Confusion with competitive cyclist fit calculator
07-28-18, 08:56 AM
#1
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Confusion with competitive cyclist fit calculator
Probably most people are familiar with the competitive cyclist fit calculator here: https://www.competitivecyclist.com/S...rBike.jsp#type
I've played around with this calculator a bit in the past but dove back into it again recently. My wife measured me and we got these numbers in inches:
actual inseam 36
trunk 24.75
forearm 14.375
arm 27.625
thigh 25
lower leg 23.25
sternal notch 59.5
total height 72.25
Putting that in as a male, on a road bike, these are the results for the "French fit", just because the frame measurements actually match a frame I have (numbers in cm... I'd post the other fit numbers, but formatting a table here is too much of a pain):
seat tube C-T 64 - 64.5
stem length 10.8 - 11.4
BB-saddle position 80.8 - 82.8
Saddle-handlebar 58.2 - 58.8
saddle setback 7.6 - 8
seatpost type: setback
Yes, I am long legged and shorter torso. I also know that these sort of things are only supposed to be a guideline, and I don't have any problem fitting a bike to me and being comfortable while riding, but I'd like to give some other fitting philosophies a try. What I'm finding is that the results don't even seem to be something I can make on a bike...
For example, say I'd like to set up a bike like the "French fit". I have a bike with a top tube and seat tube that match the calculator, but when I put the saddle setback in the region indicated, the saddle-handlebar measurement is about 52.x cm, not the 58.x cm recommended... 6cm is more than I can explain even if the seat tube angle is a few degrees different.
I'm finding similar problems with the other fit styles also in that the top tube + stem measurements don't seem to work with the saddle-bar reach. Obviously my body geometry isn't average, so I'm wondering if that is causing something in their calculator to give bad results? Have other people used the numbers from this website and had them work as something that can even be assembled on a bike? I'm thinking of ignoring the stem length and just adjusting based off seat tube length, saddle setback and bar reach but was interested what insights others had on this.
I've played around with this calculator a bit in the past but dove back into it again recently. My wife measured me and we got these numbers in inches:
actual inseam 36
trunk 24.75
forearm 14.375
arm 27.625
thigh 25
lower leg 23.25
sternal notch 59.5
total height 72.25
Putting that in as a male, on a road bike, these are the results for the "French fit", just because the frame measurements actually match a frame I have (numbers in cm... I'd post the other fit numbers, but formatting a table here is too much of a pain):
Top tube 57.1 - 57.5
seat tube C-C 62.1 - 62.6seat tube C-T 64 - 64.5
stem length 10.8 - 11.4
BB-saddle position 80.8 - 82.8
Saddle-handlebar 58.2 - 58.8
saddle setback 7.6 - 8
seatpost type: setback
Yes, I am long legged and shorter torso. I also know that these sort of things are only supposed to be a guideline, and I don't have any problem fitting a bike to me and being comfortable while riding, but I'd like to give some other fitting philosophies a try. What I'm finding is that the results don't even seem to be something I can make on a bike...
For example, say I'd like to set up a bike like the "French fit". I have a bike with a top tube and seat tube that match the calculator, but when I put the saddle setback in the region indicated, the saddle-handlebar measurement is about 52.x cm, not the 58.x cm recommended... 6cm is more than I can explain even if the seat tube angle is a few degrees different.
I'm finding similar problems with the other fit styles also in that the top tube + stem measurements don't seem to work with the saddle-bar reach. Obviously my body geometry isn't average, so I'm wondering if that is causing something in their calculator to give bad results? Have other people used the numbers from this website and had them work as something that can even be assembled on a bike? I'm thinking of ignoring the stem length and just adjusting based off seat tube length, saddle setback and bar reach but was interested what insights others had on this.
07-28-18, 09:35 AM
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IMO saddle setback measurement is kinda silly, as it uses saddle TIP as a reference.
Questionable, as saddles flare at different rates.
It’s where your sit bones go that matters, and that can vary considerably between saddles.
I don’t care about saddle tip as a reference unless I’m using the same saddle and want to repeat the fit of one bike on another.
Questionable, as saddles flare at different rates.
It’s where your sit bones go that matters, and that can vary considerably between saddles.
I don’t care about saddle tip as a reference unless I’m using the same saddle and want to repeat the fit of one bike on another.
07-28-18, 12:27 PM
#3
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Fair enough, but saddles don't generally vary by 6cm (2.3 inches) worth that it would take to make the numbers fall into sync! It's also a convenient reference point since I really can't tell exactly where my sit bones fall on a saddle to judge reach to the bars, so I'm willing to work with the saddle tip to get things started.
07-30-18, 03:34 PM
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I was just having trouble with this calculator myself. I have access to drafting software at work, so (instead of working) I plotted the fit measurements for my recommendation. I used the end of each range and assumptions on seat/stem angles that would result in the shortest horizontal top tube measurement. Long story short I could not get a resulting top tube length within the recommended range, it was always too long. To force the longest recommended top tube length i needed a saddle to bar drop of over 17cm. Which is unreasonable for the "Eddy fit" numbers i was using.
