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Cross frame sizing chart: use this to estimate your frame size

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Cross frame sizing chart: use this to estimate your frame size

Old 07-25-07, 10:07 AM
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Cross frame sizing chart: use this to estimate your frame size

I've gone through most of the posts where ppl have reported their height/inseam measurements and what frame size they are on (including model). Hopefully this will help those who are trying to determine what size frame they should be looking at.

I'll keep this document updated as more ppl post their data.
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Old 07-25-07, 10:19 AM
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Just realized not everyone may want to d/l word documents so here's a screenshot instead.
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Old 07-25-07, 12:04 PM
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I'm 70" with an inseam of 32" my poprad is a 54 and fits perfect.
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Old 07-25-07, 01:09 PM
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At the risk of over-simplifying, I've plotted frame size versus height; seems to show a good correlation. To use, find your height on the bottom axis and then draw a straight line up to meet the red line, then move left to find your frame size. I would say accuracy is plus or minus 1 cm. Should get much better as I add more data. Keep the numbers coming!
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Old 07-25-07, 07:52 PM
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I wonder if the chart would be better if you plotted cycling inseam vs. frame size. Can you try that and post it? It would be interesting to see the correlation there as opposed to height.
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Old 07-25-07, 08:06 PM
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Bike: Specialized S-Works Tricross
Frame Size: 54 cm
Height: 70 in
Inseam: 32 in

Comments:
Nice upright riding position for urban commuting. Position is cramped when down in the drops. Suppose if I wanted to favor fast road riding over commuting I would change to a longer stem.
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Old 07-26-07, 07:18 AM
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My LBS has a 2007 54CM Tricross Sport. I rode it for a few miles and really felt comfortable on it. I felt like I was stretched in the drops properly and the standover was perfect. My height is 69 inches with a 32 inch inseam.

When I can finally afford it that is most likely the size I will buy.
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Old 07-26-07, 07:29 AM
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Bike: Devinci Tosca
Frame Size: M/55 (effective top tube length)
Height: 70"
Inseam: 33.5"

Obviously I've got long legs and a short torso. I opted for the Tosca because it's a "medium" frame with a really tall headtube (140mm). Paired up with a 90mm or 100mm stem (depending on the rise) I've got a comfortable reach and I don't have to deal with excessive drop down to the bars. I see a lot of steel frame sets out there that I'd love other than the fact that the miniscule headtube length basically makes the bike unrideable for me (I don't consider pushing the number of steerer tube spacers to the limit of safety + the highest rise stem I can find an acceptable solution ... I don't like maxing out frames to get the fit right).
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Old 07-26-07, 10:19 AM
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MillCreek, frame vs inseam correlation is not as clear. Not sure why this is...my guess is that ppl choose sizes based more on comfortable reach to the handlebars rather than standover (as long as there's enough).
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Old 07-26-07, 10:22 AM
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Here's the latest plot. For you statisticians, Rsquare = .71 (vs .67 last time) Which means the line fit (in red) is getting more accurate with more data, so keep the numbers coming!
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Old 07-26-07, 10:44 AM
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Originally Posted by Sir Bikesalot
MillCreek, frame vs inseam correlation is not as clear. Not sure why this is...my guess is that ppl choose sizes based more on comfortable reach to the handlebars rather than standover (as long as there's enough).
Wow, that is interesting. I wonder if traditional vs. compact geometry can also account for the differences. Although I have not done an extensive study, it is my impression that a lot of today's cyclocross bikes are with compact geometry, in conjunction with so many of today's road bikes. I am a traditional geometry fan, myself.
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Old 07-26-07, 11:17 AM
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Actually I couldn't help but notice that if I took out the Surly Cross Check data, the frame vs. inseam plot turns out much better. Maybe because Surly measures their frame from BB to TT instead of seat post?
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Old 07-26-07, 01:58 PM
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Originally Posted by Sir Bikesalot
Rsquare = .71 (vs .67 last time) Which means the line fit (in red) is getting more accurate with more data
This interpretation of R^2 is common, but wrong.

R^2 is the percentage of the variance in frame size explained by rider inseam. It needn't increase with an increase in sample size. Even if you gathered data from a million riders, there would still be points scattered around the regression line because of other factors--personal dogma, bike geometry, frame availability, etc--which are responsible for roughly 30% of the variance in frame size.
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Old 07-26-07, 02:04 PM
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Originally Posted by Sir Bikesalot
Actually I couldn't help but notice that if I took out the Surly Cross Check data, the frame vs. inseam plot turns out much better. Maybe because Surly measures their frame from BB to TT instead of seat post?
My suspicion is that people are talking about two different inseam measurements, one being public bone height, and the other being the pants inseam length.
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Old 07-26-07, 02:29 PM
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Why doesn't your chart go any lower than 30"?

The inseam measurement on my pants is 27.5". I have to buy 30" pants and then have them altered.
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Old 07-26-07, 02:40 PM
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Originally Posted by flargle
My suspicion is that people are talking about two different inseam measurements, one being public bone height, and the other being the pants inseam length.
Always a distinct possibility. Many people are unclear as to the difference between the 'cycling inseam' and the 'pants inseam'. I always quote my cycling inseam of 32", as opposed to my pants inseam of 30".
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Old 07-27-07, 09:54 AM
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Originally Posted by jasonguard
Why doesn't your chart go any lower than 30"?

The inseam measurement on my pants is 27.5". I have to buy 30" pants and then have them altered.
Here you go. Looks like you might want to start with 48-50cm. If you're closer to 5'6" I'd go with the 50cm, if closer to 5'4" then 48cm. If you're taller than 5'6", then you have a long torso and should look at possibly 52cm even.
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Old 07-27-07, 10:47 AM
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Originally Posted by flargle
This interpretation of R^2 is common, but wrong.

