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the long-awaited "idiot's" guide to bike fit(21 posts)

the long-awaited "idiot's" guide to bike fitET
Aug 6, 2001 4:47 AM
In the thread last week which began with my post "limitations of the Serotta size cycle", I said there is a free, quick and easy way to zone in on bike fit without the Serotta size cycle and which I claimed would be especially valuable to those purchasing their first road bike, and several said they would like to see it. Here it is.

1. Take your inseam measurement with firm pressure as described in Colorado Cyclist. It henceforth will be assumed you know this inseam with reasonable accuracy. This may sound trivially obvious, but there is just no excuse not to know your inseam. I'll bet many skip this step (e.g. the "all that's important is top tube but why can't I reach the drops on my OCLV" crowd).

2. Standover: It is nice to know in advance the clearance of the bike you are considering purchasing (forget about compacts for now; no one can size those correctly anyway). You may find this helps you zone in on a more ideal seat tube length, prevents mistakes and saves you time from test-riding bikes not suited for you. Check a bike company's catalog or Web site for the standover for the given size. As an absolutely necessary check (they often print the standover wrong or not at all), your high school geometry knowledge should convince you that, for seat tube measured c-t of top tube,

STH = [(ST x sin(STA)] + BBH,

or in words, standover height equals seat tube measured c-ttt times sin of seat tube angle plus bottom bracket height. If BBH is not listed, use 26.7 cm. For the convenience of anyone who might actually print this post out, sin(72)=.951, sin(72.5)=.954, sin(73)=.956, sin(73.5)=.959, sin(74)=.961. In case your bike is measured c-c, a rough but good enough conversion is that c-c + 1.5 = c-ttt. If the frame measures to top of seat tube or collar, you must inquire further, as that offers little info as to how much over c-ttt it is. If all else fails and even if not, you can just bring a tape measure to the LBS. (Note: measure to the very top of the cylinder of the top tube. One has a tendency to underdo it a bit.)

3. Now we apply the standover info. To account for shoes and cleats, first add two cms to your Colorado Cyclist inseam. We now compare this number with the bike's clearance. If inseam + 2 exceeds clearance by either more than 5.7 cm (2.25 inches) or less than 2.54 cms (1 inch), in the first case be forewarned that unless you know you prefer a steep drop, there is a good possibility that the drop to the bars may be too excessive, at least for a newbie (i.e. the frame size as measured by the seat tube may be too small) or in the second case there may be too little clearance (i.e. the frame size is too big). As a check, you can eyeball the clearance while straddling the bike in bike shorts, shoes and cleats, but just remember your straddling clearance should look a lot smaller than you might think, since it is measured to a tight inseam.

4. Top tube: We all agree that top tube is key, and many find this the most difficult to figure out. Fortunately, there is a ballpark test which, unlike the hub test, you can apply before you even get on the bike. All you have to do (don't worry: no calculators, no tape measure) is the ever-so-simple top tube test as described recently in Cycling Plus, which takes only seconds to do (but a few more to explain on paper). Stand on the left side of the bike next to the saddle and facing the front (i.e. handlebars), with wheel (i.e. stem) aligned straight with the frame. Now just put the back of your upper right arm against the nose of the seat, with the nose touching a few inches above your elbow, and forearm parallel to the ground and at a right angle with upper arm. Your right hand should be extended in the vertical plane, with pinky on bottom and thumb on top, with the fingers touching the adjacent ones and pointed in the direction of the handlebars. Next, place your left hand in the horizontal plane with palm facing down and fi
continuedET
Aug 6, 2001 4:49 AM
4. Top tube: We all agree that top tube is key, and many find this the most difficult to figure out. Fortunately, there is a ballpark test which, unlike the hub test, you can apply before you even get on the bike. All you have to do (don't worry: no calculators, no tape measure) is the ever-so-simple top tube test as described recently in Cycling Plus, which takes only seconds to do (but a few more to explain on paper). Stand on the left side of the bike next to the saddle and facing the front (i.e. handlebars), with wheel (i.e. stem) aligned straight with the frame. Now just put the back of your upper right arm against the nose of the seat, with the nose touching a few inches above your elbow, and forearm parallel to the ground and at a right angle with upper arm. Your right hand should be extended in the vertical plane, with pinky on bottom and thumb on top, with the fingers touching the adjacent ones and pointed in the direction of the handlebars. Next, place your left hand in the horizontal plane with palm facing down and fingers pointing to your right, and knuckles of left hand meeting the middle fingertips of right hand. Well, here's the ballpark rule for top tube length: the pinky of your left hand should fall smack on the middle of the bar top. (Go ahead and laugh. We only need ballpark here to prevent mistakes way out of the ballpark, and this test gives it. In any case, I asked several cyclists friends, all with very different types of body build, to try this test on their bikes whose setup they are happy with and it was just about dead on for them all. I urge you to try it as well; it's scary how close it comes. Betcha most of you are within +/-1 cm.) If you're off by too much (so that you would need more than a minor seat or stem change), don't bother test-riding the bike.

