Fork steerer tube sizing issues

[lava]

So, I'm selling an old fork. The steerer tube is 27mm in diameter by my measurement and by the sticker on the tube. This not 1" nor is it 1-1/8". It's more like 1-1/16". So people are responding to my classified ad by asking if it's 1" or 1-1/8". What the heck do I tell them? Is this a case similar to how "700c" wheels aren't exactly 700c? I get the feeling it's 1-1/8" but I have no evidence to back this up. Any help is appreciated.

 

[hd reynolds]

That's a peculiar size. Standard sizes I know of are 25.4mm (1"), 28.6mm (1-1/2") and 31.8mm (1-1/4").

 

[lava]

Weird, I would think Trek would be very standardized. All the literature on the net about my bike states a 1-1/8" steerer tube, and I replaced this fork with an Easton EC90 SL with no problem (although I do not remember what the diameter of that fork is, and I'm not going to take it off to check).

Perhaps the inside diameter of the head tube is where the 1-1/8" measurement is made, and not the outside diameter of the steerer?

 

[gclark8]

I think you will find the "27mm" is the Crown Ring Mounting Diameter. If so, it will be a 1" fork. Check the top ID near the thread, is it 22.2 or 21.1mm or 25.4mm?

 

[hd reynolds]

I think you will find the "27mm" is the Crown Ring Mounting Diameter. If so, it will be a 1" fork. Check the top ID near the thread, is it 22.2 or 21.1mm or 25.4mm?

Its OD not ID.

 

[lava]

So, I went into my LBS and compared the fork to a few other forks. Guess what? It's a 1-1/8" fork. And a couple of the other 1-1/8" forks also measured 27-28mm just like mine. So there you go.