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  1. #1
    pvd
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    PVD/RAD. Refined.

    Ok folks,

    It's been a while and this keeps coming up in my world. An attempt has been made to clarify the concepts and reduce confusion.

    We also figured out how to take the body measurements to be repeatable and more foolproof.

    Let me know what you think and where you see the confusion so that I can get this right.

    PVD/RAD Refined | Peter Verdone Designs


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    Quote Originally Posted by pvd View Post
    Ok folks,

    It's been a while and this keeps coming up in my world. An attempt has been made to clarify the concepts and reduce confusion.

    We also figured out how to take the body measurements to be repeatable and more foolproof.

    Let me know what you think and where you see the confusion so that I can get this right.

    PVD/RAD Refined | Peter Verdone Designs

    This is brilliant!

    Though I have to restudy it, in order to familiarize the procedure.

    One thought about the use of “statistical” reference. I can only assume that these figures (about the body angle and more) are affected also by the current fashion over our sport. I mean, that if we take a look at the same values, published at the 90’s these figures will be quite different…
    Of course,
    now we know more.

    T hank's for sharing.

    UncaJohn
    Hey!
    Here at Athens, there are some idiots who are buying smaller size frames (by whatever values they are following) and equip them with really long stems. The current belief in those circles is that one may save a few grammars by following this stupid idea!
    I keep wondering how much weight they really save (adding the longish stem) and what havoc this set up will bring over the handling of their bikes.
    On the other hand you cannot argue with the stupid...

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    Interesting! I like the simplified method of finding arm length.

    So to be clear, what you term "body angle" is the angle of a line drawn between the shoulder pivot and crank axis?

    I really like it! I like the simplification of fit down to three key points. I'd like to play around with including a second triangle with measurements from a current bike they ride. A triangle drawn from the center of the crank axis to the center of the saddle clamp, to the center of their handlebar clamp. Three points that shouldn't be too hard for someone to measure on their own. Basically I'm wondering if you can use the two triangles to approximate the position of their hip pivot point, giving you pretty accurate data on what their exact current riding position is.

    I'm going to try this out. Thanks for the writeup Peter!
    Myth Cycles handbuilt bike frames
    Durango, CO
    http://www.mythcycles.com

  4. #4
    pvd
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    Quote Originally Posted by Erichimedes View Post
    A triangle drawn from the center of the crank axis to the center of the saddle clamp, to the center of their handlebar clamp.!
    The saddle is a whole different animal as for mountain biking, during the action, it's not a factor. It is at other times and can influence the bar position due to core and arm strength but I tend to go with 74 degree effective on hardtail in NorCal. It would be steeper in PNW. Things get a little different with saddles.

  5. #5
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    I got your RAD right here

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    PVD/RAD. Refined.-msub_gallery_teamriders.jpg
    "The challenge is not in developing new ideas, but in escaping old ideas."

  6. #6
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    Dayum! Them lengthy tube arrangements connecting the handlebar to the fork steerer be increasing RAD by over 100,000 microns! Where they get them futuristic things?
    "The challenge is not in developing new ideas, but in escaping old ideas."

  7. #7
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    The one question I had when drawing these diagrams up when you first wrote about them is why isn't the crankarm section drawn as vertical?

    It certainly simplifies things and I don't see it affecting things as a system. Your back and arm angle ranges would shift slightly.

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    I ran some numbers with my latest position (XL Big Honzo, fork boosted to 140, dropper shimmed to 130 and slammed)

    Broomstick fit resulted in 1450 body, 650 arm

    Handlebar grip center is 515x, 678y.

    That gives body angle of 79.2, arm angle of 35.6, which seems about right for more of a flexible XC position.

    When I measured the bike I got 870 for grip radius, which doesn't match the X/Y, so I'm going to remeasure everything.

    Using 81 and 33.6 the suggested fit is 472 on X, which seems short even if I had a more normal seat tube angle.

  9. #9
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    Quote Originally Posted by Varaxis View Post
    I got your RAD right here

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    Click image for larger version. 

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    Hey!
    I've done the same with my old San Andreas. I removed the seatpost subframe and gave it a go for a week.
    It didn't work.

    UncaJohn

  10. #10
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    Also why measure with your feet at your Q factor, but not staggered like they're on pedals? Again it just shifts your angle ranges so it's a wash, and if you're by yourself it's easy to do the measurement by standing on a ruler and running the string under that so it has a little tension.

  11. #11
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    not sure if Lee McCormack trademarked Rider Area Distance aka RAD. worth considering.

