# bike fit calculator.. feel a bit let down?



## TomH (Oct 6, 2008)

i used colorado cyclist.. 

it basically says to measure your inseam, and turns you out a seat tube size and in short, says thats all that matters, that top tube length really isnt a big deal, but seat tube length is.  

admittedly, i come from a mtb background.. in mtb top tube is everything! how are they telling me that a 54cm frame with a 55cm top tube is going to fit me just like a 54cm frame with a 53cm top tube? 

doesnt compact geometry kind of throw that theory to the wind as well? tiny frames with long top tubes? 

maybe im missing something.. it says i need a 54, and im riding a 54 now with a 55.5 top tube, and i feel stretched. i felt much better on most bikes with a 53-54 top tube. 

i have a 100mm stem, for price sake im going to try an 80mm stem first, but it just seems weird that a fit calculator wouldnt take into account arm/torso length? seems that you can always lift your seat up or down, cant really make much change to the top tube though.

any input? am i missing something?


----------



## Guest (Jan 29, 2009)

None of them are an exact science but some work better for certain people than others. Try the one at Competitive Cyclist it does use a little bit more information than that. But remember they are all flawed to a degree.


----------



## FatTireFred (Jan 31, 2005)

fit calculators are generally [email protected] they can get you in the ballpark, but don't expect to get dialed in. they usually don't consider things like fitness and flexibility, only body proportions.


----------



## C-40 (Feb 4, 2004)

*search...*

Do a little searching. There have been lots of posts regarding fit. It's too big a subject to repeat over and over.

These day seat tube lengths and "frame size" have both become meaningless. What you really need to look at is the head tube length, with the headset to determine the vertical frame size. 

The frame reach is the next item to look at. Reach takes into account both the TT length and the seat tube angle. Steeper STAs increase the reach by about 1cm per degree, so if you see one frame with a 53cm TT and 74 degree STA it will fit about the same as one with a 54cm TT and 73 degree STA. I know this may sound backwards, but it's not. It assumes the same saddle position relative to the BB on both frames.

If you know the geometry of your current frame, it's easy to compare it to any other.


----------



## Stogaguy (Feb 11, 2006)

*"Correct" fit is a process...*

IMHO obtaining correct fit is a process that happens over time. Think of your first road frame as a prototype for your next road frame. At best, a fit calculator will get you in the right ball park defined as an acceptable result for seat angle/set-back, seat tube and top tube specs. After that, there are a lot of other factors that figure in. These are better accessed by actual experience on the bike than with any formulaic calculator. After you ride your bike for a while to get settled in, start moving things systematically to get closer to ideal. Work in small increments and only change one thing at a time. Give any change enough miles so that you can truly access its impact before making any further changes. Over time, you will get pretty dialed in. Be aware that what works for you may well change over time with changes in your fitness/flexibility level as well as the tyoe of riding you are doing.

When it is time for a new bike, measurements from your current bike become the best basis to make your selection. Look for a frame that preserves the fit aspects you like from your current rig and "fixes" its short comings.


----------



## tarwheel2 (Jul 7, 2005)

I agree with just about everything posted here. Fit formulas are only a starting point. I rode a size 57 x 57 frame for years until I made the mistake of consulting the Colorado Cyclist fit formula when buying my first road bike since the mid-80s. The new bike was way too small and riding it caused me all sorts of problems. Then I had a Serotta fitting done, which got me closer to right but still too small. I'm now back to riding a 57 x 57 frame -- same as when I started road riding back in the early 80s -- and everything fits just right.


----------



## tom_h (May 6, 2008)

After lots of reading on the Web and here at RBR [especially C-40's insights], and my own personal experiences during the last year, I've concluded two of the most useful dimensions on a frame are rarely, if ever, specified.

See pic below. Pic calls the 2 parameters "stack" and "reach" ... don't know if those terms are generally accepted.

"Seat tube" length is nearly useless nowadays, although it had utility decades ago (Sheldon Brown website has interesting history).

...


----------



## tom_h (May 6, 2008)

*Fit calculators*

I've played around with the Competitve Cyclist and Wrench Science online calculators, and I did properly measure my body measurements to input. The Wrench Science also has an input for "flexibility" , with picture to guide you.

