Well stems actually have a few dimensions that one should at least know about besides the clamping one. First and second are the steerer and the bar clamp diameters. Measuring these (especially the bars) can be hard if you don't have a caliper on hand. But if you do a careful circumference measurement (by taking a strip of paper, wrapping it around the bars and then marking across the start and finish of this strip) and divide by 3,1415 (or 22/7) you get a diameter. Next is the extension length, which you stated by the 90mm reference. Do know that this is usually done fron the center of the extension and the steerer/bar intersection points. This is not the same as measuring along the top of the stem. (A very common mistake to make). Almost last is the angle that the extension makes WRT the steerer. Be awear that some companies measure from the steerer and others from a perpendicular to the steerer. And last is the steerer's clamp height. A stem with an extension raising at a steep angle needs more steerer clamp height to have the extension contact the clamp section fully. There are times when one will have to remove a steerer spacer or two to allow the stem to fully clamp around the steerer, this can place the bars at a lower height then simple math might initially suggest.


So once again we find that a simple question really needs a long and involved answer to be fully understood. Andy