Trying to measure my current fuel ex 8 to compare it against potential purchases in various sizes. when they measure ‘each’ it appears to be vertically up from the bottom bracket and across to what appears to be the stem bolt. surely it should be to the centre of the end of the stem where the bars are clamped?

No, because anyone can change a stem, but the frame will remain the same.

By stem bolt I guess you mean the headset top cap bolt which pre loads the headset bearings?

Sounds correct to me as different stem lengths and stem rise will give different reach figures. This way you know the reach of the frame and you can fine tune it with different bars and stems.

Its not measured to centre of stem cap bolt, but centre of headset bearing, otherwise a long steerer would increase stack and reduce reach. By measuring to the bearing your measuring the frame, not how youve set-up the frame.

Well really it’s measured in isolation – center of tube A to center of tube B.

No need to include headset/stem nonsense.

Of course in a practical sense unless you’re going to strip your frame you’re measuring from roughly halfway in between one tube to roughly halfway in between another.

thanks chaps – will get busy measuring this weekend