JIS / ISO BB - Does it matter?

Haha! That's what I get for regurgitating 2nd hand info. Good job I didn't wander in there asking about one.

My bad.

Also, I agree with Harry, keep clear of the Miche BB, it's horrible.

Just to contribute to this, I know this link has been posted before elsewhere but it's very clear and worth watching if yr unsure / newcomer:

http://www.fixedgeargallery.com/columns/bobgarage/indexb.htm

RE: Chapters 5, 6 & 7.

Good old Bob.

Reet, I've UTFS and read all of what Sir Brown has to offer, but if anyone can give me a simple answer to a simple question, I'd be dead happy an all that.

Right now I'm using an old MIche road double with a JIS 107mm BB. The chainline is perfect, but the BB is a piece of shit. I presume the Miche cranks are ISO, so I might as well get a good ISO BB (campag centaur or something) to replace the current one. My question is thus:

What length of ISO BB would be equivalent to a 107mm JIS BB when used with ISO cranks?

By my calculations:

"If you install an ISO crank on a J.I.S. spindle, it will sit about 4.5 mm farther out than it would on an ISO spindle of the same length."

                                                     S.B.

So to get the same chainline, I need an ISO BB that is 9mm longer over all to compensate for the crank sitting 4.5mm deeper on the spindle. Vis, I need a 116mm ISO BB... is this correct, before I drop cash on a decent bottom bracket?

Thanks, and sorry for the resurrection.

just get a shimano 107 JIS

I might as well get an ISO, as I have the choice and the cranks are designed for it. Suggestions welcome. I do already have a Shimano tool actually, so maybe you're right...

115.5mm Campag Centaur.

But is the calculation correct...?

dbr - I just swapped a Suntour (111mm JIS) for a TA (118mm ISO) and got roughly the same chainline with my Stronglight 49D cranks (ISO). BUT the cranks simply would not sit right on a JIS taper, and would creak under load, the difference between them depends on how willing you are to force the fit, hence I guess the "about 4,5mm further".

So the calculation may be correct but who knows/cares? A Campag road double is sensible given that Miche have probably followed Campag convention. If you can borrow one to try first, that would be ideal.

I'll add my 2 cents - I think there is a right and a wrong way of doing things, but in most cases they both still work. My sugino messangers came with a shit RPM BB. 500 miles later and it's f***ked, cue un54 BB thats 7mm longer (bought out of necessity). 1000 miles later and no problems - solid as a rock in fact, no more chain wear or other discernable disadvantages. I would choose a un54 over a miche BB every time (there's a lot of threads on here that testify to that). Do I care that my messangers may be wearing funny -no. I've seen a lot of horrific bodges as far as BB's go and as many examples of compatible cranks/bb's failing. This doesn't really help you - I just think some people go to extrodinary lengths (expense) to get their chainline perfect, when a mm or even 5 is still workable, it just means your drive train is slighty less efficient. Don't get me wrong - if I'm running a set of DA 7600's, I would want to run a hatta/sugino BB and I'd be a lot pickier about my chainline if I was running a dolla regina chain an 75 chainring / DA sprocket combo. A lot of situations just don't call for the same attention to detail. The other plus with shimano BB's is any bike shop has the tools to remove them and will more than likely have a spare. The same cannot be said for campag or other iso BB's

You've got a shimano tool, a un54 is £15, you don't have any guess work as your cranks are already running on an jis bb. I would just stick another shimano bb in.

Thanks for everyone's advice. Although I love the traditional look of the Centaur etc BBs, and they do require a new tool and cost a bit more. Plus I know that a JIS BB works fine with these cranks.

Tried and tested Shimano BB is is then.

I have just got a road Ofmega Mistral Crankset, I want to run it to my phil wood rear with a perfect chain line(obvs) After checking the transmission database 3 people who have posted as using a mistral but none have mentioned if its track or road and what length BB they are using, i dont know why they even bothered at all. So my question is does any one use a mistral? Is it JIS/ISO i would rather match it if possible and any ideas what length spindel is required?

Reet, I've UTFS and read all of what Sir Brown has to offer, but if anyone can give me a simple answer to a simple question, I'd be dead happy an all that.

Right now I'm using an old MIche road double with a JIS 107mm BB. The chainline is perfect, but the BB is a piece of shit. I presume the Miche cranks are ISO, so I might as well get a good ISO BB (campag centaur or something) to replace the current one. My question is thus:

What length of ISO BB would be equivalent to a 107mm JIS BB when used with ISO cranks?

By my calculations:

"If you install an ISO crank on a J.I.S. spindle, it will sit about 4.5 mm farther out than it would on an ISO spindle of the same length."

                                                     S.B.

So to get the same chainline, I need an ISO BB that is 9mm longer over all to compensate for the crank sitting 4.5mm deeper on the spindle. Vis, I need a 116mm ISO BB... is this correct, before I drop cash on a decent bottom bracket?

Thanks, and sorry for the resurrection.

Finally got round to replacing my shitty JIS bb with a nice campag one. My sums were good, it's perfect, and my drive train has stopped making intermittent clicks. Let this be a lesson to you all / anyone who is thinking of doing the same thing.

Viz:

1 Attachment

Where did you get that from?

Looks like a rehash of Sheldon Brown's flawed advice.

What's your unflawed advice?

Not mine, but Tstr's.

I wondered if Tester had pronounced on this. "Assuming a symmetrical BB, this means a chainline moved inboard 1mm if you replace a 110mm JIS BB with a 110mm ISO one." - i.e. you are going from the top right diagram to the top left diagram, or from bottom left to bottom right. I think my diagram is consistent with what he is saying, though I need to revise it if it is true that the end of the taper is the same across ISO and BB, as in my diagram I have made the base of the taper the same. I made the diagram to help me get my head around the difference between the two standards, based on the observation that they both have the same taper angle. Anyway, thanks for pointing out the Testerism.

Edited to make things a bit clearer.

That's not what I understand.

ISO BB measurements include the 1mm chamfer on each end.

So an ISO BB is in effect 2mm shorter than the stated length.

The cranks doesn't sit further inboard or outboard on either JIS or ISO.

This relates to "modern" BB: "old" Campag and Shimano are another bowl of spaghetti altogether...

(I had an interesting conversation with Cliff at Royce on the subject: the man's as dry as he's knowledgable.)

I don't think we are disagreeing. The point is that if you match crankset to BB you get the intended chainline, if you mix and match your chainline moves in or out as shown. ISO cranks have to have a slightly smaller taper hole compared with JIS for a given BB width so that they sit out far enough to accommodate the chamfered end of the ISO taper.

@mdcc_tester plz!

Square taper is shit, throw away all your old cranks and buy proper ones.

In unrelated news, I have various square taper cranks and BBs for sale 🙂

7400/2?

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