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Threaded steerer wall vs. threadless wall

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Threaded steerer wall vs. threadless wall

Old 07-04-20, 01:22 PM
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TiHabanero
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Threaded steerer wall vs. threadless wall

I have a Reynolds 531 threaded steerer tube and a 1" threadless steerer tube and compared the two for wall thickness. Why? Because the threaded tube weighs a whole lot more than the threadless and wanted to know why. Comes to this, the threaded 531 tube has 3mm thick walls straight through while the threadless tube has 2mm walls straight through. Both are 1". Just a little ol' millimeter of material adds a whole bunch of weight that is easily noticed when just holding the tubes in your hands. Now I get it, and will be using the threadless tube for the fork build. been a long journey to get to this point, but the jig is constructed and is as good as I can get it and really hope to get a straight fork out of it!
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Old 07-04-20, 05:12 PM
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So neither steerer is butted? That would be rather odd. Andy
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Old 07-04-20, 05:21 PM
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Don't the threads cut in about 1mm? So your 3mm thick wall would effectively have about a 2mm sheer strength (including multiple stress risers).

Many of the vintage steer tubes also were either slotted or had a flat spot for a keyed washer, creating a weak spot for an internal expansion stem.

The compression force on an external stem is likely more stable.

An 1 1/8" steer tube would also be made with minimal additional material, but have added strength (plus it is easier to source parts for without resorting to shims).
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Old 07-04-20, 06:13 PM
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Both steerers are straight without internal taper. I always thought steerers were tapered to save weight, but apparently I thought wrong. Yes, the threads cut in about 1mm, but that is only 2 inches of the steerer, the rest is a full 3mm wall. Super heavy, but durable!
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Old 07-04-20, 06:29 PM
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My various catalogs list steerers with 2.3 to 2.9mm walls at the bottom and 1.6 at the top, including threaded ones, as being the most typical walls. So I wonder where the 2 and 3mm "straight through" numbers came from. Actual measurement?

BTW my scratch pad math puts the root of the thread at about .85mm from the crests. So a 1.6mm walled threaded section will have close to half of the wall left below the root.

BTW if we take a 1" steerer, or 25.4mm, and subtract the 7/8", or 22.2, stem ID we are left with two 1/16", 1.6mm, walls. Andy
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Old 07-04-20, 06:29 PM
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The threaded steer tubes would be dictated by vintage standards.

https://www.sheldonbrown.com/cribsheet-headsets.html

OD: 25.4
ID/Stem 22.2 (except French 22.0).


So 25.4 - 22.2 = 3.2mm

3.2mm / 2 = 1.6mm

Crown Race: 26.4/26.5/27

It almost sounds like your steer tubes are too thick.

Vintage BMX?
26.4 Crown Race, 25.4 OD, 21.4 Stem?
25.4 - 21.4 = 4mm... / 2 = 2mm.

Last edited by CliffordK; 07-04-20 at 06:32 PM. Reason: Cat Posted It.
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Old 07-05-20, 03:43 PM
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Most Reynolds 531 steer tubes were butted (and should be stamped as such), but since 531 main tubes were available in straight gauge, I suppose the steer tube could be as well. 753 steer tubes were straight gauge, FWIW. I measure a "531 Butted" steer tube as 2.5mm thick at the crown end, and 1.6mm at the other end.
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