Why is my 90mm stem 96mm?

[FastforaSlowGuy]

I measured my zipp stem last night, and it is 96mm from bar clamp center to the headset bolt center. I know there is variability in these things but that seems like a lot. Mind you, the fit is great, so I don't care at the moment. But am I measuring this right?


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[AngryScientist]

interesting.

i also ride so-called 90mm stems, and have found a great deal of variation between brands, even when measured the exact same way. for example, i dont remember the numbers, but i know there is a fairly large [actual] difference between a deda newton and 3T 90mm stem with the same angle.

i guess as long as the fit is good, life is good!

[Raffy]

Same thing here, my Deda Newton Pista 90mm measures 95mm. Does anyone here know any steep angle 90mm stems that actually measure closer to 90mm?

[Ralph]

Maybe the horizontal measurement is 90. Your 96 measurement takes in the distance of the "rise".

[binxnyrwarrsoul]

+/- 5 mm is pretty common, it seems.

[FastforaSlowGuy]

Maybe the horizontal measurement is 90. Your 96 measurement takes in the distance of the "rise".

Good point. I'll break out my geometry skills later and test this. It would actually be pretty great if that's how the industry did things.


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[pakora]

At the other end of the spectrum I have an old junky Rocky Mountain 140mm stem that's 135mm long.

[David Kirk]

Stems are typically measured from center to center which of course is a virtual measurement in a way........meaning that there is no way to hold up a ruler and get a good solid number.



There is a trick you can do that will help get you a real number that will not be affected by the stem angle or steerer stack -

* take a piece of masking tape and place it on the side of the stem where the steerer passes through it. Now take a sharpie marker and do your best to place a dot where the centerline of the steerer and the centerline of the stem strut meet.

* now measure from the back edge of the handlebar where it enters the stem and go straight back to the dot you just made. The ruler will be running along the centerline of the strut.

* lastly - take 1/2 the diameter of the bar where it passes through the stem (typically bars are 26 mm or 32 mm so the radius will of course will be 13 mm or 16 mm) and add it to the number you just got from the bars to the dot and you will have your actual stem length.


Most people will hold a ruler on top of the stem and measure from the center of the stem cap bolt to the center of the bar and unless the stem is a 90° (some call it 0°) rise this number will be long.


Hope this helps - as usual I'm giving advice before I've finished my morning coffee so if I said something stupid let's chalk it up to that.

Dave

[nicrump]

A agree with Mr Kirk but I also see many stems that are longer than advertised. I have several 115mm WCSs laying around.

[binxnyrwarrsoul]

A agree with Mr Kirk but I also see many stems that are longer than advertised. I have several 115mm WCSs laying around.

Got a white WCS stem, 100mm laying around?

[slidey]

PM the OP; he's got your 5mm!

Ahh, I love these Missed Connections :banana:

At the other end of the spectrum I have an old junky Rocky Mountain 140mm stem that's 135mm long.

[Rob1519]

I measured my zipp stem last night, and it is 96mm from bar clamp center to the headset bolt center. I know there is variability in these things but that seems like a lot. Mind you, the fit is great, so I don't care at the moment. But am I measuring this right?


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Which way is the stem flipped? I have a 3T ARX Pro (120mm) that measures 120mm if measuring on the +6 degree and 125mm if on the -6 degree side

[wallymann]

i've actually found the measurements seem to work for me, even between brands.

if i have a stem that's 130mm and i need one that's +/-5mm and source a 125/135mm stem i've found that the new stem puts me right where i'd want with the +/-5mm difference that i expected.

has been true when using cinelli, 3ttt, ritchey, deda, ITM, FSA, and some off-brands as well.

lucky i guess. {shrug}

[rice rocket]

Good point. I'll break out my geometry skills later and test this. It would actually be pretty great if that's how the industry did things.


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17 deg?

tan(17 deg) * 1/2 stack height will give you this difference.

Zipp lists 42mm stack on their website for the Service Course SL stem, so comes out to 6.42mm difference.

[binxnyrwarrsoul]

PM the OP; he's got your 5mm!

Ahh, I love these Missed Connections :banana:
Potd.