www.bikecad.ca - bicycle
https://www.bikecad.ca/taxonomy/term/109
enFit Advisor: Customizing Fit Formulas
https://www.bikecad.ca/customizing_fit_formulas
<div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>For years, bicycle frame builders have used mathematical formulas to calculate appropriate bicycle geometry for a rider based on the rider's body measurements.</p>
<p>Some examples of how body measurements are taken by different builders are shown below.</p>
<img src="https://www.bikecad.ca/faqFiles/rider_measurement_styles.png" width="800" height="245" alt="Rider measurement styles" title="Rider measurement styles" class="blackborder">
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<img src="https://www.bikecad.ca/faqFiles/squarebuilt_rider.png" width="287" height="210" alt="Rider measurement style" title="Rider measurement style" class="blackborder floright" /><p>For convenience, the three measurement diagrams above are included in <a href="https://www.bikecad.ca/bikecadpro">BikeCAD Pro</a>. However, <a href="https://www.bikecad.ca/bikecadpro">BikeCAD Pro</a> users can add their own images to the <a href="https://www.bikecad.ca/fit_advisor">Fit Advisor</a> as described <a href="https://www.bikecad.ca/customizing_fit_advisor">here</a>. An example of a customized measurement diagram is shown to the right.</p>
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<p>If you would like to develop your own formulas for the <a href="https://www.bikecad.ca/fit_advisor">Fit Advisor</a> or modify the default formulas that are already there, start by selecting up to six body measurements to use as the basis for your fit scheme. In establishing these body measurements, be sure to reference anatomical body landmarks that will be repeatable for a variety of riders.</p>
<p>Next, find one or more riders that are already comfortable with their bike fits. By measuring these riders using our selected measurement scheme and then measuring the frame geometry of their current bikes, we'll be able to develop a fit scheme that would duplicate the fit of those riders when applied to other riders of different body dimensions.</p>
<img src="https://www.bikecad.ca/faqFiles/ridergraphic.gif" width="277" height="245" alt="Rider measurement style" title="Rider measurement style" class="blackborder floright">
<p>As an example, let's assume that we're going to use the measuring scheme on the left.</p>
<p>Let's assume that we've already measured a rider with an inseam of 32.5" and that we've also measured their saddle height and found it to be 720mm. Because this rider is very comfortable with their saddle height, we'd like to determine the ratio between the rider's saddle height and their inseam length so that we can apply that ratio to the inseam length of other riders thereby determining an appropriate saddle height for them.</p>
<p>To determine the ratio, we must first convert the 32" inseam length to millimeters. This is done by multiplying 32.5" by 25.4. The equation would be:</p><p> <em>32.5 * 25.4 = 825.5</em></p><p>The ratio of saddle height to inseam length would then be:</p><p> <em>720 / 825.5 = 0.872</em></p>
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<p>The ratio calculated above would be entered into the <a href="https://www.bikecad.ca/customizing_fit_advisor">Fit Advisor customization screen</a> as shown below:</p>
<img src="https://www.bikecad.ca/faqFiles/saddle_height_formula.png" width="623" height="31" alt="Saddle height formula" title="Saddle height formula" class="blackborder">
<p>The above formula calculates saddle height based on a single body dimension. Saddle height could alternatively be calculated from a combination of body dimensions. Dimension <em>D</em> (the femur length in this example) might also be factored in.</p>
<p>To demonstrate how more than one body dimension could be used to calculate a single bicycle dimension, consider a formula for <a href="https://www.bikecad.ca/rider_compartment">rider compartment</a>. Because rider compartment is a measure of the distance between the saddle and the handlebars, it is reasonable to assume that this dimension should be a function of a rider's torso length and arm length.</p>
<p>Let's assume that we are still developing formulas based on the measurement diagram above. The above diagram does not have a single measurement for torso. Instead, torso length could be calculated by subtracting dimension <em>C</em> from <em>B</em>.</p>
<p>Ultimately, if we'd like to calculate a value for <a href="https://www.bikecad.ca/rider_compartment">rider compartment</a> based on equal contributions from the rider's torso length and arm length. Our formula will need to be of the form:</p>
<p> <em>x * B - x * C + x * E = rider compartment</em></p>
