Author Topic: Tandem drag brake  (Read 3614 times)

Re: Tandem drag brake
« Reply #25 on: 01 September, 2020, 12:13:18 pm »
Our tandem does not have a drag brake. It was scary when all it had were the original MAFAC cantilevers. I upgraded to SunTour self-energisers, then added a third brake - an ancient Weinmann 500 sidepull salvaged from my old Falcon. It is controlled from the stoker's bar, and experience shows that it works ok so long as you have a trusting/compliant/obedient stoker. An autonomous stoker who thinks they can decide when braking is required is a disaster waiting to happen. DAMHIK... 

Arai are hard to find, but do come up now and again on ebay.  In their absence, SJS list as an alternative a Karasawa screw-on drum brake for 49.99.  But don't be fooled: precisely the same thing can be found on Amazon for the princely sum of 14.60.

https://www.sjscycles.co.uk/brakes/karasawa-screw-on-tandem-drum-brake-replaces-arai/

https://www.amazon.co.uk/sourcing-map-Electric-Scooter-Bicycle/dp/B07L8PD2Q5/ref=sr_1_3?dchild=1&keywords=bike+drum+brake&qid=1598957626&sr=8-3

Compare and contrast..

I'm in the process of building another tandem so found some twin-threaded hubs with the aim of using one of those - not from SJS! - as a drag brake.  The compromise will be being forced to use a screw-on freewheel too.  It's a budget build for occasional use so I think we can get away with another part from the box of bits in the shed.
They laughed when I said I was going to be a stand-up comedian. They're not laughing now.

Re: Tandem drag brake
« Reply #26 on: 01 September, 2020, 12:44:39 pm »
I have never seen this^^ Karasawa brake for true, but judging from the photos, it is made of thin stamped sheet metal, while the Arai was a beefy cast metal thing. Calling this a substitute for Arai drum brakes is probably a bit optimistic.

A

Re: Tandem drag brake
« Reply #27 on: 01 September, 2020, 08:41:31 pm »
It certainly looks nowhere near as hefty as an Arai, which is a substantial lump with plenty of finning for heat dissipation.  SJS include the warning that their Karasawa can get pretty hot, but that heat won't be anywhere near the rim so one of the principal reasons to have a drag brake - avoidance of popping the tyre off - is, er, avoided.  If this can be achieved by shelling out a mere 14.60 I reckon it's worth a try.  It reminds me of a screw-on alternative to Arai that aeons ago was available from the Richmond Cycles catalogue back when they were offering those oversize Balance hubs for tandems.  Eek, that was a long time ago, around 1984 or thereabouts. (Have I really gone and got that old and how did that happen?)
They laughed when I said I was going to be a stand-up comedian. They're not laughing now.

Kim

  • Timelord
Re: Tandem drag brake
« Reply #28 on: 01 September, 2020, 09:25:06 pm »
Somebody should molish one that fits to a disc brake mount...
Careful, Kim. Your sarcasm's showing...

Re: Tandem drag brake
« Reply #29 on: 01 September, 2020, 09:26:58 pm »
Somebody should molish one that fits to a disc brake mount...

 :facepalm:
If it ain't broke, fix it 'til it is...

Re: Tandem drag brake
« Reply #30 on: 01 September, 2020, 09:34:55 pm »
The Amazon one is a '90' whereas the SJS one is a '108'.  I believe that this refers to the drum diameter.

It looks like you can get the same model as the SJS one (BSZ108) from Aliexpress.  Click on the second 'color':  https://www.aliexpress.com/item/4000974788731.html

Re: Tandem drag brake
« Reply #31 on: 01 September, 2020, 10:39:27 pm »
Somebody should molish one that fits to a disc brake mount...

Oh of course, I quite forgot that carbon blingy-thingy with disc mounts lurking at the back of the shed. Silly me. I'll strip that down instead of rumaging in the parts bin for the old skool stuff... 


Meanwhile, daft as it sounds, Kim, you're not the first to suggest this, as the Q&A on the SJS page shows:

Can this be screwed to a six-bolt disc hub?
By Jon
29 Jun 2018
Just wondering if the two holes either side of the threaded centre of this hub will enable it to be screwed to a standard six-bolt disc hub (I can't find any info online on the spacing and diametre of these two holes).

SJS Customer Service:
No, this will not fit a 6 bolt disc hub.

Thanks
They laughed when I said I was going to be a stand-up comedian. They're not laughing now.

LittleWheelsandBig

  • Whimsy Rider
Re: Tandem drag brake
« Reply #32 on: 09 September, 2020, 11:51:05 pm »
ISO disc brake BCD is 44mm, considerably smaller than the existing holes. It looks at first glance like the ISO holes would end up on the dished area of the backplate, given the threads are about 35mm. You would need a tapered adaptor as a minimum. Who knows whether there is enough frame clearance at the edge of the drum though. The drum is a bit wider than a disc.
Wheel meet again, don't know where, don't know when...

