Measuring a stem length?
 

Wondering how you determine the length of a stem. For the one shown, if I measure the length as center of the steerer-post to the center of the handlebar clamp, along the length of the extension, there's a different measurement (105mm) than if I measure from the center of the steerer-post, perpendicularly, to the center of the handlebar clamp (95mm).

[IMG]http://i981.photobucket.com/albums/a...ps94tcnvy7.jpg[/IMG]

I lay my ruler on the top of the stem, then measure ctc. Conforms to what's on the stem, usually.

I would measure the center of where the steerer bolt pops out of the top of the stem , to the center of the clamp area .

Thanks.

Its the center lines of the Bar bore , and the bolt centerline* .. center to center..

*which is also the steerer tube center line .

The general convention is to measure along the length of the extension. This is illustrated in the photo below by the use of the calipers to measure the extension.

The only exception to this (that I know of) is the Nitto Pearl. In the photo below, there is an illustration on the Pearl's box that shows how it measures the distance perpendicular from the quill to the center of the handlebar.

As shown, the Pearl 9 measures 90mm using Nitto's method, while the conventional method would tend to suggest 100mm.

https://c1.staticflickr.com/1/504/30...5da717_c_d.jpg



Steve in Peoria

I agree with the above, that traditional quill stems, that have a horizontal* extension when installed, are measured center to center on the horizontal plane.

*These typically have a 17° angle between quill and extension, and so ideally fit a bike with a 73° head tube.

The problem with that, however, is that for the last 30 years or so they've been making stems with a variety of angles, which are not always indicated in a uniform manner (a stem with a 90° angle is sometimes called a 90° stem, sometimes 0° rise). Add to this the phenomenon of threadless stems that can go either easy, +10° or -10°, and so on, things can get very confusing.

When I measure a stem now, I measure it as if it had a 90° angle. That is, a dimension perpendicular to the steerer, measured center to center; this is the length of the stem, and it is a property of the stem. At the same time, I measure stem height, which is a property of the setup of the bike, since it is variable.

I suspect early 3TT stems measure differently too as a vendors description measured C to C yielded 90mm but the marking on the stem was 95mm, I don't have other references for this though.

Yeah, for some reason I had a brain-freeze when measuring one. In your example, I see how you got 100mm, but if I drew a line from the center of the bars to the center of the steerer tube, along the axis of the center of the horizontal part of the stem, it would be less by 6 or 7mm. Your example extends the reach by measuring center of the bars to top of the stem, which offsets the angle of the 73-degree horizontal plane, since you don't go along the center, but upward to the bolt's top.

Maybe i'm making it too difficult, but the engineer in me wants it to make sense, and I've seen countless ways of measuring it. My understanding is that I'm wanting to measure "reach", and I keep seeing "reach" as a horizontal measurement, since the quill stem's top is normally horizontal when installed, and that "reach" would only go horizontally if I stop my measurement at the center of the steerer, and not at the top of the bolt.

So, if I want to sell a stem and need to accurately describe its dimension, I just want to make sure I give a correct measurement, or at least make sure myself and a buyer have the same idea of what reach is.

Okay, that one makes sense, since the two extension-lines for the measurement are parallel. Now, my stem measures an even 100mm.

to clarify my earlier post, please note that I described two methods of measuring stem lengths....

1. measure along the extension (illustrated with the caliper). This is generally from the center of the bolt to the center of the handlebar. I don't know if I've seen a drawing from a manufacturer that clarifies whether it is from a line drawn through the handlebar center that is parallel to the quill axis, or through the "vertical" axis as my measurement uses. I'd have to run the math, but I think the difference would be a couple of mm at most. (edit: about 4mm)

2. measure perpendicular from the quill to the handlebar center. This is illustrated by Nitto and shown on the box in the photo.

Method #2 seems to be what you are describing in the text I quoted.


Every place I've seen the measurement defined, it was measured along the extension (i.e. method #1). The only place I've seen an exception was the Nitto Pearl.

...but... as you note, if there is any doubt, always confirm that both the buyer and seller are using the same method.
As the saying goes... "the nice thing about standards is that there are so many to choose from". :)


Steve in Peoria

Unfortunately lot's people dont use the traditional way to measure stems - or frames for that matter. as I've found out the hard way several times. ;)

Interesting thread here, I think that this subject has been discussed before?

For sure, those particular stems from Nitto, end up being longer than stated on the packaging, which is an oddity.

