I have a Shimano Nexus 8 internally geared hub wheel (Shimano centerlock disc compatible) that I’m planning to use on a cargo bike build. I have an old steel MTB frame with sliding dropouts, but no disc mount. I designed the above sliding disc mount to work with the existing dropouts and I was planning to have it laser cut at Send-Cut-Send along with a few other bits I need, but I’m not sure it’s worth the effort. I mean, v-brakes work pretty well and I have the post mounts already. The front fork I’m using has posts and a disc mount. I live in SoCal and I don’t ride during the rare rains. Thoughts?
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Personally for a cargo bike I would never consider rim brakes.
Sure they can have plenty of power but I dunno a good strong 4-pot with a properly sized extra thick rotor just inspires a lot more confidence with a big heavy bike carrying sometimes big heavy stuff. Finer modulation and more heat capacity etc.
Take my opinion however you want I’m no expert lol I just really strongly prefer disc brakes in applications that demand a lot from brakes.
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Yeah, you’re right! Guess I’d better get really good at TIG!
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I’ve designed an IS mount for sliding dropouts. If you have both the slots parallel, the caliper can hit the upper IS mount slot. It’s probably a good idea to angle the upper slot. I’ve got CAD files I can share if you want, but you can also probably get it figured out pretty easily.
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Oh I see! Guess I’ll need to have the brake caliper and disc on hand to really figure it out. Just use CAD (Cardboard Aided Design) to dial it in.
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If you’re going to laser cut your dropouts, you could integrate the IS mounts into the dropout. Then you don’t even need a jig to set them up.
Edit: didn’t read that you’re using existing dropouts.
Also, IS mounts work kinda like post. A rear IS mount using a +20 spacer is 160 rotor. But a front IS mount using a +20 spacer is 180 rotor. It might give you a little bit more room to just plan on using the front mount standard in the rear and spec the rotor accordingly.
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It’s worth looking at the Shimano BMX disc brake spec. You can locate the caliper where the wheel can slide back and forth enough without having to move the caliper.
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I would replace the whole dropout with one that has integrated IS mounts, if you can make your own even better!
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That’s a great idea! I also thought of just getting the chain tension correct, the caliper aligned, and just sending it with a standard mount! I don’t plan on switching up the gearing and if I do I can grab some half links or something.
Like these? BFS-C25 PLATE SLIDERS WITH SS FACES FOR DISC BRAKE PM SINGLE SPEED - 10 MM AXLE — BICYCLE FABRICATION SUPPLY
Those work, PWM also has some options and I do believe there is an horizontal dropout with IS tabs somewhere as well, or you could design one via SCS.
If you do make one based off a tab design, you could un-braze your original dropouts and maybe swap them out for the new one without the need for too much work, you would need a dummy axle or at least a sacrificial rear hub to keep them aligned while you braze/weld them
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Yeah, you’re right, this is the best solution and not any more difficult than trying to cut/grind/weld/braze on the existing dropouts!
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Any idea where one would track down that spec?
It’s in the Shimano frame fit specifications under BMX