New version V8. Biomechanical & sizing & fitting spreadsheet

A light bike doesn't replace good fitness.

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nitropowered
Posts: 1146
Joined: Fri Jul 17, 2009 4:10 am

by nitropowered

Take a book and ram it up against your crotch with your back to the wall. Make sure you have good pressure against your crotch with the book to try to replicate saddle pressure. Have a buddy mark the top of the book on the wall. Now measure from the floor to the mark

dee
Posts: 333
Joined: Sun Dec 28, 2008 11:42 pm

by dee

That's an inaccurate method. IS everyones distance from the crotch to their femur head the same?
Last edited by dee on Wed Jan 26, 2011 3:35 pm, edited 1 time in total.

by Weenie


KvnP
Posts: 152
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Location: Somewhere out there..

by KvnP

Also a lot easier w/ bibs on.
Parlee Z3c
Independent Fabrication SSR // 953
Independent Fabrication Planet X
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Sacke
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Location: South of France

by Sacke

Did something change with the current v.8, or is flexibility no longer a factor that influences frame size?

skouri1
Posts: 110
Joined: Mon May 10, 2010 4:10 am

by skouri1

Thanks so much for this Beatnik.
I tried your spreadsheet for the first time about two months ago, and it went horribly wrong for me. The bike just felt awful, and the saddle was definitely too high.

However, I gave it another shot last week, performing some more careful measurements. I also measured my saddle height not in line with the seatpost (which seems sort of arbitrary now that I think about it), but to the point on the saddle where my sit bones actually make contact. Voila--as close to a perfect bike fit as I have ever gotten. :thumbup: The extra setback (moved about 1.4 cm from earlier position) got rid of my cramped/arched back. I also feel that I have a better weight distribution, comfort and power (though that's totally subjective--no powermeter)

I'm still wowed that you can do this on two measurements. :noidea:

I have been struggling with bike fit for a long time--2 + of the 3 years I have been riding, so this is a huge relief!

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beatnik
Posts: 1237
Joined: Thu Aug 03, 2006 6:38 pm

by beatnik

skouri1 wrote:Thanks so much for this Beatnik.
I tried your spreadsheet for the first time about two months ago, and it went horribly wrong for me. The bike just felt awful, and the saddle was definitely too high.

However, I gave it another shot last week, performing some more careful measurements. I also measured my saddle height not in line with the seatpost (which seems sort of arbitrary now that I think about it), but to the point on the saddle where my sit bones actually make contact. Voila--as close to a perfect bike fit as I have ever gotten. :thumbup: The extra setback (moved about 1.4 cm from earlier position) got rid of my cramped/arched back. I also feel that I have a better weight distribution, comfort and power (though that's totally subjective--no powermeter)

I'm still wowed that you can do this on two measurements. :noidea:

I have been struggling with bike fit for a long time--2 + of the 3 years I have been riding, so this is a huge relief!



Yep, we often have wrong ideas about fitting comfort and performance. And all of them are in the same side, well fitted means more comfort, and comfort is performance. I´m glad you find it useful ;)
Biomechanical spreadsheet. Sizing&Fitting.

http://weightweenies.starbike.com/forum ... 8e319d185b

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beatnik
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Joined: Thu Aug 03, 2006 6:38 pm

by beatnik

I think you give me a good idea, orange arrow that indicates saddle height is not in the correct place. I´ll try to modify it for the next version. Obviously it must be in your saddle-sitbones contact point, but i think users are clever and have common sense as you´ve demostrated.
Biomechanical spreadsheet. Sizing&Fitting.

http://weightweenies.starbike.com/forum ... 8e319d185b

CrazyErrol
Posts: 366
Joined: Sun Sep 05, 2010 11:30 pm

by CrazyErrol

Ok I'm ordering a new traditional geometry (horizontal tt) Colnago frame this week and thought I'd give this a go so I can take the numbers with me to the fitting.

I'd been trying to work out for myself over the last month, based on my current bike, what my Colnago size would be and some of the Biomechanical results were interesting and encouraging.

My measurements are

Height 178.5
Inseam 86.3
Elbow/finger 51.0
Shoe 44 2/3 (uk 10 mavic)
saddle 28.5


Biomechanical results

Horizontal 57.5
Vertical 56.4

Tip to bars 54.6
seatback 8.0
drop 8.0


Some interesting things based on my current fit were that the saddle height came back -3mm but suggesting +2.5mm crank length. Also the tip of saddle to bar and drop seemed reasonably good too. I'm currently 55.5cm and 10.5cm maybe a little stretched on long distance runs so the results seem to back up what my body is telling me. Gives me a good feeling taking these numbers to my fitting.

Now I've never ridden a bike with such a large TT as 57.5cm so as I was thinking around a 57 Colnago I inserted the TT for that size frame, 55.7cm, into the next part of the spreadsheet and got a stem recommendation of 11.5-13cm.



A few questions on the chart for beatnick or anyone with the answers...


Seems to me that the 57 Colnago could be the way to go to run a longer stem and fits with the suggested seat tube measurement within a few mm, anyone have any input on this?

The seatback measurement seems to determine the saddle position so why the need to specify 2 stem lengths for different seatposts?

Are the seatpost setback and stem length not both determined by the seatback measurement?

Where does bar/hood reach factor into all of this? Are these calculations based on an average bar reach?