But there are two very common other ways that stems are measured, always parallel to the extension by the way.

Lower-end and Japanese stems, with few exceptions, measure stem extension "drafting board" style, which is center-to-center, along the centerline of the extension.

Higher-end, mostly Italian racing stems measure them across the top, from the center of the bolt to the center of the bars.
I believe that this is because actual racers and coaches are the ones who might actually make field measurements, and measuring on-center instead of across-the-top is mechanically awkward to achieve. So this is for serious users, not so much for parts-spec'rs sitting in a chair in their office.
The "Italian way" as I call it gives about a 5mm-longer measurement, so yields a 5mm-shorter stem in the real world, and this applies to all Cinelli and TTT stems and most ITM stems as well. Gravity-cast ITM stems turn up which are measured the "Japanese" or "drafting table" way, so will net a longer actual stem.

Most Nitto stems seem to be measured the "draftsman's" way, however the Nitto-made Shimano stems measure the "Italian" or "field" way, across the top, so will come up 5mm shorter as mounted.
(I've also noticed that most such AX/EX stems will accept a 26.4mm handlebar, fwiw).

Rhm mentioned measuring stems perpendicular to the quill, which makes the most sense since this is perpendicular and thus independent from the adjustment of quill height!

My own way of tagging my stems (after first grouping them by clamp diameter) is to add an "A" suffix to my written "95" or whatever, and which means "actual" or center-to-center on-center (drafting board style). This is just because I started out with a lot of cheaper equipment way back then, and the Japanese stems measured this way.

Nitto's "sometimes" way of measuring the perpendicular offset makes the most sense, but never caught on with the industry.

And like Yang07 mentioned, how the bike fits on the road (with the actual rider balanced fore-aft over the bottom bracket axis) is all that matters, at least within any particular range of riding intensity.

Stem Length Suppositions
 

ZOMBIE THREAD! ARGH!

https://cimg5.ibsrv.net/gimg/bikefor...16ee5f9e52.jpg

Yang07 we'd like to welcome you as a new member to the Forum.

Suggestion: the unofficial protocol/etiquette within the Forum generally discourages calling up older threads especially ones dormant for a few years.

One reason, other members have to scroll down through a lot of messages that may be unrelated to your interests to find your post.

The preferred/recommended approach is to start a new thread, especially if you want to post a supposition for discussion that's easy to find and starts at the top of the other posts.

As dddd mentioned "Interesting thread here, I think that this subject has been discussed before?"

A Google search of Bike Forums will find lots of related threads.

To put my 2¢ in, many quill type stems have the size stamped or molded into them. For whatever reason Nitto stems are 5mm longer center to center than the size listed on the box and the stem itself.

... and as SurferRosa mentioned, for many years, 3TTT stems came in 5mm increments. So did some early Cinelli and ATAX stems.

BITD, this was the standard method for measuring stem length. It worked as a starting point for years:

https://cimg4.ibsrv.net/gimg/bikefor...8486bb0884.jpg

The human body is an amazing organism that can quickly accommodate to a lot of physical situations like minor differences in stem length, bar and saddle height an so on.

Fine tuning those adjustments plus changing some components as needed are what helps to make a bike fit comfortably especially on rides over a few mile long.

verktyg :50:

I know there are "trained" folks who still promote this method. My question is: are all saddles the same length? Otherwise this method fails. My uneducated approach is to position my saddle then determine stem length by seeing what's needed to achieve my standard dimension from the sit bone position to the back of my brake hoods. I have frames from 56cm to 61cm in rotation but the 3 touch points are all the same and are each all day comfortable.

Right? Wrong? So what?

Said user has been posting the exact same messages on various other bike forums. It's spam without the clickbait and smells a bit like an AI bot to me.

Spam! Spam! Spam! Spam!
 

Definitely SPAM!

https://cimg7.ibsrv.net/gimg/bikefor...88056aeceb.png

Check out this post in the Commuter forum: https://www.bikeforums.net/commuting...l#post22184996

BTW, nation of origin listed as NM...

verktyg :50:

Why didn't you report it for the Mod staff to investigate?

Yang07'spost got pulled, and which now makes it look like I was the one who revived this zombie thread.

Oh well, mods got to do what they gotta do.

Gotta admit that I got pulled in by a bot, probably not the first time...

They leave it up, they get crap. They take it down they get crap.