5. Test-ride: As always, first adjust seat height to satisfy the slight-bend-in-knee-at-6- o'clock rule. Take it out as long and as far as you are able and see how it feels. This is a good time to at least try the hub test; sure, it's also a ballpark test, but it really is rather close for most people. If you are way off, beware, and make note of which way you are off (hub visible below or above bars) as a warning as to the possibility your reach may be too long or too short. If possible (which it will be if you're seriously considering buying the bike), make minor adjustments to seat and/or stem if necessary, and then repeat the top tube test, as well as test-ride. Make note of number of spacers (usually set at max of 4 cm) and approximate angle of stem (eyeballing is fine) to get ideas for which bikes you will test next so you don't have to keep starting over. Seat should preferably be close to the middle of the rails for the given setback. If possible, it may help to adjust seat fore and aft to be sure where the position is most comfortable, hence giving valuable information as to your ideal seat tube angle; once you know it, it is unlikely to ever change much. If you adjust the seat fore/aft, be sure to make note of your "effective" top tube length, i.e. add or subtract the amount of the adjustment to given top tube. To make sure your setup doesn't deviate too much from the norm, you should be aware of what the standard size stem is for a given bike (e.g.—and I'm making these up for illustration—a 52-54 however measured gets a 10, 55-57 gets an 11, or whatever); if unclear, speak to people here or elsewhere about this.

That's all there is to it. This will give a good fit for about 90% of the people. Now I'm sure I'll hear all kinds of stories from those with ridiculously short legs combined with ridiculously long torso, or someone with super-long arms or terrible flexibility or whatever. And yes, some would do better with a custom or very large size they can't test in advance. And some have to make compromises given the bikes they're limited to. Fine. But let's take care of the 90% first. In addition, w
finalET
Aug 6, 2001 4:50 AM
That's all there is to it. This will give a good fit for about 90% of the people. Now I'm sure I'll hear all kinds of stories from those with ridiculously short legs combined with ridiculously long torso, or someone with super-long arms or terrible flexibility or whatever. And yes, some would do better with a custom or very large size they can't test in advance. And some have to make compromises given the bikes they're limited to. Fine. But let's take care of the 90% first. In addition, with some common sense there are checks and balances in the above approach to aid even those somewhat outside the norm (e.g. if you have exceptional flexibility, you may want your bars to come out a bit long in the top tube test), and some might prefer a steeper drop but shorter reach or vice versa, or those who know they prefer a steep drop can go over the upper bound on standover.

I just do not agree with those who think that fit is so complicated and unique that a reasonably easy approach for most to get a decent fit is undoable. This is that approach, and it will get you real close, certainly close enough for that first real road bike. Give it a try.

