# Brompton 3 speed gearing question



## DBrown67 (24 Oct 2019)

Just had a test ride on a standard 3-speed Brompton form Evans in Leeds. Was OK really but I found the gearing to be a bit high. I think I used 3rd just once in the few hours I had it. Was nearly always in 1st with the occasional relaxed cruising on the flat in 2nd.

I'm not a fit or fast cyclist. If I'm on a downhill run I'm pulling the brakes at 20mph. I'm happy to free wheel down most hills. On my commute home from Leeds centre I'm always getting overtaken by other cyclists... but I don't care about that.

I'm interested in the Brompton B75 model as it's much cheaper and seems like a blank canvas to get exactly the parts I want. Namely mudguards and a bag with bag clip.

I see that the B75 has a reduced gearing of -12%. So that seems like a good start.... but it's just a figure to me. Is 12% a big difference? Will it be instantly noticeable?
I had the preconception of using 1st sparingly and cruising on the flat in 2nd most of the time... 3rd just a bonus for me on the few occasion s I might get speed up on a downhill. But it didn't work out like that as I was in 1st around 70% of the time and there were a two or three hills near me I just couldn't get up. But I am unfit to be fair.

Anyone had experience of both these 3-speed options? I know there's a -18% option too but that's not what comes with the B75. And buying another bike to get that option adds around £300 to the cost at least. Plus I don't get that lovely colour that I really like on the B75. Even if I had choice of all colours I'd still get that one.


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## Tenkaykev (24 Oct 2019)

I have a 6 speed with reduced gearing ( - 12 1/2 %) 
It really suits me and makes the hills so much more manageable. 

If you head over to "Brilliant Bikes" YouTube channel them have a comparison of the differences between the B75 and a standard model. 

It's worth checking out the rest of their videos, really informative and entertaining too.


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## berlinonaut (24 Oct 2019)

DBrown67 said:


> Just had a test ride on a standard 3-speed Brompton form Evans in Leeds. Was OK really but I found the gearing to be a bit high. I think I used 3rd just once in the few hours I had it. Was nearly always in 1st with the occasional relaxed cruising on the flat in 2nd.



So either you are a slow rider or you ride at a very high cadence or both. Typcally most people would use the second (and consider it a bit short while the third is too long, so upshifting is not a perfect alternative). Yes, the three speed is on the too long side in the stock configuration.



DBrown67 said:


> I see that the B75 has a reduced gearing of -12%. So that seems like a good start.... but it's just a figure to me. Is 12% a big difference? Will it be instantly noticeable?



Yes, definitively.



DBrown67 said:


> Anyone had experience of both these 3-speed options? I know there's a -18% option too but that's not what comes with the B75. And buying another bike to get that option adds around £300 to the cost at least. Plus I don't get that lovely colour that I really like on the B75. Even if I had choice of all colours I'd still get that one.


With a new Brompton a change of the chainwheel to one of the other factory options is free of charge in the uk as far as I know. The color of the B75 is one thing but you should be aware that many components are of the older generation (mainly a matter of taste) and it lacks the folding pedal (which is a pity). So the cheaper price comes at a price. I'd doubt the 300£ difference to a degree - the B75 is clearly cheaper than a M3E but if you upgrade the B75 it will add up bit by bit.


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## cosmicbike (24 Oct 2019)

-12% will be very much noticeable, my standard M3L is 3 speed and anything like a hill is a challenge. It's been on the list to change the chainwheel for ages, but since SWMBO has taken ownership for a flat ride to work and back it's gone on the back burner.


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## DBrown67 (24 Oct 2019)

Thanks for the replies guys. So it seems the -12% will be very noticeable. That's good news. Evans have told me I can try the B75 but only for around 30 mins or so as it's not a Demo model they have in store for a 24 hour test. I suppose that's next on the list then.

Even if this wasn't enough am I correct in thinking I can swap the 13 tooth rear sprocket for the 14 tooth and get the -18%? I'd try -12% first of course but that sprocket is just a few quid and seems like a simple DIY job to swap.