    I'll try these measurements and let you know what I find. I spent a lot of time working with Lee's calculator and have my RAD pretty accurate by his standards. it makes my bike fit in a pretty "compact" way, but that suits me for some reason.

    why do people insist on lousy fitting methods and other things? Sunk Cost Fallacy.

    Just remembered I posted this thread about Effective Down Tube a while back. it will catch on.
    Last edited by mack_turtle; 2 Weeks Ago at 09:21 AM.

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    I think you mixed the calculation for arm/ body lengths on the blog. the numbers I got didn't make any sense when I used it as described. it made sense after I swapped the meaning of these numbers:

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    NOPE, NEVERMIND. THOSE ARE CORRECT

    I drilled a hole in a broomstick as a reference point and measured 380mm in each direction to mimic my 760mm handlebar and masking-taped the "ends" of the handlebar. then I stood on a yardstick with my unshod feet about 6 inches apart and staggered 14 inches to mimic the position I would stand on pedals.

    I hooked a measuring tape under the yard stick and held the broomstick in the air like Moses parting the red sea. my wife stood on a chair and measured several times and got 2032 mm from the floor to the center of the broomstick. taping the level to the broomstick might help some as well.

    Then I dropped the broomstick down low with my hands at the same distance and measured 794 mm to the ground. I am about 5'9" 1740mm tall overall, if that helps for reference.

    I simply cut and paste the formulas and format you shared into a spreadsheet and got numbers that make sense in relation to the ones you shared for your own riders. I think we need more explanation of the body angle and arm angles. I don't know which to choose from your range, but I tried a few variations to see how it would affect the results.

    PVD/RAD. Refined.-screen-shot-2020-05-26-7.45.18-pm.png

    to get more accurate X, Y, and RAD measurements on your bike:

    1. stand the bike up in against a wall with the rear tire touching a wall behind it. put the bike in a trainer of you have one and level the front and rear axles. (would it be helpful at this point to set the fork at sag height on a hardtail?)

    because we don't hold the grips at the ends, I would recommend measuring to the bottom of the end of the grip to account for "upsweep" in the vertical measurement, and the front end of the grip to account for backsweep for the horizontal measurement. this is not precise, but up & back sweep could throw the number off by up to 10 mm if you use the center of the end of the grip.

    2. measure vertically from the ground to the center of the grip. then measure from the ground to the center of the BB. subtract the second number from the first. that's your BB-grip Y-axis.
    3. measure horizontally from the back wall to the center of your grip. then measure from the back wall to your BB. subtract the second number from the first. that's your BB-grip X-axis.
    4. use a little trig to determine the hypotenuse of those two lengths and the angle.
    5. confirm that BB-grip length with your measuring tape. the tricky part is that you have to find the and of the line from your BB to the grips by find the midpoint between the grips. this is a space in the air, so you can lay a flat object (that broomstick you were just using would work) and measure to a spot about 1 cm below the center. if you measured and calculated correctly, those should be about the same.

    all of this is VERY similar to the way Lee McCormack measures things, but his philosophy on bike fit, as you noted, is different. maybe it's wrong or just out of date, but it's very similar.

    regarding the formula on the Pinkbike article, that's an average based on the many bike fits he's done. He has a more complex calculator on his (paid) website that takes into account arm length and other factors: handlebar dimensions that creat the overall "setback" like sweep angles and width, the height of the stem clamp, spacer and headset stack height, arm and leg dimensions, etc. you might still disagree with the result, but it's a similar approach.

    I have been trying to get people to start using "effective downtube" (hypotenuse of the frame reach and stack) and downtube angle to measure frames for a long time. I've been calling the reach and stack from the BB to the grips eReach and eStack for a while, but I don't think much of that is catching on. most people are content to measure their bikes using the saddle as a reference point, which is utter bollocks, of course. I am glad to see PVD has given it some serious thought. hopefully some of this will make it into the lexicon.
    Last edited by mack_turtle; 1 Week Ago at 02:13 PM.

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    I used Lee's more detailed calculator a while back and he recommended for my height of 1740 mm:

    handlebar 770mm wide
    RAD of 780
    stack 660
    reach of 420

    PVD/RAD. Refined.-screen-shot-2020-05-26-7.34.41-pm.png

    in short, your formula gets me on a much longer reach and a slightly higher stack. as a matter of fact, if you take my LLB measurements and just expand them to 105% larger, you get the PVD method's measurements.

    If you take Lee's simplified formula, your height in cm x 4.47, I get 777.78 (174*4.47). I've been rounding that to 780.