This is the same error as yours, just evaluated focusing on top tube instead of saddle-bar. Imagine if you slid the top tube connection down the seat tube, bringing the stem/handlebar with it. Your saddle-bar drop increases, and your saddle-bar reach increases due to the angle of the seat tube. Eventually you will get to your 58 cm reach recommendation, but not until your drop is unrealistic.
So it appears that the algorithm used for each fit measurement is calculated independently and does not have "checks" against each other to make sure they add up in the real world. It's not a "full system" calculation, if that makes any sense.
This is the same error as yours, just evaluated focusing on top tube instead of saddle-bar. Imagine if you slid the top tube connection down the seat tube, bringing the stem/handlebar with it. Your saddle-bar drop increases, and your saddle-bar reach increases due to the angle of the seat tube. Eventually you will get to your 58 cm reach recommendation, but not until your drop is unrealistic.
So it appears that the algorithm used for each fit measurement is calculated independently and does not have "checks" against each other to make sure they add up in the real world. It's not a "full system" calculation, if that makes any sense.
07-31-18, 08:28 AM
#5
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Cool, glad I'm not the only one! I've been thinking the same thing that their calculations for stem and top tube length may just be based off one or two body measurements and have no relation to each other. Are your proportions outside of average as well, perhaps?
I've been focusing on bar reach and throwing out top tube length in trying these. 58cm reach to the bar is a lot, but I'm finding it interesting to try the different fit styles anyways. I would love if gave a knee-pedal offset number instead of saddle setback
I've been focusing on bar reach and throwing out top tube length in trying these. 58cm reach to the bar is a lot, but I'm finding it interesting to try the different fit styles anyways. I would love if gave a knee-pedal offset number instead of saddle setback
07-31-18, 10:28 AM
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We are roughly the same height. I have kind-of long legs (yours are crazy long seems like). I have much shorter arm reach though, so my reach numbers are way lower than yours despite a longer trunk. It's telling me I need a 54cm top tube. I'm not super confident in my arm reach measurement. It may be the easiest to mess up since there is a ton of variation in shoulder position.
I think the saddle-bar reach and seat height may be usable, but not the rest. Unfortunately i wanted to use it to size a frame to buy online. Without stack/reach output or an accurate top tube result it's worthless for me.
Actual Inseam 34.625 In
Trunk 25.5 In
Forearm 13 In
Arm 25 In
Thigh 24 In
Lower Leg 22.625 In
Sternal Notch 59.5 In
Eddy Fit
Top Tube Length 53.8 - 54.2 Cm
Seat Tube Range CC 58.2 - 58.7 Cm
Seat Tube Range CT 59.9 - 60.4 Cm
Stem Length 10.1 - 10.7 Cm
BB Saddle Position 80.4 - 82.4 Cm
Saddle Handlebar 53.2 - 53.8 Cm
Saddle Setback 6.7 - 7.1 Cm
Seatpost Type Setback
Total Height 72 In
I think the saddle-bar reach and seat height may be usable, but not the rest. Unfortunately i wanted to use it to size a frame to buy online. Without stack/reach output or an accurate top tube result it's worthless for me.
Actual Inseam 34.625 In
Trunk 25.5 In
Forearm 13 In
Arm 25 In
Thigh 24 In
Lower Leg 22.625 In
Sternal Notch 59.5 In
Eddy Fit
Top Tube Length 53.8 - 54.2 Cm
Seat Tube Range CC 58.2 - 58.7 Cm
Seat Tube Range CT 59.9 - 60.4 Cm
Stem Length 10.1 - 10.7 Cm
BB Saddle Position 80.4 - 82.4 Cm
Saddle Handlebar 53.2 - 53.8 Cm
Saddle Setback 6.7 - 7.1 Cm
Seatpost Type Setback
Total Height 72 In
08-02-18, 08:08 AM
#7
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Thread Starter
We are roughly the same height. I have kind-of long legs (yours are crazy long seems like). I have much shorter arm reach though, so my reach numbers are way lower than yours despite a longer trunk. It's telling me I need a 54cm top tube. I'm not super confident in my arm reach measurement. It may be the easiest to mess up since there is a ton of variation in shoulder position.
I think the saddle-bar reach and seat height may be usable, but not the rest. Unfortunately i wanted to use it to size a frame to buy online. Without stack/reach output or an accurate top tube result it's worthless for me.
I think the saddle-bar reach and seat height may be usable, but not the rest. Unfortunately i wanted to use it to size a frame to buy online. Without stack/reach output or an accurate top tube result it's worthless for me.
I'm basically where you're at in terms of implementing their numbers, but I'd add setback to the numbers to use. The combination of saddle height and setback is what results in the ultimate distance from your hips to the crank. The end result we're looking for after all is where your hips go in relation to the crank, and where your bas are in relation to your hips.
Yes, the calculator would be far more useful with a stack/reach output. I did take saddle-bar reach and subtract both stem and saddle setback to approximate reach as well as work some trig off seat tube length and an assumed tube angle to approximate stack. Each of the fit styles did have a separate range for stack and reach when I did that, so there's some consistency.
Knee/pedal offset and crankarm length would be a nice output also instead of saddle setback. I suspect there is a lot of black art comes into the picture though.
