The Blatt - another year on

For discussions about bikes and equipment.
cycle tramp
Posts: 890
Joined: 5 Aug 2009, 7:22pm

Re: The Blatt - another year on

Postby cycle tramp » 12 Oct 2020, 10:24pm

Valbrona wrote:Nice looking, very functional bike.

I know nowt about drum brakes, but would be grateful for a lesson.

Would you be kind enough to give the model name of the front and rear drum brake hubs. I notice the rear is able to take a cassette. And do they build into wheels able to fit into a regular frame, ie. 100mm OLN front and 135 at the back? Or does a frame for drum brakes need special fitments for the actuation arms?

Thanks.


The front hub is a XL-FD Model, which fits a front drop out of 100mm, the rear is a X-RD Model, which uses a 135 rear drop out spacing. Clips to attach the brake's reaction arms to the frame are included with the hubs along with cables.
The hubs were bought from Saint John Street cycles, who also built up the wheels. The rear wheel was spaced for a 7 or 8 speed freewheel, (rather than a freehub cassette) but was re-spaced for a 5 or 6 speed freewheel - although it meant I lost a couple of gears, it allowed for the rear hub to be more centrally placed along the axle, and allowed for a more equal spoke tension to be used, building a stronger wheel.
Hope this helps :-)

Valbrona
Posts: 2356
Joined: 7 Feb 2011, 4:49pm

Re: The Blatt - another year on

Postby Valbrona » 13 Oct 2020, 1:23am

Thanks.

And what brake levers are you using?

I almost switched to hub brake on my utility bike a couple of years ago, but was put of by the expense and the fact that I was told my current brake levers (that operate full sized V brakes), and which are integrated with the shifters, are not a satisfactory match for hub brakes.
I should coco.

iandusud
Posts: 517
Joined: 26 Mar 2018, 1:35pm

Re: The Blatt - another year on

Postby iandusud » 13 Oct 2020, 8:04am

cycle tramp wrote:
iandusud wrote:
Cycletramp, I do like your utilitarian bike. What gear range do you have?

Ian


Thank you :-) the current gear range is best described as narrow, (however the 5 speed gear did replace a 3 speed hub so perhaps it's all down to prospective) I currently am using another IRD freewheel (which I found in the shed, which has teeth; 13, 16, 20, 24, 28) with a 34 tooth chain ring it currently gives me 68, 55, 44, 36, 31.5 inches. If I ride with a group then I get left behind when the group uses larger gears to make the best of a headwind.
When I first built the bike I used a 38 tooth chain ring which gave me 76, 62, 49, 41, 35 inches. It suited group riding better, but it also meant with a 18 kg load I had to walk the bike up the hill where I live...
...Blatt 2(diet blatt? Son of blatt?) will not be a dedicated load carrier which means I can use a larger chain ring again


Out of interest as you are using derailleur gears rather than IHG why not fit say a 7 speed freewheel say 11-34 giving you an 80" top gear (ample in my books) and a 26 bottom gear?

Ian

Brucey
Posts: 41015
Joined: 4 Jan 2012, 6:25pm

Re: The Blatt - another year on

Postby Brucey » 13 Oct 2020, 8:38am

cycle tramp wrote:... The rear wheel was spaced for a 7 or 8 speed freewheel, (rather than a freehub cassette) but was re-spaced for a 5 or 6 speed freewheel - although it meant I lost a couple of gears, it allowed for the rear hub to be more centrally placed along the axle, and allowed for a more equal spoke tension to be used, building a stronger wheel.
Hope this helps :-)


The spacing for a 7s freewheel would be different from the spacing for an 8s freewheel. The correct spacing for a 7s freewheel is very similar to that of a 6s freewheel, because 7s sprockets are spaced more closely than 6s. As Ian points out above a 7s freewheel could give you more range etc; the reasons a 6s one was used in the Supercommuter included that more gears/range were not required and that 6s indexing should go longer between being fiddled with.

The scope for redishing the wheel whilst retaining the same axle is limited by the fact that the X-RD axle is shouldered (where the cartridge hearings fit to it) so it cannot be shuffled sideways as you would be able to do in (say) a typical hub with cup and cone bearings. In the 'Supercommuter' build the hub was redished to a narrower OLN by taking spacers out on the RHS and adding a smaller amount on the LHS. The latter wouldn't really have been possible had the frame had thicker aluminium dropouts. SA make different axles but IIRC the alternatives are not as long, so at 135mm OLN there isn't that much wriggle room.

