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I've got an old road bike. I'm not exactly sure what the frame is as it was repainted. I've reason to believe the that bottom bracket is wrong because the crankset ring is too close to the chainstay.

The crankset is a shimano golden arrow, similar to this picture https://c2.staticflickr.com/8/7067/6994214279_d19b265a9a_z.jpg

enter image description here I'm concerned about the offset as you can see above in this picture. On the non drive side the crank looks like it is designed to be much further in and on the drive side it is really close in.

Please advise me how one knows which bottom bracket is right for X bike. Shell width is reasonably obvious because otherwise it wont fit but what about axel length.

The frame is a late eighties / early 90s cinelli steel frame.

Some BB shells also have different design for the casing which means there is more space between the side of the shell and the crank. Are there any hard and fast rules for BB choice?

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    Basically your "standard" square-shaft bottom bracket cartridges come in symmetrical and asymmetrical versions. The symmetrical version is OK for a double front, but you need the asymmetrical ("offset") version for a triple. The offset (when present) is typically 3-5mm. Unfortunately, the offset is hard to measure on your standard Shimano cartridge because the cartridge itself is built asymmetrically, due to having one integral cup. – Daniel R Hicks Dec 21 '14 at 1:49
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    No, the issue is that different cranksets require different spindle lengths, regardless of whether they are symmetrical. See Paul Lincoln's answer below. – Michael Lemberger Dec 23 '14 at 15:11
  • Looking at that picture, I don't see a problem. – Daniel R Hicks Dec 29 '14 at 13:13
  • its subtle, but I had to grind off a bit of the bb screwed in on the drive side - a couple of mm did it, but when I ride I feel slightly like the line isn't right and occasionally knock the inside of my shoe on the crank arm. – Andrew Welch Dec 29 '14 at 13:41
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In general, BB lengths follow the specification of the crank. Thus if you have a look at this site, it will state the BB length for this particular crank http://velobase.com/ViewComponent.aspx?ID=5d1f43ed-82ec-48d0-b6e2-65f92ecdfcbe

If your crank specifications are not available, then i'd start by measuring the current chainline as per Sheldon Brown (genuflect now) http://sheldonbrown.com/chainline.html

Then measure your BB spindle length and adjust accordingly.

Also a good start is to know what crank you are using. If its Shimano, its likely using British ISO type BB. If its an Italian or French branded crank.. and depending on its age etc.. it could be using more 'exotic' BBs

You can do a search for Sheldon Brown Bottom bracket for info on that.

  • So this looks like my crankset velobase.com/… BB Length 119mm english, 122mm italian / BB Style Square Taper (JIS) – Andrew Welch Dec 29 '14 at 9:18
  • Yeah the existing bb is the wrong size. It is 116mm english. – Andrew Welch Dec 29 '14 at 13:08
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It's probably a ISO BB with JSO cranks or vice versa. A lot of modern BBs and cranks are JSO, a lot of older BBs are ISO which are slightly narrower so when you put the crank on, it sits closer to the frame. I know that's not a full answer but hopefully puts you in the right direction.

  • ISO vs. JSO really has nothing to do with the issue of a chainring being too close to the stay. The real issue is that the spindle length is not correct for the crankset in question. – Michael Lemberger Dec 23 '14 at 15:09
  • Though there is a high likelihood of the original poster having incorrect length spindles. ISO and JIS cranks have a different taper. thus mixing the two standards may/will cause (according to Sheldon) either ill fitting crank arms or changes in chainline – Paul Lincoln Dec 26 '14 at 7:57

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