What makes the Brompton so slow?

your weak legs?

Mainly the engine.

Well I know that but it still seams quite slow compared to other bikes.

Because it's not designed for speed? It's a steel folding bike with several hinges that only serve to increase weight and flex.

Granted, the same "engine" on a carbon road bike will go faster, but then it wouldn't fold as small or be able to carry as much.

It's like asking why is an MPV slow?

Joking aside, it's actually a good question and not that easy to answer. Exactly what is causing it to be slower?

1. Weight. Roads are most often not exactly level, so a heavier bike will be slightly slower on slight imperceptible uphills.
2. Position. A more upright position will have more wind resistance and slow you down.
3. Wheels. Smaller wheels have more rolling resistance, due to more rubber movement relative to big tyres, and more revolutions on wheel bearings, and generally slower tyres.

So a lighter, more aero, with sskinny wheeled bike will be faster than a Brompton. But it won't be as convenient.

I have been commuting daily on a folder (20 inch wheel Dahon like though not a Dahon) for couple of months. Here is my observation:
I can keep up with most fast road bikes except really fast ones(), can beat casual bikes, low spec (e.g single speed) or tired/lazy road bikes. I beat almost all other folders I came across.

Want to go faster here is the points:

1. Gear inch, what's the max gear inch on your Brompton? I know the 6 speed one has really high max gear inch (100 or more). If you can keep on that gear probably you can beat most road bikes. So if yours is only a 2 speed, probably the max gear inch is still pretty low, so no matter how fast you spin (will increase speed to a certain point) you are still slow. My folder has max gear inch around 95, so it has the potential to be very fast though in reality I rarely goes to the max gear because I am not a super man.

2. Fit. this is probably the most important one. Normally you don't have a good fit on a folder as on a proper fitted road bike. So you are less aerodynamic and less optimal in the peddle strokes. I spent a lot of my time trying to figure out the best fit I can get from my folder, and different positions techniques. So far I am happy with the result. If you are really into it, you can change the handle bar to drop bar etc, I saw some people doing it.

3. Specs. This includes weight, wheel size etc. My folder is around 10 kg, so not too bad even for a road bike. Wheel size is important for bad roads. 16 inch wheel will drop a lot of speed on a bump while 700c may have little effect.

OP, if you are running the stock schwalbe marathon tires, i would suggest ditching those and going for a slicker high-pressure tire like the primo comet. keep the tires inflated to max pressure and you will definitely notice a significant improvement in performance - under-inflated tires have an elongated contact patch and that equals greater rolling resistance.




if that doesn't improve your speed significantly, then i would suggest trying a smaller diameter front wheel. 305 or maybe 254. think about it - if you have a smaller front wheel then you will constantly be going downhill. it's just physics, man.

Running Primo Comets on it.

I ride my Brompton at the same speed as my other bikes, or at least attempt to, it takes more effort, or it seems to. I have had other small wheel bikes in the past, R20, a 64 Moulton /Huffey, Dahon. These also were an upright position. They seemed quicker. It is not that the ride is bad, just more effort.

The only thing I can come up with is is that the rear shock flexing. I have the stiffer one.

makes sense. there are quite a few after-market suspension blocks available. some soft, some firm. but, before you spend 100 +, i would suggest using a couple of hose clamps on your existing elastomer to determine if too-soft/ bouncey suspension is throwing off your pedal cadence and slowing you down.

try this: How to stiffen the suspension on a Brompton folding bike « Practical Biking

Thanks Smallwheeler, looks easy enough to try.

an inexpensive experiment..

Rider is not in that Big a Hurry, (speaking For Myself)


Re the engine (Quiz) How long is a lap at the 2014 Brompton World Championships, and what was the Winner's Lap time?

It’s not matter of being in a big hurry. I ride in New Orleans and traffic and it dampens my speed than the firm shock absorber. It’s about efficiency. It is not that big of an effort.

I flunked the quiz.

NB if you gear it High enough like the 54t chainring turning the 12 cog the GI of that 16" wheel is.. 72"
now put that cog combo on a sturmey archer SRF5(N)5 speed Hub and that gear is 160% higher ..

The BSR takes a 13t Cog and its High is 133% overdrive.. 88" now with the current spider crank any 130 BCD chainring will fit
How about a 60t?

Though you still have to contend with that Thick, Damp NO LA Air Resistance that wont voluntarily move out of your way.

You will automatically be faster in Colorado (or La Paz) at a lower air density

Upright riding position = more wind resistance = more drag = slower.
Time to fit a S-type stem with my Aberhallo stem hack and then you can get down in the drops and add about 10mph...
Sorted.

you mean like this.

[MENTION=314606]smallwheeler[/MENTION] - yes like that but perhaps with less gold and pink bling

I posted a couple of years back on my experience of being overtaken by a roady who was coasting while I was pedalling quite hard on the Brompton. I watched him shrink into the middle distance apparently without any effort. And I've spend a fair amount of time tinkering with my hubs, maximizing efficiency etc.. With small wheels one can feel the bike slow over rough ground (or anything other than smooth ground) as force is redirected vertically and ones' hands get pummeled.

I thought Greenspeed Scorchers were the fastest 349 tire? No?

Bicycles are the only vehicle about which I routinely hear suspension makes them slower. Or maybe I'm not not quite following you.

I have read that the scorchers won't fit.

most compact folders are slow. they can be made much quicker with areo bars or bull bar mods. drop tend to interfer with fold.
a brompton withbull bars about44cm or wider fold just as flat as a standard bike as the bars fit either side of the front folded wheel.
i have put bullbars or silumar on mezzos,broptoms,downtube, and mission space genie with good results. add jokacks and your well away

not on Bromptons, the Frame clearance is too tight*, Schwalbe Kojacks are slick and 32 wide 349. They will fit ..
likewise primo comet, they are not as wide as the 'scorchers'

* Bike Friday's Tikit has more tire clearance..

I have a Scorcher on the front. It's a very nice tyre, rolls very well and reduces vibrations significantly.

Good to know? Will Scorcher fit on back? If not, why?