welding disk brake mounts onto aluminium?

[nomm]

I have a 1992 cannondale tandem. In an ideal world I would like to put disk brakes on it to replace the canti's.

Would it be possible to add the mounts? Would it pointless anyway as the frame is not designed for load in that area? Are there any other ways/ideas of improving the braking power?

If it is possible where should I go? (live in south-west)

Thanks

[yakdiver]

Here for the rear
http://www.halfords.com/cycling/bike-pa ... Aif48P8HAQ
for the front new forks.
Oh look I've made my 1000 post

[willcee]

Personally i would look at what Magura has to offer.. hydraulic rim brakes.. unless you are descending the Alps ie long hot brake for many K'S, where the rims get very hot... imo they should work well in uk conditions.. will

[bikes4two]

I have the Magura HS33 on my Santos tandem and they really are superb. I've traveled widely and fully loaded with camping kit and come down some fairly long descents without over heating the rims but I've not done alpine descents yet where I would expect to use the 3rd brake.
Having said that I have on the odd occasion got hot rims on my solo tourer at which point I've rested and/or dunked the rims in water for cooling.

The HS33 are of course a flat handlebar brake solution.

[Brucey]

a 1992 Cannondale is a fully heat treated frameset in an age-hardening alloy. A welded modification won't be heat treated; all the material around the weld will revert back to the solution annealed condition (which is about half the strength it is elsewhere in the frame). I would weld a cannondale frame (but not in every location...) if it saved it from the scrapheap, but not otherwise, not willingly anyway.

The other thing is that disc brakes have at least as many problems for tandems as any other sort of brake does; they are just different. Only a small proportion of disc brakes are any good on a tandem IMHO; it is very far from an 'automatic upgrade'.

If you want good tandem brakes, get three brakes (if you don't have them already) and learn how to use them. The third (drag) brake can be a drum brake on the rear wheel, which does not require a frame modification to allow its fitment.

The extant rim brakes can doubtless be improved; but the best route depends on how they are configured at present.

cheers

[tim-b]

Hi
Apart from the frame losing the benefits of its heat-treatment around the weld sites, I'd be very wary of attaching a disc brake to a fork that probably isn't designed for a disc...
(Edit, forgot this bit)...and for advice ,where they build tandems
Regards
tim-b

[nomm]

Yea I thought the weld idea was a bit of a long shot, I did ask my sister (material engineer) who basically laughed at me when I started asking questions.

So a rear disk mount as suggested not a great idea? (I have several BB7s lying around the garage)

Continue to experiment with the canti's performance and future upgrade of a drag brake wheel for the rear. Any particular make or recommended systems?

I have used Magura's before, back in the early 2000s on my trials bike, but I would always be a bit weary of hydraulics for touring, but then again I haven't got much planned outside of Europe atm. Will I then be limited to non-drop bars?

[Brucey]

For many years the favoured drag brake for touring was the Arai unit. Not because it was very powerful or lightweight (it isn't) but because it is reasonably well cooled vs other brakes and it would survive getting to the point that smoke would start to come out of it, and then carry on working normally again once it cooled down.

When these brakes get too hot it is clear that something is up; this is when you use the other brakes to stop the bike and let the drag brake cool off. Most other forms of drag brake are either less capable to start with and/or don't have a benign failure mode when they get too hot.

Magura rim brakes are, in use, fine brakes and will often be slightly more efficient than a cable operated brake (at any given running clearance/nominal MA value) because there are no friction losses in the cable. But if you want drop bars, you are looking at obscure levers that have not been made for some years and can now only be bought used. Also if you do have a problem out on the road, it'll be somewhat less amenable to a roadside fix, just like with any hydraulic brake.

Most Magura rim brake users find their brakes are reliable for many years at a time but when you get troubles it can be a plumber's nightmare; I would therefore suggest that if you can get a cable operated brake that works well enough, that would be a more pragmatic choice.

You can buy kits that allow a rear disc caliper to be bolted on to a frame. A-to-Z rings a bell. These don't fit every frame and usually react the brake force up to the LH canti boss which can be complicated on a tandem with three brakes.

A BB7 is a fine brake (better than most other disc brakes IMHO) but as a drag brake on a tandem it (like most discs) has some problems. The disc itself can easily overheat and turn blue (and who knows at what point the disc itself will be liable to fail...?) many types of pad will fade when they get properly hot for the first time, the wear life (in this use) of many pad types will be very short indeed (just a few days of moderate or hard use in some cases) and when a BB7 caliper gets properly hot the adjuster knobs tend to look like a Salvador Dali rendition...

But at least it doesn't boil up like a hydro disc will (and last time I looked I couldn't find a hydro brake that is known to be immune to this in tandem use). So if you have to have disc brakes a BB7 is better than most. Note that there are two versions; one for 'road levers' and another for 'V' type levers.

For cable operated rim brakes, V-brakes are an easy choice; they offer a high system MA but

a) that MA can't be adjusted and
b) there are only a few drop bar levers that can be used with full V's

Modern (most recent Shimano 'New Super SLR' type) STIs work with 90-95mm arm length mini-Vs and this gives a high MA and (with the right pads) a powerful brake.

