stocksy

We have a Dawes Galaxy Twin, we've had the bike a couple of years, but the rear brake has never seemed quite... right.

The tandem currently has Tektro 720 cantilevers with Shimano BL-R400 levers. The front brake works very well, I'm able to apply more than enough force to bring the tandem to a halt abruptly, but I'm concerned that I would not be able to bring the tandem to a stop using the rear brake in the event that the front brake fails.

The lever feels very soft and the braking force is so weak that I'm not able to lock the rear wheel even when riding solo. If I set the brake so that there is sufficient clearance for the wheel to rotate freely, the lever hits the bars before I get enough braking force.

I've replaced the brake cable and housing, but this had little effect. I know about setting the height of the yoke and length of the straddle cable in order to vary the mechanical advantage of the cantilever, but the geometry of the frame limits my options here, since the stoker half of the frame is very small to accommodate my 5"1' stoker:




The frame does have mounts for a disc brake, so I wouldn't mind fitting one if this might solve the problem. What should I do?

merlinextraligh

First thing to try is new brake pads. Put on Swiss Stops and see if that helps.

rebuilt13

First thing I would do is clean the rims with alcohol and scuff the pads. If that doesn't help make sure the pads are hitting the rim square and also check your cable housings. Pull off the ferrules and make sure the housing ends are square and they aren't fraying.

thompsonpost

Long brake cables will feel mushy. It's the nature of the beast. Feeling less effective is the result.

joe@vwvortex

When I was looking at buying a tandem we test rode different tandems each with a different brake setup. I road down a pretty good size hill and checked to see which would stop the tandem with JUST the rear brake alone. I tried a Dura Ace Caliper, Avid Vbrakes and an Avid disc. ONLY one to stop the tandem was the disc. Not even close. We aren't a light team either - over 350lbs. I bought a tandem with a rear disc. I've since switched to dual discs - and it's nice having one finger braking at any speed.

conspiratemus1

You have identified the root of your problem, Stocksy. It's not your adjustment skill and cleaning the rims or changing the pads won't help much. You are a victim of geometry. Rear cantilevers with a short stoker seat tube, like you (and we) have, just don't work. It's impossible to raise the straddle cable yoke high enough to find the sweet spot where mechanical advantage works out right because it will bang up against the cable stop when you try to apply the brake. (On your bike you would actually need to raise the cable yoke above the level of the cable stop which is of course impossible.) If you place the yoke low enough to allow vertical cable travel, the pads won't move far enough to clear the rim without the lever bottoming against the handlebar. (And yes the problem is compounded on a tandem by the long stretchy rear cable.) Tall people (or teams with tall stokers) just can't empathize with what we short people go through!

Possible solutions:

1) Far and away the best one is to remove the cantilever and install a rear disc brake since your frame has the fitting for it. Can be finicky to set up because the long stretchy cable consumes some of the lever travel. And you need a hub with a flange to mount the rotor on. But this will give you the best braking. You'll enjoy how well it works in the rain, too. Just be careful not to lock up the rear wheel with a light stoker.

2) mount a side-pull dual pivot caliper brake. Tektro makes long-reach calipers that might work with your brake bridge. Their long arms (to clear those fenders) will give less braking force than conventional short-arm road-racing calipers but on the rear this is not so crucial. Just remember to grab harder when you use that rear brake. It'll still work better than a canti that can't be dialed in.

3) a linear-pull brake might work. Have never used them on a tandem but lots of tandems come that way. Their advantage is that, like side-pull calipers, they don't rely on a cable stop hanging down from the seat lug to crowd the installation. They work best with a "matched" lever; brifters won't work -- too much mechanical advantage -- unless you install a Travel Agent.

stocksy

Thank you for the thoughtful replies everyone. Having made the cable, cleaning and other checks suggested, my plan of action will be:

1. Purchase swiss stop pads. This might be a simple fix and even if it doesn't work, I'll just move them to the front brake.

