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[Brompton] Sturmey-Archer drum brake?

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Old 01-24-18, 07:25 AM
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Winfried
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[Brompton] Sturmey-Archer drum brake?

Hello,

Has someone investigated building a Brompton front wheel with a Sturmey-Archer drum brake?


Sturmey-Archer | Products

I know Greenspeed in Australia made some and is currently working on a new batch , but with labor + shipping, it's a bit pricey.

So I was wondering if it's doable even without being an expert.

Thank you.
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Old 01-24-18, 07:38 AM
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rhenning
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From the picture it looks doable. I would talk to a wheel builder and get his or her opinion. I have one of those hubs and with a 16 inch rim the spokes are going to be very short. Probably as short as a rear hub using an IGH. Any custom wheel will be pricey. Roger

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Old 01-24-18, 07:55 AM
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Thanks.

According to this Sheldon Brown page, the spacing of the Brompton fork is 74mm, while S-A offers a 70mm drum brake.

I'm not technical: Isn't it possible to simply add spacers on each side to fill the gap?

As for the actual wheel building, I have access to a DIY bike co-op with a competent wheel builder for help.

I also notice the S-A brake has 36 holes while Brompton wheels only have 28. Sun has one :-)

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Old 01-24-18, 08:17 AM
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Originally Posted by Winfried View Post
...the spacing of the Brompton fork is 74mm, while S-A offers a 70mm drum brake.

I'm not technical: Isn't it possible to simply add spacers on each side to fill the gap?
Believe you're confusing diameter with OLD.
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Old 01-24-18, 08:22 AM
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I just measured: The OLD (distance between the internal side of the dropouts) is actually 70mm, so it looks like spacers wouldn't even be required.
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Old 01-24-18, 08:33 AM
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A couple of pictures from my junk bin in the basement. NOS SA drum hub and a Raleigh RSW 16 inch rear wheel. Comparing these parts as I said you would end up with maybe 125mm spokes or shorter. Could you give the reason for wanting the drum brake. I ask because I have a Winter bike that uses the drum brake and to be honest rim brakes work better in non-icy conditions. The drums work but as I said they are not a stopping improvement. It is your bike and it will be a good swap but I am not sure what your goal is for doing it. Roger
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Old 01-24-18, 08:55 AM
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The reason is that braking on the Brompton isn't very good, especially in the rain or after going off-road while touring. Besides, I have to get new wheels after barely two years.

"On the road, the first impression is of near silence compared to a caliper or V-brake. The drum is powerful, but progressive. A gentle squeeze on the lever gives a strong stop of 0.3G – 0.4G, but grab the lever in panic and brake force rarely exceeds 0.56G. In practice, this means that a drum brake is less likely to send you flying over the handlebars than a fiercer and less forgiving V-brake.The drum will also be unaffected by water, oil or mud. In extreme conditions it gets warm, but there’s no risk to the tyre, and it soon cools down. The rear caliper brake is still grinding away at the rim, of course, but we found we tended to make more use of the front drum, so rear brake life should be slightly extended too. When you come to fold the bike, the cleaner front wheel is very welcome." http://www.atob.org.uk/bicycle-acces...ton-hub-brake/

I don't mind ordering custom spokes. At 55 for the hub + 35 for a 36H Sun rim, it's still a lot cheaper than getting a custom fork with disk brake from Kinetics.
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Old 01-24-18, 10:21 AM
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Yes, Greenspeed, recumbent trike manufacturer and distrubuting importer for Brompton, in Australia

has re machined SA drum brakes to fit in the narrow forks, and build wheels around for Bromptons...

they also re machine the frond drum brake hubs to be single end axle supported for their trikes
(Unless they now buy enough to have that work done in the factory.. )

More likely 24 hole rims rather than 28, since the hubs just come in 36 hole...

Or spread the fork out from 74 to 100.. use the hubs as is.

after market electric conversions already required fork spreading.





...

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Old 01-24-18, 10:27 AM
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I put a SA hub brake on a 26" touring bike front wheel and was disappointed with its breaking. YMMD.
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Old 01-24-18, 10:58 AM
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As you are in France I'd rather think about getting a 100mm fork with disc brakes from Ben Cooper / Kinectics than to spend serious money for a drum brake on the front of the Brompton if breaking power in the wet and rim wear ist the problem that you want to solve. How many kms did you do on your Brommi in these two years?

