I was about to order a new square tapered BB for some folding bike.
Normally I would opt for Shimano UN55, since they tend to last a long time. However I noticed that some new variants were offered: UN300 and UN100.
Since I could not find any detailed info on Shimano's page (nor got a response from the webshop), I ask here.
- Does anyone have press-releases regarding these UN300 and UN100 parts?
- Are UN300 as durable as UN55?
- Do the Chain-case and E-bike variants indicate a lateral offset? (how much?)
After a bit of digging I bring my preliminary conclusion (partly based upon comments), although nothing is confirmed:
- UN55 and UN26 are no longer available so probably UN100 and UN300 will be the replacements
- UN300 have a "stabilizer", which is probably just the small plastic spacer on the axle, that will line up flush with the crankset (on the images it looks like UN100 have this too)
- UN100 is so far only available with 122.5 mm axle, so they probably only target the most-used axle length (and for low-end bikes you might not care much about the chainline)
- The 3x variants (Normal/K/E) seem to differ in the how the right (drive-side) of the shell looks at the outermost part (see the image). Normal version have more axle exposed, and the E-bike variant have a few mm without threading (to allow for a sensor?). Furthermore the chain-case seems to provide a spacer (see the exploded view)
- UN300 have aluminium shells on both sides, UN100 have resin shells
- In terms of price: UN100 6,2 €, UN26 ~8 €, UN300 10,5 €, UN55 15 € (bike-discount.de 2020-06-09)
My guess it that UN300 is a minor upgrade from UN26, by having alu shells and some convenient improvement with spacers (to me it seems unrealistic that new product in this category is 30% cheaper and more durable). I kind of doubt Shimano will introduce a new "high end" square BB on par with UN55.
Update after receiving UN300s and UN100
In general it looks like a production evolution of the previous designs like UN55 and UN26.
TL;DR: UN300 looks to be a well-made unit with good seals, but maybe not as tough as UN55. UN100 looks identical, except for plastic shells.
Let's get the weight out of the way:
- UN300 270g for a 113mm axle
- UN100 285g for a 123mm axle... so kind of identical.
The shells look like they are fitted/glued on. On the old UN55 the main unit with drive-side looked as if it was machined from a single piece of steel. The new UN300/100 is 1x steel axle, 2x shells (alu/plastic), 2x cartridge bearings and one middle piece (steel), although the drive-side shell is not immediately removeable.
The bearing on both models are 6903RS (ID17mm, OD30mm). I bought 2x UN300 and 1x UN100, on one UN300 I felt some subtle irregularities/bumps when turning by hand, but I guess that goes away after a bit of use.
The UN300 has the same white powder coating like UN55, and I guess this is similar to blue loctite you find on many bolts. The UN100 does not have this, but for plastic you do not have to care about corrosion anyway.
The finish of UN300 looks great, and has laser etched name + tighten direction.
The shells have seals that attach to the axle and it looks like an effective way of keeping water and dirt out.