Bicycle Mechanics - Cold Spacing a steel frame with Disc tabs

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MIN
12-25-07, 10:52 AM
Hi,

I'm interested in cold spacing my frame (130mm rear Lemond Poprad disc) to accomodate 135 mm hubs. I've read about the procedure, per Sheldon Brown, but what's unclear to me is how I can keep my disc tabs aligned, relative to the rotor.

There is a certain about of rotational "flex" in the mounting system for the Avid BB7 calipers so this might mitigate any misalignment issues, but I am not sure.

(1) Any insights into this?

(2) Should I cold space to 132.5m so I can run both 130mm and 135mm?

(3) I am running road double cranks. If I went to 135 mm rear, will this mess up my chainline? Or will this change be minor? I am not sure what a 2.5 mm deviation from the stock chainline would do for my shifting.

TIA.

MIN in PDX

Deanster04
12-25-07, 10:59 AM
The word is cold setting the frame. This is one issue that I would try and find a bike builder in your area and discuss it with them. Ordinarily there is a tool for the derailluer hanger that you can straighten out the alignment of the hanger with but a set of disc brakes????? There might be a way of using a shaped shim to correct the angle.
Send an Email to Sheldon Brown...not too many issues he hasn't thought about. Good luck. Your problem certainly isn't a trivial one (or not).
MIN
12-25-07, 11:05 AM
Cold setting... yes... thanks for the clarification.

kenhill3
12-25-07, 12:59 PM
I am assuming this frame is steel? Cold setting aluminum not the best of ideas. All this aside, the disc tabs issue would seem to be the most critical. I am not qualified to answer on this, so let someone else weigh in.
nitropowered
12-25-07, 01:03 PM
You can probably just squeeze the hub into the dropouts.

The chainline shouldn't change
kenhill3
12-25-07, 01:23 PM
You can probably just squeeze the hub into the dropouts.

The chainline shouldn't change

Wouldn't just squeezing the hubs in force the dropouts out of parallel? What about the disc tab issue?
d_D
12-25-07, 01:49 PM
There are tools to face disk mounts if you can find a shop with one. Hope make a tool that isn't out of the home mechanics price range. Even so it's still pretty expensive for a tool you will probably only use once.

If you stick with post mount calipers I don't think there will be a problem. The mounts should have enough wiggle room to account for the misalignment. A bit of maths would tell you for sure.