Adam187

Hello,

I'm new to bike forums and hoping someone can help me with a current build.

My single speed bike has a 103mm square tapered bb for which I bought a set of Miche primato cranks. What I soon realised is that there are two types of taper and miche require ISO kind and I believe a 107mm bottom bracket .

What I'm asking is can I replace a 103mm bb with 107mm or would that push my chainline too far? Is it possible to buy a 103mm iso type taper ? And will that fit the miche crankset.

I appreciate any help with this and please understand I'm no expert in bikes but have always worked on them and was really enjoying this particular build up until this bump..

Many thanks

Jicafold

This would probably not push the chain line out too far. That’s only 2 mm on each side. And depending on what kind of fixie cog or single speed freewheel you are running you could always put a spacer in there to keep the chain line straight.

veganbikes

So you want to go with the Bottom Bracket the crank manufacturer recommends. Different splined cranks have different needs for bottom brackets, A lot of track cranks for whatever reason tend to go ISO and some are 107 and many especially for Japan and the NJS market are 109mm (though Sugino says that their B.B.s are not ISO and only S75 tapered but I call hooey as people have ridden them with ISO B.B.s just fine)

Sugino Messengers and a good bit of 130 BCD single speed cranks I have seen tend to go 103mm JIS taper. They are fine cranks but you do tend to find higher quality chainrings in 144 BCD simply because that is the track racing standard so more likelihood for higher quality for those that are actually racing or just want the best. But I will say my Sugino Messengers are fine cranks and I haven't had issues.

I would NOT use spacers. I would not worry about any chain line issues on a proper single speed or fixed gear bicycle. Maybe on a conversion I might a little but honestly chain line doesn't really matter that much on a proper FG/SS bike and those who worry about it need help. Unless the frame is utter garbage and was not built right it is hardly an issue. Much noise comes from cheaper components smooth running and properly round components will work better and quiet down the drivetrain.

ofajen

Have you installed the Miche cranks on that BB? While not the preferred match, it may work ok.

It will sit farther out than it would on an ISO BB of the same length but you have a shorter BB. Per Sheldon Brown’s website, they should sit 4.5 mm farther out, but you are already 2mm in on each side with the 103 mm BB.

So the net would be 2.5 mm farther out for chainline, which should be ok. Bottoming out will not be a concern. The main thing is whether the crank has enough contact area on the taper of the BB to reliably withstand hard SS use.

Otto

Kabuki12

The only way I got it to work on my seventies Japanese bike when I wanted to put a set of nice Campy NR cranks on was to set up the spindle on one of my precision tool grinding machines and grinding .002” off per side of the square taper. I came up with that number by checking the insertion depth of the original crank vs. the depth of the Campy one on my optical comparator. That is not something the average bike mechanic has access to. It worked really well until I found a nice Campagnolo Bottom Bracket for the bike.