Are the stays on an old PX-10 frame (531) sturdy enough for disc brakes? I ask this, because this frame has nice, wide stays for wide rims and tires for use as a bad-weather bike. I would consider having disc mounts brazed on if I knew the stays could withstand the forces.

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    Even if they stays weren't strong enough, you could just replace those two. But really, what's the point for a bad-weather bike. Just use rim brakes, or get a different frame. Rim brakes have worked sufficiently well for a hundred years. – whatsisname Dec 18 '16 at 7:07
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    You're just doing rear disc brakes? The front will stay rim? Because the front brakes do at least 75-100% of your braking. If you're going to go disc, change your forks. – RoboKaren Dec 18 '16 at 8:38
  • The frame question is a duplicate of at least three others, starting bicycles.stackexchange.com/questions/37227/… – Móż Dec 18 '16 at 10:02
  • If it's about wet weather stopping distance, you might find a drum brake hub worth looking into for both front and rear. The Sturmey Archer ones I have are very resistant to water intrusion and don't require disc mounts. – Yolo Perdiem Dec 19 '16 at 4:14

Answer: Its not worth doing, from a financial stand point.

Adding disk brakes to a frame is expensive, risky, and ruins any vintage value the frame had. The stays are not engineered or designed for the new sideways loading.

Also, you talk about stays, but braking on the rear wheel is nowhere near as good as braking on the front.

If you're dead-keen on fitting disks to this frame, then a better solution is to buy a new front fork with disk mounts, a new front wheel or hub with disk mounts, a front caliper and rotor, new cable/hose, and a new brake lever that suits. Keep the old fork and parts too, that way you can revert to original spec for no cost.

If you want a disk brake bike for bad weather, buy a second-hand MTB and fit mudguards, leaving your loverly vintage bike for rides.

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