Centering hub on rear axle

[Eidetic]

I bought a used bike, and though it rides fine, the rear wheel appears to be a few mm off the centerline of the bike.

What is the best way to measure how centered a wheel is when mounted on the bike? (I checked for center alignment of the wheel itself on my truing stand. The wheel is fine.)

What I'm after is something a little more accurate than flipping the wheel to see lateral movement vs. the brakepads, using a feeler gauge between rim and pad, and moving the hub half the measured offset.

 

[dorian]

You need a dishing gauge. You can accomplish the same thing by fllipping the wheel back and forth in your truing stand.

 

[dorian]

You could also have your rear dropouts checked for alignment. I've never tried it, but there's a "string test" that I think you can find on roadbikerider.com. I don't know how accurate it is, but it may be good enough.

 

[Eidetic]

Dorian, thanks for your thoughts. The assumption is a properly dished, completely true wheel. The rider wants the centerline of the wheel in the centerline of the bike. Most truing stands are self-centering. If the centerline of the rear triangle of the bike is not exactly perfect, there's a mismatch of wheel centerline and rear triangle centerline. That's the problem I've got. There's less than one mm of movement when I flip the wheel (after adjustment using the feeler gauge between brakepad and rim method, and move the hub half the measurement), but this seems crude for, say, a TdF bike. Perhaps the only more accurate way is to replace the brake calipers with measurement calipers, mount the wheel without tire, tube, or liner on the truing stand, scribe the center of the rim, then move the wheel to the bike for measurements and adjustment.

 

[Eidetic]

Good tip about the string test. It shows what I suspected, one dropout is about 2 mm closer to the centerline than the other.

 

[pudster]

This is just a thought on the string line test. When aligning a frame all measurements should be taken from the BB. If your seat tube is not perpendicular to the BB the string line with not measure the alignment of the rear end. I hope this does'nt ruin your day. A good shop should have an alignment table to determine the alignment of your frame. The alignment table takes the frame and clamps the BB and you would measure the height of the tubes off the surface plate. Then you could use a string test or the park alignment tool to align the rear end. I think it would be better to get a simple dishing tool and center the wheel on the hub. Even though you have done this the front end and the rear end could be still out of alignment. I hope this helps you out.

 

[Eidetic]

pudster, thaks. I'll look for a shop with an alignment table. That's a new one for me.

 

[Eidetic]

Solution: measure from rim to chain stay, left and right sides. with wheel installed. Again, the wheel itself is centered on the hub and true. This avoids flipping the wheel and trying to deal with measurements from rim to each brake pad.

 

[Eidetic]

I've now ridden the bike for about 75 miles after moving the wheel centerline on the axle 2 mm to match the bike centerline. There is noticeably better tracking, esp. at speed.