Spreading the 74mm fork to 100mm does not sound like a good idea to me. Also in terms of electric support the fork ususally has to be spread to ~80mm on the Brompton, not to the 100mm of normal forks as this is what most motors that are used on the Brompton require.
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Old 01-24-18, 11:58 AM
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Shouldn't one be worried about the extra load on the fork blade?
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Old 01-24-18, 12:56 PM
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Originally Posted by Schwinnsta View Post
I put a SA hub brake on a 26" touring bike front wheel and was disappointed with its breaking. YMMD.

YMMV indeed.. I happen to dis like the sudden all at once braking of the BB7 disc on my 20" wheel bike friday..
barely 1 finger or over the bars or off the saddle I come.

and am glad the SA drum brakes on my winter studded tire bike is so much easier to stop smoothly..

now there is a 90mm drum , even more braking surface,

might even be quite fade resistant when held on as a drag brake on long downhills..
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Old 01-24-18, 01:08 PM
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The S-A drum brake is available in 70mm, while the OLD on the Brompton is 74mm. So, a couple of 2mm spacers could fill the void.

I'm told that Shimano also has 70mm Roller Brake drum brakes, but their web site makes it hard to find infos. It looks like they have two series (BR-IMx and BR-Cx), with the latter being stronger (per an employee at HollandBikes).

At 55 for the hub + 35 for the rim + 20 for a set of spokes, it's cheaper than ordering one from Greenspeed in Australia (150? including shipping + tariff), and much cheaper than getting a custom fork with disk brake from Kinetics (500)

Hence the investigation.

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Old 01-24-18, 01:36 PM
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yea, You are definitely confusing drum diameter 70 or 90 mm and the axle over lock nut distance which is 10cm .

unless as re-machined custom , which is what green speed did..
they use the inner face of the drum portion of the hubshell drilled, as the other spoke flange.
& cut down the other flange , from what I saw ... looking, 10 years ago..

putting out the money to Ben Cooper in Glasgow, would get you a disc brake front wheel ,
and an Alfine 11 speed disc rear wheel with his custom made front forks and rear portions..


Post Brexit it could cost More..


.....

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Old 01-24-18, 02:10 PM
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Originally Posted by invisiblehand View Post
Shouldn't one be worried about the extra load on the fork blade?
Good call.


The Smut Pedaller: Braking... Bad: Part 1
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Old 01-24-18, 02:52 PM
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I have mine on an exceptionally stiff Tange ChroMoly MTB fork, not a low cost mild steel Raleigh thimble crown .

you sure the bike pictured did not hit something and it was only from the brake?


Hole all the way thru the lower lug is probably from removing the rod brake linkage.. it likely a 50+ year old frame & fork...






...

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Old 01-24-18, 03:34 PM
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Originally Posted by Winfried View Post
Good call.
Whoa!

At least it wasn't an aluminum fork!

If you were only worried about long descents and wanted a drag brake, I'd still use an ordinary fork with the drum brake.

Maybe this will be a good alternative for quick stops.

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Old 01-24-18, 03:55 PM
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We're onto something.

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Old 01-24-18, 06:52 PM
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The stress on the fork would be very close to the same with a V-brake and a drum brake. The load comes from where the tire meets the road. I have been around a few drum brakes. None of them stopped as well as I would have liked. Try new pads on your BB-7. Mine work great---it is my favorite disc brake.
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Old 01-25-18, 04:32 AM
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I don't see what BB-7 and disk brakes have to do with Bromptons.

As for brake pads, I'm told to use soft pads, since it's easier and cheaper to change pads than getting/building a new wheel, but that doesn't solve the issue of sad braking in the rain and/or steep descents on a Brompton.

I'm also told having to buy/build a new wheel every couple of years when riding a Brompton frequently is not unusual.
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Old 01-25-18, 07:02 AM
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This thread is not about tires, but about getting a better front brake.
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Old 01-25-18, 08:24 AM
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Originally Posted by Winfried View Post
As for brake pads, I'm told to use soft pads, since it's easier and cheaper to change pads than getting/building a new wheel, but that doesn't solve the issue of sad braking in the rain and/or steep descents on a Brompton.
Personally I do not have issues with the Brompton-Brakes, neithter when touring nor downhill in the Alps nor in the wet. As long as the post-2013 brake levers (or an equivalent) and any of the post-2000 Brompton brakes are on the bike for me everything is fine, with the original brake pads, too. Koolstop salmon-pads are often recommended and I like them too. Siwsstop (I think the green ones) have been another recommendation but I do not have personal experience with them. It just seems that a number of people have issues with the brake power while others do not. Luckily I am on the happy side.