Both calculators would stretch me out _considerably_ more than I like to ride now, about another 1.0-1.5" (_huge_ amount), with respect to the sum of the stem & effective top tube lengths

That's enough to put me on a frame that's one size too large -- it would make for an expensive and very unhappy mistake.

be wary, with those calculators.


----------



## Stogaguy (Feb 11, 2006)

*I agree...*

I agree that "reach" and "stack" as defined in your illustration are very important. I would add to this "setback" as illustrated in this diagram from the Calfee site. The key issue with setback, is does the frame get you into the right ballpark. If "yes", then setback can be fine-tuned with seatpost selection and saddle rail adjustments. If "no", then it may not be possible to establish your preferred saddle position (fore/aft) relative to the bottom bracket.


----------



## TomH (Oct 6, 2008)

hey nice name! :lol: 

on a mountain bike i can hop on and know exactly whats off and where i want what.. its a bit harder on a roadbike, i think part of the problem is that im not even quite sure what i want myself. i worked with a couple lbs's to try out some new bar/stem combos, i think im getting some kinks worked out, but have a way to go still (new setup has my knees hitting my elbows in the drops!)


----------



## Peter P. (Dec 30, 2006)

Stogaguy said:


> IMHO obtaining correct fit is a process that happens over time. Think of your first road frame as a prototype for your next road frame. At best, a fit calculator will get you in the right ball park defined as an acceptable result for seat angle/set-back, seat tube and top tube specs. After that, there are a lot of other factors that figure in. These are better accessed by actual experience on the bike than with any formulaic calculator. After you ride your bike for a while to get settled in, start moving things systematically to get closer to ideal. Work in small increments and only change one thing at a time. Give any change enough miles so that you can truly access its impact before making any further changes. Over time, you will get pretty dialed in. Be aware that what works for you may well change over time with changes in your fitness/flexibility level as well as the tyoe of riding you are doing.
> 
> When it is time for a new bike, measurements from your current bike become the best basis to make your selection. Look for a frame that preserves the fit aspects you like from your current rig and "fixes" its short comings.


Stogaguy gets it.

You may buy your first frame based on inseam only. You'll ride it and find the top tube/stem combination is too long/short. You try different stems then decide to buy a bike with a different top tube length. In the meantime, you read some literature and gain an understanding of frame geometry. You measure yourself using one of the methods you've found and mentally you're comparing it to your current bike. You make more changes. You repeat the process until you're satisfied. The point is over time, you became educated about frame fit.

In your instance, you already know that sizing by seat tube length alone is too vague. Of course, sizing someone to a frame based on measurements alone is still less than optimum but when those measurements take arm plus torso into account then there's a definite effort to come closer than through inseam alone, and for sure you can feel more comfortable with the results.

So no; you're not missing something. You're actually a very well educated bicycle consumer. You are doing the wise thing by trying to make your existing bike fit by swapping stems. Once you are comfortable with your position, you can modify the numbers to give yourself a slightly shorter top tube and longer stem (in my opinion, an 80mm stem on a 53/54 cm frame is too short from a handling as well as aesthetic standpoint). You should also seek out and try some of the fitting methods available on line as well as in books (see Lennard Zinn's "Zinn and the Art of Road Bike Maintenance, Appendix C). You'll soon see the common thread in all the fit methods and the numbers you calculate for yourself will fall within a small , acceptable range. With a solid knowledge from self-fittings and experimenting on your current bike, you'll be able to confidently purchase your next frame, even if it's from Colorado Cyclist!


----------



## tom_h (May 6, 2008)

Stogaguy said:


> IMHO obtaining correct fit is a process that happens over time. Think of your first road frame as a prototype for your next road frame. ....
> 
> ... When it is time for a new bike, measurements from your current bike become the best basis to make your selection. Look for a frame that preserves the fit aspects you like from your current rig and "fixes" its short comings.


I agree whole heartedly . Very sensible advice.


