Tapered fork steerer tube measurement

Question

I have a used a carbon fork i'm looking to sell (I bought it used and never ended up using it).

When I bought it, it was meant to be tapered 1 1/8 to 1 1/4 (1.125 to 1.25).

I'm measuring it (with measuring callipers) before I post the ad:
The top of the tube is exactly 1.125" (as expected), but I found the bottom was 1.326", which is a bit different from the 1.25 I expected (but it's way below 1.5 to think that I had the wrong specs of the fork).

Could someone shed some light on this, please?

Is this normal for a tapered 1 1/8 - 1 1/4 fork? Or is it a defect or something?

I wanna make sure I'm selling a good fork that matches the description.

Thanks in advance.
Khaled

PS. There's no crown race on the steerer. This is just the steerer on its own.

PS2. If it's any help/relevance, the fork is for a Cannondale CAAD10 (don't know about the year).

Nathan Knutson · Answer

This is what it was purported to be. The crown race seat area where you're measuring should be more like 33.03-33.09mm (or around 1.302") but I suspect you're not pulling the caliper quite tight enough when you take the measurement.

Originally, though they've never been a common size, there was such a thing as a 1-1/4" non-tapered steerer tube. If you had one of those to measure, you would find the diameter of the steerer was indeed 31.8mm/1.25". But the crown race area down at the bottom is always a little larger. What's confusing here is that because of how the taper has been done, there really isn't a straight 31.8mm/1.25" section to measure.

All that said, this fork is mostly only useful as a replacement for certain CAAD and Synapse models. It won't fit many other bikes.

Tapered fork steerer tube measurement

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