The Blatt - another year on

[cycle tramp]

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[speedsixdave]

How is the horn?

Am I right in thinking the f&f are Thorn? How do you think the forks are coping with the 90mm hub brake? I ask with selfish interest as I recently put a Sturmey X-FDD dynamo / 70mm hub brake on the front of our Thorn tandem in addition to the Magura rim brake. Mostly i use it as a temporary drag to allow the front rim to cool down, but I can't help worrying whether the fork is up to a hub brake when banging down a 1-in-5 with precious cargo stoking behind me!

[cycle tramp]

How is the horn?

Am I right in thinking the f&f are Thorn? How do you think the forks are coping with the 90mm hub brake? I ask with selfish interest as I recently put a Sturmey X-FDD dynamo / 70mm hub brake on the front of our Thorn tandem in addition to the Magura rim brake. Mostly i use it as a temporary drag to allow the front rim to cool down, but I can't help worrying whether the fork is up to a hub brake when banging down a 1-in-5 with precious cargo stoking behind me!

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[speedsixdave]

Can I ask how you find the performance of the 70mm drum brake?

Not enormously whelming, but:

(a) they've not been on terribly long, so may bed in further with time. Apart from the fairly flat pottering around South Derbyshire that we normally do on the tandem, which doesn't require a lot of serious braking, the only major work the hub brake has done was a week touring in Kent & Sussex in September and although it's quite undulating there with the occasional steepie, it wasn't too challenging. So there may or may not be more power to come if it beds in further.

(b) I have it on a reverse lever (a Tektro time-trial brake lever) on my left hand (as is the front brake), so I generally pull it with my two small and weak fingers.

(c) Because of my slight concern about the fork strength, I've not really given it the full beans yet. Your experience with a 90mm on a solo bike and solo fork gives me confidence to pull a bit harder on my 70 though.

Having said all that, it definitely does the job for us, which is that it's capable of preventing further acceleration when descending without using the primary front brake, so I'm certainly keeping it. I have also put a 70 on the back of my touring Moulton and I've been absolutely loving that while touring recently in the hilliest bits of Wales.

The irony with the X-FDD on the tandem is that part of the reason for going for it was that I found the front brake (Magura HS33, Koolstop Salmon pads) very juddery with the flexible fork, and consequently I didn't much like using the front brake and looked for an alternative. So I had the Sturmey built into a Mavic rim I had spare and swapped out the original SON hub and Sputnik rim for this wheel. And now the front Magura doesn't judder at all, so it was the rim all along! Hey ho. The SON/Sputnik wheel is now doing service on my Battleship commuter with a disk brake, so the rim no longer has to do braking duties and will last until dinosaurs rule the earth once again.

[Valbrona]

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.

[mikeymo]

How is the horn?

Am I right in thinking the f&f are Thorn? How do you think the forks are coping with the 90mm hub brake? I ask with selfish interest as I recently put a Sturmey X-FDD dynamo / 70mm hub brake on the front of our Thorn tandem in addition to the Magura rim brake. Mostly i use it as a temporary drag to allow the front rim to cool down, but I can't help worrying whether the fork is up to a hub brake when banging down a 1-in-5 with precious cargo stoking behind me!

Well, it's happened at least once:

http://smutpedaller.blogspot.com/2014/01/braking-bad.html

Some people on thou forae say not to worry.

But it's happened at least once.

[iandusud]

How is the horn?

Am I right in thinking the f&f are Thorn? How do you think the forks are coping with the 90mm hub brake? I ask with selfish interest as I recently put a Sturmey X-FDD dynamo / 70mm hub brake on the front of our Thorn tandem in addition to the Magura rim brake. Mostly i use it as a temporary drag to allow the front rim to cool down, but I can't help worrying whether the fork is up to a hub brake when banging down a 1-in-5 with precious cargo stoking behind me!

Well, it's happened at least once:

http://smutpedaller.blogspot.com/2014/01/braking-bad.html

Some people on thou forae say not to worry.

But it's happened at least once.

I have to say that I wouldn't risk fitting a drum brake on the front of our tandem unless it was fitted with a fork that was designed for the job for the same reason that fitting of disc brakes is ill-advised on forks that are not designed for that purpose.

Cycletramp, I do like your utilitarian bike. What gear range do you have?

Ian

[Brucey]

Interesting that you should have had a freewheel body that went peculiar; I was sufficiently concerned about this that I specified additional seals and specific lubricants in the 'supercommuter', (even though the idea was to replace the whole freewheel when the chain/sprockets wore) . One freewheel was fitted without these elements and it lasted mere weeks before the innards started to corrode (lots of road salt hereabouts). IRD freewheel bodies can be rebuilt with new pawls; However I'm not sure they aren't identical to pawls found inside lots of other freewheel bodies.

Re hubs; at the rear X-RD model accepts a screw-on freewheel and has a 70mm drum brake. The alternative is X-RDC which has an 8/9s freehub body if you want to use a cassette.

I wouldn't fit a 90mm drum brake to anything other than a heavy duty fork (maybe the Thorn qualifies as this?) and I certainly wouldn't try to do stoppies either. [IMHO the only reason Smutpedaller's fork didn't bend before was that the original front brake wasn't capable of enough force for a stoppie; had it powerful enough for that the fork would probably have bent in a similar fashion; those forks bend pretty easily.] If there was any doubt about the fork strength, one way this can be addressed is by extending the brake reaction arm. If this is extended as far as the fork crown the loading on the fork becomes very similar to that of a rim brake, so far as the fork is concerned.

cheers

[sjs]

Some people on thou forae say not to worry.