----------



## Bob Ross (Apr 18, 2006)

tom_h said:


> I've concluded two of the most useful dimensions on a frame are rarely, if ever, specified..."stack" and "reach" ... don't know if those terms are generally accepted.


I just yesterday had an exhaustive professional fitting session with one of the top fitters in NYC, and his opinion confirms yours: He said the most critical dimension(s) is the distance from the bottom bracket to the handlebar center, measured as an X,Y coordinate.

IOW, "reach" & "stack" as portrayed in your drawing.



Oh, and regarding online fit calculators: about two years ago I spent a day getting measured and plugging those numbers into the online fit calculators at Competitive Cyclist, Wrench Science, Colorado Cyclist, and the downloadable Accufit application from Bill Boston Cycles.

I wound up with four completely different recomendations for frame size...only two of which were even close to one another, and none of which were remotely close to the bike I was riding at the time...which, as of yesterday's fit session, appears to be within a half centimeter of ideal.


----------



## acid_rider (Nov 23, 2004)

i tried several cyclfit calculators and they all failed me in one way or another. so i dont recommend their use except perhaps as a starting point to someone buying their very first cheap road bicycle. and even then, be prepared for possible failure, just in case. there are just too many individual variables and many of the dynamic variables meaning statis measure-based calculators will fail because they dont take dynamic issues into account (how could they?).


----------



## choppedsled (Sep 18, 2008)

TomH, I know what your feeling. I've just started on the road after a a decade on the BMX track. I commuted on a road bike in the 80's for fitness reasons. TT length is almost everything in BMX, and MTB about the same. The distance from the bottom brackt to the head tube being the other biggie. I knew exactly what I needed, but that took years to learn. I did the static measurements and picked the brain of the guys at competative cyclist. I settled on a 56 and it felt so long when I first went for a spin. All I could think of was damn long TT length. But then I worked on my flexability, and it doesn't feel so long anymore. I'm not there yet because I just started, but I can see just as the advice on this forum that it's a long process. At least for us noobies. I don't question the size of my frame anymore, just positioning, and my fitness level. Best of luck !


----------



## PlatyPius (Feb 1, 2009)

Any "calculator" that only considers standover/inseam is worthless.

Honestly, the only way to *really* know what size to buy and how to set it up is to have a professional fit done by a real person.

Online calculators that want ALL of your measurements to give a result will be good enough to buy the right size bike; usually. It takes an actual person though to be able to recommend which bike/frame might work best for you.

It's ultimately a matter of how well you want the bike to fit. Yes....I work at a bike shop. I've fit all of my bikes myself, and done a crappy job. The one bike that my boss (the fitter) fit for me was the most comfortable bike I've ever had.


----------



## ronbo613 (Jan 19, 2009)

There are differences between a "sloping top tube" type frame and more traditional frames as well as differences in geometry between frame manufacturers that make frame sizing a challenging proposition.
(Hope my new Cervelo frame fits me)


----------



## tom_h (May 6, 2008)

ronbo613 said:


> There are differences between a "sloping top tube" type frame and more traditional frames as well as differences in geometry between frame manufacturers that make frame sizing a challenging proposition.
> (Hope my new Cervelo frame fits me)


There shouldn't be a difficulty interpeting between horizontal & sloped top tube (TT). because virtually all Mfrs spec the "_Effective_ TT length".

ie, extend an _imaginary_ TT , _horizontal_ from the head tube, until it intersects the real seat tube.

Confusions can arise, because IIRC some Mfrs define seat tube (ST) length to the _top_ of the ST, while others define ST length to the centerline of the Effective TT.


----------



## AlexCad5 (Jan 2, 2005)

Stogaguy said:


> IMHO obtaining correct fit is a process that happens over time. Think of your first road frame as a prototype for your next road frame. At best, a fit calculator will get you in the right ball park defined as an acceptable result for seat angle/set-back, seat tube and top tube specs. After that, there are a lot of other factors that figure in. These are better accessed by actual experience on the bike than with any formulaic calculator. After you ride your bike for a while to get settled in, start moving things systematically to get closer to ideal. Work in small increments and only change one thing at a time. Give any change enough miles so that you can truly access its impact before making any further changes. Over time, you will get pretty dialed in. Be aware that what works for you may well change over time with changes in your fitness/flexibility level as well as the tyoe of riding you are doing.


