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Slowtwitch Forums: Fitters:
Going from X/Y to Stack/Reach

 

   


hanijuha

Dec 2, 12 12:25

Post #1 of 14 (1899 views)
Going from X/Y to Stack/Reach Quote | Reply

I have an older fit bike that gives X/Y coordinates and I just did the F.I.S.T. certification.

So after my first test fit on one of my athletes, I got

x=535
y=530

And if I plug it into http://www.slowtwitch.com/.../bar_bore_calc_X.php

I get
Input Bar-Bore Y 530mm Bar-Bore X 535mm Head Tube Angle 73° Stem Length 100mm Stem Angle -17° Stem Clamp Height 40mm Spacer Height 10mm Headset Topcap 5mm
Output Stack 497mm Reach 445mm
The athlete, prior to the fit, has already purchased a 2012 Cervelo P2 size 51. Stack 482 and a Reach of 405

http://www.slowtwitch.com/....html#Anchor-CERVELO

My question is this. Stack looks good, but the reach of the bike seems to be shorter than recommended and I already used a 100mm stem to compute Stack /Reach. So does the athlete simply longer stem?


(This post was edited by hanijuha on Dec 2, 12 12:25)


Slowman

Dec 2, 12 13:47

Post #2 of 14 (1891 views)
Re: Going from X/Y to Stack/Reach [hanijuha] [In reply to] Quote | Reply

what's the profile of the athlete? very steep seat angle? lots of armrest elevation drop? what aerobar did you use during the fit? how tall is this athlete and what's his saddle height?

Dan Empfield
aka Slowman


hanijuha

Dec 2, 12 19:18

Post #3 of 14 (1871 views)
Re: Going from X/Y to Stack/Reach [Slowman] [In reply to] Quote | Reply

Attached are the results from the fitting. 80 degrees was the desired seat angle.

Aero bars are an old Syntace set. I remember you recommended Zipp?? bars that may be a good option

Athlete is 5'6" woman. She is an accomplished 1/2 ironman athlete that is making the jump to full next year.

Dan,

I really appreciate your help. I am getting comfortable doing the fittings but I want to make sure that I can use the data in the Stack and Reach tables.
Attachments: Generic Results.pdf (16.3 KB)
  syntace aero bar.JPG (45.7 KB)


Slowman

Dec 3, 12 6:35

Post #4 of 14 (1854 views)
Re: Going from X/Y to Stack/Reach [hanijuha] [In reply to] Quote | Reply

the reach is waaaaay long for a 5'6" woman. the stack is appropriate, or even high, because the syntace bar is itself so high-profile that it pushes the bike low. i'm very uncomfortable with that sort of reach for her. did you take a pic of her aboard the fit bike?

Dan Empfield
aka Slowman


hanijuha

Dec 3, 12 7:05

Post #5 of 14 (1850 views)
Re: Going from X/Y to Stack/Reach [Slowman] [In reply to] Quote | Reply

Here is the photo. I am also uncomfortable with the calculated reach. What is also interesting is her other fit numbers (seat angle, seat height, cockpit distance, saddle to arm rest) are identical to the Cervelo that she is riding. I have done 2 practice fits now, and both times the fit looks good but the calculated reach from X/Y seems to be too high.


Slowman

Dec 3, 12 7:21

Post #6 of 14 (1847 views)
Re: Going from X/Y to Stack/Reach [hanijuha] [In reply to] Quote | Reply

i'm not seeing a photo.

Dan Empfield
aka Slowman


hanijuha

Dec 3, 12 7:37

Post #7 of 14 (1843 views)
Re: Going from X/Y to Stack/Reach [Slowman] [In reply to] Quote | Reply

attempt #2 at a photo
Attachments: Fit.png (203 KB)


Slowman

Dec 3, 12 8:31

Post #8 of 14 (1835 views)
Re: Going from X/Y to Stack/Reach [hanijuha] [In reply to] Quote | Reply

the position is fine. you calculated reach wrong. i don't know what you did, i don't think that bike has stack and reach notated on it, but, whatever you did, reach at least, if not stack, is calculated wrong. why don't you tell me where you from, and to, and we'll start there.

Dan Empfield
aka Slowman


hanijuha

Dec 3, 12 9:50

Post #9 of 14 (1827 views)
Re: Going from X/Y to Stack/Reach [Slowman] [In reply to] Quote | Reply

Thanks Dan for confirming the fit. Thanks to your fit process, I find it to be easy. But I knew I was doing something wrong with the stack/reach.