I'm aware of the older parts on the B75 but that doesn't bother me. Price has always put me off Bromptons and £745 is still a lot of money (to me). So it has to ride spot on for it to even start to be money well spent.

Berlionaut you're right... M3E model with exact same spec as B75 comes in at £975. M3E will have up to date brakes, saddle etc. but it's still £230 more (I was £70 out... close but no cigar). And it's not available in that lovely B75 colour.  I'm almost sold on it. Depends on another short test ride.


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## TheDoctor (24 Oct 2019)

Changing the chainwheel or sprocket is hardly a massive job, or massively costly. If the bike otherwise is suitable, I'd go for it and fettle the gearing later if need be.


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## Tigerbiten (25 Oct 2019)

The gears on a Brompton are +33% apart, so -12% is roughly 1/2 gear down.

Do you have or can you borrow a geared bike.
If so then your best bet is to cycle along a flat road in still air at your normal speed.
From this work out what your ideal sized flat land gear is, chainring / sprocket x wheel size = gear size.
Then adjust the brompton gears so that the middle gear is around this size.
This will give you first gear for uphill and/or headwinds, middle gear for flat work and third gear for downhill and/or tailwinds.

Luck ...........


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## steveindenmark (25 Oct 2019)

I think a standard Brompton has a 50T chainring. The - 12% is a 44T chainring and you can go down to a 39T chainring from SJS Cycles. 

Buying a new chainring and chain is quite cheap and takes 10 minutes to change over. I have a 6 speed and so cant really comment. But I also think Bromptons are hard to ride with a 50T chainring. The 44T makes it much easier. The 39T is good in hilly areas but I spin out on the flat You need a seperate chain for each chainring as you need to remove links.


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## berlinonaut (25 Oct 2019)

There's more than one way to Rome. 50/13 as from the factory is too long, but 44/13 is more or less equal to 50/15, so you could either change the sprocket for a bigger one or the chainwheel for a smaller one. 
https://ritzelrechner.de/?GR=SAAW&K...V=development&GR2=SAAW&KB2=44&RZ2=13&UF2=1325

Personally I'd recommend riding a 2-speed as a comparison as well - cheaper, lighter and (at least in my eyes) more pleasant to ride than the three speed. With the B75 you are of course set on the three speed.


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## Tenkaykev (25 Oct 2019)

steveindenmark said:


> You need a seperate chain for each chainring as you need to remove links.



When I first swapped out a standard 50 for a 44 tooth chainwheel I left the chain as is. 
It worked perfectly well, the chain tensioner taking up any slack. 

When I decided that I much preferred the 44 tooth and it was staying permanently on the bike I removed a link from the original chain. 

So I suppose if you did envisage Swapping between the two chainrings you could still leave the chain as is.


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## steveindenmark (25 Oct 2019)

Tenkaykev said:


> When I first swapped out a standard 50 for a 44 tooth chainwheel I left the chain as is.
> It worked perfectly well, the chain tensioner taking up any slack.
> 
> When I decided that I much preferred the 44 tooth and it was staying permanently on the bike I removed a link from the original chain.
> ...


Yes you can. But I found the 44T runs better by taking a link out. For the 39T I removed 2 or 3 links. If I go back to the alps I will certainly carry the 39T and chain for the big climbs. Switching them over with the 44T is simple.


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## simon.r (25 Oct 2019)

Even if you can’t picture gear inches, this chart from Brompton gives you an idea of the differences.







Personally, as a not-fast cyclist I like my 6 speed -12% gearing. I rarely use top or bottom gear, but they’re there when I need them.


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## rogerzilla (25 Oct 2019)

Fit a 14T or 15T sprocket and find an extra link of chain - that's the cheap option.


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## Kell (25 Oct 2019)

As you might already have guessed, it's not a big or hugely expensive job to swap out these components for yourself at home.

