Sturmey Archer Hub Brakes

For discussions about bikes and equipment.
iandusud
Posts: 198
Joined: 26 Mar 2018, 1:35pm

Sturmey Archer Hub Brakes

Postby iandusud » 17 Dec 2018, 8:24am

Probably one for Brucey!

I have finished my cargo bike, with the exception of adding electric assist (Woosh are waiting on 48V hub motors), and enjoying using it for my weekly shop, trips to the allotment etc. I'm fairly happy with the performance of the brakes, which are V brakes front and rear. However I haven't tried stopping in a hurry down hill, in the rain, with a heavy load yet! I was planning of fitting a SA front dynamo hub and then it occurred to me that I might fit a Sturmey Archer XL-FDD brake like this

https://www.sjscycles.co.uk/hubs-intern ... w-36-hole/

at the same time and kill two birds with one kettle of fish. How good are these brakes compared say to a V brake or a cable disc brake?

I'm not looking for outstanding performance, as the weight distribution, like on a tandem, allows for a lot of braking on the back and in fact with not much load on the front it's quite easy to lock up the front wheel.

Cheers, Ian

Brucey
Posts: 35987
Joined: 4 Jan 2012, 6:25pm

Re: Sturmey Archer Hub Brakes

Postby Brucey » 17 Dec 2018, 11:02am

XL-FDD has a 90mm drum brake, X-FDD has a 70mm drum brake. These brakes improve once they have been bedded in (which may take months or even years depending on the way the brakes are used). They are essentially completely impervious to weather, unless you leave the bike outside in the rain, leaning to one side.

On an unladen solo the 90mm brake is strong enough to do stoppies and the 70mm one isn't, quite. Modulation (which varies depending on how well the brake is bedded in) typically isn't quite as good as a good rim or disc brake. If you have a strong rearwards weight bias and a 90mm front brake all this can translate into a locked front wheel; maybe you would be better off with a 90mm drum brake on the rear wheel?

The *-FDD generator hubs have an effective, but somewhat inefficient generator part; when measured the drag is about the same whether the lights are on or off. This means that if you ride with the lights on at all times, there is no penalty. However if you are worried about a couple of watts going missing on your carrier bike and you ride with the lights off, there are more efficient generator choices than one of these hubs. Given that typically you might be tipping ~30W each into tough puncture resistant tyres on such a carrier bike, and it will usually have the aerodynamics of a brick too, IME losses of this sort are liable to get lost in the noise.

cheers
-------------------------------------------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

iandusud
Posts: 198
Joined: 26 Mar 2018, 1:35pm

Re: Sturmey Archer Hub Brakes

Postby iandusud » 17 Dec 2018, 11:33am

Hi Brucey,

Thank you for your helpful reply. I generally ride with lights on all the time and as you suggest with all the other loses taken into consideration the drag of the generator is immaterial. I think the potential problem of locking the front wheel is only an issue with an unladen bike and I can always bias towards the rear brake. Does chamfering the leading edge of the brake shoes help alleviate snatching?

A drum on the rear would be nice as well but when my rear hub motor arrives it won't be possible.

Cheers,

Ian

Brucey
Posts: 35987
Joined: 4 Jan 2012, 6:25pm

Re: Sturmey Archer Hub Brakes

Postby Brucey » 17 Dec 2018, 11:44am

chamfering makes a difference but more than that how the brake is most often used determines exactly what shape the shoes become, and how the brake behaves.

All brake shoes flex a tiny bit, and the flex varies with the pressure applied. Through wear, brakes that are only ever used lightly end up with slightly differently shaped linings than brakes that are usually used hard, and this shape difference normally means the brake modulates differently.

This whole subject is complicated but in a nutshell brakes that are mainly used lightly are more likely to become grabby and less likely to be really powerful. Brakes that are more often used at high power are more likely to be both powerful when needed and to modulate (in a non-grabby fashion) at lower powers.

cheers
-------------------------------------------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

iandusud
Posts: 198
Joined: 26 Mar 2018, 1:35pm

Re: Sturmey Archer Hub Brakes

Postby iandusud » 17 Dec 2018, 11:52am

Thanks again for the benefit of your wisdom/experience. A 90mm one it is.

Ian

cycle tramp
Posts: 561
Joined: 5 Aug 2009, 7:22pm

Re: Sturmey Archer Hub Brakes

Postby cycle tramp » 17 Dec 2018, 7:29pm

Hope you don't mind me asking, what size front wheel does your load carrier use? I find the 90mm hub brake works fine in a 26 inch wheel and a four finger brake lever.... in a 20 inch wheel the brake could be a little more fierce
...Hey, don't forget to post a photo of your load carrier... i'd really like to see it :-)

Brucey
Posts: 35987
Joined: 4 Jan 2012, 6:25pm

Re: Sturmey Archer Hub Brakes

Postby Brucey » 17 Dec 2018, 7:46pm

FWIW I have seen a 90mm brake used successfully in a Bakfiets (20" front wheel), but that has a front-biased weight distribution so maybe it is better suited.

