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Discussion Starter · #1 ·
sorry, I am mathematically challenged.

I have a flipped up +8 degrees 100mm stem (BBB) on my 54cm Madone. Not sure what its HTA is in 54cm size (~73 or 73.5 degrees?). It's STA I think is ~74 or 73.75 degrees but I doubt it matters in this case.

Question: if I were to change nothing but flip the stem down to -8 degrees (same stem, 100mm) then how much lower would my bars be, in mm? 20mm? 25mm? 30mm?

I realise this would also effectively lengthen the stem by ~9mm. To compensate a little I was going to twist my bars/hoods a little bit upwards to be more in line with -8 degree stem angle (they are currently twisted a bit down with +8 stem). Would this help? I guess this would make my drops further out to reach?

Thanks in advance
 

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Discussion Starter · #2 ·
HTA is 73 degrees

acid_rider said:
sorry, I am mathematically challenged.

I have a flipped up +8 degrees 100mm stem (BBB) on my 54cm Madone. Not sure what its HTA is in 54cm size (~73 or 73.5 degrees?). It's STA I think is ~74 or 73.75 degrees but I doubt it matters in this case.

Question: if I were to change nothing but flip the stem down to -8 degrees (same stem, 100mm) then how much lower would my bars be, in mm? 20mm? 25mm? 30mm?

I realise this would also effectively lengthen the stem by ~9mm. To compensate a little I was going to twist my bars/hoods a little bit upwards to be more in line with -8 degree stem angle (they are currently twisted a bit down with +8 stem). Would this help? I guess this would make my drops further out to reach?

Thanks in advance
More info: Madone geometry for 54cm size states HTA is = 73 degrees and STA is = 74 degrees. This is just in case this helps to figure out the bar height decrease although I don't see how it could given we are not changing the spacer set-up or stem in any way other than flip it from up to down angle.

I tried to measure it myself and it looks like ~ -20-25mm less going from 98 down to 82 (for 100mm length) but there must be a more reliable scientific way.

thanks again
 

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acid_rider said:
More info: Madone geometry for 54cm size states HTA is = 73 degrees and STA is = 74 degrees. This is just in case this helps to figure out the bar height decrease although I don't see how it could given we are not changing the spacer set-up or stem in any way other than flip it from up to down angle.

I tried to measure it myself and it looks like ~ -20-25mm less going from 98 down to 82 (for 100mm length) but there must be a more reliable scientific way.

thanks again
26 mm difference.

How did you get the 9mm increase in length figure? That is correct. You should be able to get the other measurements along the same reasoning. That reliable scientific way is know as trigonometry. Remember the Native American chief SOHCAHTOA and his right triangle.

Sin (angle) = Opposite/Hypotenuse
Cos (angle) = Adjacent /Hypotenuse
Tan (angle) = Opposite /Adjacent

I learned that acronym long ago, it has served me well. Useful indeed.

You must've learned it in school, but maybe it's been a while. You got the 9mm and you "knew" that the head tube angle played a role in the calculation.
 

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Discussion Starter · #4 ·
thank you!

re 26mm. Thanks I was afraid it was that much.

I might just remove 10mm of spacer and see if it works for me before I flip it down.

Related question: is it better to ride with a 98 degree stem with ~10-15mm spacer or 82mm degree stem with 30mm of spacer given then have ~about the same bar height? Assume stem length is ok either way.

Thanks again.
 

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a minor difference...

To answer the question about which angle and stem setup is "better", the higher rise stem would produce a more rigid setup, but most find that much angle not very pretty. Lots of spacer isn't real pretty either, but it wouldn't be wise to use a flipped stem and little or no spacer (with the steering tube cut down), then decide later you don't like it.

One minor error that's inevitable with these calculations if that it's a simplified model, where the stem is modeled as a line that intersects the center of the steering clamp. In the case of the flipped stem, you have a 25 degree angle from the horizontal (98-73). With the 100mm length as the hypotenuse, the height is 42.3mm and the horizontal length is 90.6mm. When the stem is flipped down, the angle is 9 degrees from the horizontal (82-73). The height is 15.6mm and the horizontal length is 98.8mm. That makes the height difference a theoretical 26.7mm. In reality, the height difference is quite likely to be a few millimeters less because the centerline of the stem extension does not usually intersect the exact center of the steering tube clamp. It varies with the brand.

Notice how using this "convention" (let's not call it a standard) of specifying the stem angle as 82/98 makes it simple to figure the stem angle from the horizontal, just by subtracting the HTA? The other stem angle "convention" calls this stem a plus or minus 8 degree. It's certainly more confusing to start with 90 degrees, subtract 73, then add or subtract 8 to come up with two angles of 25 and 9. Perhaps if HTAs were specified as 17 from vertical, then the convention would be more sensible.

Tilting the bars up will help reduce the reach by bringing the brake hood up and closer to the saddle. Usually, there is not much room for adjustment, without fouling up the angle in the drop section of the bars. I always adjust the angle of the drops first, then adjust the brake hood position to a comfortable level.
 

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C-40 said:
One minor error that's inevitable with these calculations if that it's a simplified model, where the stem is modeled as a line that intersects the center of the steering clamp. In the case of the flipped stem, you have a 25 degree angle from the horizontal (98-73). With the 100mm length as the hypotenuse, the height is 42.3mm and the horizontal length is 90.6mm. When the stem is flipped down, the angle is 9 degrees from the horizontal (82-73). The height is 15.6mm and the horizontal length is 98.8mm. That makes the height difference a theoretical 26.7mm. In reality, the height difference is quite likely to be a few millimeters less because the centerline of the stem extension does not usually intersect the exact center of the steering tube clamp. It varies with the brand.
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I didn't go over your calculations, but I believe you on this. It is a simplified model, but also we're only going to be able to get within a few millimeters here of there on bar drop. We don't have infinite adjustment on the stem height since we're using spacers. Also stem length measurements do vary with brand like you said. I've got 2 3ttt forgie stems. one an 110 mm and another 120 mm. They measure 115mm and 125 mm respectively from the center of the plug bolt to the center of the clamp for the handle bar, I've wondered about that.

as to the original poster, I don't like the look of the upturned stem on a road bike. But that's only a visual issue.
 

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stem length..

Newer style stems measure along the side, from the steering tube centerline to the center of the bars. Measuring along the top typically produces a 3-5mm longer measurement. In the old days when nearly all stems were horizontal, you could measure across the top.

In the picture, notice the gap between the centerline of the steering tube and the extension line for the length. The centerline of the stem extension also does not intersect the center of the steering tube clamp.
 

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I figured it had something to do with how they (manufactureres) measured it. I have a Profile Stem that is 110mm and I measure that as I mentioned above. It has the same angle and is also a threadless. Probably similar to how some frames are CC or CT or Center to top of Seat tube. Handle bar reach is another are where I've seen measurements all over the board. I think it's gotten to the point that if you really want to "dial" everything in, you're going to have to have the part in hand and take a tape measure to it.
 
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