IME when building one of these wheels there is nearly always more dish than you would like to have; this means the tension balance is worse than you would choose. The options here are to use higher than normal (probably excessive) DS tension or to use threadlock on the NDS spokes. I've seen one of these hubs break on the DS, presumably through excessive tension. In the Supercommuter the rear wheel was built with normal tension but without threadlock on the NDS, in the anticipation that it might have to be added later. It soon became evident that it wasn't optional; the NDS nipples started to back out in use so threadlock had to be added retrospectively; the wheel has been fine since then.

Re brake levers; SA recommend their S80 model levers for their drum brakes. These are optionally available with a parking button etc. These levers have the correct pull/MA for drum brakes, cantis, roller brakes, and older caliper brakes. A while back I refurbished a couple of pashleys and at some point they had both been fitted with the wrong brake levers; the brakes were absolutely feeble as a consequence. On one machine the (Dia Compe) levers were convertible between V and canti pull, so it was just a matter of reconfiguring them. On the other machine I had to pony up for replacement levers.

If you have V-brake compatible combined brake levers/shifters I suppose you could use travel agents but the brake will be spongier. Some V-levers are made so that the cable shackle could be put in one of two places in manufacture. This means that you can sometimes convert the levers, but this requires drilling holes and re-riveting the shackles; there are fairly obvious dangers if your workmanship isn't perfect here, so I don't recommend this route unless you are 100% confident about it.

One of my mad ideas is to make longer versions of the brake arms on the brake plate, thus making the drum brakes compatible with V-levers. The same dangers exist of course, but the brakes should also be improved because the cable tension is reduced.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

iandusud
Posts: 517
Joined: 26 Mar 2018, 1:35pm

Re: The Blatt - another year on

Postby iandusud » 13 Oct 2020, 5:42pm

Sorry I hadn't spotted the post explaining the respacing of the rear hub. However as you say Brucey a 7 speed freewheel would probably fit, with possibly a tad more spacing. Brucey are you suggesting that the hub flanges on these hubs are not strong enough? If not then I can't see why a suitably strong wheel couldn't be built for this bike, particularly as it sports big tyres, maybe with the use of single butted spokes if necessary.

Ian

Brucey
Posts: 41015
Joined: 4 Jan 2012, 6:25pm

Re: The Blatt - another year on

Postby Brucey » 13 Oct 2020, 6:18pm

iandusud wrote:….. Brucey are you suggesting that the hub flanges on these hubs are not strong enough? ….


strong enough for bad wheelbuilding and salt spray in service?

No...!

The problem is the tension balance in the rear wheel.

SA's own documentation for the X-RD

http://www.sturmey-archer.com/files/catalog/files/327/SPECIFICATIONS%20-%20REAR%20DRUM%20BRAKE%20HUBS.pdf

says 7s freewheels fit the X-RD 135mm OLN hub as standard, and the RH flange is 20.7mm from the centreline and the LH flange is 43.5mm from the centreline.

If you feed these numbers into a wheelbuilding calculator it predicts a 47% tension balance. This is a worse tension balance than is achieved in an 11s 'road' wheel.

Why so 'bad'? Well the RH flange is in a more or less 'normal' location but flanges are further apart than in many rear hubs. This normally makes for an inherently stronger wheel but the problem is that the NDS spokes have low absolute tension values in them.

If you have well-lubricated nipples then depending on the service conditions and other build details, you might need between 65kgf and 90kgf in the NDS spokes to make them reasonably proof against the nipples unscrewing. This means that you might end up with tensions NDS/DS of 65/138kgf or 90/191kgf if you rely on tension alone to hold the NDS nipples. ~140kgf is possible with some rims, but ~190kgf is enough to break nearly everything; rims, hubs, you name it. Many rims are limited to about 100kgf maximum tension before they are likely to crack in service.

This effectively means you need to use lower spoke tension and threadlock on the NDS nipples in most cases.

If you can shuffle both flanges just 2mm rightwards, this improves the tension balance by 7%. Every mickle makes muckle...

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

cycle tramp
Posts: 890
Joined: 5 Aug 2009, 7:22pm

Re: The Blatt - another year on

Postby cycle tramp » 13 Oct 2020, 6:49pm

iandusud wrote:
Out of interest as you are using derailleur gears rather than IHG?

Ian


Oh, that was Dave. Before the Blatt had 5 speeds and drum brakes, it had a front rim brake and a geared hub and some sort of drum or roller brake (it was either the 3 speed and drum brake, or the nu-Vinci and roller brake, can't remember which) Dave and I were coming back from a sunday evening ride, and we'd parked up for a breather, and we were looking at each others bikes (as you do) and he knew I wasn't happy with the geared hub and was thinking of changing it.. but i wasn't sure for what and then Dave turned to me and says 'Yeah, but what are you gonna do when it breaks ?'

