more question, do you happen to have the official wheel building dimensions for the 74mm Pantour Delite Suspension Hub? It looks to be symmetrical and I've measured the width from center to flange to be 23.5mm & the diameter of the flange to be 52.2mm, spoke holes seem to be 2.8mm. Just want to know I'm on the right track with those measurements before calculating spoke length.
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Old 04-01-09, 07:56 PM   #7
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lewis - don't have them sorry - Pantour manual leaves a lot to be desired. I built mine using a vernier caliper to measure the sizes; front hubs are always symetrical as far as I can tell.
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Old 04-02-09, 03:57 AM   #8
Lewis Butler
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Thanks anyway Pixel, just thought I'd ask.

I've eventually got Pantour to answer my e-mail, so hopefully I'll be able to cross-reference *my* vernier calliper measurements with their take on reality.
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