cheers
-------------------------------------------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

iandusud
Posts: 198
Joined: 26 Mar 2018, 1:35pm

Re: Sturmey Archer Hub Brakes

Postby iandusud » 17 Dec 2018, 9:57pm

Yes, I'm using a 20" front wheel. I'm happy to use a 90mm hub - I'm sure when it's got a good load on I'll appreciate it. Brought around 65kg of shopping back today and then a trip to the local brewery to pick up a couple of sacks of wet used hops for compost, probably around 70kg. I even overtook someone on an e-bike!
Image Attachments
IMG_20181208_142150.jpg

cycle tramp
Posts: 561
Joined: 5 Aug 2009, 7:22pm

Re: Sturmey Archer Hub Brakes

Postby cycle tramp » 17 Dec 2018, 10:21pm

That's a great looking bike! I guess a 90mm hub brake in a 20 inch wheel is possibky all the front brake you'll need .. especially if you use a compressionless outer cable. Thanks for posting it :-)

Brucey
Posts: 35987
Joined: 4 Jan 2012, 6:25pm

Re: Sturmey Archer Hub Brakes

Postby Brucey » 17 Dec 2018, 10:26pm

is that a DIY build? If so, nice effort, any 'in progress' photos?

cheers
-------------------------------------------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

iandusud
Posts: 198
Joined: 26 Mar 2018, 1:35pm

Re: Sturmey Archer Hub Brakes

Postby iandusud » 18 Dec 2018, 8:05am

Brucey wrote:is that a DIY build? If so, nice effort, any 'in progress' photos?

cheers


Hi Brucey,

Here are some pics. Please excuse the state of my garage!

I'm very pleased with the result. My only concern is that at a certain highish speed I'm getting some shimmy. There's no play in any of the linkages or headsets etc. I suspect that the steering rod isn't stiff enough. I'm going to add a fillet on the bends to see if that helps, otherwise I'll uprate the tube. Currently it's 5/8" x 1.5mm (sorry for the mixing of metric and imperial!).

Ian
Image Attachments
IMG_20181112_095340.jpg
IMG_20181113_111253.jpg
IMG_20181117_152328.jpg
IMG_20181119_120806.jpg
Last edited by iandusud on 18 Dec 2018, 8:12am, edited 2 times in total.

iandusud
Posts: 198
Joined: 26 Mar 2018, 1:35pm

Re: Sturmey Archer Hub Brakes

Postby iandusud » 18 Dec 2018, 8:08am

And a few more.
Image Attachments
IMG_20181129_154200.jpg
IMG_20181127_115359.jpg
IMG_20181129_173409.jpg

9494arnold
Posts: 867
Joined: 21 Jan 2007, 3:13pm

Re: Sturmey Archer Hub Brakes

Postby 9494arnold » 18 Dec 2018, 8:28am

Just stumbled across this.
Whilst you have the welding torch out is it worth dropping a fillet in behind / around the head tube/front frame member? .
Drum brakes can be a bit fierce , I am the current custodian of a trike, the previous owner broke the original forks with a hub brake.
Plus you might induce skidding on an unloaded machine like that. Just thinking out loud.

Brucey
Posts: 35987
Joined: 4 Jan 2012, 6:25pm

Re: Sturmey Archer Hub Brakes

Postby Brucey » 18 Dec 2018, 8:49am

Nice job!

re the shimmy; any castor will want to shimmy, it is just a question of making the parts so that

a) the road speeds at which shimmy will occur are not ones you use and/or
b) the parts are stiff enough that the capacity of the frame to flex (and store energy that helps to drive the resonance) is reduced and/or
c) the resonance is damped in some way.

The last of these is the only saving grace for many lightweight bikes; the hands on the handlebar add significant damping and 'no hands' can create violent shimmy at certain speeds.

So in the case of your carrier bike I would consider some combination of


1) reinforcing the main spar; most commercial machines have a gusset behind the lower headset parts (similar to Arnold's suggestion)
2) varying the steering ratio; for example lengthening the arm on the side of the forks would mean the steering input required for a tight turn would be increased but shimmy might be reduced
3) doubling up on the steering linkage. On some machines I have seen a steering arm both sides; I think this may be to reduce the chances of shimmy. It certainly adds a failsafe element to the steering.
4) modifying the steering geometry (eg so that the trail is reduced)
5) using a tyre with a different contact patch/carcass construction (eg a marathon) with more inbuilt damping
6) using a damper on the steering.

By damper I mean a proper hydraulic damper, not one of those spring things that are sometimes fitted to dutch bikes. If the steering linkage is stiff enough the damper can be located at the long steerer tube (IIRC Niholas are built thusly) but in the case of a machine like this I think the damper ought to be connected directly to the forks.

If you have shimmy the one thing you shouldn't do is to ignore it; the shimmy will pass high loadings into critical steering components which could significantly reduce their life expectancy.

cheers
-------------------------------------------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

iandusud
Posts: 198
Joined: 26 Mar 2018, 1:35pm

Re: Sturmey Archer Hub Brakes

Postby iandusud » 18 Dec 2018, 10:04am

Thanks for the input. I will try one thing at a time. I did in fact change the front tyre yesterday for a 20x1.75 Marathon in order to get mudguard clearance and have a decent tyre. I haven't had it up to "shimmy speed" since.

I did wonder about a fillet at the join of the horizontal spar and front tube, as in this design:

Image

however this joint does seem very rigid. The box section is 50x50x2mm so very strong. The above design uses a spar of 40x40x1.5mm

I set it up with around 59mm trail but this was based on guess work as I'm not really sure what the requirements of a cargo bike are. I don't really want to change that if I don't have to as getting the front end aligned in all three planes was probably the most difficult job without a jig.

I will stiffen up the steering tube as I think this is the most likely culprit and report back, although not today as it's p-ing it down!

Interestingly what helps reduce the shimmy is loosening my grip on the bars, which I think supports my theory but we'll see.

Ian