    If I reverse your calculations, I get a factor (?) of 5.04. I wonder if you get enough data, that you'll start to see a pattern that might find that one can find a PVD "RAD" fit by dividing their height by 5. you can make a bike fit that crank-grip length in several ways with different heights and lengths using handlebar and stem dimensions, so long as the hypotenuse remains the same.

    not everyone is good with spreadsheets. If you want to gather a lot of data, create one that people can download or an online form that will record the findings for your records and spit out some numbers that readers can use.

    Hope all that helps.
    Last edited by mack_turtle; 1 Week Ago at 05:51 PM.

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    i think our motivation may be at cross-purposes, as you're a frame designer/ builder who would want to build a frame based on the contact points that are ideal for the rider. my interest would be to find off-the-peg bikes that fit me, and find way to help other riders do the same.

    Oddly enough, I have had two professional fits done on my bike:
    in studio, on the bike. fitter put my bike on a trainer and moved my 5' 9" self (5' 8.5"?) around on the bike. it was a medium Niner Ros9, which has a pretty tall stack and short reach. I had a 70mm stem on it with a 25mm riser. the details are unimportant, but he insisted on putting a 100mm stem, angled down, with a no-rise handlebar. the result was a RAD of about 820mm. (he also insisted on shoving my cleats waaaay forward under my toes, presumably for achieve KOPS—ugh.) the bike fit me better, but that long stem + wide bar put the handling in the toilet. I asked him if I should stop for a new, longer frame for my riding style and he said I should ride the ROS 9 with a long stem. He could have sold me a frame but he left it there. weird.

    the second was on a Retul fit system. He put my own handlebar, pedals, and saddle in the and machine and motion capture camera did the same. I was trying to set up a medium Vassago Jabberwocky to fit me, which has a considerably longer reach. the result was a 80mm stem with the low handlebar, resulting in a RAD of ... you guessed it, 820mm.

    I am currently on a medium Karate Monkey, which has a much shorter reach and stack than the other two due to high BB, shorter front end. I have it set up with a 50mm stem, handlebar low, and the result is close to the 780mm RAD that Lee's method recommends. I measured the the effective reach and effective stack and they are 410mm and 660mm. I have a SQlabs 12º handlebar, so the rotation affects the reach and stack by quite a bit. I have no science to back this up other than it works for me. maybe a tad cramped. I think a modern medium frame with a 450mm reach would be unrideable for me, but perhaps I could learn to embrace it.

    the interesting thing is that your fitting scheme matches what two fitters have confirmed, but I have rejected that fit in favor of something more compact. I'm a pretty capable rider but definitely middle of the pack. I ride singlespeed with some folks who just mop the floor with my abilities, but that is about time in the saddle more than anything, of course.

    In context: I don't have access to flowy trails, mountains, or much in the way of jumps. lots of slow chunk and ledgy trials stuff. I have horrible flexibility. the more compact fit suits me, but I could go longer. too much longer and I don't know if I would like it.

    Hope that gives you some data to work with.
    Last edited by mack_turtle; 2 Weeks Ago at 04:13 AM.

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    edited above.
    Last edited by mack_turtle; 1 Week Ago at 05:52 PM.

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    The author should at least give Lee McCormack credit for the definition of RAD
    :-)

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    Lee McCormack's diagram illustrating "handlebar setback"

    On the topic of handlebars: their shape affects reach and rise. a handlebar 780 wide with 9º of backsweep is have a different affect on the reach than a handlebar of the same width and shape as one with 12º. this is likely why some companies make some handlebars with extra backsweep with a forward wiggle. throw in the variations that come with the bar rotation and you have a lot of variables there. If I remember correctly, Lee was riding a SQlabs 16º low riser for his wrist orientation and the reach-shortening affect.

    question: If a bike with one handlebar fits and handles well but the riders decides to use a handlebar that has more sweep and a resulting shorter reach, can the rider use a longer stem to push the reach back out without affecting handling? what's more important for handling: stem length or where the hands end up relative to the steering axis? (not sure if I am describing that accurately, but correct my terminology if it's off-base.)

    What Bars? The Bicycle Handlebar Database needs a lot more data point to be useful, but it's a good start. not a lot of conventional handlebars on there yet.

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    Stem length by itself has no effect - it's where your hands end up.

    Coincidentally I just switched to the SQLab 16 bars and needed a 60mm stem to get my hands in the right place.

