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Chainstay part of frame stretching?

Old 08-02-20, 11:57 PM
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RowdyTI
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Chainstay part of frame stretching?

A mechanic told me he thought my frame where I do up the rear thru axle had stretched a bit because when he tightened the thru axle he could feel the frame coming in a bit. Have you heard of an under-tightened thru axle causing the frame to spread out a bit?

He seemed to believe ideal torque was going as hard as he could go with his mini tool. Stretching the frame at that portion sounds bad to me as it could lead to premature fracturing.

One of the reasons I've been messing with that portion of the bike is that when I go down hills and do any cornering, I'm hearing disc rub. Someone said they got this when their thru axle was overtightened, and conversely it could happen if the axle is done up too loosely, so I'm been experimenting, but I'm really not noticing a correlation: the rub at those times is still there, like quick tick sound of engagement of the pad against the rotor.

To avoid confusion, max torque for that axle is 11 NM, so not very high.

Last edited by RowdyTI; 08-03-20 at 12:02 AM.
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Old 08-03-20, 05:16 AM
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dsaul
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Your frame is not stretched. The dropouts may be spaced a bit more than the exact width of the hub, but that is not a problem and makes it easier to insert the wheel in the frame. I build frames and the dummy axles we use are generally 2mm wider than the axle width. Most of that is to account for the dropouts pulling in from welding the stays to the bottom bracket, but some excess width is desirable to make wheel insertion easier.

If you are getting disc rub and the caliper is properly centered, the rotor could be out of true. It certainly isn't caused by the axle being too tight.
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Old 08-03-20, 06:18 AM
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Wow, you are having so much trouble with those thru axles. Maybe look into swapping for a similar bike with rim brakes and QR? Seems as if thru axles may not be right for everyone
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Old 08-03-20, 07:11 AM
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Wow, I'd consider a different mechanic if unable to work on it myself.
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Old 08-03-20, 08:28 AM
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Was something done to the hub? If so, I'd check the measurement of it and between the frame. Maybe he goofed putting it back together. Maybe used parts for another hub.

However if the distance is only a mm or two, then that's close enough for me. I've had bikes with skewers and the drops spread more than that and less than the hub width. Can't think of how that would be a safety or functional concern
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Old 08-03-20, 10:40 AM
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What??? Frame stretch? And just when I’m shrinking.

John
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Old 08-03-20, 10:57 AM
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I have a Co-motion frame that has 132.5 OLD spacing on the rear. That way you can use wither a 130 OLD hub (which I use) or a 135 OLD hub, and only have to compress/widen the dropouts 2.5 mm, which is no problem with a steel frame. So what is the measured OLD of your frame and the OLD or the rear hub? Also, I thought one of the big reasons to use thru axles was that it prevented the hub from any movement in the dropouts when properly tightened.
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Old 08-03-20, 12:16 PM
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Yes, that mechanic also was ham-fisted and stripped the screw head a bit by trying to tighten it without having the tool fully inserted. Now I only let senior mechanics work on my bike. This also weeds out those doing the job for the money versus being passionate about it as a long-term life choice. I was a fool letting just anyone touch the bike. Not all mechanics are equal. He probably commented on "stretching" of the frame just to be negative because he doesn't really enjoy what he does versus having a passion for helping riders.
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Old 08-03-20, 04:10 PM
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Does this torque make my chainstays look fat?
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Old 08-03-20, 04:32 PM
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Bill Kapaun
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Originally Posted by Eggman84 View Post
I have a Co-motion frame that has 132.5 OLD spacing on the rear. That way you can use wither a 130 OLD hub (which I use) or a 135 OLD hub, and only have to compress/widen the dropouts 2.5 mm, which is no problem with a steel frame. So what is the measured OLD of your frame and the OLD or the rear hub? Also, I thought one of the big reasons to use thru axles was that it prevented the hub from any movement in the dropouts when properly tightened.
A "Bunch" of years back, some frames were spaced at 128mm to handle 126/130mm also.

I'd say your mechanic lacks experience. Using the term "mechanic" is being way too generous to MANY LBS employees.
They only know what they've seen and haven't been around long enough to have seen very much.

Last edited by Bill Kapaun; 08-03-20 at 04:36 PM.
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