Changing to disc brakes

[FredS]

I was looking at a new set of rims for the old 25 year old Bounty Hunter MTB bike, I came across someone who has a nice looking set but they are strictly for disc brakes for $120. He also had a disc brake kit (Front: 74mm post mount or IS, Rear: IS only, Wheels: ISO 6-bolt rotor mount) for $80 and said it should fit most bikes. My question is what is an IS mount for the brakes?

[Joe_W]

A quick google turned up this:
http://www.bikeman.com/bicycle-repair-tech-info/bikeman-tech-info/1638-51mm-international-standard-74mm-post-mount

Basically there exist different mounting standards. Depending on the frame you have one or the other. There do exist adapters. On a 25 year old fram you won't have disc brake mounts, nor will the frame be built to withstand the torque at that point. So: stick with rim brakes. Get another set of wheels. I'd go for a hand-built 32 spoke laced cross-3, double butted spokes (more reliable), with mid-range hubs (LX?) depending on your way of riding.

[FredS]

Thanks Joe

[nfmisso]

I would not go with a disc brake conversion either.

I would go with 36 spoke wheels, 3 cross lacing. I am heavier than most, and 36 spokes result in a stronger wheel compared to 32. The rear wheel on my commuter has 40 spokes.

Why do you want a new set of rims? And why not build them yourself?

[RobAR]

'IS' = International Standard. The other option is 'PM' or Post Mount.
A 25 yr old frame is highly unlikely to have mounting points for either.
Totally FORGET any of the "bolt-on" junk that you may see advertised. A frame or fork MUST be designed from the very beginning to handle the forces that Joe mentioned.
I agree with the above by Joe and Nigel and would steer you away from a disc conversion. I have been a hardcore MTBr for over 20 years and also a bike mechanic for almost as long. Never have I impaled myself on a cedar tree for lack of braking power from quality V (linear pull) Brakes. V's are lighter and much easier to set up correctly by a novice - particularly when we get into discusion of Hydraulic Disc.
Heck, I still ride one particular bike that is laden with Alivio cantilever binders and I trust it with my life on roads covered in Ice!

Fred - just get what you need and ride!

[xerxes]

My twopence.

Good V-brakes are better than cheap disc brakes, but good discs do have some advantages over V-brakes, but also some disadvantages. Disc brakes are heavier, but on the plus side they do work better in the wet and when it's very muddy because they largely stay clear of it in the centre of the wheel, they also still work if your rim gets knocked out of shape a bit on a ride.

However, converting a bicycle that wasn't originally designed for discs isn't straight forward. First you need disc specific hubs and disc specific forks, ordinary forks may snap, even if you have a disc brake tab brazed on because the blade of the fork itself needs to be stronger to cope with the torque generated at the end of the fork by the disc brake. Similarly, I've seen some bolt on brackets for the rear stays of the frame for fitting discs, but frames made for discs will often have some extra bracing to cope with the stress, so I don't think I'd trust bolt on adapters personally.

All in all, I would stick with good V-brakes rather trying to adapt an older non-disc frame for disks. A set of good Shimano or Avid V-brakes together with some good brake pads/shoes like Koolstop or Swisstop will give you a lot of stopping power and are a doddle to set up.