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Discussion Starter · #1 ·
I believe that what you have listed is an inch too long in all cases. I have successfully used this Stack/Reach Calculator in many cases for many different bikes:

bb2stem

Every time I've used it, the calculated Stack/Reach is within a tenth or two of the manufacturer's listed Stack/Reach values. For the SB-95, the Reach is off by an inch. Here is an example for a Large SB-95 with a 120mm Fox 34:

Geometry from Yeti Website:
Top Tube = 24.1" (612.1 mm)
Head Tube = 4.90" (124.5 mm)
HTA = 68.5
STA = 72
Fork Length = 21" (533.4 mm) --> I used 536.8 mm (see below)
Fork Rake = 2.01" (51 mm)

For Bottom Bracket Drop (BBD), I used 32.7 mm. This is based on the listed Bottom Bracket Height of 13.2" subtracted from a 29er wheel/tire radius of 368 mm (311 mm + 2.25" tire). I also added 4 mm to Fox's listed Fork Length (532.8 mm) to account for a Cane Creek 40 Zero Stack lower cup stack height.

Here are the results:
Stack - Listed = 24.8", Calculated = 24.8"
Reach - Listed = 17.1", Calculated = 16.0"

And for different sizes...

Small
Stack - Listed = 23.7", Calculated = 23.7"
Reach - Listed = 15.5", Calculated = 14.4"
Medium
Stack - Listed = 24.0", Calculated= 24.1"
Reach - Listed = 16.3", Calculated = 15.3"
XL
Stack - Listed = 25.3", Calculated = 25.4"
Reach - Listed = 17.7", Calculated = 16.7"

The same ~1" difference in Reach holds true for the geometry with 140mm front travel as well.

As a double-check, I plugged the different numbers into this calculator (which I've also found to be consistent), and became even more confused:
<:: Welcome to Slowtwitch.com ::>: Custom Tri Geometry Calculator

Using the listed Yeti Reach (17.1") yielded a Wheelbase that was consistent with the Yeti geo chart (46"), but a top tube that was not (listed 24.1", calculated 25.2"). Using my calculated Reach (16.0") yielded a top tube that was consistent with the Yeti geo chart (24.1"), but a Wheelbase that was not (listed 46", calculated 44.9").

So there you have it, I'm confused.
 

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Savechief, sounds like a great question to contact and ask Yeti directly about. Since this is a forum you'll probably get a bunch of "answers" from people who claim to know things but don't. Maybe a discussion of the answer Yeti gives you after you contact them would be something to discuss.
 

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Savechief, sounds like a great question to contact and ask Yeti directly about. Since this is a forum you'll probably get a bunch of "answers" from people who claim to know things but don't. Maybe a discussion of the answer Yeti gives you after you contact them would be something to discuss.
Using the pdf from yeti's website, and adobe acrobat, I can measure that spec drawing. It's not perfect, but you can use the chainstay measurement as a constant (~1.87" on the pdf = 17.5"). I found that the bike pictured is a Medium (that ratio yields a 23.1" ETT). And I then found that the reach pictured is ~16.35" (middle of BB to middle to headtube).

Interesting...
 

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Discussion Starter · #5 ·
Where are you seeing a published reach measurement? I see a TT measurement but no reach published:

Yeti Cycles / Home

Are you saying you believe the TT measurement is off by an inch too?
Yeti Cycles / Home --> Click "Bikes" --> Click "SB95" (takes you to Yeti Cycles / Home) --> Stack and Reach are measurements "L" & "M" from the geo chart

I have no idea what the source of the error is. I personally believe that one of the initial inputs into the Stack/Reach Calculator is wrong, but I don't know which one. The inputs are:
1) Top tube length
2) Head tube length
3) Head tube angle
4) Seat tube angle
5) Bottom bracket drop
6) Fork length
7) Fork rake

The measurements that I'm skeptical on are the top tube length and seat tube angle. All others are fairly straightforward in terms of how to measure them, and can be pretty easily verified. But I have seen several philosophies on how to measure top tube length and seat tube angle.
 

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OP, did you try emailing Yeti to see why their numbers are off? I tried the calculator for the SB75 and it was off by an inch. just for giggles, I typed in the Santa Cruz Solo specs, and their reach matched exactly the same.
 

