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Old 10-17-09, 06:44 PM   #1
Chris W. 
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Making room in the chainstays for fatter tires?

I'm looking for hints or direction for manipulating/pinching the chain stays (steel) to make room for bigger tires. I'm oly looking for a few MM. I know somewhere on the internet I saw a picture of this using a bench vice with a dowell pressed against the inside of the chainstay, but dang if I can find it again
Has anyone here done this themselves?

Thanks much,
Chris
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Old 10-17-09, 07:22 PM   #2
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That kinda seems like a bad idea. The chainstays are under a fair bit of stress as it is, and a dent cannot be a good thing. Then again, manufacturers do seem to do it without catastrophic failure. There must be a trick to it.
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Old 10-17-09, 07:52 PM   #3
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I'm looking for hints or direction for manipulating/pinching the chain stays (steel) to make room for bigger tires. I'm oly looking for a few MM. I know somewhere on the internet I saw a picture of this using a bench vice with a dowell pressed against the inside of the chainstay, but dang if I can find it again
Has anyone here done this themselves?

Thanks much,
Chris
Don't do this.

I've put a controlled dent in the driveside stay for crank spider clearance once. It was very minimal though.
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Old 10-17-09, 09:31 PM   #4
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That kinda seems like a bad idea. The chainstays are under a fair bit of stress as it is, and a dent cannot be a good thing. Then again, manufacturers do seem to do it without catastrophic failure. There must be a trick to it.
The trick to it is that the dent is formed in the tubing during manufacture, then the tubing is normalized through heat-treatment before being welded into a frame. Reworking a frame after it's been welded together could be done, but that's going to weaken tubing in an already highly-stressed area.

I did this once to a Schwinn Varsity frame in order to fit 26 x 2.125 balloon tires in it. It lasted a couple months before the frame broke behind the cranks.
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Old 10-17-09, 09:50 PM   #5
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What model bike and what kind of tubing? If it's a low-end bike with hi-tensile 1020 tubing, it'll be fine. A couple off millimeters is not a problem, but you want to make it very gradual and blended with no sharp creases. I've even heated up 4130 chromoly to cherry-red and done the dent-with-a-dowel trick. However, I wouldn't do it with any of the higher-strength heat-treated tubing.

I wouldn't bother with aluminium or carbon. Although an out-of-true wheel from having someone crash into me in a rain road-race scraped a nice 3mm gouge out of the left chainstay of my Specialized Allez Epic after 50-miles of road-grit sanding. It's held up for 40k-miles and 15-years since. Then again, I've also snapped the chainstays just behind the BB-shell on a Trek 5000 and a 5500 under normal usage as well. YMMV

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Old 10-18-09, 05:26 AM   #6
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Originally Posted by Chris W. View Post
I'm looking for hints or direction for manipulating/pinching the chain stays (steel) to make room for bigger tires. I'm oly looking for a few MM. I know somewhere on the internet I saw a picture of this using a bench vice with a dowell pressed against the inside of the chainstay, but dang if I can find it again....
Hey, that's me! You'll need a set of Park Dropout alignment tools. You'll also need to know how to use them. I worked in a well know frame shop/bike store for 8 years, smashing 1020/Chromoly stays are fine if the frame is brazed. I can't comment on a welded frame, does the steel harden are cooling down? I thought the tubing/welding rode system was designed to be air cooled without excessive hardening.
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Old 10-18-09, 02:03 PM   #7
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The varieties of alloys used on welded steel bikes is quite diverse as is the manufacturing techniques. A lot of the "air hardening" ideas spewed about is just marketing spiel; pretty much all steel alloys will air-harden in post-weld cooling. The degree to which this occurs varies based upon the type of torche used and how hot the HAZ was. Personally I've always though the cooling-rate is too quick and would prefer to have the HAZ annealed and spread out afterwards with an oxy-acetylene torche.

This is a common procedure when building roll-cages for race-cars and the debate continues endlessly over DOM (1020) tubing versus 4130 chromoly. In actual practice, 4130 wins on a weight-to-strength basis, but does require annealing the welds afterwards to prevent cracking due to the more concentrated HAZ with the thinner tubing.

I think your procedure is different than what the OP was referring you. Yours provides for significant increases in clearance and requires bending the stays. Given the double crimps already present in your photo, any weakening due to additional bending wouldn't be significant as most of the loss-of-strength has already occured. The OP's dowel procedure leaves the stays intact and just creates a small dent on the inside with a wooden dowel. This is a more common procedure on round chainstays used on MTBs.

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Old 10-18-09, 03:00 PM   #8
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BTW, I did this on an old 26" x 1 3/8 EA3 Robin Hood three speed so I could install 26" x 1.75" MTB tires. Rode it for 20 years, never any issues.
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Old 10-18-09, 08:58 PM   #9
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Thanks to all for the replys!

The frame is a cromoly Japanese Bianchi from the early 80s. I'm still looking at my build options, one of which was a 650B conversion, I have about 39 mm where the tire would end up.

Cheers,
Chris
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