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-   -   tandem rear disc brake (http://www.bikeforums.net/tandem-cycling/639972-tandem-rear-disc-brake.html)

ironglen 04-26-10 12:28 AM

tandem rear disc brake
 
Hey, I've just purchased a '99 burley samba and need to fit it with disc brakes for the terrain we will ride. I will be either installing a rigid fork with disc tabs or a beefy 80mm suspension fork (if I can find it) as the original has a rigid fork with v-brake posts and I can't add too much front end height. I'd like to use a thru-axle fork as it will provide superior rigidity and I want to get disc compatible hubs anyway. If anyone has any leads on a suitable fork, please let me know.
Also, I could really use some help finding how to fit the frame with a rear disc brake as the frame only has v-brake posts along with the pac-man mount for an old arai drum brake (which is now unavailable). I saw pics of some european disc mods along with a screw-on metal adapter for the arai-threaded hub, however the adapter only addresses the rotor connection to the hub and does not account for the needed frame modification or bracket needed to attach the caliper at the frame. Anyone encountered this that can help?
Thanks, Glen

TandemGeek 04-26-10 06:14 AM

For the kind of money you're getting into with all of the proposed mods to an 11-year old tandem, have you considered looking for a used Cannondale MT that came stock with dual discs?

Arai drum brakes are still available on the 2nd hand market and from a few tandem specialty dealers who stocked-up before they stopped producing the Arai's.

There are rear disc caliper adapters such as the 'Brake Therapy' on the market that by-pass having I.S. disc tabs brazed onto a frame.

Again, if you havent' done so, I'd recommend making a full accounting of what the total cost of these modifications would be and add that to the fair market value of your '99 Burley to figure out how much $$ you'll be sinking into this project. Then, with that figure in hand, do some checking around at www.tandemmag.com/classified, Craigslist, etc... to see what's out there that's already configured the way you need it.

Example from a 15 second search on Craigslist with the following search string: site:craigslist.org cannondale tandem MT
http://boise.craigslist.org/bik/1696496212.html

ironglen 04-26-10 09:24 AM

I follow you. I haven't seen a suitable bike that will gain much over the samba for the price; the cannondale would need disc brakes, the suspension fork, rear suspension post, shipping/travel cost, and maybe more dependent on condition. I read about issues with their rigid forks with disc brakes on some models too. I picked up the samba for less than $500 and figure to spend $500-$1100 for a total investment of $1000-$1600, completely decked out. I can't find anything close to that with similar components, which I figure are aftermarket parts that could be transferred to a dedicated mtb tandem frame in the future.

Thanks for the ideas, I'd not heard of the 'brake therapy'- I'll check it out. I've called about the arai and no one had it. If anyone knows of someone, please speak up.

Onegun 04-26-10 01:40 PM

Quote:

Originally Posted by ironglen (Post 10724387)
I've called about the arai and no one had it. If anyone knows of someone, please speak up.

Last we heard here, Tandems East still had some stock.

mkane77g 04-28-10 07:20 AM

If U put a disc on the front U won't need a rear disc. I ran a set up like this 4 years, much better than a rear disc.

chichi 04-28-10 09:42 AM

Quote:

Originally Posted by mkane77g (Post 10735063)
If U put a disc on the front U won't need a rear disc. I ran a set up like this 4 years, much better than a rear disc.

My understanding of tire traction is that a given tire has x amount of grip, you can use that grip for braking, accelertating or steering, if you exceed X the tire will slip. The more grip you use for braking the less grip you will have available for steering. The more braking you can generate out of the back tire the more steering you will have available with the front tire.

WebsterBikeMan 04-28-10 10:55 AM

Braking force at the tire is proportional to the coefficient of friction (which depends on the tire and the surface it is in contact with), and to the force pushing those two surfaces together. At rest the force pushing the two surfaces together is gravity. When decelerating, the bike tends to pivot forward, with the force between the rear tire and the road falling with increasing deceleration and the force between the front tire and the road increasing. At the extreme you lose contact with the rear tire, and there's no braking force coming from back there. This is nearly impossible for a tandem, but what happens before that is that the rear tire starts to skid, because the friction drops to less than the force required to decelerate.

mkane77g 04-28-10 03:54 PM

The only reason I no longer have a front disc is the Alpha Q fork has no provisions for one. I can lock up the rear disc at most speeds and all this does is flat spot a 65$ tire. Also, I do all my hard braking before a turn. I really do miss my front disc brake at times. There are downhills in Sonoma County that I will not attempt on the tandem without a front disc.


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