Indirect determination of steerer diameter

[Slider77]

Quick question. A friend of mine located on another coast was asking if I could tell her what size steerer she has with a threadless integrated headset from just the measurement of the topcap (e.g. OD of the stem clamp). She is paranoid about taking the cap loose to examine the steerer itself. By her measurements the top cap diameter is 1-1/4 to 1-5/16". Can you confidently tell whether it is a 1' or 1-1/8" steerer from this? Thanks.

 

[Fat Hack]

I don't wanna give you a definitive answer unless I stuff it up, but if this helps, my 1 inch steerer topcap measures ~32mm (1.259 inches)

I'm sure you've told her already, but it's pretty easy to take the cap off, measure the steerer, then put the cap back on with the same tension.