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roydyates
11-11-2011, 07:43 PM
Almost every rider I know has a road bike whose size is within a centimeter of

"Your height in inches" - 14.

For example, I'm 6 foot 1.5 inches = 73.5 inches.

73.5-14=59.5. I have 4 bikes that are 60cm and 3 bikes that are 59cm.

The biggest exception I've heard about is Shawn Bradley. From the Shawn's stolen bike thread, I learned his bike is 80cm, but his height is 7 ft 6.5in = 90.5in. The rule of 14 says he should be riding a 76 or 77. :)

So, I'm wondering how often is the rule of 14 wrong. How many people around here are exceptions? If I had to guess, the exceptions here will be young guys with the flexibility to ride small frames with slammed stems.

chuckroast
11-11-2011, 07:50 PM
No exception here. 5'-11", ride 56 and 57's.

fjaws
11-11-2011, 07:52 PM
I'm your height.... 57cm Serotta, 56 Cervelo, 56 Van Dessel.

ergott
11-11-2011, 07:53 PM
Too big for me. I ride 53-54 (even some 52s) and that formula gets me a 55 (5'9").

fourflys
11-11-2011, 08:01 PM
68", ride a 54 to a 54.5 top tube...

e-RICHIE
11-11-2011, 08:05 PM
So, I'm wondering how often is the rule of 14 wrong.


it's wrong atmo -
you cannot determine the frame measurements and contact points without using leg length and foot length.
a rider's height is completely irrelevant.

ps

arrange disorder

:) :) :)
:cool: :cool: :cool:
;) ;) :p

tannhauser
11-11-2011, 08:11 PM
What does size even mean? ST or TT? If it's ST then the rule is off by a factor of a million for me.

Kirk Pacenti
11-11-2011, 08:16 PM
As a rule of thumb it could be a useful starting point for test riding an off the peg bike. But I would hardly recommend it as a way to determine your proper size.

At 72" tall, it happens to work for me. Most of my bikes are 58cm c-t-c. Though I have always preferred bikes that would be considered on the large size for someone my height, compared to what most shops would recommend, (usually 56cm).

I have heard it expressed another way that yields similar results; your height in feet and inches, minus two... i.e. 5'-9" = 57cm. ymmv. Of course all bets are off if you're considering a compact frame design.



Cheers,
KP

Louis
11-11-2011, 08:23 PM
My numbers:

6 x 12 - 14 = 58

Off the peg I ride 60 ST, custom I ride 61 ST

Explanation: my legs are long compared to my torso length.

Rules-of-thumb are good for average ratios, but fail at the tails of the normal distribution.

ergott
11-11-2011, 08:26 PM
I have heard it expressed another way that yields similar results; your height in feet and inches, minus two... i.e. 5'-9" = 57cm. ymmv.


Cheers,
KP

Yikes. Me on a 57cm would be a bad idea.

Frankwurst
11-11-2011, 08:58 PM
I'm 70 and have 2-56's, 1-58, and 1-59 right now but none of them are square. :beer:

roydyates
11-11-2011, 09:02 PM
it's wrong atmo -
you cannot determine the frame measurements and contact points without using leg length and foot length.
a rider's height is completely irrelevant.

ps

arrange disorder

:) :) :)
:cool: :cool: :cool:
;) ;) :p
As others point out, one number hardly describes the size of a bike just you observe that one number hardly describes the size of a person. Perhaps one number for a bike frame is even less precise since we all agree on how to measure the height of a person but there are a bunch of ways to measure the size of a frame.

The fact that it's wrong but in the right ballpark makes it more interesting to me. :)

tannhauser
11-11-2011, 09:07 PM
It's not even close.

roydyates
11-11-2011, 09:10 PM
As a rule of thumb it could be a useful starting point for test riding an off the peg bike. But I would hardly recommend it as a way to determine your proper size.

At 72" tall, it happens to work for me. Most of my bikes are 58cm c-t-c. Though I have always preferred bikes that would be considered on the large size for someone my height, compared to what most shops would recommend, (usually 56cm).

I have heard it expressed another way that yields similar results; your height in feet and inches, minus two... i.e. 5'-9" = 57cm. ymmv. Of course all bets are off if you're considering a compact frame design.