Originally Posted by Winfried View Post
I'm also told having to buy/build a new wheel every couple of years when riding a Brompton frequently is not unusual.
There seems to be a bit of black magic around this topic. A while ago I tried to find out what mileage can be considered "normal" for a Brompton rim, asked a lot of Bropton riders and it turned out that there is no such typical value. Some people manage to break through the rim in less then 5000 km while others have more than 20.000 km on their rims and everything is still fine.

Some discrepances are obvious and for a reason as Brompton has used different rims over the years, brake-pads may be diffierent as is riding style. Riding all through the year or a lot in dirty/muddy conditions fosters wearout. In general rims seem to have enhanced - with the MK2 early wear seems to have been quite common, with the later MK4 wear was something do look for but no dramatic or surprising issue and since the new double-wall rims of 2013 I did not hear from anyone yet who already needed to change the rims due to wear. This is why I am interested in the mileage you have done to your Brompton until now.

However at least one relevant thing is left to mention: Typically the rear rim wears faster due to all the dirt in that area in comparison to the front one. Thus making less use of the rear brake, especially in muddy conditons should enhance the lifetime of the rim massively. Should not be big problem as due to physics most of the brake-power is applied on the front anyway. And regarding riding style: When going downhill in the Alps (or other steep descents) I typically let it roll and do short, hard breakings rather than breaking constantly but less intensive. I would assume that this also fosters the lifetime of the rims.

Personally I did not yet manage to break through the rim of any of my Bromptons, so I seem to be a soulful breaker.
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Old 01-25-18, 09:41 AM
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I read that after two years, you now need to replace the rim. Over what distance is that? As you're almost certainly aware, the smaller rim will wear out faster. Based solely on geometry -- 622/349 -- not quite twice as fast. If you're using the bike regularly for commutes and travel in all sorts of weather, replacing a rim every four years on regular sized bikes is on the quick side but not unheard of.

With respect to braking power, I always found Bromptons a bit lacking even after they came out with the dual pivot brakes. Although it was never clear to me whether it was more of a function of geometry and the relatively upright posture or the brakes/frame-flexing/housing. I'm not sure it's convenient for you to try out disk brakes on the Brompton first, but if it's an expensive conversion or has other negative side effects on say the fold, it might be worthwhile to test.

As for wheel building, I'd avoid a 36-hole 349 wheel. That's a lot of spokes in a small area. I imagine pumping air into tubes would be inconvenient and, if you have spokes crossing, you won't have a lot of room to fiddle around. Mind you, using a tension-meter will already be tricky with such short spokes -- it's probably impossible with the standard Park Tool tension meter ... even with a small flange hub -- and wheel building a small wheel when everyone's experience is with 26" and up wheels will take some additional patience.
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Old 01-25-18, 09:48 AM
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Originally Posted by Winfried View Post
This thread is not about tires, but about getting a better front brake.
Ive found their recent double pivot, with stock Fibrax pads, fine.. but I changed the inserts to Kool Stop Salmon compound, any how..


put KS Continental in the CLB single pivots , on the Mk2.. that took some creativity..


Brompton uses 28 hole rims, Mk2 front was 20 spoke, bike friday Tikit and I presume Pakit, use 24 spoke , and can lace to 36 hole IGH, etc.






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Old 01-28-18, 09:39 AM
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Originally Posted by rhenning View Post
From the picture it looks doable. I would talk to a wheel builder and get his or her opinion. I have one of those hubs and with a 16 inch rim the spokes are going to be very short. Probably as short as a rear hub using an IGH.
Thanks.

It's been done by Greenspeed, and there are some e-bike kits such as Sparticle's for Brompton that use a front wheel motor:



Considering a drum brake is not heavier than a motor, I assume the spokes will be ok. I'm more concerned about the force from the retention arm against the fork.

--
Edit: It looks like 70mm is the width of the drum brake vertically, while the internal distance between the drop-outs (OLD) is 100mm :-/

What Greenspeed seems to have done, is 1) cutting the axis so it fits the 74mm Brompton fork, and 2) drilled holes in the hub for the spokes:

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