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    I illustrate my point, here are two handlebar that I own:

    The Answer handlebar is "flat" and has a 8°/4° back/up sweep and is 750mm wide, measured at the aft-facing tips of the grip tube. I stood it up on the floor and leaned it against a wall as best as I could to simulate the maximum backsweep of the shape. eyeballing it with a small metric ruler, the "setback" of the bar at the tips is about 50mm.

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    The SQLabs bar that I have had on my bike for a long time has 15mm rise 12°/4° back/up and is 755mm wide when measured in the same spot as the bar above. measuring the setback in the same way as above, it's more like 70mm.

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    (I removed the grips but left the bell in position. that has to be perfect!)

    The actual measurement of "setback" is useless in isolation, but the difference in affect on reach on two handlebars of the same length but different angles in this case is 20mm!

    I bought the SQLabs bar partially because I liked the angle (reminds me of a typical BMX handlebar) but I felt that the reach-reducing fact would be helpful to keep the fit on my bike compact. with a 50mm stem, that puts my hands on the grips right in line with the steerer tube. I am not sure how this affects my riding, but it's not holding me back. If I were to put a 70mm stem on my bike, that would put my hands closer to being in line with my axle. again, I am not sure if that means what I think it means.

    if dr.welby is correct, I should effectively have the same fit and steering with the 8° handlebar and a 50mm stem, or the 12° handlebar and a 70mm stem. does that check out?

    relevant? Exploring the Relationship Between Handlebar vs Stem Length

    Dialing in your Steering/Hands Offset by Lee McCormack


    If I hold the very back tips of my SQ 12° handlebar, those line up just a few millimeters befind my steering axis.

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    I should have made the handlebar line up with the tiles on the floor. sorry.

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    with my hands in a rational place, it's safe to say that a 50mm stem with this handlebar in a neutral up/back position puts my hands right about in line with the steering axis. lengthening of shortening the stem would put my hands in front of or behind it in a predicable way with the same handlebar. anyone care to make any statements about where the ideal SHO position is for different applications?

    obviously road bikes have a very broad range of SHO. riding on the hoods puts your hands pretty far out, but riding the ends of the bar put your hands close to the steering axis on most modern compact drop bars. for a bike that effectively only has one hand position, is it ever advantageous be put that position behind the steering axis? in front? how much?

    Quote Originally Posted by dr.welby View Post

    Coincidentally I just switched to the SQLab 16 bars and needed a 60mm stem to get my hands in the right place.
    What was the stem length before? do you have an idea of what the setback of the old and new handlebars is?
    Last edited by mack_turtle; 1 Week Ago at 02:13 PM.

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    It had a 50 with stock Kona 9/5 handlebars. I didn't measure the bars before I installed them. The 50 stem was a 35mm bar, so I tried the SQLabs with a 31.8 45mm stem I had and that was too short. I ended up with a 60, and took out a 10mm spacer under the stem too.

    I think with modern bar widths in the 760-800mm range differences in handling from having you hands in front of or behind the steerer tube's center axis by ~30mm or so are very minor.

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    Quote Originally Posted by dr.welby View Post
    I think with modern bar widths in the 760-800mm range differences in handling from having you hands in front of or behind the steerer tube's center axis by ~30mm or so are very minor.
    I would think that having your hands in 30mm front of or behind your steering axis would make a big difference in how your bike handles.

  22. #22
    pvd
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    Hand position relative to the steering axis is completely meaningless.

  23. #23
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    Speaking of discussion, Pete, you said in the first post "Let me know what you think and where you see the confusion so that I can get this right."

    You've gotten some feedback and questions, but you've spent all your time posting here in the meantime telling everyone they're wrong about other stuff.

    So do you do want feedback or not?

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    I'd really like to see a statistically relevant survey of riders' body dimensions and bike measurements taken. there will be outliers representing people who are riding bikes that have bikes that are functionally too big/small, but if you take a "wisdom of crowds" approach, you may find a trend in the middle. I believe that is what Lee McCormack has done (or says he has) and the very basic calculation he offers for free in that PinkBike article is an average of what trends in the middle of his observations. you can disagree with him, but he's reached his own conclusions with a similar approach to what PVD is offering here.

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    Here ya go Pete. I programmed a spreadsheet with your formulas for everyone to use so you can gather information for your experiment.

    PVD RAD spreadsheet

  27. #27
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    Very cool.
    It needs a permission to open.
    Can I share the link on my page?

