Square Taper BB's – UN54 or bling?

As I’ve just gone back to the old school with some Middleburn cranks, is it worth getting something posh in the bottom bracket department or just bung in a Shimano UN54 ‘cos they’re cheap and they work pretty much as well as anything else?

I think I’ve probably answered my own question, but let’s hear your thoughts anyway…

Good timing with that question, I just won some White Industries on e-bay and was having same thoughts.

UN54s, I had bling but had issues with water ingress.

Gone back to old school cartridge BB’s, last ages, less faff.

Standard Shimano square taper. Think mine is a UN73? Fitted 3 and a half years ago and never had any problems – just beginning to feel a slight bit of play. I ride on average 15 miles offroad a week. Every week, so I rate them!

Square taper BB’s are so reliable that they had to invent other “standards” or “improvements” to keep their business growing.

If weight is an issue then bling otherwise it’s obvious, my current UN54 is at least 3 years old on an all year round off road commuter.

UN54 are just bombproof

I thought that might be the answer.

Are UN73’s still available anywhere?

LX and above will do fine and pretty much bombproof so should last an age, I think the XT are UN72’s. I couldnt find one for my cross bike and fitted the UN54 which, if memory serves, is the LX version.

I also have a couple of bikes with ancient Royce BB, one of which has been in for 8 years, serviced occasionally, but still going strong!

you pays yer dosh and makes yer choice. If it s bling build buy a bling BB, if not Lx/XT will be fine.

Token BBs are very light and so far are working very well.

Older Shimano are excellent but some are heavy.

XT and XTR will last for years….just try finding one in the axle size you need….

PaulD

Having had Phils, White Ind, Royce I’m now back to good old Shimano. They just keep on trucking and are cheap as chips. Had a new UN-55 arrive and it looks pretty good, metal non-drive cup as well.

I’ve got some exprience on this one!

I’ve been using UN54 and UN72/3 for the last ten years or so. I do ride a fair bit and find either of the above last me the same – one year no longer and they’re grindy and have play. As I’ve said I ride a fair bit!

Recently, I’ve bought some new Middleburn’s and decided to go with a bling Royce BB. It is massively lighter for a start, feels absolutely smooth and yes it really is very noticable when riding – just makes me want to go faster! The down side is that there can be problems getting them to bed in to the crank taper. Mine creaked and squeaked for a year despite following the set up instructions religiously! Now, it doesn’t make a sound, but I have also noticed that some play in the bearings is developing after two summers use. In summary this product is nice but can be temperamental and may not last any longer before it needs bearings (serviced at Royce) than replacing a UN54/72/3 but it does feel incredibly nice when riding. I’ll probably take a chance and get another for my next build!

What’s the difference between UN-54 and UN-55?

My last Shimano square taper bb was a un71. Lasted a good 10 years before finally giving up. Have also used Hope and tnt ti ones which were lighter but creaked loads & didn’t last so well.

What’s the difference between UN-54 and UN-55?

1

I think it’s just the metal non drive side cup on the 55 as opposed to plastic on the 54.

Not all the UN5x series are the same though are they? Some have hollow axles so are a bit lighter but I cant remember which!

I’ve been using a couple of UN54 and UN72 BBs for around ten years on various bikes (on and off road) and they still feel smooth. The tricky bit, I find, is working out what axle length you require.

I’m running the UN72 with some old Truvativ Compact drive triple cranks on a Five and they sit a bit too far out, so I’d be interested to know where to go to get a new one. Mind you, the current setup does allow me to run 22/36 and a bash ring without fouling the pivot on the Five.

UN51 = solid axle
UN53 = solid axle
UN54 = hollow, plastic NDS cup
UN55 = hollow, alloy NDS cup
UN72 = hollow, ?? cup
UN73 = hollow, alloy NDS cup
UN91 = hollow, alloy NDS cup
Token = hollow CroMo or Ti axle, alloy NDS cup

PaulD

UN54 is decent. Not sure I see the point in bling square taper?

UN54 and 55 also have a smaller hole through the middle than UN72 etc so presumably are marginally heavier. I used to put a hub QR through to hold the removal tool in place without slipping – but the qr won’t fit through a 54 / 55.

Thanks use full info!!

The Royce BBs are lovely, noticeably lighter/ smoother than UN55 – so you will notice a difference. But is it worth it?

I use grease ++ on the tapers, contrary to Royce’s instructions. This cured my creaking.

I have Royce on one bike – took a bit of fettling to get it to settle down. Also use copperslip on the tapers. Building a winter hack at the moment, have a Royce BB spare but think I’ll just use a UN54 for hassle free fitting

Not sure I see the point in bling square taper?

Because you’re worth it.

got a square taper phil wood in my fatbike, lovely and smooth, if only the same could be said for the rider !!!

As mentioned Shimano BB’s are a safe as bet last ages.

Although i managed to get second hand Raceface Taperlock Titanium and that has been spot on for 18 months or so now.

Ditched them external BB’s on my main bike a few years ago and got some Middleburn cranks and chain rings

The BB (UN54) has been in for about 3 years now? and last time I rode, it sounded a bit squeaky. if its goosed, its still lasted about 2 and a half years longer than the external BB’s did

Just bought a new UN55, to be sure.

Wouldn’t go back to external BB’s. not worth the grief for weight saving.

UN70 series bottom brackets haven’t been available from Shimano for a few years now.
A few folks round here are using TA Axix titanium BBs. Very light and the bearings are easily replacable.

Been running the same UN72 that came in my ’99 dekerf. It’s spent a year in a parts bin and since done 2500 miles in the commuter. Still smooth.

I’d have another!

Had an UN54 then moved to phil wood.

The phil wood definitely spins a lot better (smoother) and I noticed it while pedaling.

The adjustable cups mean you can shift the BB 5mm within the frame, improving chainline alignment if that makes a difference to you

EDIT: UN54 is still ok in my eyes though!

Another square taper devotee here.

All 6 of my bikes run them.
Unfortunately Ive only got one UN72 left in one of the bikes, one sitting in the shed thats 108mm – and one next to me on the desk that I took the grinder to to see what the axle looks like. (The BB had died I promise, I got it second hand 10 years ago…)

TBH Ive compared the weight with a plain non-hollow axle and the weight penalty is negligible so I guess some of the savings must be in the shells/bearings?

Ive resigned to using UN54s for now as I just cant justify £100 for saving about 100g. I still keep a weather eye on eBay – probably just like 100s of other UN72 junkies 🙁

I’ve just built up a Whyte 46 with square taper (UN55 and FSA crankset). The BB has been in my bit box for several years and still runs smoothly.
I still ride my Giant Track (1989) with its original UN?? BB as my rigid bike and the combination of BB and XT cranks is still a joy to ride (original XT Thumbies too…)

So another vote for shimano here.

Just took my UN54 out to replace with a UN55 because I thought it was a bit creaky. It’s just over a year old, checked purchase history on CRC.

Anyway, it still feels smooth as silk but the crank ams weren’t exactly tight. Cleaned the outside up, put a bit of grease on it and popped it back in, but with the metal collar from the UN55 instead of the plastic one.

Probably good or another year at least.

Got a spare UN55 in the toolbox now anyhow. It won’t go off.

I’d probably have replaced external BB’ at least once by now if I hadn’t gone ack to square taper.