Cheers,
KP
5' 9" =57cm is an even goofier rule :) since there is a nonlinear mapping of inches of height to cm of bike size. That is, 12 inches in a foot adds 10 cm but each inch in the inches category adds a whole cm.

e-RICHIE
11-11-2011, 09:12 PM
As others point out, one number hardly describes the size of a bike just you observe that one number hardly describes the size of a person. Perhaps one number for a bike frame is even less precise since we all agree on how to measure the height of a person but there are a bunch of ways to measure the size of a frame.

The fact that it's wrong but in the right ballpark makes it more interesting to me. :)
there was a time, not too long ago, when the industry standard to see if a bicycle
would be in the ballpark for a user consisted of the words, "stand over this". that,
too worked well for the masses atmo.

ps

arrange disorder

;) ;) ;)
:p :p :p
:) :) :cool:

roydyates
11-11-2011, 09:13 PM
What does size even mean? ST or TT? If it's ST then the rule is off by a factor of a million for me.
A factor of a million! Wow! Are you some sort of Wagnerian size?

tannhauser
11-11-2011, 09:18 PM
5'11" 162lbs.
50cm ST, 58cm virtual TT, 12cm stem, 7cm drop.

So tell me, what does size mean?

Kirk Pacenti
11-11-2011, 09:29 PM
Blah, blah, blah, rule of thumb blah, blah, blah starting point Blah, blah, blah, blah, blah. Blah, blah, would hardly recommend blah, blah, blah-bidy, blah.

Blah, blah, blah, happens to work for me. Blah, blah, blah, 58cm c-t-c. Blah, blah, blah, blah-blah, blah, blah. Blah blah, most shops would recommend 56cm.

Blah, blah, heard it expressed another way blah, blah, blah; blah, blah, blah, blah, blah, blah = 57cm. ymmv. Blah, blah blah, all bets are off blah, blah, blah, compact frame design.



Cheers,
KP

roydyates
11-11-2011, 09:31 PM
5'11" 162lbs.
50cm ST, 58cm virtual TT, 12cm stem, 7cm drop.

So tell me, what does size mean?
Compact frame? I'd say your bike is a 58. I'd prefer to say it's a 57 (but you never mentioned the number 57) since 5'11"=71 inches and 71-14=57.

Any chance your effective ST is 57?

tannhauser
11-11-2011, 09:33 PM
But blah blah no compact blah blah stupid rule blah blah way too general blah blah must make crazy theory blah fit blah to blah put blah blah custom blah builders blah blah blah out of

BLAH.

Waldo
11-11-2011, 09:33 PM
Dead on for me -- I'm Kirk's height and frame size. Looking forward to sampling some of his bikes :beer: .

tannhauser
11-11-2011, 09:37 PM
Compact frame? I'd say your bike is a 58. I'd prefer to say it's a 57 (but you never mentioned the number 57) since 5'11"=71 inches and 71-14=57.

Any chance your effective ST is 57?

Not compact, no chance. Effective ST is 51.5 cm, barely any slope to the TT.
Long and low, I'm flexible.

General metrics don't work for me; I need a custom for the bike to be dialed. The theory is silly.

Kirk Pacenti
11-11-2011, 09:40 PM
Not compact, no chance. Effective ST is 51.5 cm, barely any slope to the TT.
Long and low, I'm flexible.

General metrics don't work for me; I need a custom for the bike to be dialed. The theory is silly.

Rules of thumb become rules of thumb for a reason.

When did "rule of thumb" become "theory"?

tannhauser
11-11-2011, 09:43 PM
When did "rule of thumb" become "theory"?

Well, if by "rule of thumb" you mean "not even in the same ballpark", yes.

Kirk Pacenti
11-11-2011, 09:46 PM
Well, if by "rule of thumb" you mean "not even in the same ballpark", yes.


The answer is 4.

tannhauser
11-11-2011, 09:47 PM
The answer is 4.

The Rod is Wagnerian, yo.

roydyates
11-11-2011, 09:48 PM
Not compact, no chance. Effective ST is 51.5 cm, barely any slope to the TT.
Long and low, I'm flexible.