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    Permission granted. Let me know if I got those formulas right. I typed one in with one function incorrect at first and it threw everything off. I tried uploading a XLSX file to mtbr and it would not let me. there's probably a good reason for that. I am not certain I feel good about using my personal Google account to share this. If you can, copy the data in that spreadsheet and host your own version of it, please.
    Last edited by mack_turtle; 1 Week Ago at 06:37 AM.

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    part of this discussion should be: what does that number represent relative to the body's range of motion? is this calculation of RAD a minimum, maximum, or medium? the human body is adaptable and can physically ride a bike that is much smaller or larger than this calculation yields. at what point is RAD too much of the maximum range of motion that is practical for wrangling a bicycle, and at what point is it not enough to take advantage of that range?

    If I remember my reading of his material correctly, I think Lee McCormack's number seems so small because he wants riders to start in an athletic position where there's room for the bike to move away from and toward the rider without the bike getting away. his position is that bikes are getting so big these days that the handlebar-grip position starts at close the maximum range of motion that is available to the rider's body. when the front wheel drops away from the rider, we don't have Go-Go Gadget arms to stretch out and maintain control, so the body is pulled forward.

    longer front-centers and dropper posts mitigate this, and maybe that's the answer. while most of use have adopted longer F-C and droppers, would you want a bike that has a long RAD with a shorter F-C and a rigid post? is the longer RAD only useful in light of these developments?

  30. #30
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    Why do you keep talking about Lee McCormack? His information is terrible as noted. You should forget basically everything he's said.

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    why don't you engage in the discussion you started?

    you critiqued Lee's idea without feedback from him. Rider Area Distance is his idea, unless I missed the part where you wrote about it first.

    based on what you presented, you made a straw man out of his theory, didn't use his full calculator, and declared victory. I provided you with a detailed experiment using your theory and you have not responded to it. I put your calculation into a spreadsheet for you and pointed out a serious error in your blog post. are you interested in this discussion or just pontificating to the ignorant masses?

  32. #32
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    What was the error in my post? I haven't been paying a lot of attention to this thread as it seems to be about Lee McCormick's junk than mine.

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    I thought body length and arm length are swapped. the equations seemed to be for the wrong variable.

    Quote Originally Posted by mack_turtle View Post
    I think you mixed the calculation for arm/ body lengths on the blog. the numbers I got didn't make any sense when I used it as described. it made sense after I swapped the meaning of these numbers:

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    somehow that didn't translate well into the spreadsheet. give it a second look.

    edit: I'm not math whiz. clever enough to derive the same thing a different way that made more sense to me, but not smart enough to notice that they are the same thing. the spreadsheet I sent you calculates the same thing with a slightly different way but it should not change anything. I make no guarantees about that spreadsheet, but if a novice like me made it work, maybe you're onto something to make this process easier.

    most of my response has been about your theory and applying the dimension the way you describe measuring dimensions and applying , measurements, and calculationsto my experience. I'd like to know if I am doing it right since part of your stated goal is to make this foolproof. I am little more than a fool, so if I can't get it right, it's missing something.

    did I do it right?

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  34. #34
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    Your math looks fine.

    I think that the problem is that you have been 'professionally fit'. Most fitters are charlatans or at best, are working in a box defined by road bike hogwash. I have yet to meet one that could do much for a mountain biker aside from saddle height. They often do the opposite of what a mountain biker will need.

    Have you tried the numbers generated with the angle range that I provide? We just did some work on my wifes setup for a flat bar gravel bike. She likes a very upright position 83.2 body and 37.2 arm. Very similar to her MTB position. She's 5'6" tall and has 1356.5/603.5 body numbers. Her bar numbers are 448/673.

    You really need to go out and test this on the bike for extended periods on different conditions.

  35. #35
    mtbr member
    Reputation: mack_turtle's Avatar
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    the odd thing is, my two professional fits gave me a RAD of 820mm, which is bigger than the numbers your calculation gave me. I rode my bike in that position for a few rides and rejected them. they made the bike feel enormous and out of control. the RAD that I have now is 780mm. I calculated by your method in the most forward, low orientation and the most upright, and both are still quite a bit longer than what I have found works for me through personal experience.

    I am probably an outlier. terrain, goals, and fitness play a role. I'm a middle of the pack rider at best. I'll try something a little longer but my riding style and horrible lack of flexibility might say otherwise. the offset with my handlebar is pretty severe so a longer stem feels comfortable that I won't confound conventional wisdom, not that I should care.

    I look forward to seeing a larger sample. sorry I am the only person on here who seems to be really trying. I am really interested in a scientific way of fitting bikes because I've had such disappointing experiences with fitters who put me on a mountain bike like its a road bike.

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