converting frames to take disc brakes

[nic]

I've often wondered about the safety factor of welding lugs onto a frame in order to take discs if the frame wasn't designed to take discs.

It doesn't seem to me to be a good idea, though I may be being overly cautious. What do people think?

 

[Pfennig]

I've always been put off by the cost to be perfectly honest. I would think on a steel frame you would be ok strength wise. On alloy you may interfere with any heat treatment the frame has had

 

[B3]

I've just done this to my son's GT, it's a cro-mo frame, the bracket fits on the end of the tube (where it's thickest) and the dropout. I'm using a 140 disc to keep the braking forces lower, but figure they can't be any worse than the loads fed into the middle of the seatstay from canti's.

I made the tab myself and TIG'd it on, all it's cost me is fresh powdercoat, some new decals and a bit of time, but them i'm lucky to have all the equipment.

 

[kanerdog1x1]

well done, thats a clean job. what tig you got?

 

[B3]

Cheers, just bought a Murex Transtig 203i

 

[kanerdog1x1]

ac/dc, most jobs covered then.

 

[kaiser]

B3 how did you set up the positioning? Nice job BTW

 

[terryhfs]

Absolute braking force remains the same but the nearer the force is applied to the hub the greater that force is relatively speaking - the spokes act as a lever multiplying the force.

In English - the load on a disk mount is potentially a lot more than the load on cantilever bosses.

 

[nic]

but what about the load on the frame at that point?

 

[perry]

if you imagine the disc rotating and the caliper clamping , the rotation will put the seatstay - dropout joint under more stress . thats why most put a tube from that point to the chainstay . or a disc mount that has a continuous weld along the stay from eye to eye to act as a gusset