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Old 03-02-10, 01:47 PM   #1
rivendell
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chain line, hub spacing question

Hello, I have an MB-3 bicycle that I restored about a year ago except for getting new wheels. It currently has a MT62 Shimano rear hub, which is 130mm and 7 speed. I bought an M732 XT hub for it, which is 7 speed but uses 135mm. These have proved hard to find in the first place, especially nos and I was hoping I could just remove spacers but the whole hub body is of course wider. I've thought about spreading the frame but wouldn't that put my cassette further out? I'm currently using a M442 crank but am planning on putting a Sugino AT on it. With its low Q, I'm thinking my chain line would be funky. I'd rather not remove spacers if the strength of the wheel is at stake.

Any thoughts?
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Old 03-02-10, 02:17 PM   #2
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Why did you buy a 135 hub for a 130 frame, any special reason?

If you could respace the hub you would have 2.5mm of extra axle on each side. This might prevent the quick release skewer from properly clamping the wheel in the frame. You can hacksaw or grind off the extra axle in that case. I am not familiar enough with this hub to know if there is enough axle sticking out to monkey with it.

-j
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Old 03-02-10, 03:58 PM   #3
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I wanted an XT 7 speed hub, and this is the only one they make. They do make it in both lengths, but they are rare enough for me not to be too picky.
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Old 03-02-10, 06:41 PM   #4
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Spreading the frame will not be difficult. Just remember to do it equally from both sides to preserve the centerline. There's also one more step fro a proper job, and that's to re-establish the parallelism between the dropouts which will now be slightly opened into a "V" A special tool is required, so unless you have a friend who has one, you might shop around for a LBS to do the spreading for you.

You might be tempted to take a shortcut and simply spring the frame and force the wheel in, but that's not a great idea since it doesn't address the dropout parallelism.


BTW- I said "shop around for a LBS" advisedly. Spreading a rear triangle is the kind of job where you'll get quotes all over the board, so do your homework, and look for someone who'll do it right for a fair price.
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Old 03-02-10, 07:28 PM   #5
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I wanted an XT 7 speed hub, and this is the only one they make. They do make it in both lengths, but they are rare enough for me not to be too picky.
You could've just bought any modern 8/9/10 XT hub and throw a 4.5mm spacer to use a 7 speed cassette. This is a much bigger problem than it needs to be now that you've bought into a problem.
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Old 03-02-10, 09:54 PM   #6
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You can fix this "problem" in less than 30-minutes. Check out Sheldon Brown's guide to frame-spacing: http://sheldonbrown.com/frame-spacing.html
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Old 03-03-10, 11:17 AM   #7
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You could've just bought any modern 8/9/10 XT hub
One, I'd like to keep it somewhat era correct. Two, the freehub body on 8 and up speed hubs is longer, correct? Meaning more dish than the shorter 7 speed one? Or am I wrong? I think I might just spread the forks after all.

Mainly I want to know, if I take a spacer out to fit it in the 130mm, will I have more or less dish than one made for 130mm?
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Old 03-03-10, 11:32 AM   #8
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Originally Posted by rivendell View Post

Mainly I want to know, if I take a spacer out to fit it in the 130mm, will I have more or less dish than one made for 130mm?
All other things being equal, added spacing using the same cassette width moves the centerline of the hub to the right by half the added space (2.5mm in this case) reducing the dish in the wheel. That's why they widened the frame standard in the first place. Conversely removing a spacer from the left would increase the dish.
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Old 03-03-10, 02:02 PM   #9
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Alright. I think I should reword my question. The 130mm hub on there now has x amount of dish. If I take a spacer out of the 135mm one, the hub body between the spokes is still wider than the original hub. What does increasing that dimension do to the dish of the wheel?
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Old 03-03-10, 02:14 PM   #10
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It might help if you draw yourself a rough sketch.

Assuming you remove 5mm from the left side of a 135mm hub (you usually can't remove anything from the right) that would move the axle/frame centerline of the hub to the right by 2.5mm. Since the shell is unchanged that puts the right flange 2.5mm closer, and the left 2.5mm farther from the centerline. (note you're not moving the flanges, you're moving the centerline)

Since the right flange was already closer, moving it yet closer increases the dish (difference in R/L center (or rim) to flange distance). Increasing the difference in the relative flange to center distance means that the R/L difference in spoke tension will be greater.

If you can find a compatible shorter (fewer gears) cassette body and remove space from the right side then the opposite would be true.
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Last edited by FBinNY; 03-03-10 at 02:25 PM.
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Old 03-03-10, 06:23 PM   #11
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Originally Posted by rivendell View Post
One, I'd like to keep it somewhat era correct. Two, the freehub body on 8 and up speed hubs is longer, correct? Meaning more dish than the shorter 7 speed one? Or am I wrong? I think I might just spread the forks after all.
Irrelevant anyways. Properly spec'ed and built wheelset isn't going to fail because of the slightly increased dish. And, you can at any time go to 8/9/10 if you wanted to.
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Old 03-03-10, 07:56 PM   #12
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Irrelevant anyways. Properly spec'ed and built wheelset isn't going to fail because of the slightly increased dish. And, you can at any time go to 8/9/10 if you wanted to.
Well, I already have this hub and any newer one is going to be 135mm anyway unless I go road, which I'd rather not do for personal preference. So I don't know what going with a modern hub is going to accomplish. I can also go to an 8 speed using my 7 speed body too, using 9 speed spacers and chain, but this isn't my goal.

Quote:
It might help if you draw yourself a rough sketch.
I went ahead and did this, and had a guy at one of my lbs's explain it a little bit. It looks like the longer hub body with the respacing won't affect things too much from the original hub, but I wanted to get more opinions first. Still, if taking out a spacer works I'll just do that to keep my frame original and my chain line the same.

http://i65.photobucket.com/albums/h2...7/untitled.jpg

The measurements are approximate.
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