Older STIs (all until 2008, some after) have a shorter cable pull and these give a spongy but powerful brake with mini-Vs, where the lever can come back to the bar if the brake blocks wear on a long descent. If you want to use this type of lever then I'd suggest cantis; you can adjust the system MA using straddle geometry changes (provided you use a mid-arm design) and this can give a brake that has the same system MA as a V brake if you put your mind to it. Shimano BR-CX70 brakes (or CX50 with upgraded brake blocks) fit a wide variety of frames and if you use a conventional straddle wire (instead of the unit link) you can adjust the geometry (and the MA) to get the brake feel/power you want.

Note that the above comments apply to frames where the bosses are set so that they are ~25mm below the rim centreline. If your bosses are set different to that, this will change the system MA just as much (if not more) than if you chose the wrong levers or something. Occasionally it works out so that you can (say) use road levers with a full V brake or something but more often it is just a problem.

If you have a weird boss height then one way out of this is to use an older XT-type V brake; these have a linkage (and in some instances squeal intractably by virtue of this) but because they have a 'parallel push' they have a MA that doesn't vary with boss height in the same way as it does with most other brakes. (Maguras have a similar feature too, of course.)

hth

cheers

[DaveP]

If your concern about a possible inability to fit drop bars is mainly about having a front to back "bit" to hold onto you could look at the Albatross bar made by Nitto. Similar to a moustache bar in appearance but accepts flat bar levers - while still accepting bar end shifters. Best place to view is the Rivendell site. They are quite clear about dimensions, but when I looked on e bay the situation was quite confused so buy with caution.
If you mainly use the tops this might work for you, but if you live on the drops - don't bother!

[Dave W]

Disc brakes are fine on a tandems in most UK conditions, they don't turn blue or melt the callipers. If it were my Cannondale I would simply fit quality V brakes I can't see any point in bodging a bike of that age or any point in spending large amounts of money, welding, changing forks and fitting disc ready hubs.

Just my opinion.

[goatwarden]

I have a 1992 cannondale tandem. In an ideal world I would like to put disk brakes on it to replace the canti's.

Would it be possible to add the mounts? Would it pointless anyway as the frame is not designed for load in that area? Are there any other ways/ideas of improving the braking power?

If it is possible where should I go? (live in south-west)

Thanks

Seeing that you only bought it last week, had you considered trying the existing brakes first? You may be surprised how effective they can be.

[Brucey]

Disc brakes are fine on a tandems in most UK conditions, they don't turn blue or melt.....

plenty of folk have turned 160mm discs blue 'in UK conditions' on their solo bike. When I see people trying to use similar brakes on a tandem I do worry.

I'd argue that almost any tandem needs a degree of skill to avoid overheating the brakes on a steep hill; if you have a skilful crew and/or you don't ride big/steep hills, maybe it is going to be OK. But otherwise you can easily get into trouble.

For all their faults, rim brakes usually give clear signs that they are too hot; they start to make a lot more noise than normal. This generally happens well before the brakes go away or the tyres blow off, so you have a chance to do something about it.

Other brakes do not always give such clear signs that they are in distress; it is very easy to ride them up to the point where the brake is overheated (and the pads just go away, the brake boils up if it is a hydro, or the disc turns blue, etc etc) with no clear indication that this is about to happen.

cheers

[nomm]

I have a 1992 cannondale tandem. In an ideal world I would like to put disk brakes on it to replace the canti's.

Would it be possible to add the mounts? Would it pointless anyway as the frame is not designed for load in that area? Are there any other ways/ideas of improving the braking power?

If it is possible where should I go? (live in south-west)

Thanks

Seeing that you only bought it last week, had you considered trying the existing brakes first? You may be surprised how effective they can be.

Yes in the wet, down a steep hill in Bristol with only myself riding and no load. Didn't fill me with confidence, but while I have ridden tandems quite a bit before, I haven't got anything recent to compare it to.

I have some jaunts planned this weekend so the V-brake seems like an good option if required.

[hamster]

I run Magura HS33 on my Dawes 26" wheel touring tandem. Braking has never been worrying - it even pulled up cleanly down a 1 in 5 in Devon during torrential rain with the rims completely soaked (and 15cm of water running down the road). This was a loaded tandem towing a child trailer.

To mitigate the heat issues I run heavy Rigida Rally rims to provide a decent weight of metal to soak up the energy.

Cantis lose lots of effort to cable stretch to the rear, hydraulics virtually none. At £150 for a set of Maguras it's a good first try a lot less than discs which would require the brakes plus frame mods and new wheels - you can get a set of Maguras for £70 or so used on well-known auction sites - or from me for around £40.

Bung a front one on for starters and see what you think...

[iandriver]

I noticed a while back flicking through Orbits pages that they are using discs and a VEE on the rear which seems to be on a bar end shifter as a quasi drag brake. I wouldn't use it as a drag brake like I would an Arai, but guess you could alternate between the two as an option under the usual constraints.

http://www.orbittandems.co.uk/orbit-tan ... our-36.php