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Discussion Starter · #7 ·
I haven't contacted Yeti, and I honestly don't know when I would have a chance. The good thing is, I already own an SB-95, but I wanted to make sure that potential customers weren't led astray if the numbers happen to be off. Because I was curious, I took some measurements last night off my size Large SB-95:

STA = 72.8
HTA = 67.7
Top Tube = 24.1"
Wheelbase = 46.2"
Chainstay = 17.5"
Head Tube = 4.9"
Headset Upper Stack = 16mm
Headset Lower Stack = 4mm
Stack = 24.9"
Reach = 17.1"
Bottom Bracket Height = 13.2"
Bottom Bracket Drop = 1.5" (38mm)

So my measurements seem consistent with the Yeti geo chart, with the exception of my HTA being a bit slacker (chart shows 68.5) and the STA being a bit steeper (chart shows 72). I'm also a bit unsure if my fork is currently at 120mm or 130mm. I wasn't able to measure accurately enough to discern 10mm difference in A2C distance. My HTA would indicate that maybe it's at 130mm, but I thought all SB-95's from a couple years back shipped with the fork set at 120mm. The measurement that I'm least confident in is my top tube. What I measured is consistent with Yeti's published numbers. However, if I take all my measured numbers and use them in the Stack/Reach calculator, but substitute in a top tube length of 24.8", then everything works out to match the published and measured Stack/Reach numbers. Even the second calculator from Slowtwitch returns the expected top tube, head tube & wheelbase numbers when Stack/Reach and the other variables are used as inputs. So I'm inclined to say that the published top tube number may be a bit shorter than it actually is, by about 0.7".
 

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I just measured my small SB75 also. Found the STA to be at 75 degrees vs the published 73 degrees. all other measurements were the same. using the calculator with the correct STA of 75', the reach came out to 16.22 inches where the published reach was at 16.2.
I also physically measured the reach which came out to around 16.2 inches.

Steep seat tube doesn't bother me, and actually helps quite a bit on long climbs and seat is out of the way during downhill runs. My biggest concern was the reach, which is what I based my decision to buy this size frame.
 

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Hey guys-

Some really good observations here. I discussed this with our design team, and here's what I found out:

The geometry displayed on our website is of the actual ST angle, not the effective. The effective ST angle is quite a bit steeper as a result of the forward ST offset. Also, the TT-length listed is relative to the actual ST angle. This is what is causing the discrepancy between your calculator and the listed values. At the time, we listed the geometry in this way to stay consistent with our 26” models (inherently less variation between actual and effective ST angles).

The listed stack and reach values you show are correct.

With three wheel sizes now we realize listing the geometry in this way is no longer clear. We will be modifying the way we display geometry on our website to be more consistent and to make comparisons simpler. All listed ST angles will be effective, and all TT-lengths will be based on this effective ST angle. This will be a gradual transition starting with the next new model. Stack and reach will also be shown for all models going forward.

Try these values in your calculator:

Top Tube = 618.4mm (Relative to effective ST angle)
Head Tube = 125
HTA = 68.5
STA = 73.75 (effective)
Fork Length = 532.8 mm
Fork Rake = 51 mm

BBD = 31.75mm

Lower Cup Stack Height = 4mm

Note that you still may get a small discrepancy because the effective ST angle is based on a saddle height reference point.

I hope this helps.

Cheers guys!

JP
 

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Discussion Starter · #10 ·
John P (I'm also a John P.), thanks for the clarification. I suspected that it might have to do with effective vs. actual seat tube angles and the resultant top tube length. I realize that offsetting or curving the seat tube is necessary to make us all not whine about long chainstays on 29ers, but it sure does complicate geometry charts. You guys have to pick an arbitrary saddle height for each size to calculate the effective seat tube angle, which then propagates into the effective top tube length. For a rider with an actual saddle height higher than your arbitrary saddle height, their effective STA will be a bit slacker. The opposite is true for those with saddle heights less than the arbitrary point. Such is life, though.

The numbers work out for an effective STA of 73.5 and an effective top tube of 24.5". They also work out for an effective STA of 73.75 and an effective top tube of 24.3", as you said.

Thanks for your input on the issue.
 
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