BB-UN55 vs BB-UN300; which is the better square taper bottom bracket?

In this video I’m going to delve into the BB-UN55 and what makes it one of the top choices if you’re looking for a new square taper bottom bracket.

And I’m also going to cover why, in a BB-UN55 vs BB-UN300 shoutout, the BB-UN55 comes out on top.

[xKillYourTVx]

Just got a brand new bb55 for 12$ ! Thanks for the video that lead me to it. Let's see how it is.

[kan]

Thank you for producing this insightful and informative video.

[Gromitdog]

Shimano's cartridge bottom bracket was revolutionary, taking a component that required frequent servicing to a maintenance free reliable component that so long as you didn't blast water and degreaser into the seal and wash away the grease would last a very long time. Too bad nothing higher than the UN26 is readily available. The UN72 was amazing and silky smooth.

[Autonomous_]

Back in the olden days when I started biking at a young age, I would save up and upgrade components as I could but now that I can afford to own bikes and restore them I just go with whatever the bike originally had, obviously while trying to find the best option but I like to keep them as period correct as I can

[valixt]

230903: about "Square Taper Bottom brackets need to go some day": Currently almost all ebikes I saw under 2000$ used this type of BB's because it is easier to install the cadence sensor for pedal assist on them.

[AB-egei]

I have never opened a BB-UN55 but I´m pretty sure that internally it is a "cup and cone" type bearing. The correct technical description would be, that it has two angular contact bearings where the inner race is directly ground into the spindle, the outer races are fitted into the cartridge shell. The BB-UN300 is completely different. Two radial roller bearings ("industrial bearings") are pressed onto the spindle. One advantage of the first type is, that the balls are bigger. Another difference is that angular contact bearings can be fitted with quite some preload. Radial roller bearings can only be preloaded very lightly. You can feel that preload when you take a new UN55 out of the box, it`s smooth but a little bit stiff. What happens when you start riding is that the bearings will "set", it basically means that races and balls will grind against each other on a microscopic level until they fit perfectly, the UN55 will loose the initial stiffness within a couple of hundred kms and will typically last a very long time without any service. With the BB-UN300 I can´t tell. This type of construction is usually found on cheaper square taper bb. The fitting is probably not as tight, it can not be preloaded the same way, maybe the components are of a lesser quality, who knows? There are high quality versions of this type around (phil wood) as noted in the video and the "industrial bearings" can be replaced. But again these types also rely on a tight press fit between the bearings and the spindle, so for the average user it is not that easy to replace the bearings. Hollowtech 2 is much simpler to service in this regard, but comes with it´s own set of problems. HT2 relies on the frames BB shell for the alignment of the bearings. If the frame is not perfect, you might get problems with creaking and/or rapid wear of the bearings, a problem that was pretty much unheard of with the high quality shimano cartridge type BBs.

[V_screw_electric_cars]

I've had UN 300 fail very quickly as water got into it and cartridge bearing was all rusty inside, those fancy seals are useless, at least the one the non drive side. I used to have old bike with plastic cup shimano bottom bracket and that one lasted a long time I think it was some cheapest model that they used to have. The UN 300 isn't even that cheap I wouldn't recommend unless you live in some nice place not a hellhole with 6 months of winter like I do.

[markjmaxwell]

The BB-UN300 is pretty hard to beat for twenty dollars.
My last bike had a non sealed caged bearing bottom bracket the BB-UN300 is a huge step up from my old bottom bracket...
I hope my new bike has a BB-UN300 or a Hollowtech 2 bottom bracket...

[PowDRider]

One of the benefits of a Square Taper Bottom Bracket is in travel/tourning bikes. It is much easier to separate the crank from the frame and pack in a bike suitcase for travel. Here I am referring to a Travel Tourning Bike with S&S Couplers, but applies to other bikes as well for travel.

[DoNNiEdx]

it's a pity that the BB-UN55 is now discontinued.

[paulywogtheburninr]

Too bad they stopped making the un55 and now they are in limited supply, the un300 seems fine, but I’ve been reading about how they are more prone to failure. I guess Shimano is just shifting away from square taper. There are options from other brands which are affordable and seem solid such as the Tange LN-3922 and 3912 as well as the IRD QB55 which seem solid. IMO any sealed bb will be solid since loose ball/cage bearing bbs just don’t keep out the water great.

[potsy]

Unless your a weight stickler and need to run the widest boost tire options available square taper is perfectly reliable and performs just as well.

[stephenknig]

I think you talk a lot of sense here. Totally agree.

[tocaamerillo]

BB-UN26 has failed on my bike after a couple years, so I'm now looking for a replacement... What's left of Shimano's square taper lineup is frankly not very encouraging. I've narrowed my choice to be between UN300 and Neco B920AL (I don't care much for it being aluminium, but it comes with extra seals in the cups compared to steel Neco models). I'm veering towards Neco because of... well, just compare the sizes of the bearings! I haven't seen UN300 in person, but on all the photos I can see its bearings appear to be maybe 60-70% width of the bearings you can find in cheaper brand BBs. I understand this might not be telling the whole story, but surely for the part that has to bear such stresses size does matter.

[MarshWaha]

Sucks the Shimano BB-UN55 is discontinued. It’s way, way better! I freaking love this Bottom Bracket it rocks. Very disappointed that square tapered BB’s are not as in demand, this model is the best on the market now it’s rare and hard to find.

[DeiviZZZ]

hi, it would be awesome if you did a disassembly of both, and compared internal parts.

[guitarfreakfalko]

My BB-UN300 failed after 4 month and about 1000km, but i believe i may have overtightened the nondriveside cup. If you find that after tightening the nondriveside cup the axle is difficult to turn, you might want to backup like an eighth of a turn until the axle is turning freely again.

[Goodman-]

Why exactly is the 300 inferior then? You didn't say anything apart from the fact that it's placed at a lower level than the 55. What technical specification led you to this conclusion?

[lereveure]

Thanks for the video, but didn't see a lot of +s and -s comparing the two.. maybe next time outline those :)

[f]

Does anyone know what the hard black plastic ring on the drive side spindle is on the UN 300? I see the same one in this video, so I wondered what the purpose of this odd ring is sitting in the middle of the spindle is for.