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Old 07-10-11, 07:33 PM   #1
koosk
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bottom bracket size for 2011 trucker

Hey guys, I'm trying to figure out which size bottom bracket I need for my 2011 LHT. The surly website says the stock bb is a "Shimano, UN53. 68x118mm" Seems simple enough- but when I look at the phil wood website, their bb are sized by length (113, 118, etc) and then for diameter it says something like "68/73". What the heck does "68/73" mean? And will a "68/73" mm bb fit in the space of a "Shimano, UN53. 68x118mm"? Thanks for your time!
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Old 07-10-11, 09:10 PM   #2
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It depends .. on the Crankset that You have chosen.
80s M 730 a 118 is ok but .. those are water under the bridge..

I have an M730, with a Rohloff hub chainline requirement, 1 chainring
in the inside position on that 110 (74) crank and it uses a 127.5 ..
so it all depends .. on multiple variables.

ask the crankset seller..
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Old 07-11-11, 05:51 AM   #3
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68mm is usually considered English standard (diameter of the frames BB), while 73 is Italian. The 118 is how long the spindle is, 118 usually being for a tripple, narrower for a double crank. Is it a splined crank, square taper, gen 1 or gen 2 of the same splines, ISIS, etc, etc! Don't even get started on the press in bearing holders for the hollow cranks! As anyone can see the bottom bracketts can be confusing even in the same manufacture, much less across manufactures!
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Old 07-11-11, 08:16 AM   #4
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Quote:
Originally Posted by uciflylow View Post
68mm is usually considered English standard (diameter of the frames BB), while 73 is Italian. The 118 is how long the spindle is, 118 usually being for a tripple, narrower for a double crank. Is it a splined crank, square taper, gen 1 or gen 2 of the same splines, ISIS, etc, etc! Don't even get started on the press in bearing holders for the hollow cranks! As anyone can see the bottom bracketts can be confusing even in the same manufacture, much less across manufactures!
Not quite. 68 mm is the old British standard shell width and now commonly found on new road bikes, 70 mm is the old Italian standard BB shell width and 73 mm is oversized British and is commonly found on mountain bikes and some road bikes.

Brad
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Old 07-11-11, 08:33 AM   #5
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Yeah, so in the case of a system like the Phil, where the parts are sold separately, you need to get the 118 part based on that need, and there will be a set to mate it to the BB shell. Apparently there are 68/73 BB shells that fit the english threads, which I suppose is why they use that notation, anybody? You can measure your LHT to see whether it is 68 or 73, but it's going to be 68. 68 isn't always dead nuts 68 depending on how the frame prep was done.
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Old 07-11-11, 08:45 AM   #6
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Thanks bradtx

See what I mean about confusing! hehe
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Old 07-11-11, 08:58 AM   #7
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Quote:
Originally Posted by bradtx View Post
Not quite. 68 mm is the old British standard shell width and now commonly found on new road bikes, 70 mm is the old Italian standard BB shell width and 73 mm is oversized British and is commonly found on mountain bikes and some road bikes.
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Originally Posted by koosk View Post
...What the heck does "68/73" mean? And will a "68/73" mm bb fit in the space of a "Shimano, UN53. 68x118mm"? Thanks for your time!
Most BB manufacturers sell their BBs ready to fit the two most common shell widths, 68 and 73mm. They accomplish this by including a 2.5mm spacer, so that installing it between the shell and drive side BB cup will allow a spindle sized to fit a 73mm wide shell also fit a 68mm shell. The spacer recenters the BB by moving it 2.5mm to the right of a 68mm shell, thus placing it in same location as a 73mm shell, so that chain alignment is maintained.

The 68/73x118 Phil is the proper replacement for a Shimano 68x118.

I thought about getting one once, till I saw the price of ~150-175, vs 25 for a Shimano UN-xx. Very hard to justify the additional cost IMO. Shimano square taper BBs last for thousands of miles despite their cheap plastic cups and appearance, and are truly a great value among Shimano components.
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Old 07-11-11, 08:59 AM   #8
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Quote:
Originally Posted by koosk View Post
Hey guys, I'm trying to figure out which size bottom bracket I need for my 2011 LHT. The surly website says the stock bb is a "Shimano, UN53. 68x118mm" Seems simple enough- but when I look at the phil wood website, their bb are sized by length (113, 118, etc) and then for diameter it says something like "68/73". What the heck does "68/73" mean? And will a "68/73" mm bb fit in the space of a "Shimano, UN53. 68x118mm"? Thanks for your time!
I haven't looked at the PW website, but it's possible that their BB is delivered with two 2.5 mm spacers for installation on a 68 mm wide BB shell.

Brad
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Old 07-11-11, 10:55 AM   #9
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Koosk still using the original out of the box [LHT] crankset?..
Or what?

