New version V8. Biomechanical & sizing & fitting spreadsheet

A light bike doesn't replace good fitness.

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MortenB
Posts: 107
Joined: Mon Jul 20, 2009 12:54 am
Location: Denmark

by MortenB

Feedback time Beatnik :beerchug:

I found your spreadsheet when I was building up a new bike and I used the guidlines in the spreadsheet when ordering the frame and setting up the bike. I have now done 1000 km on the new bike, and the fit feels amazing! The only things I have changed from the data in the spreadsheet is to lower the seat 5-7 mm and move it 7-8 mm forward. The changes made based on my feeling on the bike.

Today I went to the LBS to have my fit checked according to their body-scanner. They were scratching their heads because they had never seen a bike set-up so well by someone not having access to some ''pro set-up tools''. According to their measurements my seat is 2,1 mm to high, and the seat is 1,5 mm to far back. Everything else within ''measurement errors''. You can actually say that the mentioned measurements for the seat is also within measurement errors, but I mention them here to indicate that the fit is spot on.

Thanks for the excellent spreatsheet. Without it I would have bougt a frame one size to big, ordered 172,5 mm crank arms instead of 175 mm and I would never had gotten such a nice fit without the guidlines :thumbup:

PS... I'm glad that I could participate (you now use a picture of my arm in the spreadsheet) :wink:

Cheers,
Morten
My BMC SLR01 Team Machine: viewtopic.php?f=10&t=75502

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Regge
Posts: 8
Joined: Mon Jun 08, 2009 9:55 am
Location: Switzerland

by Regge

Hi beatnik,

great spreadsheet ... it helps a lot :thumbup:

What reach of the bar you consider in your calculation? I'm using a compact bar with a reach of only 72mm, so I ended up with 10mm longer stem as proposed in your calculation.

Regards, Regge
09 Pinarello Prince
05 Time VX Edge
03 Canyon MR8

by Weenie


janez
Posts: 66
Joined: Fri Mar 19, 2010 2:08 am

by janez

i'll try this one :thumbup:
"Invest in the frame which will last a lifetime, play with the components to keep it fresh and to meet your weight needs." Darren Crisp

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

by beatnik

Thx for your feedback. :up:
Biomechanical spreadsheet. Sizing&Fitting.

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

gryfon
Posts: 22
Joined: Tue Jun 08, 2010 8:33 pm

by gryfon

Beatnik,

Thanks for all your work. It's very interesting, and quite some distance from where I currently am. I am going to give this a go and move towards the suggestions. It seems my custom fit frame was made with a very slack seat angle, and probably for good reason (72.5 degrees I think), so I can't get very close to the seat to bottom bracket setback (Still +2cm), but then my femurs are very long. So it's all a matter of compromise. Whilst the changes will certainly enable me to move forward and down, which I think will be a good thing.

I'm in the process of getting a new race bike so it's time to try things out before I buy. I'm going for a fitting later this week so I now have another set for reference.

:beerchug: Cheers.

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Arky
Posts: 522
Joined: Sun Sep 23, 2007 5:06 am

by Arky

This is a really good calculator. It repeated my current fit (tt + stem) within 1cm but with much less drop (which probably accounts for the 1cm of extra stem given).

I am curious, is there a specific seat tube angle that is assumed? I broke out the trig and gave up trying to figure it out.

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

by beatnik

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.
Biomechanical spreadsheet. Sizing&Fitting.

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

Ralphi
Posts: 279
Joined: Wed Nov 19, 2008 9:46 pm
Location: Paradise City

by Ralphi

Hey erm.. i came across this while searching for some bikefitting help. The link is however broken. Can i get it somewhere else or... ?!

DanW
Posts: 1037
Joined: Fri May 02, 2008 5:39 pm
Location: Here, there and everywhere

by DanW

Hi,

I am very interested in bike fit as I have recurring medial knee pain.

Clearly there are lots of factors affecting a good fit and lots of balancing of these factors in order to get the best fit for an individual.

My question is this: What are the overall biomechanical goals of the correct bike fit (for me this would mainly be in relation to comfort rather than performance)? Forget frame lengths, saddle setback and so on, what are we trying to acheive in terms biomechanics?

For example what are the kinematics and kinetics of the lower limbs that are desired and where do these values come from? References? A knee flexion angle of 150-155 degress has been mentioned here for example, but how about internal/ external rotation of the knee, ankle and hip motion, joint moments within the hip, knee and ankle etc...

I realise accurate kinetics and kinematics can not be checked by eye but that is the benefit of have access to skin marker based motion analysis and fluroscopy amongst other little goodies :D

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

by beatnik

x Danw Buy Qrings is the best advice for you and your knee.

Link is working ;)
Biomechanical spreadsheet. Sizing&Fitting.

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

SW
Posts: 207
Joined: Tue Mar 25, 2008 12:04 pm

by SW

This certainly seems really accurate and thanks for you're work on it! I'm just confused as to how it can have so few measurements for your body? Am I missing something, or can this really be done with only the inseame and forearm, plus flexibility??

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

by beatnik

I have another version that includes torso length as critical measure (See the graphic below). But it´s not easy to measure correctly you must find the top of your ilium and measure perfectly vertical till the top of your clavicle, and yes,you need another person and a taylor meter, or for sure you go wrong.

If you take your measure correctly you will find that in most of the cases that measure is identical than your inseam perhaps one or two cm. up or down. Once you have torso length m. you need a complicate calculation, with angles, sine and cosine in order to find the perfect angle for your torso. And you must install some other excel trigonometric module and...you know it´s more difficult than v8 datasheet for any language.

From the practical point of view, this formula could be simplificated as this

(Put this measure as you inseam in datasheet)

Virtual Inseam Length = ((102/100)*(Real Inseam length-((Torso length-Real Inseam Length))/2))

Is not exactly because is not trigonometric, but works. And perhaps must be included, in order to obtain more accurate results, nevertheless i´m pretty satisfied with v8 because is as easy as it can be and give very good results. Sometimes "perfect" and "very good" are big enemies ;). Greetings and thx for your feedback.
Attachments
SKELETON.JPG
Biomechanical spreadsheet. Sizing&Fitting.

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

SW
Posts: 207
Joined: Tue Mar 25, 2008 12:04 pm

by SW

Thanks for the response, I'm really impressed by your work!

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

by beatnik

Somebody asks me how to put the correct measurements

Image
Biomechanical spreadsheet. Sizing&Fitting.

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

L3X
Posts: 284
Joined: Wed Feb 25, 2009 8:39 pm

by L3X

Which way is most accurate to measure your inseam?

by Weenie


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