My’s son’s Brompton was stolen in London last week. It’s his main mode of transport, and was a gift to him nearly 5 years ago when he left for Uni.

It’s a very unique bike – converted to an Alfine 8 speed hub, with 32 spokes in the rear wheel.

 

 

 

If you come across it, look for the frame number: 436821

Thankfully the bike was insured – but how to replace something quite so unique?

I decided to buy the stripped down version of the Brompton – the B75 – and use this as the basis to recreate the old bike. The B75 first came on the market at £750 – pretty reasonable for a three-speed Brompton – but has since gone up to £850. (Pandemic? Brexit? More people cycling?)

At the same time, other Brompton versions have also shot up in price. I bought my M6L 4 years ago through cycle to work, and the shop price was around £1000. Today, a typical price for the equivalent is £1275. Ouch.

But that extra £525 on top of the B75 will pay for a lot of upgrades.

 

So I’ve set myself a challenge:

to convert the B75 to an Alfine 8 hub,

with all the features of a brand new M6L

– for less than £1275.

 

I’ll post about this as I go along; but first, let’s establish the baseline. What is the B75, and how does it differ from the M6L I might have bought?

The Brompton B75

The first thing to say is all the essentials are here. This is not a cheap imitation of a Brompton – it’s the real thing, with just a few compromises to shave a few – well – hundred quid off the price. So how have they done it? So far as I can see, the savings are here:

  • saddle – more generic, but still with Brompton name on it
  • the saddle pentaclip has gone, replaced with a clunky old steel bracket
  • no mudguards
  • three speed only – which means the hub is the Brompton Standard Range of gears, and can’t be upgraded to 6 speed without replacing the hub (which uses the Brompton Wide Range hub) The three speed standard range has an overall range of 178% from bottom to top, while the wide range hub (combined with two-speed derailleur – 3×2=6) has a range of 302%.
  • no folding left pedal. Left and right pedals are more mountain-bikey – wide and flat.
  • older-style brake levers. But they work.
  • hard rubber bar grips, rather than the soft foam version.
  • 44t chainwheel – a matter of choice, and not really a cost saver – it’s just you don’t get any choice. This is low-geared option. If you wanted the higher gear you’d be paying extra.
  • Another change is the curious white suspension block – anyone? Not clear if it’s ‘firm’ or standard.

That’s really about it. Not a terrible list of sins, even if the saddle bracket is slightly blasphemous. What’s more, there are two features that I really like, that actually add value:

  • extended seat post as standard. I’m 5’11” and need the full height of the extended post to avoid cramped knees. This extended post is great news for many average/taller people.
  • the colour! I’ve always gone for black rather than pay the additional £70-ish for a special colour. The water-blue on this is really rather nice.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

A note on gearing:

With a 44t chainwheel and 12t rear sprocket, the overall range of gears is 178%.

The ‘metres of development’ (how far you travel on a full circle of the pedal) for the three gears are 3.63m, 4.84m, and 6.45m.

It may be helpful to compare this to a 6-speed Brompton with a 44t chainwheel (and 12 and 16t rear sprockets) (overall range 302%)

Here the metres of development for the six gears are 2.32m, 3.09m, 3.63m, 4.84m, 5.69m, 7.59m.  From this you can see that gears 1 and 2 of the B75 equal the 3rd and 4th of the 6-speed, and the B75 top gear falls about halfway between gears 5 and 6 of the 6-speed. Other sprocket sizes are available.

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