Thy fora?

[mikeymo]

Some people on thou forae say not to worry.

Thy fora?

Yes, you're right. Deepest apologies for my appalling lapse in grammar. I'm just a simple country boy, not an "intellectual".

[mikeymo]

Interesting that you should have had a freewheel body that went peculiar; I was sufficiently concerned about this that I specified additional seals and specific lubricants in the 'supercommuter', (even though the idea was to replace the whole freewheel when the chain/sprockets wore) . One freewheel was fitted without these elements and it lasted mere weeks before the innards started to corrode (lots of road salt hereabouts). IRD freewheel bodies can be rebuilt with new pawls; However I'm not sure they aren't identical to pawls found inside lots of other freewheel bodies.

Re hubs; at the rear X-RD model accepts a screw-on freewheel and has a 70mm drum brake. The alternative is X-RDC which has an 8/9s freehub body if you want to use a cassette.

I wouldn't fit a 90mm drum brake to anything other than a heavy duty fork (maybe the Thorn qualifies as this?) and I certainly wouldn't try to do stoppies either. [IMHO the only reason Smutpedaller's fork didn't bend before was that the original front brake wasn't capable of enough force for a stoppie; had it powerful enough for that the fork would probably have bent in a similar fashion; those forks bend pretty easily.] If there was any doubt about the fork strength, one way this can be addressed is by extending the brake reaction arm. If this is extended as far as the fork crown the loading on the fork becomes very similar to that of a rim brake, so far as the fork is concerned.

cheers

I've always thought that "doing a stoppy" is the ultimate test of whether a brake is good enough. If you can, it is. I'd certainly not feel comfortable riding a bike where I had to keep the thought at the back of my mind - "don't brake too hard, the fork might bend".

Do SA have any sort of caveat in their literature about the drum brakes - "should only be fitted to strong enough forks" - type of thing? I can't see anything like that on any of the docs on their website.

I've never seen one of the SA brakes in the flesh, how easy would it be to extend the reaction arm? Is it possible to take it off and swap it with specially fabricated one? Or an extension welded to the original, or something? As far as I can tell from the SA web site it's riveted to the brake assembly body.

I've got a couple of Carrera Subway 8s (busy decaying in the shed) that have Shimano roller brakes on the front. They're attached to disc brake tabs, so I'm assuming (perhaps incorrectly) that the fork is designed for discs. Though given what modern production is like, it's quite possible that those forks were also used for bikes with actual disc brakes, and repurposed for the Subway 8.

[Brucey]

...I've always thought that "doing a stoppy" is the ultimate test of whether a brake is good enough. If you can, it is. I'd certainly not feel comfortable riding a bike where I had to keep the thought at the back of my mind - "don't brake too hard, the fork might bend"...

There is such a thing as 'too much brake'.

IME in a real emergency (where you have to stop promptly), having a brake that is powerful enough to do a stoppie is definitely counterproductive. [The reason for this complicated but in essence it is to do with the fact that your stopping distance is highly dependant on your initial rate of retardation, within the first 0.5 seconds of the brake being applied. If the brake isn't powerful enough to do a stoppie you can go 'full gas' on the brakes which will usually be a higher rate of initial retardation than you will safely manage with the more powerful brake. Sure you can increase your retardation with a more powerful brake, but it takes 0.5s at least to do this and by then it is too late; you will have travelled up to another 5m at full speed if you don't get on the brakes properly.]

So I'd recommend that you don't fit a brake so powerful that you can do a stoppie; this is (IMHO) more of a concern than the prospect of bending forks, because you are likely either not to stop as quickly as you should with such a powerful brake, or you will actually tip yourself over the bars in an emergency braking situation. A 90mm brake is likely to be appropriate for a machine that is routinely heavily laden, where the extra power is useful, but is often 'too much brake' otherwise. The bottom line is that a 70mm front brake is -once bedded in- usually more than enough for an unladen solo, and -simply because you can apply the brakes fully with confidence- you will often stop more quickly in an emergency than with a more powerful brake, which is counterintuitive. It is pretty much the same trade as is made with car brakes; ABS doesn't stop you as quickly as a skilled driver in the dry using non-ABS brakes can manage, sometimes. But an average driver in real conditions is better off with ABS than not.

Engineering different arrangements for reaction arms is not for the faint-hearted. If you have the required skills to do this you will know it. Otherwise you are probably better off not modifying brakes.

I've got a couple of Carrera Subway 8s (busy decaying in the shed) that have Shimano roller brakes on the front. They're attached to disc brake tabs, so I'm assuming (perhaps incorrectly) that the fork is designed for discs. Though given what modern production is like, it's quite possible that those forks were also used for bikes with actual disc brakes, and repurposed for the Subway 8.

Those forks will accept a disc brake, if that is what you want.

cheers

[cycle tramp]

Well, it's happened at least once:

http://smutpedaller.blogspot.com/2014/0 ... g-bad.html
.

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[cycle tramp]

I have to say that I wouldn't risk fitting a drum brake on the front of our tandem unless it was fitted with a fork that was designed for the job for the same reason that fitting of disc brakes is ill-advised on forks that are not designed for that purpose.

Ian

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[cycle tramp]

Cycletramp, I do like your utilitarian bike. What gear range do you have?

Ian

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