Assuming it is well-received, I'll save this text to re-post later for new newbies seeking help on fit. Buy and ride!
my brain hurtsHank
Aug 6, 2001 7:57 AM
I'm a believer in the old .65 x your inseam gets you your size c-c. But it doesn't work that well for some people, especially women. Also, the old elbow against the seat measurement won't work for all people, either. These are all just ballpark measurements. Your standover height obsession, the way I understand it, would lead me to believe that I should be riding a larger size Merckx vs. my custom frame (my Merckx has a lower bb). Everyone goes through a slight evolution, too, as they grow older and/or get more experienced. And there's no accounting for taste.
"Measuring for Euclids new bike", or: "The Idiots Guide"Pogue
Apr 20, 2002 3:12 PM
Correct me if i'm wrong, but the title of your post the "idiot's guide...." is supposed to imply that you have simplified the process of fitting yourself for a road bike so that the average person can figure it out. You must be on drugs.

All that you have done here is make it more complicated. With all of your fancy geometric formulas from high school (college?) that, trust me on this, nobody except you remembers how to solve six months after graduation, you just turn people off. I find it suspicious that you claim to simplify this annoying chore with an arcane math formula.

Smells like elitism to me.

If you really want to help, break the process down into small, understandable steps that "idiots" like the other 99% of the human race can follow.

And edit out the bullshit jargon while you are at it. The average person does not know what OCLV means, or LBS for example. (Definitions for any normal humans reading this: Overly Condescending Little Vole, and Lay on the BullShit.)

In addition, I expect that people with "ridiculously long torso, or someone with super-long arms or terrible flexibility or whatever... ." might be just a tad insulted by your tone of voice. "One legged dwarves with asthma may have difficulty with this one."

Since I'm ripping the other annoying aspects of your "guide" I should mention the pretensions: "One has a tendency to underdo it a bit." One? ONE? Who is this "One" person? How many people do you know who have this tendency? One? Or is this somebodys name? Let me guess, is your name "Two"? Are you British or something?

And lets all try to understand this sentence, shall we?
"If inseam + 2 exceeds clearance by either more than 5.7 cm (2.25 inches) or less than 2.54 cms (1 inch), in the first case be forewarned that unless you know you prefer a steep drop, there is a good possibility that the drop to the bars may be too excessive, at least for a newbie (i.e. the frame size as measured by the seat tube may be too small) or in the second case there may be too little clearance (i.e. the frame size is too big)."
Huh? I'm sure that YOU know what you mean, but I don't. Does anyone else? Heres some advice: you're not a robot, don't write like one: "Warning Will Robinson! Do not exceed this clearance!"
"Measuring for Euclids new bike", or: "The Idiots Guide"castrello
Sep 24, 2002 9:42 AM
I think he´s very clear. I did not have any problems understanding him whatsoever. And then Im not even english-speaking.

LBS-local bike shop
OCLV-treks carbon fiber
Who's the idiot ...? nmMrDan
Feb 10, 2003 6:01 PM
hub testMGS
Aug 6, 2001 3:21 PM
This test has been describe with the rider in both the drops and riding the hoods.
To which one are you referring?
hub testPsyDoc
Aug 7, 2001 9:42 AM
Both methods have been recommended, but keep in mind that the "hub test" was somewhat normed on racers and is just a general guideline, not etched in stone.
continuedBrillig
Aug 10, 2001 6:31 AM
Heh?

"upper right arm?" What do I do with my lower right arm?

But the big puzzler is "and knuckles of left hand meeting the middle fingertips of right hand". Which knuckles on the left hand, I have three on each finger? And what is a middle fingertip? Do you mean "tip of the middle finger"?

Thanks.
top tube + stem fitcharlieblue
Sep 20, 2001 8:23 PM
Thanks! I am in the market for a new bike and had the frame size figured out, but was struggling with what stem to start with. My old bike feels comfortable, but I was sure most people would think I am too stretched out. I tried your method, and my left pinkie fell right on top of the bar. I think I'll stick with that.
Thankskenyee
Aug 6, 2001 6:42 AM
I'm keeping this description in my useful info file :-)

