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Chainstay length vs tire size

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Chainstay length vs tire size

Old 09-22-19, 07:17 PM
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IcemanYVR
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Chainstay length vs tire size

I'm designing and building a new frame as a project for me, and I have a decent understanding of frame geometry and what I want, but one area of confusion still exists.

With a chainstay length of 420mm, STA of 73 degrees and BB drop of 75mm, is it possible to run 700x38 tires?

Are there clearance issues? What would be the minimum chainstay length required to run 38c tires? The bike will mostly see 28c tires, and rarely above 35. Would just like to have the option to go 38 if necessary. I like short chainstays, and would like to keep as much of the responsiveness of the bike that I can.

Thanks
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Old 09-22-19, 07:22 PM
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This is where modeling programs (Bike Pro, RattleCad being two) come in handy as they do the math for you. Otherwise the answer is either actual math or measuring existing bikes and "making a judgement". Andy
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Old 09-23-19, 06:13 AM
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I put those numbers into Rattlecad and it shows 9.9mm between the tire and the seat tube with a 700 x 38 tire.
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Old 09-23-19, 06:49 AM
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Originally Posted by Andrew R Stewart View Post
This is where modeling programs (Bike Pro, RattleCad being two) come in handy as they do the math for you. Otherwise the answer is either actual math or measuring existing bikes and "making a judgement". Andy
Originally Posted by dsaul View Post
I put those numbers into Rattlecad and it shows 9.9mm between the tire and the seat tube with a 700 x 38 tire.
Thank you, I didn't even know about Rattlecad. Purchased it and am playing with the numbers. I had been using bikecad.

It seems clearance to the seat tube is ok, but it rubs on the chainstays. Makes you wonder how builders like Mosaic and Argonaut can run 38c tires with 420mm stays. They must use custom tubing or something.
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Old 09-23-19, 07:31 AM
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I make my own chainstays out of 3/4" .035 tubing, but you should not have a problem making clearance for a 38 tire at 420mm with oval chainstays and some dimpling. The chainstay length in the picture is 425 and easily fits a 42mm tire. and a road crankset on a 68mm bottom bracket. I don't rely on modeling to figure these things out. I draw out everything on paper and lay the chainstays on the paper to confirm clearances.
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Old 09-23-19, 07:52 AM
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Originally Posted by dsaul View Post
I make my own chainstays out of 3/4" .035 tubing, but you should not have a problem making clearance for a 38 tire at 420mm with oval chainstays and some dimpling. The chainstay length in the picture is 425 and easily fits a 42mm tire. and a road crankset on a 68mm bottom bracket. I don't rely on modeling to figure these things out. I draw out everything on paper and lay the chainstays on the paper to confirm clearances.
Wow! Those are gorgeous chainstays. Nicely done. Bc
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Old 09-23-19, 08:30 AM
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Yes, dimples are your friend. Have you made any tubing manipulation tools yet? A dimplier comes in real handy. Here are a couple. Andy
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Old 09-23-19, 10:10 AM
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I'm curious where you can buy rattlecad since it is FOSS. I guess you can give Fred money for it if you want.

I have decided to be a lot less concerned with chain stay length. In my enfeebled old age, it's not like a little more compliance is going to hurt me riding. I have a frame I made back before I made this decision that should fit 28mm tires and fenders, but really it barely fits 25mm tires with fenders. I really wish I could get 32mm tires in there, but they hit the seat tube.
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Old 09-23-19, 10:35 AM
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Originally Posted by unterhausen View Post
I'm curious where you can buy rattlecad since it is FOSS. I guess you can give Fred money for it if you want.
He's always taken donations but the latest version (4.0.xx) has reasonable Pro and an Amateur licensing fees structure.
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Old 09-23-19, 10:59 AM
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Originally Posted by unterhausen View Post
I'm curious where you can buy rattlecad since it is FOSS. I guess you can give Fred money for it if you want.
IĎd never heard of it until this thread. Googled it, and payed $25 CAD for the hobby version. Not a bad price.
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Old 09-23-19, 11:12 AM
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thanks, didn't realize it wasn't foss any more. Never really learned it because I have bikecad pro, so I guess I'm never going to learn it.
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Old 09-23-19, 11:16 AM
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Originally Posted by Andrew R Stewart View Post
Yes, dimples are your friend. Have you made any tubing manipulation tools yet? A dimplier comes in real handy. Here are a couple. Andy
Thatís above my pay grade, but easy to see how your chainstays turn out so good.
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Old 09-23-19, 02:31 PM
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Originally Posted by IcemanYVR View Post
Thatís above my pay grade, but easy to see how your chainstays turn out so good.
My "dimpling tool" is a bench vise, half of a Paragon tube block, and the top of a pipe wrench.
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Old 09-24-19, 11:08 AM
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Buy prebent oval chainstays from Nova, BFS, Framebuilders I have not had a problem fitting 40mm tires between them. Another option buy an 86mm wide bottom bracket (Paragon Machine) and use a BB with internal bearings.
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