Steerer tube/headset diameter

Burnsey#23

Thinking of buying a new 130mm stem to fit onto a 2012 Giant TCR Comp but unsure of steering tube/headset diameter.
Most stems online are 31.8mm, is the Giant this standard size?

spanner239

31.8mm is normally the diameter of the handlebar clamp not the steerer tube. Most steerer tubes will be 1 and 1/8th of an inch or 28.6mm some are 1 and 1/4 of an inch or 31.75mm but much rarer. Just measure the inside diameter of your existing stem by taking off the top cap.

spanner239

It is odd the way the steerer is usually referred to in inches but the handlebar in mm's! Anybody know why?

Burnsey#23

Cheers for the info....just found on the Paulscycles website that it has an Overdrive 2 fork steerer 1 1/8 - 1 1/4 bearings. Am I right in thinking 1 1/8 would be the right size stem clamp?
Cheers

spanner239

It should be 1 1/8 at the top of the steerer 1 1/4 at the bottom, so 1 1/8 is the right size. Just measure to make sure.

nicklouse

spanner239 wrote:

It is odd the way the steerer is usually referred to in inches but the handlebar in mm's! Anybody know why?

steerer standards have been arround inchanged for years. or pre-existed. bar diameter changes are more recent but still use imperial sizes as there base hence the xx.xmm