2. Tektro R556 caliper.

3. The frame and hub is disc compatible, so if all else fails, I'll buy a disc brake. I'd like to avoid this in the first instance because I found that it makes it much more difficult to remove the rear wheel on the road in the event of a puncture.

I will report back with results.

Brainrider

I have the same Dawes tandem but it has straight handlebars with v-brakes and an Avid BB5 disc brake in the rear. I recommend getting a disc brake and avoid getting punctures, though taking the wheel off is really no problem. My modified 2nd hand Galaxy Twin has the disc brake control on the captains left handlebar with the rim brakes controlled with the one lever on the right bar but I believe the disc brake is standard on Galaxies with the stoker controlling it. My first tandem so I'll take it as it comes. The disc brakes makes a huge difference in stopping - it's the equal of the two rim brakes.

Retro Grouch 

All brake housing isn't created equal. Compressionless housing, like Jagwire Ripstop, can make a big difference. The longer your cable housing the more it helps.

conspiratemus1

Agreed. It just takes a little practice. When replacing the wheel, you need to watch both the dropouts and the brake caliper since the rotor has to slide into the space between the pads at the same time the axle is engaging the dropouts. Do it a few times at home before you have your first puncture in the rain. The less you think about it the more automatic it is. You'll find it's actually easier than trying to wrestle the tire between those close-riding cantilever pads.

bobthib

1+. I put Kool Stop MTB pads on mine (the dual compound type) and they are great. I don't have cantis, but changing the pads and truing the wheels and adjusting the brakes made a HUGE difference.

merlinextraligh

you wouldn't expect any bike to lock the rear wheel using the rear brake alone. Most braking force, even on a tandem comes from the front brake.

In our experience DA calipers have enough braking force to lock the wheels at speed. If you can skid the tires, the brakes can't give you anymore stopping power.

From there the issues are heat dissipation, fade, and modulation.

conspiratemus1

This doesn't sound right to me. It's pretty easy to lock the rear wheel and skid it for exactly the reason you mention: most of the braking force comes from the front wheel as the weight shifts forward and "un-weights" the rear wheel. That's why it skids. It would be correct to say that you can't expect a bike to stop safely using the rear brake alone. You're right though that properly adjusted rim brakes (caliper or cantilever) have more than enough power to stop a tandem. The OP's problem is that his short seat tube prevents him from being able to properly adjust his rear cantilever and I'm kind of doubting that even a long-reach caliper will fit. Also, he'll likely have to buy a pair of calipers but he can easily buy a single disc. So he's left with a disc as his best option.

tandem rider

If cables, housings, and pads don't improve your braking consider V (linear) brakes. Either Avid or Shimano are good choices. My first tandem, in the early 90s, had a rear brake that would not brake well even with several attempts to adjust it.

tiggermaxcocoa

It also might help to just try another canti brake, like Paul neo retro or the Rodrigurz big-squeeze. These brakes are designed specifically for handling big braking loads, while the tektro is just a cross/touring brake. I've seen large differences in braking power between cantis on my touring bike, so I can only assume the problems with a mediocre one will be magnified on a tandem.

Chris_W

I've heard that the brake you're using is good for mud clearance, but is not the best at braking power. I might therefore try a more "low profile" canti brake. However, I'd probably skip that completely and go for a V-brake with a Travel Agent (St John Street Cycles in the UK carries them). Unfortunately, this might not work with the positioning of your rack stays - if you have a V-brake on another bike that you can put on to try check out the positioning before buying anything then that would be best.

Better cable housing, better pads, and cleaning the rim are all good suggestions, but I would try something more major here.

joe@vwvortex

I didn't mention anything in my post about locking a wheel. I couldn't lock the rear wheel my test ride with the Dura Ace caliper though - in fact I don't remember locking the wheel with any brake I tried. I'll take the slight weight penalty of the dual discs - they work wonderfully. I don't even worry about brake fade or rim heat anymore and we regularly ride long steep downhills.