Cheers!

teddysaur
Posts: 119
Joined: Tue Jan 10, 2006 4:28 am

by teddysaur

Thanks Beatnik, your bike fit calculation works wonder. Recently, I swapped my 110mm stem to 90mm just to meet your bike fit. I should have done that much MUCH earlier.

subzro
Posts: 61
Joined: Sun Apr 04, 2010 10:48 am
Location: Australia

by subzro

Thanks Beatnik, I have been looking around this site for a couple of years now and just found this spreadsheet last night.

I have been working on my bike fit over the last year after reading Andy Pruitt's book cover to cover six or seven times and making numerous small adjustments over the last six months after initially making more significant ones a year ago. I was just saying to a riding buddy of mine two weeks ago after I made a 2mm change to my saddle setback that I had almost found the holy grail of bike fit lol.

I'm pleased to say after putting my measurements into your spreadsheet that every measurement was within 1 or 2mm of what I currently have. I was pleasantly surprised. Before reading Andy's book I had a look at other static fit calculators and they put me in a terrible fit position.

The only noticable difference in fit is that your SS puts me on 172.5mm cranks whereas I currently run 175mm (I'm 82 cm inseam and size 43). I have used 172.5mm but think I prefer 175mm. This is an area of bike fit that Andy Pruitt stays well clear of and I think I have probably read 100 different opinions on crank length. It would be interesting to hear yours.

Just one clarification on this bolded comment.

beatnik wrote:Bigger Seat tube angles means only more setback and longer effective T.T., better handling and nothing else. Most important thing is to fit the bike acording to your body. Nevertheless bike handling will be different but if your bike is well fitted, you will avoid muscle stress, you will have more power and less fatigue.


By bigger angles do you mean seatpost leans rearward more? Or bigger degree number (seatpost more straight up)?

i.e a Giant TCR has a seat tube angle of 73 degrees and a BH G5 has a seat tube angle of 72.5 degrees .... all other things being equal which would handle better?

Interesting comment on the Q-Rings too.

teleguy57
Posts: 187
Joined: Thu Jun 25, 2009 5:29 am

by teleguy57

A question on measuring saddle-to-bar distance. Riding an SMP Pro with the pronounced drooping "beak." Is the measurement still from the physical nose of the saddle?

teddysaur
Posts: 119
Joined: Tue Jan 10, 2006 4:28 am

by teddysaur

That was one of my concern initially. I measure from my SMP drooping "beak" to the bar distance. It seems to work very well for me.

jontawn
Posts: 6
Joined: Thu Jan 11, 2007 2:55 pm
Location: Hampshire

by jontawn

Hi All,

I am fairly new to road riding (MTB while I lived in the North of England) and and most keen to set my Giant TCR up as best I can.

I bring a few questions to the bike-fit arena and I wondered whether there may be some advice.

I have limited up/down movement in both feet, more so in my right foot, where my right leg is approximately 20mm shorter than my left, so is your spreadsheet suitable for me?

Overall it seems pretty damned good, saddle height seems good (although left leg overall, quad, calf & tib seems more muscular/stronger) but my reach seems a little long (but I suspect its because i'm used to a 90mm stem and riser bars on my old mtb)

Anyway, some food for thought and any help would be gratefully received.

cheers,
Jonathan

Lorang
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Joined: Mon Mar 28, 2011 3:14 pm
Location: Rio de Janeiro, Brazil
Contact:

by Lorang

beatnik wrote:... For example, i calculated "the best stem lenght" as an aproach, for setback or non setback seatpost (mtb-road). It´s not very accurate, because i haven´t considered frame angles, but you will find that your best stem length is exactly what i suggest.
The correct procedure is this one. (if you have the right frameset size or at least not very wrong)

1.- Fit your saddle height
2.- Fit your saddle-b.bracket setback ´
3.- Fit your saddle nose- handlebar axis lenght, and choose your best stem length according to your top tube length.
4.- Fit your saddle - handlebar height.
... :lol:


Hi All

I am new in the forum and would really like to have a help from you.

I am assembling a new MTB and have doubts on the size of the stem.

I am using a 19,5" frame that has a long Top Tube Lenght = 62,8cm.

My body measurements are:
Inseam - 86cm
Elbow-Middle Finger - 49cm
Height - 178cm
Flexibility - 8

The BiomecyclingV8 showed the following results:
Saddle->Handlebar - 55,9cm
Saddle Handlebar drop - 7,9cm (+/-1cm)
Saddle-Pedalier Seatback - 8,4cm
Stem Lenght - 4,7cm (for Seatback seatpost / saddle lenght = 26,5cm / horizontal size = 62,8cm)

But if I fit all measurements like the recomendations above, for a distance of 55,9cm from the saddle to the handlebar, I will need a stem with 6,0cm while the Biomecycling recomends 4,7cm.

What should I do??

What is more important?? Saddle>Handlebar distance or stem lenght??

Thanks for any help on the size of stem.

by Weenie


uncle-gee
Posts: 76
Joined: Tue Nov 07, 2006 4:29 pm
Location: Outaouais

by uncle-gee

Hi folks, Beatnik, questions remains...

Question A

Is the saddle height mesured:

1) from center of bottom-braket to saddle along the seat tube; or,
2) from center of bottom-braket to saddle at the reference spot on the saddle*

*the reference spot being 40mm ahead of the 100mm width mark on the saddle
(here refering to Giant DK's post on page 7 of this thread (1st post on page 7 of this thread))

Question B

The value obtained for the saddle setback (horizontal from nose of saddle to center of bottom-braket), does this value takes into account that different saddles may have different "nose to 100m width mark" lengths ?


Thanks!

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