R^2 is the percentage of the variance in frame size explained by rider inseam. It needn't increase with an increase in sample size. Even if you gathered data from a million riders, there would still be points scattered around the regression line because of other factors--personal dogma, bike geometry, frame availability, etc--which are responsible for roughly 30% of the variance in frame size.
Good info about Rsquare. You're right that it needn't increase with sample size, however, I think we're in a regime in which the current sample size is insufficient to represent the actual mean and variation of the parent population. The fact that Rsquare is increasing with more data so far is encouraging though, and indicates to me that the linear dependency is strong enough to show through the other factors you mentioned that contribute to the variance.
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Old 07-27-07, 10:49 AM
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All I have to add is that this is great and thanks for doing this Sir Bikesalot. I'll post my data once I get my frame picked out. I'm 6'1.5" and have an inseam of 32, I'm guessing between 56-58 cm size frame (58cm top tube length should fit me) will work. I rode a 58cm Motobecane fantom cross last night on the road and it was pretty comfortable. I'll have to try some mounts and dismounts later this weekend to see if it will work.
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Old 08-03-07, 10:24 AM
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Thanks El Duke, my hope was that ppl would find it useful for narrowing down their possible frame size and it looks like it might actually be working!

Here's the latest plots. Use the following preocedure to get the most accurate estimate: 1) Find your frame size using both plots; 2) average the two numbers to get the final result. For example, I come out with 59cm (6'2", 35").
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Old 08-03-07, 10:37 AM
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This is a great attempt at some difficult data gathering/crunching. If you'd like to add the Fuji Cross Pro (and Comp), the Lemond Poprad, and the Spec TriCross Comp, here are my meausurements. I am a 34.5 true inseam (but 32 in pants), and 6'0. I just bought a 58 Cross Pro. The 56 was ok, but the 58 was absolutely ideal. Same with the TriCross-58. 57 in the Lemond. Hope this helps. Good job!
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Old 08-03-07, 10:59 AM
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Okay, I am 6'1" and just finished the fit calculator on competitivecyclist.com. Here's the results from my body measurements:

Measurements
-------------------------------------------
Inseam: 33.75
Trunk: 25.625
Forearm: 14
Arm: 26.625
Thigh: 26
Lower Leg: 22.75
Sternal Notch: 60.75
Total Body Height: 73


The Competitive Fit (cm)
-------------------------------------------
Seat tube range c-c: 55.5 - 56.0
Seat tube range c-t: 57.2 - 57.7
Top tube length: 54.9 - 55.3
Stem Length: 11.5 - 12.1
BB-Saddle Position: 73.4 - 75.4
Saddle-Handlebar: 54.7 - 55.3
Saddle Setback: 6.8 - 7.2
Seatpost Type: SETBACK


The Eddy Fit (cm)
-------------------------------------------
Seat tube range c-c: 56.7 - 57.2
Seat tube range c-t: 58.4 - 58.9
Top tube length: 54.9 - 55.3
Stem Length: 10.4 - 11.0
BB-Saddle Position: 72.6 - 74.6
Saddle-Handlebar: 55.5 - 56.1
Saddle Setback: 8.0 - 8.4
Seatpost Type: SETBACK


The French Fit (cm)
-------------------------------------------
Seat tube range c-c: 58.4 - 58.9
Seat tube range c-t: 60.1 - 60.6
Top tube length: 56.1 - 56.5
Stem Length: 10.6 - 11.2
BB-Saddle Position: 70.9 - 72.9
Saddle-Handlebar: 57.2 - 57.8
Saddle Setback: 7.5 - 7.9
Seatpost Type: SETBACK

I have found a good deal on a 56 cm Ridley Crossbow frame, which I am pretty sure I will be able to set-up for a good fit. I suggest that everyone at least try the fit calculator at competitivecyclist, just for knowlegde sake and to take the guess work out of sizing/fitting.
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Old 08-06-07, 09:34 AM
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This is interesting, and I have a question.

I'm looking at an IRO Rob Roy. Tony says I should get the 58. I'm 5'10" with about a 32 cycling inseam (I wear 30 pants). I've got a pretty average torso, and actually shortish arms.

I know IRO measures differently, and Tony has this frame's S/T c-c listed as 54 cm and a 32" standover. That puts me restin' the package on the top tube when I straddle the bike.

What do y'all think?
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Old 08-06-07, 10:00 AM
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Originally Posted by climbhoser
This is interesting, and I have a question.

I'm looking at an IRO Rob Roy. Tony says I should get the 58. I'm 5'10" with about a 32 cycling inseam (I wear 30 pants). I've got a pretty average torso, and actually shortish arms.

I know IRO measures differently, and Tony has this frame's S/T c-c listed as 54 cm and a 32" standover. That puts me restin' the package on the top tube when I straddle the bike.

What do y'all think?
Hmm, you and I sound like pretty much the same size, and I have a sleeve length of 32/33". That being said, I wonder if the frame you are looking at is a bit on the large size. Depending on the geometry and how they measure, I would probably be looking at the 54 to 56 cm. range.
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Old 08-06-07, 10:12 AM
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Originally Posted by climbhoser
I'm 5'10" with about a 32 cycling inseam
I'm skeptical of these measurements. 32" seems low for somebody of your height.

My recommendation is to take a careful set of measurements by closely following these instructions:
https://zinncycles.com/fitsystems/DimensionPage.aspx
Enter them here:
https://zinncycles.com/fitsystems/default_ie.aspx
And then post the results.
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