 The most difficult part of this is your body gets used to what it has become accustomed too, not that it is the optimal position. You have to listen carefully to the signs; like are your hands going numb? Is your neck stiff? Do you feel stretched out or cramped? And then you have to correctly interpret this 'information.'
I think you would need to try it in two positions and see which feels better than the other, kind of like an eye doctor does, and then try two more positions, continually narrowing the selection. If there is too much time in one position, that will start to feel 'natural' even if it is not correct.


----------



## CleavesF (Dec 31, 2007)

When in doubt. ALWAYS SIZE DOWN. ALWAYS.


----------



## spastook (Nov 30, 2007)

Stogaguy said:


> IMHO obtaining correct fit is a process that happens over time.
> 
> I couldn't agree more. I've recieved a number of fittings over the past 30 years although I haven't gotten one in nearly 15 because I realize what a waste they are. They're only as good as the fitter and even then there are too many variables. The last one I got was done personally by one of America's most respected custom framebuilders and his fitting gave me numbers that were way off base. I'm a very averaged sized guy 5-10 with a 32 inch inseam 160 lbs. You'd think I'd be easy to size up properly and I am but only if I personally determine what I need based on experience. Expecting non medical types i.e. (bike mechanics) to locate specific bones take measurements and come up with a size that will be perfect for you is a recipe for disaster. Test ride a few different sized bikes, take some notes as to what felt good or bad about your positioning and try and make an informed decision by yourself. It's O.K. to get some advise or a few pointers from a seasoned professional but to leave it all in their hands is not such a good idea. IMO


----------



## tom_h (May 6, 2008)

spastook said:


> Stogaguy said:
> 
> 
> > IMHO obtaining correct fit is a process that happens over time. ... . I'm a very averaged sized guy 5-10 with a 32 inch inseam 160 lbs. You'd think I'd be easy to size up properly and I am but only if I personally determine what I need based on experience. Expecting non medical types i.e. (bike mechanics) to local specific bones take measurements and come up with a size that will be perfect for you is a recipe for disaster....
> ...


----------



## PlatyPius (Feb 1, 2009)

tom_h said:
 

> I would agree with that.
> There are NO objective , certifable criteria for "fitters", AFAIK. Anybody can call themself a "fitter".
> Would anyone like it, if any individual could call themselves a "surgeon" ? ;-)
> 
> There ARE organizations & individuals who seem to have established high standards and expertise, eg Andrew Pruitt and the Boulder (CO) Center for Sport Medicine ... but they are _quite_ expensive ... and it seems impractical for recreational cyclists who don't live nearby.


F.I.S.T. is one that triathletes look for. (Fit Institute SlowTwitch).
The owner of the store I work for has a Masters in Exercise Physiology (and is F.I.S.T. certified as well.)

But in general, there IS a shortage of certifications that matter. Not everyone is going to go to college for 6 years or so to get a Masters. F.I.S.T. is a good one, I hear, but I can't get past the name. lol


----------



## vmajor (Mar 16, 2008)

As an "easy" quick reckoning way to narrow down your size range, try this.

With the current frame designs (back to the future really) with long head tubes, the most significant measurement is the virtual length of the top tube.

The rest of the frame geometry in such frames largely revolves about these two measurements (head tube, top tube).

Thus, figure out what top tube length you need and the proper fit should be achievable by varying the saddle position, stem length and handlebar shape.

V.


----------



## teleguy57 (Apr 23, 2006)

*Specialized Body Geometry Fit process?*

I know this thread talks about fit calculations, but I'm wondering what experience people have had with the dyamic fit process used by those certified by Specialized based on the work Andy Pruitt has done with Specialized. Looks like I can get that done locally for about $150 for their full dynamic analysis. I'm thinking I'm pretty good with my current frame and position, but hoping to get it dialed in a bit more. Have worked by feel/visual/measurements but I'm thinking a professional look, particularly at varus/valgus and reach/drop would be helpful....


----------

