Hello,

I'm not technical but I could find someone who knows about welding/brazing/soldering.

Out of curiosity, what would it take to add a disk brake to the original fork? Do I just need to add a contraption on the fork to hold the disk caliper?

I'm interested in having a disk brake in the front, but €500 is a bit too much money.

Thank you.

Probably at first a wider original fork. currently the original needs a 74mm hub (vs. 100mm "usual" size) - when adding a disc brake it would to be even slimmer. Not sure if i.e. Dahon or Tern do have 74mm disc hubs. Other than that I would not be sure if the current original Brompton forks are suited well to fit the forces from disc brakes (that are different from those of rim brakes).

Looking at the Brompton fork shape I think it is designed to flex a little to soak in the bumps. This will not be ideal for disk brakes as the caliper will rub the rotor even if you manage to weld/braze a mount. I am not an expert and maybe it's doable if you are riding around town and not going down mountain passes. Road bikes without shocks have disk brakes now.

A disc means that you have to have a much stronger fork blade to avoid bending it. A regular large wheel bike would have to have a much stronger fork than a small wheel bike, but still even on your small wheel bike you are risking damage to the bike and yourself if you try it.

Thanks for the feedback.

has to be 10cm wide too, not 7.4 , you need to buy Ben Cooper's upgrade frame parts .

get the set with an Alfine disc hub compatible rear end. too..

you can even use French-British rail via the Chunnel, get to Glasgow, in Person.




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I notice there are 74mm disk hubs, and adapters are available to retrofit disk calipers on bikes with rim brakes.

Would a Brompton fork have to be significantly hardened to withstand a disk brake?

And to avoid increasing the depth of the bike while folded, what about installing the disk on the right instead?

Can't provide any input here, but just wanted to say that it would be nice to have at least one disk or the option for disk brakes. My first mile is a long descent and I don't particular like using calipers to slow down, especially when wet. My rims get quite toasty.

If no one's done it and people shell out big buck$ for tailor-made forks from Kinetics, Eerder Metaal, et al., I guess it's either not doable or unsafe with the original fork.

Incidently, several manufacturers* offer a front hub motor to turn a regular Brompton into an e-bike.

If the original fork is strong enough to withstand a hub motor with a torque of about 50Nm, wouldn't it be able to also take the force from a disk brake?

If all it takes is finding a competent LBS to weld a disk caliper adapter on the right side to fit the Brompton's folding, getting the kind of 74mm wide hub I mentioned above, and building a wheel… it'd be a nice upgrade.

Of is the effort from a disk brake very different from a hub motor?

* AKM-F, Crystalyte NSM/SAW20, Swytch, MkXR, Q70, etc.

Braking forces are much greater because the acceleration is much stronger. Your braking from speed in just a couple of seconds. That is a lot force. F=MA where A is the change of speed with time.

You can buy a carbon fork with disk tabs and 74 mm dropout on aliexpress for $65, but I'd sooner have tabs welded onto a steel fork. Those adapters are pretty weak. I paid $3 for one and decided it was it really flimsy, and it only fits certain fork geometries. Some people just tack weld them to their forks and add a little reinforcement.

My Downtube (100mm suspension forks) has tabs for disks, but I would have to spoke a hub up to get rotor capability. I've found that in general, adding rotors/calipers to a bike that had good rim brakes is a wash at best. It's only good if you do a lot of wheel removal.

Are there standard forks that fit the Brompton?

It s not just the fork you need to upgrade, you need a strong headset too and the Brompton OEM bearing are unlikely strong enough to handle the added cantilever load.
to convert to front disc brake (especially hydraulic with 160mm disc), you would be a 16" fork with 100mm hub space that follow this design:
https://www.planetx.co.uk/i/q/FOOOCR...fork-disc-only
Or a Aluminium Hydro fork or carbon (not cheap or easy to hand craft)

and you would need to fit something like a BMX headset

Basically do what tern did with the Verge x11 or get Ben Cooper's kit: https://www.kinetics-online.co.uk/fo...n-disc-brakes/

Without what is known as a thru-axle, a disc brake will not live up to its potential and, could be very disappointing. If the disc fork has a "C" shape in the part of the dropout where the axle goes, I recommend leaving it to rot on the retail floor. If investing in a custom-built disc fork, make sure that it's made with a thru-axle.

My big bike with disk brakes has an open fork (not thru-axle)

I agree, I have several disc brakes bikes, none has thru-axle but braking is excellent (including on a tandem bike on which the brakes must stop a much higher load than on a solo bike).

Remember that disc brakes were used well before thu-axle and performed very well.

What is well needed on the fork dropout is something that prevent the wheel to jump out of the dropouts.

So, as an option, Brompton could offer a 74mm wide disk fork — with the disk on the right-side to avoid interfering with the fold à la Birdy — without making the bike much wider.

That's what the thru-axle system is. You are refusing a good thing (thru-axle) just to refuse it.

The Birdy has a 100mm OLD front.

But the disc mount is not only on the right side of the bike, the disc is also placed closer to the center of the wheel than on a standard front disc wheel (actually, the distance from the dropout to the disc of the Birdy front wheel is the same as the distance between dropout and disc on a standard rear wheel).

The thru-axle is just one solution, the others with pins or grooves.. also work.