Hi,
A friend and I are building a cargo bike and are facing the challenge of lowering the rack area. Originally we had planed to use a bmx style 20" steel fork. The problem with those is the high A-C dimension. So I decided to think about designing a fork that reduces that by a few cm.
I have got the dimensions I need and am designing a fork in rhino. One way to go would be using a suspension fork crown as the starting point. I could buy a crown similar to the one pictured here locally and use 28 mm tubing as fork blades.
My question is: does the cast aluminium on these fork crowns hold up the forces that would work here considering there is no suspension effect?
Please consider that I dont have a brazing set at hand, so either I would be welding everything together or just gluing and securing (like the aluminium crown).
I hope I could explain the issue well and would love to hear your feedback.
I donât know anything about strength, but did see someone used a suspension crown to build a cargofork.
So itâs done before, no feedback though
Def made a note in my brain.
In the meantime I went down another rabbit hole: double crown forks. My thought was that I could minimize the distance between top of the tire and the crown race. While that is possible (goes down to about 20 mm), it kind of pushes the problem upwards. Meaning I would have to create more space above the head tube to accommodate the top plate, spacer and top cap, which goes against my final goal.
It seems that I have to stick to building a biplane fork. Which to be honest is the most fun and challenging outcome of this research.
I was facing the same problem with trying to get the cargo area as low as possible on a cargo bike build. I researched cargo forks and the Omnium forks have the shortest A-C and a 45mm Offset. The steerer is 1 1/8â and threaded on top, so you can use an Omnium threaded cap to adjust preload and secure it. If youâre not a confident builder I would be careful with a DIY fork as is can be very fatal if it fails.
you are right. I should be very careful. in the end, one should start somewhere right. i will be posting the results here so those with more experience can also take a look here and say if it looks okay.
24mmĂ tapered Columbus track legs with Columbus SL top tube off-cuts as brazed-on shims to take them up to 25.4mĂ. Rode them for 10 years with no problems at all. A little flexy perhaps, but that was the tapered legs, not the crown.
My only real concern was the strength of the M5 clamp bolts, since they are under tension from the clamping which increased during loading and braking.
I didnât know if they were the original RS bolts, so swapped them out for reputable supplier 12.9 (DIN 912) steel capheads.
Might also be worth looking for Manitou or Pace crowns which are bolted in the same way, but used 28.6mmĂ legs.