Re: Tandem drag brake
« Reply #33 on: 20 November, 2020, 10:29:55 pm »
Just a point about the CSS rims DaT says are (or were?) on both wheels of the Raven Twin.

I put one on the back of our Thorn Adventure to replace a worn out Sun Rhyno (using the old spokes) and it has been a great success but I would not want them for both wheels. Once they have been used for a while, not so long a while with a tandem, they get smoothed off and after that although they still give very good braking in the dry and in light rain, they are less good once there is heavy water around. The Kool Stop special CSS blocks are a bit better once the rims are smooth than the Swiss Stops blues and SJS has the thicker R16 V2 version of the Kool Stop blocks which are good with the Andra 30 rim width.

With the CSS and appropriate blocks the rim looks like it should last for many X 10,000s and the blocks last well too making the combination good long term value compared to a normal alloy rim.

An option for control of a cable disk is to use a road type disk brake and one of the auxillary levers (cross levers) as a primary lever so you have two brake levers on the left of the captain's bars. I've found road BB7s work well with this set up and it has the advantage that you are sitting more upright on braked descents to aid air braking. I guess with flat bars you could just add a second lever with the appropriate pull for a V brake and use the MTB version of the disk brake but I've not tried that.

LittleWheelsandBig

  • Whimsy Rider
Re: Tandem drag brake
« Reply #34 on: 21 November, 2020, 11:55:49 am »
HK found much the same with discontinued DT ceramic rims on the front of her upright trike and her foul-weather commuter. They ate brake pads for a while, regardless of being standard material or ceramic-specific. Once the rim coating smoothed out, she started complaining about wet weather braking with ceramic pads. Scrubbing the rim with a synthetic dish scourer improved matters but I ended up building a Al rim for her foul-weather commuter despite the additional grot. The trike has two V-brakes on the front rim, so one brake dries off the wet rim for the second brake.
Wheel meet again, don't know where, don't know when...

Re: Tandem drag brake
« Reply #35 on: 16 December, 2020, 05:18:02 pm »
more than one person has told me that once CSS rims have smoothed off properly, you can change back to standard 'salmon' type Kool stops and wear rates are acceptable. I've not BTDT myself though, and maybe DT rims are different to that.

Using a threaded freewheel on a tandem of course  means that the spectre of axle breakage may raise its ugly head.  To combat this, it is possible to install an 'outrigger bearing' beneath the freewheel.  In combination with a decent quality CrMo axle the whole arrangement seems to be pretty reliable.  Since a threaded brake mount can be converted to disc if needs be, it is probably the more flexible choice in the long run.   The rise of e-bikes with cheap wheel motors has meant that the screw-on freewheel format -instead of continuing to die a death- has remained a viable format. You can buy 8s, 9s, and 10s screw on-freewheels and they can come with 11T top sprockets.

I've not used the Karasawa brake on a tandem but I've got one in the spares stash just in case the Arai spits the dummy and  I need it. I am pretty sure the karasawa is going to get super-hot on a tandem.  One of my mad ideas is that it might be possible to add a bolt-on aluminium heat sink to the back of the karasawa drum. Another is that it may be possible to water-cool the brake drum using a drip feed of water from a nearby bottle cage, using a modified bottle with a tube and bleed valve.

I note that it is also possible to squeeze a suitable rear hub (eg which is threaded for a freewheel one side and has a six-bolt disc mount on the other) down to 100mm OLN, at which point it should go into a front fork.  I don't know how easily the clearances work out (because I have yet to try this out in anger)  but in theory if the threaded end of the hubshell is used on the left side with a threaded disc converter on it, this means the six bolt mount can be used on the other side and you can have twin discs up front. Or a drum on the left and a disc on the right.  A significant worry on a tandem is that (because the CoG is so much further backwards) you might get into a situation where the increased front brake torque might either overload the fork or cause a front wheel lock-up. 

However provided the second brake is only ever used as a drag brake, and/or alternately with the other one (there may be a clever way of doing this BTW) then you may not be in danger of overloading anything, more than you usually are, anyway.

cheers

Morat

  • I tried to HTFU but something went ping :(
Re: Tandem drag brake
« Reply #36 on: 20 January, 2021, 09:34:13 pm »
Using rim brake in that fashion could overheat the rim and cause a blow-out.     

Been there and got the gravel rash. Luckily we were down to walking pace but it was still bad enough and the wheel was totaled.
Tandem Stoker, CX bike abuser (slicks and tarmac) and owner of a sadly neglected MTB.

Re: Tandem drag brake
« Reply #37 on: 24 January, 2021, 08:53:27 pm »
https://youtu.be/-obLQbhdNrI is what you need  ;)
And Darkness and Decay and the Coronavirus held illimitable dominion over all.