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PostPosted: Sat Aug 27, 2011 2:26 am 

Joined: Thu Nov 15, 2007 7:23 pm
Posts: 21
Hmm. Your spreadsheet is surprising for me.

My specs:
Inseam: 78
Trunk: 66
Forearm: 34.5
Arm: 65
Thigh: 56.5
Lower Leg: 52
Sternal Notch: 143
Total Body Height: 173

Elbow-middle finger: 45.5

According to your spreadsheet, I should be on a 52cm effective top tube, 51cm seat tube, and a 11.1cm stem with a no setback seat post.

According to the competitive cyclist, I should be on a 55-55.5cm effective top tube, a 50.5-51cm seat tube, with a 11.2cm stem.

What gives with the extreme difference in effective top tube lengths? Do I have a weird body? For what it's worth I ride a bike with a 54.5cm top tube, a 68cm center of bottom bracket to saddle top (along seat tube), a 100mm stem, and a 1cm drop. I ride on top of the hoods unless I'm doing a climb (then I'll go into the drops).

Posted: Sat Aug 27, 2011 2:26 am 

PostPosted: Mon Sep 19, 2011 12:19 pm 

Joined: Mon Sep 19, 2011 12:01 pm
Posts: 1

My first message to this forum...and i would like to ask is this saddle-pedalier seatback for the road or mtb-bike?

My rider data was:

Inseam: 84,5 cm
Elbow-middle finger: 48,3 cm
Saddle lenght: 27,8 (Selle San Marco Regale FX)

And results:

Flat- hadlebars 52,7 cm
Saddle height 75,1 cm
Saddle-handlebar drop 7,5 cm +-1
Saddle-pedalier seatback 8,2 cm??

All other measures is just that i have in my bike but seatback is almost 3 cm smaller in my bike now. So is this 8,2 cm to road or mtb-bike?

Thanks, Jani

PostPosted: Mon Sep 19, 2011 4:23 pm 

Joined: Mon Oct 12, 2009 6:36 pm
Posts: 246
This spreadsheet is a nice idea but lacks a little bit of accuracy.
Seat tube angle has a big influence on fit yet it is not accounted for in the spreadsheet.

For example, with a seat height of 75 and a setback of 8 (which the spreadsheet suggests in my case), actual vertical saddle height as measured from the bottom bracket is different.

Seat tube angle = 72 degrees: seat is at 71.3 cm vertical
Seat tube angle = 74 degrees: seat is at 72.1 cm vertical
Now this is a difference in height (Y) of almost 1 cm while setback (X) is given and remains the same. With longer legs this difference becomes bigger.

Now consider handlebar reach. This is a very complex calculation but the difference between a 72 degree and a 74 degree seat tube comes down to a difference in reach of about 2 cm. This means that, given the top tube remains the same, with a 74 degree seat tube the distance between your saddle tip and handlebars will be 2 cm longer than with a 72 degree seat tube. I think 2 cm is quite a big difference.

I do think this is easy to adjust and then you would have a great tool!

PostPosted: Wed Sep 28, 2011 6:36 am 
User avatar

Joined: Mon Jan 23, 2006 3:03 pm
Posts: 1305
Location: Denmark

Try a see my comments in my the post on page 7.

Technical editor at Cykelmagasinet Denmark

My Simplon Pavo II

PostPosted: Thu Oct 06, 2011 8:23 pm 

Joined: Thu Sep 23, 2010 8:55 pm
Posts: 3

PostPosted: Thu May 10, 2012 8:15 am 

Joined: Sat Apr 21, 2012 12:13 pm
Posts: 2
I like it, it sounds like a good starter for newbie cyclists!
I'll definitely take a look at it. :beerchug:

PostPosted: Sun May 20, 2012 9:29 am 

Joined: Thu Apr 09, 2009 5:26 am
Posts: 2
Location: Romania
Thank you for the spread sheet,it is a good starting point for the correct bike fit.
But I have a problem with the setback.It doesn't take into account the femur/tibia proportion.
For example : let's take 2 persons with identical inseam,upper body and flexibility.The result of the ss will be the same for both of them: they both need the same reach,setback,etc.
But person 1 has a shorter femur and a longer tibia. Person 2 has a longer femur and a shorter tibia. But,remember,the inseam (femur + tibia) is the same.Because of that, no 1 (short femur,long tibia) will need less setback and longer stem and no 2 (long femur,short tibia) will need more setback and shorter stem,so for both of them to have the same reach.

I noticed this problem in my case (short femur,long tibia),for my MTB (Trek 4300 frame). My numbers are:
inseam : 88 cm
arm : 49 cm
flex : 0
height : 182 cm (irrelevant)
shoe-size : 46
saddle length : 28
horizontal frame size : 58.3 cm
no setback seatpost

The setback recommended is 8.9 cm with a 8.4 cm stem. I have 5 cm setback with 12 cm stem. In this position I have knee over spindle.

I also have the saddle-hablebar drop = 1 cm with no sag,so about 3 cm while riding vs 8.4 +/-1 recommended, which brings me to the other thing I noticed : the recommended saddle-handlebar drop is the same no matter what the flexibility is,which I think is wrong.

Anyway,thank you for this ss,it's a good tool in finding a good position on a bike. With a few tweaks it can become an excellent one.

PostPosted: Tue Jun 24, 2014 5:31 pm 

Joined: Mon Jun 02, 2014 4:34 am
Posts: 40
Although it is an old post, but a great reference for bike fitting. I am using it right now and still testing the new measured fitting.

PostPosted: Sun Jul 13, 2014 1:05 pm 
User avatar

Joined: Thu Aug 03, 2006 6:38 pm
Posts: 1228
Clever ones did notice that frame angles are irrelevant

Biomechanical spreadsheet. Sizing&Fitting. ... 8e319d185b

PostPosted: Wed Jul 16, 2014 8:35 pm 

Joined: Mon Jul 07, 2014 8:19 pm
Posts: 9
Well that was interesting. Sitting around watching the tdf and browsing the forum, so I decided to try this spreadsheet to see how it compares to my fit that I've settled on over a few years of trial and error.

86cm inseam, 50cm arm-finger, 8-9 flexibility, 45 shoe, not many variables here are there?

Suggested top tube = 56.5cm
current best fitting frame = 56.5cm

Suggested saddle height = 76.5cm
Actual saddle height crank center - sit bone contact point = 76.5cm (really)

Suggested setback = 8.4cm
Actual setback = 8-9cm range

Suggested stem length for 56.5tt = 115mm
Actual stem length for 56.5tt = 120mm

Suggested drop = 8cm +/- 1cm
Actual drop = 8.5-9cm

Suggested crank length = 175mm
Actual crank length = 172.5mm

Interesting... I'm not sure how I would feel about 175mm cranks but maybe I should give them another shot one day. Also not sure if I would be on a 19" mountain bike like it says, my friends' 19" 29er is massive and I feel like 17" might be better. Similarly the 130mm mountain bike stem estimation is probably inaccurate for modern 29er geometry based on what I've seen.

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