Chris_W

One more idea. Given that the cable stop is on your seat post clamp, it might be possible to move it up. You could use a regular seatpost clamp in the current position, then get a shim to put around the seatpost higher up, and put the current clamp, with the housing stop, in a higher position, anywhere you want along the seatpost. You'd still be limited by the straddle wire interfering with the rack stays, but it looks like you might have a couple cms before that happens. You might then be able to get a decent amount of mechanical advantage.

merlinextraligh

But my point is that its not a reasonable test of a set of brakes whether the bike stops downhill with just the rear brake, given that most o fthe braking force comes from the rear brake.

Out of curiousity, I tried this on my single bike, Dura Ace Calipers, Zipp pads (which are really Kool stops) dura ace aluminum rims. Brakes closely adjusted to the rims. At 20 mph using the rear brake alone, I couldn't skid the rear wheel even with a substantial amount of hand force.

Without the front brake shifting the wieght forward, its not that easy to skid the rear.

I took what you said as bieng that it wouldn't lock up. Since you're saying that the bike wouldn't stop, by definition the brake wouldn't lock up. At the point the bike stops, the brake is locked. Thus if you could lock the brake, you'd skid to a stop.

But the broader point is that any bike is going to brake comparitvely poorly with the rear brake alone. The relevant question is how the bike brakes using both brakes.

steve53mg

Stocksy, It looks like you might have a sharp "S" bend between the rear cable stop and the brake. I would try disconnecting the cable from the brake and put some resistance (pull) on it while, at the same time depressing the lever. You night feel the stickiness in that bend and can experiment with longer or shorter housing to alter the radius. In most cases a v-brake (or linear), which is a very poerfull brake, will fit on the same bosses as your canti brake, but I think that you will probably need to reshape your rack mount. I performed this change on my old Santana with a Blackburn rack that looked very similar to yours, with good results. I did need to use a cable amplifier (travel agent) to match the amount of cable pull. If your bike can accept a disc, that is what I would go with. It is superior on many levels. I would remove the canti altogether and route the disc cable to the right lever. I would recommend not running two canti brakes to the same lever, with the disc seperate. It is very hard on the hand!

conspiratemus1

I didn't mean to start an argument. I certainly agree with you that trying to stop a bike with the rear brake only is not a good test of any braking system. And I particularly commend you for doing a test to get actual data and reporting it. Bravo. You've made me "curious-er" than I was before. And that's a good thing.

Funny: you spend your whole cycling career learning how to keep your bike from skidding and crashing in the rain, snow, on ice -- it's hard to get out there and try to make it skid!

joe@vwvortex

I won't argue that most of the braking force is from the front brake. However - my options in front were limited to either V-brake or caliper at the time - since no front discs were available. I wanted to see which rear brake was the most powerful and when it came down to it - the disc proved that it was more powerful than either of the other two. Both the Vbrake and caliper brake in front were similar but since they had different brake pad compounds it was hard to say which was better. In fact - the same held true for them in the rear.

twilkins9076

4) Shorten your straddle cable. Doing so will definitely change your mechanical advantage...it will go to more of an all or nothing situation. If you do that, you'll also likely need to go with fewer spacers on your brake pads. It's not the best solution, as it requires a pretty picky adjustment, but I had to do that on my commuter. It also didn't have enough space for the seat tube cable stop.

See https://springfieldcyclist.com/2011/03/01/brake-woes/
and https://springfieldcyclist.com/2011/0...es-and-brakes/

Ray R

I recommend adding either a disc or a drum brake to the rear wheel and operating it with a friction thumb shifter for use as a "drag brake." Leave the calipers on as well. I've been in situations where I've had to use all three brakes while descending. Set the thumb shifter to the desired position to bleed off speed. This will prevent the rim from heating up to the point at which the tire blows off the rim.

merlinextraligh

A disc brake is not to designed to operate as drag brake.

The OP could replace the rear rim brake with a more powerful disc brake, or add a disc brake as a third brake. But it shouldn't be operated as a drag brake, stting a thumb lever to bleed off speed. Rather the disc brake needs to be used like a conventional brake, i.e. on and off, not drug.