<p>Since <em>x</em> represents the ratio by which we'll be multiplying body dimensions <em>B</em>, <em>C</em> and <em>E</em> to obtain the recommended value for rider compartment, we can rearrange the equation to solve for <em>x</em>. The resulting equation would be:</p>
<p> <em>x = rider compartment / (B - C + E)</em></p>
<p>Again, since we already have a benchmark rider with known body dimensions and we have measured the <a href="https://www.bikecad.ca/rider_compartment">rider compartment</a> on that rider's bike, we can substitute values for <a href="https://www.bikecad.ca/rider_compartment">rider compartment</a>, as well as <em>B</em>, <em>C</em> and <em>E</em> to solve the equation. Assuming our calculated value for <em>x</em> was <em>0.52</em> the resulting <a href="https://www.bikecad.ca/fit_advisor">Fit Advisor</a> formula would be entered as shown below:</p>
<img src="https://www.bikecad.ca/faqFiles/rider_compartment_formula.png" width="657" height="32" alt="Saddle height formula" title="Saddle height formula" class="blackborder">
<p>Ideally, your final <a href="https://www.bikecad.ca/fit_advisor">Fit Advisor</a> formula would be obtained by averaging the calculated ratios from a number of benchmark riders and their respective bicycles.</p>
<p>Over time, you may feel the need to develop several more specific fit schemes. For example one fit scheme might cater to elite road racers, while another scheme might be more suitable for recreational road riders.</p>
<p>In developing BikeCAD Pro, the focus has been on creating a system where builders can apply their own fitting philosophies in an automated way. There is no expectation that builders will take the default values in the BikeCAD Pro Fit Advisor as gospel. Still, it is hoped that the default <a href="https://www.bikecad.ca/fit_advisor">Fit Advisor</a> values will yield good geometry for a wide range of riders. Therefore, if you have feedback or suggestions to improve the Fit Advisor in <a href="https://www.bikecad.ca/bikecadpro">BikeCAD Pro</a> it would be great if you could share your thoughts in the BikeCAD <a href="https://www.bikecad.ca/forum/5">Forum</a>.</div></div></div><div class="field field-name-field-tags field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/98">Fit advisor</a></div><div class="field-item odd"><a href="/taxonomy/term/99">fit adviser</a></div><div class="field-item even"><a href="/taxonomy/term/188">formula</a></div><div class="field-item odd"><a href="/taxonomy/term/109">bicycle</a></div><div class="field-item even"><a href="/taxonomy/term/100">fitting</a></div></div></div>Sat, 22 Oct 2011 21:35:35 +0000bcurry1942 at https://www.bikecad.cahttps://www.bikecad.ca/customizing_fit_formulas#commentsTire Diameters: Understanding
https://www.bikecad.ca/tire_diameters
<div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><img src="https://www.bikecad.ca/faqFiles/standard_wheel_menu.png" width="138" height="170" alt="Standard wheel menu" title="Standard wheel menu" class="blackborder" style="float: right; margin: 0 0 5px 6px;" />
<p>The library of standard wheels in BikeCAD serves as a good reference for the tire diameters of numerous standard tires. These diameter values have been determined by physically measuring numerous sample wheels. It should be understood that actual wheel diameters can vary greatly between different tire brands and models. When in doubt, be sure to measure the diameter of the wheels you plan to use.</p>
<p>It has sometimes been assumed that one should be able to calculate the wheel diameter from the published ISO bead seat diameter of the rim and the published width of the tire. For example, a 700c rim has an ISO bead seat diameter of 622 mm. If that rim is fitted with a 700 x 23c tire, some have assumed that the overall diameter of the wheel would be 622 mm + 2 * 23 mm = 668 mm. While this sort of makes sense, it just never seems to work out. Remember, the tire company only publishes the width of the tire. (It should be noted that even the published width dimension does not always accurately reflect the true width.) And of course, the height of the tire may be different than the width.</p>
<p>Again, when in doubt, measure your own wheels!</p>
<div style="clear: both;"></div></div></div></div><div class="field field-name-field-tags field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/107">tire diameter</a></div><div class="field-item odd"><a href="/taxonomy/term/108">wheels</a></div><div class="field-item even"><a href="/taxonomy/term/109">bicycle</a></div><div class="field-item odd"><a href="/taxonomy/term/104">dimensions</a></div><div class="field-item even"><a href="/taxonomy/term/110">700c</a></div></div></div>Tue, 27 Sep 2011 20:27:09 +0000bcurry1020 at https://www.bikecad.cahttps://www.bikecad.ca/tire_diameters#comments