It's too bad this msg board doesn't have a FAQ area.
re: the long-awaited "idiot's" guide to bike fitbikedodger
Aug 6, 2001 6:47 AM
Wow, an idiots guide that uses trigonometry! Us idiots am getting smarter every day.
not really trigET
Aug 6, 2001 7:08 AM
Since the sin values are already given and you just plug in the appropriate one, it's really only addition and multiplication. Threfore, hopefully, this can still be called an "idiot's" guide. :-)
Am I an "idiot" if i dont understand the "idiots" guide? nmLBS Guy
Aug 6, 2001 6:59 PM
Am I an "idiot" if i dont understand the "idiots" guide? nmstoopid
Sep 21, 2001 3:34 PM
yes, but more specifically you are a meta-idiot.
Nice...PsyDoc
Aug 7, 2001 9:52 AM
...I think you have done a valuable service for the "newbie" looking to purchase a new bike. After reading this post, a newbie will be further educated about bike fit and less likely to fall prey to an LBS who is adamant (not to be confused with Adam Ant) about moving a certain size frame. I do have a couple of suggestions, though. First, you may want to point out that "firm pressure" actually means that you want to pull up as hard as you can; in other words, you want to measure to the pubic bone. Second, you may want to think about qualifying the information you present on reach/top tube length. For example, suppose we have two newbies who have the same proportions. Newbie #1 is not very flexible and cannot even touch his/her toes when bent over. Newbie #2 is flexible and can put his/her palms on the ground when bent over. I think that Newbie #2 would be less comfortable on the same size bike as Newbie #1, because Newbie #2 will be somewhat cramped. Granted, a more appropriate stem would take care of such situations. I do not recall where I heard this, but if you can bend over and place your palms on the ground, then you can add 2cm to your overall reach. If you can bend over and touch the ground with the tips of your fingers, then you can add 1cm to your overall reach.
Nice...kingmoose
Aug 28, 2002 6:57 PM
i just used your guide on my current bike and based on your formula my tt and stem combo is off by a whopping 7cm! i'm sorry, but that just can't be right. that means instead of a 55 cmtt and 11ccm stem, i need a 59 cm tt and 14 cm stem. At 5'10" I think your formual is way off!
re: the long-awaited "idiot's" guide to bike fitRB
Aug 13, 2001 3:31 PM
No really. If I know my inseam what's the formula to find the right road bike size?
re: the long-awaited "idiot's" guide to bike fitwobblenut
Aug 26, 2001 5:02 PM
Dear Assumers,

Precision doesn't have to hurt your head!
Wobble-naught precision fitting systems at www.wobblenaught.com uses CAD to find the solution that is your solution only. You might be the same height, but have different limbs,body, etc. You can use it to fit the bike that you already have or use it to find your dream bike. If you get to Boise, ID voted #1 for biking in the USA. You can have Wobble-naught use their cross-hair laser to set you up w/in 1mm of your body type. They use the laser to find the correct stem rise/length to the millimeter.

It all starts w/ the cleat longitudinal placement, cleat lateral placement,saddle height, seat fore/aft position. Your body is a link system. After attaining the motor then you can find the correct (effective body extension) from your sit bones to the stem. This keeps your spine netural (those curves that you got after you were born, then their CAD places your arms where they are best used, plus finding the rise and length to the mm.

The solutions work, last year 25 wins in only 9 2000 Wildrockies mt. bike series. This year many wins in road (4 national champships) not to forget the triathlon, time trials, and duathlons wins.

Wobble-naught is on-line and can be use to find your fit solution. Many custom frames made by Titus were made after finding the solution first. The store I work at called George's in Boise uses the system to help people find the perfect bike. No guesswork and customer satisfaction is "The real deal".

The real deal, USA mens nat.road champ, and 3 NCAA road wins. Many wins on mt. bikes against some of the best in the world.

There is no key point. Every thing in your anatomy is important,and if your hip and spine are not correct, pain will come. The last time I checked that is where the nerves enter your spine. If they don't line up, you suffer.

Why be ballpark, when you can get it to the mm.
re: the long-awaited "idiot's" guide to bike fitdeliriou5
Oct 3, 2003 9:04 AM
lol this post is hilariou5....

while he's at it, i have some oceanfront property to sell ya.... let me know if you're interested