Hello all,

Recently while I've been riding there has been the issue of the cranks being at 12 o'clock and 6 o'clock and when I go to pedal, they snap down horizontally with a very unpleasant sound. Visited a few LBS and they all told me that I need to replace my BB. Now that I'm financially stable enough I was going to purchase a Phil Wood. I wasn't very sure about EXACTLY what size, length and taper I needed for my frame. A buddy of mine gave me a banged up BD Dawes SST frame and I built it up from there. I decided to email their service department and ask exactly what I would need. They responded verbatim "68mm". To me that doesn't sound TOO detailed, so if anybody is familiar and could help me out, that would be greatly appreciated.

Stephen G-

what cranks do you ride? yust mesure your old bb?!

they're just the stock cranks and BB. I haven't torn it down yet, just wanted to see if anyone knew a bit before I started

The info your looking for may be stamped or printed on the bb you have in there now. otherwise, if you are using the stock cranks just look up the specs for your bike on the manufacturers website.

The first thing you want to do is make sure you're getting the right type of BB. Now I'm assuming it's square taper, well there are 2 types of square taper. There's ISO (Campagnolo, Miche, Sugino NJS stuff etc.) and there's JIS (Shimano, regular Sugino, etc) The thread pattern needs to be the same. This will be something like "English 24x1.27" or something like that.

Then, the BB shell width needs to be the same. You can measure this on your frame easily. 68mm is for most track, road etc. 70mm is for some Italian stuff, 73mm for mountain bikes.

Your crank alone will determine the type of head

As long as the type of head is correct; the combination of your cranks and your rear hub (and to a slight degree, your cog) will determine your spindle length. This is the "complicated" part.

Your frame alone will determine you BB shell width.
Then, finally, you need to achieve the proper chainline by getting the right length of spindle. If you have a chainline of 42mm, as on a track bike with rear 120mm spacing, you will generally need about a 103-109mm spindle length, depending on your cranks. If you have road cranks, they have a wider chainline. If you have road spacing in the rear, you need a wider chainline, so if you're using a road spaced fixed gear/SS hub with a 46mm chainline, you'd need a bigger BB.

Think of this example: let's say you have a crank that would achieve a "track" 42mm chainline with a standard track BB spindle length of 103mm. BUT let's say you want to use that crankset on a road spaced bike, and you have something like a Surly 130mm hub. Well, you could use that crank, but you need the chainline to be 4mm outboard of track standard. So you need 8mm wider BB spindle length. So you would get a 111mm BB.

If you mix ISO with JIS square tapers things get different. They are slightly different shapes and the cranks will either slide on less than they should or more than they should. Look it up on Sheldon Brown's website.

The crank and not the bottom bracket shell determines the proper BB sizing.

Almost all road and track frames have a 68mm shell.

The difference in Phil (and other) bottom bracket sizes refers to the length of the spindle, or the crank axle.

For example, in order for the chain ring to give a perfect 42mm (or 44mm) chain line, the bottom bracket spindle length/width and the amount of "dish" in the crank spider have to work together to produce that chain line.

Different crank spiders have differing amounts of dish, and therefore require different length spindles in order to put the chain ring in the proper relationship to the cog.

Look up your crank set on the internet, and someone will say what bottom bracket spindle length will best work with that crank.

I've seen spindles from 103mm to 110.5mm, and it would not surprise me to learn of cranks requiring a longer or shorter spindle.

Happily, the Phil bottom bracket cups allow 5mm of movement left or right, and so Phil lists both a 108mm spindle and a 110.5mm spindle as workable with a Sugino 75 crank.

Talking to the folks at Phil, though, they specify 110.5mm as the correct spindle for the Sugino 75 crank.

whew, blowing my mind. I'm trying to take everything in right now and comprehend what's going on. I'm going to tear apart my bike and scrutinize the thing until I know what you guys are talking about.

Stepheng's crank has something written on it.

A brand name like Sugino.

Search the crank, especially the right side with the star, inside and out, for anything that will identify its make and model.

We can tell stepheng which bottom bracket to get with that much information.

FSA Vero Cranks. Stock on the Dawes SST.

couple places indicate 110mm.
https://www.velosolo.co.uk/shopcrank.html
save a lot of coin, just get a shimano bb.

Do this or something similar. Phil stuff is great, but so high dollar I really can't see spending for it until I make way more money than I do now, and even then I think I'd just put the difference in cash somewhere else.

I decided to go with a cheaper BB and get a new saddle and pedal setup! Thanks for the help everyone