u/littlewing1208

I’m looking to upgrade my 24” Torker with square taper hub to a Nimbus with an ISIS axle and I was dismayed to learn about the bearing situation for ISIS unicycles. Namely that the 42/22/12 bearing is hard to find and expensive for completely unknown quality bearings. I can get high quality Japanese (NTN, Koyo, NSK) or Swedish (SKF) bearings for a few bucks for a square taper hub (40/17/12) but for the ISIS axle that 22mm ID means you are paying $15-20 a bearing with no QA/QC or specs and hope they last. Given all of the “skip the square taper Unicycles and get an ISIS hub” you read, I’m surprised there isn’t a reputable source for the ISIS bearings.

I have found that 60/22 (44/22/12) bearings are available from real brands (NTN/NSK at least) for ~$12 so i was wondering if anyone had a machine shop machine the bearing housing’s diameter 2mm larger (1mm radius which shouldn’t affect rigidity at all)?

Does anyone understand the point of this isospeed implementation? I took mine apart last night to try to solve a creak only when I’m in the saddle and I have doubts about it.

I always assumed that rubber bit that is between the seat tube and top tube acted as a bushing similar to how an automotive control arm bushing works where an outer and inner shell separated by rubber/polyurethane can move centers relative to each other. After disassembly, I realized this is not the case. The rubber bit you can see near the seat tube simply surrounds the joint and maybe isolates vibrations between the two tubes. In terms of the hardware that connects the two you have a fastener where both ends rigidly touches the top tube. It has a few washers (one is a wave washer that 100% flattened for me over 5000 miles) and then on the “tongue” on the seat tube, an aluminum sleeve with two split aluminum bushings attach to each end of the sleeve. The fastener goes through this assembly and there is no rubber or polyurethane involved in this assembly so the top tube and the seat tube are rigidly attached (the axis of the fastener and the axis of the ST tongue with the sleeve/split bushings cannot move relative to one another).

The only thing I can think of is that the upper portion of the seat tube has a pivot that is slightly in front of the seat tube and slightly lower than the top of the top tube which allows the seat tube to flex a smidge more (longer moment arm?) than if the ST/TT were solid molded carbon fiber? Maybe that coupled with the fact the bushing/sleeve assembly allows the ST to pivot as it flexes is what offers the “comfort”?

Any thoughts?