crank centered

cmeb said:

How can I tell if the crank is centered on the bike, and how can I adjust it if it's not centered?

Probably the easiest way to tell if it's centered is to compare the distance between each of the crankarms where they pass by the chainstays.

How to center the crank if it's not centered depends on what kind of bottom bracket you have. A few bottom brackets are designed to move sideways a bit to center the crank. If the drive side has to go outward by a couple of millimeters, you can put a spacer behind the drive side of the bottom bracket. If it's off by more than that, you may have a 73mm bottom bracket in a 68mm frame or vice versa.

cmeb said:

How can I tell if the crank is centered on the bike, and how can I adjust it if it's not centered?
Thanks

Ballpark is to lay a steel rule, or a string, in between the ring gears and the center of the cassette. The ring gears and cogs should look parallel to this line. If not. the rear wheel or crankset/ bottom bracket has to be moved left or right. How to do this depends. But it usually can be done by moving the bottom bracket left or right by how you position and tighten the bottm bracket mounting cups that screw into the frames bottom bracket tube.

[b said:

cmeb][/b]How can I tell if the crank is centered on the bike...

As per Retro Grouch

[quote="Retro Grouch"]Probably the easiest way to tell if it's centered is to compare the distance between each of the crankarms where they pass by the chainstays.[QUOTE]

I find it a bit easier to measure from the braking surface of the rear rim out to the crank arms. I use the depth gauge part of an ordinary vernier caliper.

Eastway82 said:

I find it a bit easier to measure from the braking surface of the rear rim out to the crank arms. I use the depth gauge part of an ordinary vernier caliper.

Thanks everyone, my drive side is out by 1/4 inch. I'll bring it to the bike shop to have them adjust it. I don't want to mess anything up.

cmeb said:

Thanks everyone, my drive side is out by 1/4 inch. I'll bring it to the bike shop to have them adjust it. I don't want to mess anything up.

Ok, I just came from the bike shop, and I was told that the drive side is supposed to be out further from the chainstay than the left side. I have a triple crank, so it is a little further out than a double would be. Is this so?

cmeb said:

Ok, I just came from the bike shop, and I was told that the drive side is supposed to be out further from the chainstay than the left side. I have a triple crank, so it is a little further out than a double would be. Is this so?

Thats a lot of BS... that can lead to hip, knee or ankle pain situation.

hd reynolds said:

Thats a lot of BS... that can lead to hip, knee or ankle pain situation.

Well, I did have knee pain, until I moved my cleat around, that's how I noticed the space difference. I'm going to try a different bike shop.

cmeb said:

Ok, I just came from the bike shop, and I was told that the drive side is supposed to be out further from the chainstay than the left side. I have a triple crank, so it is a little further out than a double would be. Is this so?

I agree with HD. Sounds like you may have the wrong sized BB. The drive side is a bit farther out from the chainstay on a triple than on a double, but the left is also an equal amount farther out. I.e. the triple as a larger Q-factor, but should still be symmetrical.

A couple of mm difference is probably negligible though.

cmeb said:

How can I tell if the crank is centered on the bike, and how can I adjust it if it's not centered?
Thanks

Chainline is the relative alignment of the front chainrings to the cassette cogs. Per Lennard Zinn, the cogs and the ring gears should be parallel to a line running thru the center of the middle ring gear and the center of the cassette. In the case of a double crankset, the line should be run centered between the two ring gears. If you need to adjust it more accurately, and there are ways to do so, than the parallelism the human eye can resolve, you got other problems.