General metrics don't work for me; I need a custom for the bike to be dialed. The theory is silly.
I'm really curious to see a picture of your bike. Is the STA super slack?

lavi
11-11-2011, 09:54 PM
Close....but no cigar, or a bike.

tannhauser
11-11-2011, 09:55 PM
I'm really curious to see a picture of your bike. Is the STA super slack?

I don't have one, but a slack STA would imply longish legs, which I definitely do not have.

STA is 73, HTA 74.

It's like Craig's geo, like this but with less drop:

http://farm3.static.flickr.com/2681/4540691097_c3de4f3d39.jpg

Actually, the drop looks pretty similar.

martinrjensen
11-11-2011, 09:58 PM
My "sleep number" is 58 and that's the size of my best fitting bike. I have a 60 that I was able to make fit, and a 57 which was an easy fit, so formula works with me. This might be more true with old classic style frames but that is 3 of my 4 bikes also

Kirk Pacenti
11-11-2011, 10:13 PM
5' 9" =57cm is an even goofier rule :) since there is a nonlinear mapping of inches of height to cm of bike size. That is, 12 inches in a foot adds 10 cm but each inch in the inches category adds a whole cm.

French Fit? ;)

Fivethumbs
11-11-2011, 10:50 PM
doesn't work for me. I have long legs and long feet. Most of the leg length seems to be from the knee down. The formula says I should ride a 61 but ride a 63 - 64 with a not very slack STA.

bicycletricycle
11-11-2011, 11:21 PM
75 - 14 = 61

pretty close

mike p
11-12-2011, 12:55 AM
74-14=60.......I ride 57's and 58's.

Mike

Sandy
11-12-2011, 02:09 AM
it's wrong atmo -
you cannot determine the frame measurements and contact points without using leg length and foot length.
a rider's height is completely irrelevant.

ps

arrange disorder

:) :) :)
:cool: :cool: :cool:
;) ;) :p

I don't think the original poster was suggesting that one could simply use rider's height in determining the size of the frame. I believe he simply noticed, for the people he knows, that the rule seemed to be true, and he wondered if the rule applied for other cyclists.


Sandy

PS- Hope your family/loved ones are doing well. Ever get another dog? I know Spencer was dearly loved by you.

Chance
11-12-2011, 11:02 AM
A rule of thumb is a principle with broad application that is not intended to be strictly accurate or reliable for every situation.
The rule seems to be a close approximation most of the time because of two factors:

First, average people have an inseam that is roughly in proportion to their height. For riders who deviate a lot from average the rule can’t work.

Secondly, subtracting “14” from height regardless of a rider’s height adjust for the fact that most crank arms are of similar length (certainly don’t deviate in proportion to rider height since most are in 170 to 175 range, which is only 1/5 of one inch) and most all bikes generally have a “virtual” exposed seat tube length that is within a small range.

Looking at it another way “rule #14” simply states that seat tube length is in the range of roughly 31 percent of body height for typical size riders. Very short riders calculate to about 30 percent and very tall riders closer to 32 percent. As long as the rider is built with typical proportions and doesn’t ride excessive seat post showing then the rule will come close. Most of the time.

oldpotatoe
11-12-2011, 11:09 AM
it's wrong atmo -
you cannot determine the frame measurements and contact points without using leg length and foot length.
a rider's height is completely irrelevant.

ps

arrange disorder

:) :) :)
:cool: :cool: :cool:
;) ;) :p

Next in line is inseam, femur length, yes, inseam, notsomuch.

PLUS a '58' Oneframe is different, in terms of seat tube angle, top tube length, Than just about all other '58s. Measuring seat tube length, whether C-C or C-T, means notamuch.


BUT, I am 72 inches, ride a 58cm Merckx, DeRosa, Waterford, Moots.

Chance
11-12-2011, 11:14 AM
FWIW mine are 1 cm taller than rule so they are close.

thegunner
11-12-2011, 12:55 PM
Too big for me. I ride 53-54 (even some 52s) and that formula gets me a 55 (5'9").

werd 5'7" here and i mostly ride 51's (occasionally a 48 even :p)