I got back to thinking about Brucey's Supercommuter and thought, 'yeah that's the answer. Everything is cheap enough to keep in the garage as spares, its basic enough that bits from one manufacturer should fit bits from others, and all the parts are pretty easy to pull part and put back together'.

To be fair I've tried three or four different hubs, I liked the 3 speeds, but in a head wind I found the spacing just too large between the gears... the nu-Vinci was very easy to use by with an efficiency of about 85%? It would drain your energy. The rolhoff hub (borrowed) was an absolute machine. It helped me climb every hill when I did Lands End to John O'Groats... but there wasn't any challenge when you used it. It was like using an expensive 4x4 to go around the world... of course it's going to get you there. It was also too expensive to leave parked up for any length of time. I developed more of an emotional bond with my 3 speeds than I did the rolhoff and the 3 speed hub returned the sense of challenge...
Last edited by cycle tramp on 13 Oct 2020, 10:15pm, edited 1 time in total.

cycle tramp
Posts: 890
Joined: 5 Aug 2009, 7:22pm

Re: The Blatt - another year on

Postby cycle tramp » 13 Oct 2020, 10:12pm

iandusud wrote:why not fit say a 7 speed freewheel say 11-34 giving you an 80" top gear (ample in my books) and a 26 bottom gear?

Ian


That's such a great question. It's all down to where I live and the purpose of the bike.
I live on a small-ish hill in the middle of the Somerset Levels. I've got to cycle for something like an hour in any direction before I hit any large hill (Mendips, Quantocks, Blackdowns) and I can reach any of the more interesting towns, Wells, Glastonbury, Cheddar without even having to climb a hill.
One of the purposes of the Blatt was to be able to carry heavy loads, I regularly carry 10 kg or more on the rear rack... ages ago I remember reading a book by Tony Oliver, about touring bicycles. One of the chapters was given over to wheel designs. Tony Oliver believed that you could build an almost completely dishless rear wheel, if you used a 5 speed freewheel. Having a dishless rear wheel is something of the Holy Grail for cyclists - it means that the rear wheel is stronger, than those rear wheels which have been dished. Brucey is right - because the spacing of the rear hub was changed, I had to move the whole axle a good few millimeters over to the right - it means that there wasn't enough axle thread on the left hand side to use a washer and axle nut.. so I'm using just an axle nut.
But you're right, if I had lived in a hillier area and wasn't asking my bike to carry heavy loads then a seven speed freewheel would give a better range :-)

cycle tramp
Posts: 890
Joined: 5 Aug 2009, 7:22pm

Re: The Blatt - another year on

Postby cycle tramp » 13 Oct 2020, 10:21pm

Valbrona wrote:Thanks.

And what brake levers are you using?

I almost switched to hub brake on my utility bike a couple of years ago, but was put of by the expense and the fact that I was told my current brake levers (that operate full sized V brakes), and which are integrated with the shifters, are not a satisfactory match for hub brakes.


I'm currently using a pair of 4 finger brakes used for calipers or cantilever brakes. They seem to work alright. The 5 speed deraileur is operated by a thumb shifter from the 1980's :-)

Brucey
Posts: 41015
Joined: 4 Jan 2012, 6:25pm

Re: The Blatt - another year on

Postby Brucey » 14 Oct 2020, 9:29am

one of the issues with X-RD (and in fact any hub which uses a screw-on freewheel, pretty much) is if/when the axle is likely to break. I know of three or four SA X-RD axles which have broken; one was in a bike with an ill-advised singlespeed conversion (the chain unsurprisingly derailed off the HG sprocket and this bent the axle) and the others were fatigue failures on bikes that were regularly loaded. IIRC one forum member here has reported that his X-RD axle lasted only 10000 miles on his (loaded) touring bike. Another I know of was used for ~60000 commuting miles before the axle broke, and toted rear panniers every single day.

Even if the life is not exactly predictable, clearly these axles don't last forever, and being solid, if the axle breaks it is a show-stopper; you are walking home.

So the plan for the Supercommuter is to fit an 'outrigger bearing'; all the parts are ready and when the transmission has its next renewal it will be installed. My chum has become stronger since the bike was built, and very rarely uses the lowest gear (even though it is not that low) and also 'taps along' about one gear higher than he used to. The gearing is to be revised to reflect this; it'll be upped by 10% courtesy of a larger chainring.

I also have plans to install outrigger bearings on other similar hubs. A snag which I anticipate may crop up is that the outrigger bearing may not want to come out of the freewheel (even when strong magnets are used on it); if this happens then there are other options; e.g. the freewheel body can stay (just renewing the sprockets) or the freewheel body will have to be dismantled so that it can be gripped by other means, or the axle may be driven out rightwards (it should move a small distance at least), taking the outrigger bearing with it.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~