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is an 11 stem always an 11stem?(9 posts)

is an 11 stem always an 11stem?ET
Mar 22, 2001 11:02 AM
I measured real carefully my 3T Forgie 11 stem. It measures 11.3 (center of screw to end where it clamps) and seems a little longer than another 11 stem which was put on my bike temporarily right before I bought it. Anyone know for sure how this stem measures?

Shouldn't all 11 stems be exactly 11? Or what?
'virtual' measurement?Dog
Mar 22, 2001 1:13 PM
You measured center to center?

If a stem angle is not level, then its actual length will not match it's effective length (sort of like sloping top tubes). For example, if the stem rises 45 degres from level, it only goes forward half of it's real length, right? (An extreme example would be if the stem angled staight up - the effective length would be zero.) Suppose that has anything to do with it?

'virtual' measurement?Skip
Mar 22, 2001 1:46 PM
Right idea, but "fuzzy math". If it rises 45 degrees, to be an effective 11 cm, means that it is actually 15.556 cm, not 22 cm.

are you asking me or telling me?ET
Mar 23, 2001 5:11 AM
You're saying (maybe) they measure a stem by its effective horizontal distance (similar to an effective for a sloping top tube)? Wow, learn something new. Working backwards, 11/11.3 = arccos(theta), and solving and switching to degrees gives 13 (or 77 if the other angle is used). Does that make sense? Or, if I was off a bit, maybe it was 11.43, giving 74. Does this make sense?
Mar 23, 2001 5:20 AM
I'm just wondering, really, whether that could account for the difference. I'll leave the math to the engineer types. :-)

? on "?"ET
Mar 23, 2001 5:50 AM
By the question mark in your post title, I take it you're not sure whether you're asking or not. :-) Hey, just throwing in a little lighthearted humor. Please keep that in mind, cuz I don't want any evil jinxes cast on me which might cause me to end up as another, uh, killing on the road. :-)
? on ? on "?"Dog
Mar 23, 2001 5:54 AM
Frequently, I think I've maybe read something about something, but only the concept sticks in my mind. This is one of those things. I think I read somewhere that some makers measure that way, but I'm not sure enough to state it as fact. So, it's a possible maybe, as it sounds reasonable, you know? :-)

"Or what" is the answerDMoore
Mar 22, 2001 1:39 PM
There are at least two ways to measure stem length.

1. From the center of the quill bolt to the center of the handlebar, measured along the top of the stem extension. This is the traditional method, and is commonly used for forged Al stems like Cinelli, etc.

2. From the center of the quill to the center of the handlebar, measured along the center of the stem extension. This is frequently used for newer style welded stems of Al, steel or Ti.

I have several stems, most of them called "12 cm." There is a noticeable variation in length between them. It's kind of like measuring a frame's seat tube, c-c or c-t? Both are widely used. Like everything else, the only way to be sure is to measure it yourself.
Mar 23, 2001 5:29 AM
I got over c-c and c-t in frames (it's just regrettable that c-t can mean different things). Now I have to deal with this in stems as well?

Your two cases could be abbreviated as ct-ct and cc-cc (center/top to center/top and center/center to center/center); I wish the stats would be published for all stems, e.g. on Web sites and catalogs. This isn't a minor point: someone finding his stem just a wee tad too long may just need to switch to a same-sized stem measured another way, rather than come down a centimeter.

Concerning your two ways to measure a stem, I don't think it works out either way, because going to center of bar would make the stem measure way way too long. (There's a gap between stem clamp and bar center. You sure you want to go to bar center?) I originally measured it by your first method, center-top but to top end of stem (clamp), since to bar center it comes out way too long; as close as I can measure, this is between 11.3 and 11.43 (the latter suspiciously being 4.5 inches). This morning, I remeasured, ala your method 2, from along the center of the stem extension to the clamp as it touches the bar, and that's close, but still a tad long. Am I supposed to include the thickness of the clamp? If you minus that out, maybe it would work exactly. I presume I should get exactly 11 somehow, shouldn't I? Or could even that figure be rounded? In any case, I think you're confirming that two stems with the same nominal sizes measured consistently could have different lengths, even effectively, ala Doug's comments.