FWIW, examples.. M900 sits further out on the same length
of BB axle, that an M730 fits perfectly.
If you went the other way, a BB that fit the M900
will be way too short for using the M730

Generally, both same years Shimano cranksets .. XTR/XT

Crank and BB need be considered together..

If it came with an 118, and you keep the same crankarms,
get the Phil in JIS Taper 118, the shell width 68/70/73,
does not matter because Phil Mounts on internal rings,
doesn't engage the shoulder of the BB Shell of the frame..

Last edited by fietsbob; 07-11-11 at 11:04 AM.
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Old 07-17-11, 06:09 PM   #10
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Talking about square taper: Phil will sell you the cups separate from the rest of the BB. You get the BB in the required spindle size; if you're getting a new BB for the original crank, get the JIS 118. You buy the cups according to the frame; yours has a "standard" english threaded 68mm BB shell. The frames out there with 73mm BBs are still english threaded; no spacers are required b/c the spindle is free from crank arms, and the BB is designed to center and work well whether it's housed in a 68mm or a 73mm shell. The 70mm size will NOT NOT NOT work, as the TPI of the threads are different, as is the inner diameter of the BB shell. Buying a phil for your LHT? As some others have mentioned, the move is a BB set with a 118 JIS spindle and a set of english threaded cups. I'd go for steel, but that's just me.

You'll need the install tool. Spring for the shop tool, or get two of the home mechanics tool. (Having 2 will make it easier.to install.)

The spacers for BB cups come into play with the new outboard BBs, because the crank axle(which replaces the spindle on a conventional BB) is attached to one crankarm. If you try to run one designed as a 68/73 in a 68mm BB shell without spacers, there will be excess axle showing, and won't engage the bearings properly. FWIW, modern road cranks tend to come only in a 68mm version (many are also offered for use with the 70mm italian BB; this is why many manufacturers do not sell road cranks with the BB included) because no one is making road bikes with 73mm BB shells. With mountain bikes, 73mm is very commonly seen, as is 68mm. (Incidentally, no one is making MTBs with italian BB shells, as far as I know.) This is why many modern MTB cranks come with an included BB; they feel pretty sure that the bike will have an english threaded 68/73mm shell. There are some 29ers and DH bikes with wider BB shells, and these'll need special cranks with longer crank axles, but now I'm digressing severely.But, this is why they have outboard BBs that employ spacers for modern mtb cranks. Use the spacers if you have a 68mm shell; do without the spacers if you have a 73mm.

Where does this all fit with touring bikes? Well, touring bikes are basically roadish things, with 68mm shells, but they often run mtb cranks, which will (in the case of outboard bearing systems) need spacers. I've sidestepped the new and ghastly BB "standards" (BB30, BB86, BB92, and their various permutations) b/c these haven't shown up on normal production tour bikes yet.

Sorry for the dissertation on BBs; i just saw lots of helpful and well-intentioned ppl contributing to the thread, but there was some misinformation there. Trying to prevent an expensive mistake for the OP and anyone who finds this thread in an archives search.

-rob
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Old 07-18-11, 09:28 AM   #11
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on a side note, I just recently learned how to take out a square tapered sealed bb on my old late 90s Rockhopper (which is a 73x107) It recently started up a noise from the bb under a decent amount of torque, and up until now, I thought taking out and reinstalling a BB was complicated--and was pleasantly surprised to see how simple it is.

funny that now these type of bb's are "old school" now, the last time I had taken a bb apart was the really old type with big ball bearings and adjustable cups and such. So with the $15 tool, pulled the bb out, cleaned out all the threads, liberally regreased all the threads on the bb and plastic thing on the non drive side and sound is gone when I reassembled it. Thanks to the LBS who explained the driveside reverse thread and the sequence of starting with loosening the driveside, then the other side; and to reinstall with drive side first.

thanks rob for the extra information. I guess the next thing to learn for me will be outboard BBs when and if I have a bike with them.
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Old 07-18-11, 04:23 PM   #12
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DJB: The outboard bearings are the easiest to install IMO. Some of the early SRAM/truvativ systems were seriously flawed, but they've worked the kinks out of it. Aside from the looks of some of them, I've been extremely happy with most of the ones i've used/worked on. The exceptions: poorly sealed RaceFace BB(the raceface cranks are compatible with shimano outboard BBs) and the truvativ cranks before they had the reverse-threaded locknut to keep the crank bolt from backing out on its own.

To be honest, I really like the old unsealed cup/ball/cone square-taper BBs. Aside from needing more attention, they offered a lot of benefits: low resistance, ease of adjustment/installation, and handsome good looks. I still have a bike running 'em.

-rob
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