The -12% option is simply swapping the chainring out. 10 minutes with a size 5 (IIRC) allen key and you're set to go. Chainring is £25, so it's not a big expense if you can do that yourself.

The -18% is swapping out both the chainring and the rear sprocket. Again, another easy enough job, it's just fiddly if you've never done it before as you have to remove the indicator chain and the chain tensioner, before you get to the wheel nuts. 

It's a pretty good exercise to do anyway, as if you understand how it all comes apart (and goes back together) in the dry at home, it's a lot better than being forced to try and understand it in the dark, in the rain when you're mid-commute.

But once the wheel's off, all you need is a small flat head screwdriver. Sprockets are about a tenner + plus a bit of your time.


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## byegad (25 Oct 2019)

I can't speak to bromptons in particular. But having ridden 3 speed SA bikes around Durham City for 15 yrs, I can tell you I dropped the gearing so that 3rd was my 'on the flat' gear, still good into a breeze, thus giving two lower ratios for the hills, of which Durham has a few!


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## DBrown67 (25 Oct 2019)

Thanks for all the advice guys... very helpful!

I would like to reiterate that the bike I tested was factory standard 3-speed. The B75 is already -12% so I'd have to do nothing if it suits me. Only other Brompton option is to fit the 14 tooth rear sprocket to get the -18%.

It's nice to see the 3rd party option from SJS for the 39 tooth ring. Didn't know about that. But as you say you're getting into the realms of having another chain and I certainly won't be riding around any mountains. Though I do live in Yorkshire and there's a few hills knocking about once I get outside Leeds.

Been doing my due dilligence and it's good to see there's a thriving 3rd party market for Brompton parts and accessories. I have looked at other folders like Dahon but their range is so big and they seem to discontinue models on a whim. With Brompton the frame is the same throughout. Just everything around it is choice.


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## jay clock (25 Oct 2019)

I have a S3L and found the standard 3 speed tough. Dropped the front ring from 50 to 44 I think and problem solved. On the flat I am between 2 and 3 and spinning out at about 30kmh.


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## 12boy (26 Oct 2019)

The nice thing about Bromptons is how easy they are to modify. Easy to swap sprockets and to add a chainring, sprocket swapping being the cheapest. Because the wheels are small, a Brompton sprocket doesn't last as long as the same size sprocket on a larger wheel. You will be replacing them fairly frequently, at least as often as you replace a chain or two. A 1 tooth difference on a sprocket changes gear ratios far more than on a few on a chain ring. Right now, for example, I am running 58 and 38 chainrings and 12 and 17 tooth sprockets on a two speed, saving some pounds from an SA 3 speed. Since Shimano sprockets work fine and I have a cluster or two lying around I may try 18 and 19 tooth sprockets to incease my range. Going up a steep hill for any distance calls for gear inches in the lower 30s if not lower, especially if there is a headwind as well. As a grinder, not a spinner, I prefer higher gear inches than you folks appear to, but that is just my preference.


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## DBrown67 (17 Dec 2019)

Thanks for all the help guys... I take delivery of my B75 in 2 days from Halfords (got 10% British Cycling discount). I've already got mudguards ordered and plan to ride the standard bike a short while and see how i go before making any other decisions. 

But just as a thought...would this crankset fit a 3-speed Brompton? It seems to have the correct square taper fitting.
http://vi.raptor.ebaydesc.com/ws/eB...tegory=109118&pm=1&ds=0&t=1564939840000&ver=0

Reason I ask is because I have a Giant Escape 2016 model fitted with this crankset that I am currently not using. The granny ring is removed on mine so is just a 48/36 at the moment. Would be great to try out for a quick 6 speed if it fits. Might be some overlap though and probably wasting my time. :P


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## 12boy (17 Dec 2019)

Looks like a 110 BCD crank and I have one on my Brompton with 58 and 38 tooth chainrings. The only issue with the 58/38 is the chain comes off when folding with the 38. Shimano crankarms are JIS and should fit on the BB. You might check how much closer to the ground your pedal will be with a 175 crank arm though.


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