Attached is a picture of where I am measure the x/y for the bar bore and then I am using the x/y calculator. Picture attached ( x marks the spot in the picture).

Measurements are done with respect to the bottom bracket along the x and y plane

The resulting coordinates can be seen in my first post.

Let me know what other information you need
Attachments: fit stem.JPG (100 KB)


Slowman

Dec 3, 12 9:56

Post #10 of 14 (1824 views)
Re: Going from X/Y to Stack/Reach [hanijuha] [In reply to] Quote | Reply

you're measuring to the right place it looks like. it's just looks like a technical problem with how the measure is calculated. tell me precisely how it is you're measuring it. explain the exact process of measuring. how you do it.

Dan Empfield
aka Slowman


hanijuha

Dec 3, 12 11:07

Post #11 of 14 (1820 views)
Re: Going from X/Y to Stack/Reach [Slowman] [In reply to] Quote | Reply

Tools being used : Digital Level 4'; ruler 4'

Step 1: Orient level to 90 degrees vertical
Step 2: Align edge of level with center of bottom bracket
Step 3: Measure horizontal distance from level edge to Bar Bore : this is the measure "X"
Step 4: Orient level to 0 degrees Horizontal
Step 5: Align edge of level with center of bottom bracket
Step 6 Measure vertical distance from level edge to Bar Bore : this is the measure "Y"

I can provide a picture later if this is not enough

Adding some pictures to show the actual measurements and also a close up of the aero-bars. Should I be accounting for the delta between the clamp and the set back of the pads


(This post was edited by hanijuha on Dec 3, 12 21:14)
Attachments: stem.JPG (21.3 KB)
  bike.JPG (43.0 KB)


Slowman

Dec 5, 12 5:26

Post #12 of 14 (1778 views)
Re: Going from X/Y to Stack/Reach [hanijuha] [In reply to] Quote | Reply

yep, you're measuring correctly. i would just suggest, measure it again. make sure that if you line the level up with its front even with the bottom bracket, you're not measuring from the back of the level. it's just not likely at all that you're getting 530mm for bb to handlebar clamp with that lady.

Dan Empfield
aka Slowman


hanijuha

Dec 7, 12 12:44

Post #13 of 14 (1743 views)
Re: Going from X/Y to Stack/Reach [Slowman] [In reply to] Quote | Reply

Thanks Dan for the confirmation. I am certain about both measurements. Heck, I even had my wife measure it. Btw, I have done 4 fits now, they have all resulted in happy customers with body angles and arm rest drops that perfectly in the norms that you provided. The issue seems to be converting X/Y to Stack and reach

Y(Stack) is easy as that is straight forward.

But now I am realizing, as you already know, the reach is dependent on the Aero bar geometry used for the fitting vs the stem and aero bar geometry desired for the new bike purchase. Right?

I don't remember the technical term, but when looking at the fore/aft position of the arm rests with respect to the bar bore.

The current aero-bar on the fit bike has an arm rest setback of 85mm from bar bore and I just bought a new profile bar T2 bar that can be adjusted to have a set back of as small as 35 mm ( aero-bar sitting on top of handle bar).

So taking into account the stock stem size that comes in with a bike and the detla between the arm rest positions, the reach can change dramatically. Right?

I am also going to remeasure these people so I can double check this stuff.

Thanks for the help


Slowman

Dec 7, 12 17:27

Post #14 of 14 (1733 views)
Re: Going from X/Y to Stack/Reach [hanijuha] [In reply to] Quote | Reply

"the reach is dependent on the Aero bar geometry used for the fitting vs the stem and aero bar geometry desired for the new bike purchase. Right?"

the stack and the reach of the bike you're looking for are both dependent on the aero bar you've chosen. now, maybe the problem is that the syntace bar pads sit so far back behind the centerline of the pursuit bar that you've got to have a really long bike (or really long stem) in order to get the pads positioned properly. but i don't remember the pads being that far back. maybe if you set the pads back even further back, via available holes in the pad holder, you might create this problem. this seems to be what you're suggesting.

to my memory, the CENTER of syntace pads sit about 4cm behind the center of the pursuit bar. as i recall it was syntace you were using for this fit. if the center of the pads sit a lot further behind the pursuit bars, then, yes, this might be the issue.


Dan Empfield
aka Slowman

   
 
 
 



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