Bicycle Fitting and Sizing

Why Fit

Different Philosophies

Serotta

Serotta has been a leader in bicycle fit for quite a while. The established the Serrotta Cycling Institute to further the goals of a better understanding of bike fit.

Fit Bikes

My fit bike

I got myself one of the Calfee/Mikkelson Sizer Cycles. Fun!!! I also have a PowerTAP rear wheel for it to measure power gains in different postitions.

Goniometers

http://en.wikipedia.org/wiki/Goniometer

A goniometer is used to measure the angle of the knee as well as other joints on the body when doing a fit. The goniometers that are sold throught medical channels are just too short to get good results. You need between 18" and 24". I have found a couple of very good alternatives.

Quint Measuring Systems, Inc. P.O. Box 280, San Ramon, CA 94583 (800)745-5045 http://www.quintmeasuring.com/

24" True Angle Tool - Contractor Grade (Heavy-Duty)
18" True Angle Tool
4" Attachable Dial
7" Attachable Dial

I got the 24" version because it is more rugged and thicker.

Kits

Retul, 3D computer anylisis
Fit Kit
Bikefitting.com
Bike Fit Systems
Accufit by Bill Boston

Local Fitters

NorCal Cycling in Santa Rosa. $75. They do a pretty good job. Much better than the average bike shop in the bay area. This is where I send most people that need a basic fitting.
Whole Athelete, San Anselmo, CA, $220-295
Craig Upton of Performance Lab HC , $150
PK Racing, in Fairfax. $450-500. Primarily pro road/tri experts. They are very expensive and I have no personal experience with them other than the fact that they are only 3 blocks from my house.
Cycle Sport, in Oakland. $125
AriaVelo, in Santa Rosa.
HyperCat Racing, SF

or search Serotta by zip code

Links

Ergo Bike Competition Bicycle Size/ Proportions Analysis By Edward C. Zimmermann
Jack's Bikes - A fit kit walk through
Cyclemetrics link page
Pruitt
Steve Hogg

A cool poster from Ritchey Logic: http://ritcheylogic.com/media/File/5022_FIT_LOGIC_POSTER_090909lowres.pdf

Some Traditional Numbers

Weight Distribution

Road:

In drops decending: 45% Front / 55% Rear
On tops climbing: 40% Front / 60% Rear
On hoods, out of saddle, sprinting: 50% Front / 50% Rear

MTB:

For trail I prefer a setup that sets the rider as far back as possible while maintaining control on steepest climb without too much fussing.

Fox racing shox recomends 55% for X-Country, 65% for Freeride, and 70% for Downhill.

When designing a frame from scratch, wheel offset from BB along wheelbase can be used as a ballpark start.

Road - 58.5%F/41.5%R
Trailbike - 61%F/39%R
MTB Race 60%F/40%R.

Cleat Position

"5. Make sure that the ball of your foot [centre of the first metatarsal joint] is in front of the pedal axle with the crank arm forward and horizontal. For a rough guide for shoe size metric 36 - 38, 7mm in front; 39 - 41, 8mm in front; 42 - 43, 9mm in front; 44 -45, 10mm in front. It is unlikely that your feet are bigger than that. Don't forget to move the right cleat further back again as outlined in point 3. I know that this is at variance with the commonly given advice but you will find as you try it that it works."

http://www.cyclefitcentre.com/pdf%20final%20docs/SHOE%20AND%20PEDAL%20ARTICLE%208_final.pdf

http://www.cyclingnews.com/fitness/?id=2004/letters07-26#Cleat

http://www.cyclingnews.com/fitness/?id=2004/letters10-11#Ball

Crank Length

39.5% of femur length.

L(mm) = 2.16% x I(mm)

http://www.polaris.net/palmk/crankset.html

"As a matter of fact, a large, persistent drop in cadence is usually a good indication that the crank is, in fact, too long."

2.10% for taller riders

Popular Guides Height Inseam Cranklength

under than 5' <=70 cm. 165

5' to 5'2" <=74 cm. 167.5

5'2" to 5'7" <=80 cm. 170

5'7" to 6' <=86 cm. 172.5

6' to 6'5" <=93 cm. 175

taller than 6'5" <=99 cm. 177.5 - 180.0

Traditional Recomendations Height Inseam Cranklength

under 5'7" 74 to 80 cm. 170

5'7" to 6' 81 to 86 cm. 172.5

Over 6' longer than 87 cm 175

http://www2.bsn.de/Cycling/cranks.html

18.5% from top of femur to floor.

Inseam:

< 29 inches - 165 mm crank
29 - 32 inches - 170 mm crank
32 - 34 inches - 172.5 mm crank
> 34 inches - 175 mm crank

Frame Size:

54 cm or less, 170 mm
55 - 58 cm, 172.5 mm
59 cm or greater, 175 mm

Gonzalez and Hull, Bivariate optimization of pedaling rate and crank arm length. Journal of biomechanics 1988, vol. 21, no10, pp. 839-849

Danny Too; Gerald E. Landwer, The effect of pedal crank arm length on joint angle and power production in upright cycle ergometry. Journal of Sports Sciences, Volume 18, Issue 3 March 2000 , pages 153 - 161

Knee Angle

30-35 Degrees. More bend conserves more energy, less bend for more power.

31-32 is optimum.

Saddle Height

Inseam (with cycling shoes) x 0.883 = Top of the saddle to the center of the bottom bracket. (beware oversized feet using this)
Inseam (with cycling shoes) x 1.09 = Pedal spindle to top of saddle with pedal parallel to seat tube.

LeMond Method - Adjust the saddle to a distance equal to your PBH* x .883, measured from the top of saddle to the center of the bottom-bracket
Petersen Method - Adjust the saddle to a distance equal to your PBH x .873, measured from the top of saddle to the center of the bottom-bracket
Hamley Method - Adjust the saddle to a distance equal to your PBH x 1.09, measured from the top of saddle to the pedaling surface (with the crank at bottom-dead-center inline with the seat tube)
Holmes Method - Adjust the saddle so your knee is bent 25-35 degrees with the ball of your foot on the pedal (with the crank at bottom-dead-center inline with the seat tube)

Trunk Angle

About 30-40 degrees from level. (45 at most)

Shoulder Angle

90-100 degrees.

Elbow Bend

15 degrees

Stem Length

Shoulder angle 90 degrees +/- 5 degrees.
When in drops, axle obscured by bars.
With arms bent 15 degrees in drops, plumb line from nose bisects stem at bars.

Handlebar Height

1-2 inches below the saddle for small riders
up to 4 inches for taller riders.