[Benton]

Friday night I was installing a Breakout with Hayes 8" rotors. I didn't realize the Breakout was set up for 6" rotors and I would need an adapter. The local shop didn't have one and I had to ride on Sunday. It seemed to me that all I had to do was move the calipers out 1" (since the radius was 1" more).

So, I made one this morning in the machine shop. I didn't have any examples to go from so I just made it up. Basically I just got really long M6 bolts and made a U shaped block out of aluminum. It is 3.5" wide by 1" tall. Each upright of the U is drilled out 0.25" to allow the M6 bolts to slide through. The Uprights of the U allow the body of the caliper to rest between them.

Here's my concern: This adapter is basically just a pair of linked spacers. The force of the rotor on the caliper will cause the caliper to roll upward. This torque is applied at a larger than usual moment on the threads in the fork. The U does very little to prevent the calipers from sliding up.

The "real" adapters require 4 screws, and 4 holes off set from each other. Two screws hold the adapter to the fork, and 2 more hold the caliper to the adapter. This requires the calipers move up as well as out to allow wrench access to the bolts. In this case all the forces on the threaded parts seem to have smaller moments.

So, what do you think? M6's are pretty beefy bolts, and as long as their tightened down the adapter should handle the stresses I think.

I'm going to ride it tomorrow and see what happens. In parking lot test runs it seems to work well.

 

[Kornphlake]

I think you should be okay as long as the web connecting the two holes has a generous amount of material. If there is sufficient contact between the bolt heads and the caliper, the caliper and the adaptor and the adaptor and the fork then as the caliper tries to move with the rotor the parts attatched to the bolt will want to rock, if the bolt is tight it will put the bolts in tension and the adaptor will carry shear stresses, the ideal plan would be to have as much surface contact between the adaptor and the caliper to reduce the leverage on the bolt, if that makes sense. Since you have access to a shop you might consider taking a second stab at an adaptor and make one that's curved so you can use 4 shorter bolts, typical adaptors place the caliper out and up slightly.

 

[Benton]

Yeah, I might try to remake the part. The difficult part then is that I have to do a little math in order to move the calipers up and out while keeping them in the path of the rotor just right.

I took it out for a ride yesterday and everything seemed to be just fine with it. The M6 bolts are super beefy. I think I will take my time and really try to do the next one just right.

 

[RhinofromWA]

Yeah, I might try to remake the part. The difficult part then is that I have to do a little math in order to move the calipers up and out while keeping them in the path of the rotor just right.

I took it out for a ride yesterday and everything seemed to be just fine with it. The M6 bolts are super beefy. I think I will take my time and really try to do the next one just right.

NOw that you have the spacing figured out and you are in the fabricating mood....
why not just make a one peice 8" adapter? Half the fun is making things.....right?

 

[Benton]

NOw that you have the spacing figured out and you are in the fabricating mood....
why not just make a one peice 8" adapter? Half the fun is making things.....right?

It is already one piece. The new one will also be one piece. Half the fun is making it, but that often takes away from time that could be spent riding.

 

[RhinofromWA]

It is already one piece. The new one will also be one piece. Half the fun is making it, but that often takes away from time that could be spent riding.

Oh crap : sorry I thought you meant you made a U shapped spacer (1" worth) to add onto the spacer you already had..... requiring the longer bolts.

My bad. Is not the first time I got something wrong and as most that know me on this site.....it probably won't be the last.

 

[Benton]

Oh crap : sorry I thought you meant you made a U shapped spacer (1" worth) to add onto the spacer you already had..... requiring the longer bolts.

My bad. Is not the first time I got something wrong and as most that know me on this site.....it probably won't be the last.

Oh, I gotchya. Yeah, I didn't do that, but I guess I could've. It's just one U-shaped spacer with long bolts. In any case it has to be re-done. As soon as the brakes start behaving.