height/inseam



tonttu

New Member
Apr 18, 2005
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Hi everybody! I would like to know what a regular height to inseam ratio is. Being 5'9" with an inseam of 33" I always feel that my 56 frame is way too
long for me. To be really comfortable I would need 50 or 60mm short stem
which doesn't exist. How do height, inseam, top tube and stem length really relate?
Thanks for your input!
 

tonttu

New Member
Apr 18, 2005
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And since I am already at it, what about crankarm length? Long legs=long crank arm?
 

palewin

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Oct 29, 2004
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Tonttu: There is no particular "relationship" between height, inseam, etc. However, standard bike geometries are based on "average build" and it sounds like you have a short torso/long legs. As a very general rule, bike fittings these days start with top tube length and work from there. You would end up with a smaller frame, more seat post extension, and spacers/up-tilted extension to get the bars up somewhat. Your best bet would be to look for frames which have relatively short top tubes (in contrast, Lemonds are known for having relatively long top tubes for a given frame size, while some of the Italian frames are shorter; Merlin used to offer a short top-tube option, although I don't know if they still do). Since women typically have the short torso/long leg build, the women's design Treks, etc. are closer to your proportions (if they come in sizes large enough). Since I'm in your "grouping" (just under 5'8" and 32" inseam) I ended up getting a custom frame. There is a lot of argument about crank length vs. leg length, again as a real general guess, you're in the most-common 172.5mm area.
 

531Aussie

Well-Known Member
Apr 11, 2004
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tonttu said:
And since I am already at it, what about crankarm length? Long legs=long crank arm?

Firstly, make sure that's a proper inseam measurement and not a pants inseam or a lazily flopped measuring tape dangled to the floor.:) The best way to measure inseam is to shove a clipboard (or similar) right up your crotch, then put the perpendicular side of the board against a wall, mark the spot, then take the reading.

Here's a couple of online bike fit calculators which should give you at least a rough idea of the right size for you. I think they both take into account torso length.

http://www.wrenchscience.com/WS1/Secure/Fitting/Height.asp
http://www.competitivecyclist.com/za/CCY?PAGE=FIT_CALCULATOR_INTRO

The simple, "general" method is to multiply your inseam by 0.66 ish, which makes you a about 56.....D'OH!!:p
Doesn't matter: I'm a 58, but I also like a shorter top tube.

They are a few proponents of proportional crank length who recommend a crank length of ~21% of inseam. Most suggest at least 20%, with Lennard Zinn from Velonews recommending 21.6%.

http://www.cranklength.info/
http://www.zinncycles.com/cranks.aspx
http://www.billbostoncycles.com/crank_length.htm
 

SKAUFMAN12

New Member
Jul 12, 2004
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tonttu said:
Hi everybody! I would like to know what a regular height to inseam ratio is. Being 5'9" with an inseam of 33" I always feel that my 56 frame is way too
long for me. To be really comfortable I would need 50 or 60mm short stem
which doesn't exist. How do height, inseam, top tube and stem length really relate?
Thanks for your input!

I am 5'9" and I have a 32.5" cycling inseam. I have 2 bikes. One is a medium Giant (compact geometry - 54cm frame witha 55.5 TT) and the other is a 56cm C-C frame witha 56 TT. For me, the jury is still out as to which one I prefer in terms of fit. I bought the 56 used with some miles on it so I may switch the components out if I find another frame.
 

Conniebiker

New Member
Jan 1, 2005
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I am 5' 9" and 32" inseam. My frames are 17 and 20 inches(mtb). The 20" being the nicer fit.
 

tonttu

New Member
Apr 18, 2005
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Thanks everybody! First thing I did was checked the bike fit calculators Aussie posted. It turns out I had my seat 2" too low. Only the one at wrenchscience gave me some indication about my reach though. It is supposed to be 64cm, i.e. top tube + stem. With a regular stem that would mean that I would have to downsize to a 54 frame which feels kind of right to me. Is there any problem with too much seat post extension? And then I did measure my inseam kind of sloppy. It is actually closer to 34.
Today I did my first ride with the higher seat. It was kind of strange at first but it didn't cause me any discomfort. Guess I just have to get used to it.

By the way, are road compact frames similar in their dimension to Mtb frames? A 20" would be roughly 50cm then?
 

531Aussie

Well-Known Member
Apr 11, 2004
12,652
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tonttu said:
With a regular stem that would mean that I would have to downsize to a 54 frame which feels kind of right to me. Is there any problem with too much seat post extension? ?
Not sure about the compact question. I just measure them across the top, as if they had a horizontal tube, from the head tube to the point on the seat post where the tube would normally be.

If you change down a frame size, just be aware that this will normally mean you'll have a shorter head tube, so you obviously won't be able to have your bars as high as you could on the 56
 

el Ingles

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Oct 3, 2003
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tonttu said:
Thanks everybody! First thing I did was checked the bike fit calculators Aussie posted. It turns out I had my seat 2" too low. Only the one at wrenchscience gave me some indication about my reach though. It is supposed to be 64cm, i.e. top tube + stem. With a regular stem that would mean that I would have to downsize to a 54 frame which feels kind of right to me. Is there any problem with too much seat post extension? And then I did measure my inseam kind of sloppy. It is actually closer to 34.
Today I did my first ride with the higher seat. It was kind of strange at first but it didn't cause me any discomfort. Guess I just have to get used to it.

By the way, are road compact frames similar in their dimension to Mtb frames? A 20" would be roughly 50cm then?

how the hell did you get the seat hight wrong by two inches ???????????

that aside I have the opposite problem - the frame is too short so I have to us a 130mm stem ( did try a 140 mm but it was just too much )
and that´s the problem - they make , and sell , bikes for " average people but most of us are not average - why do you think there´s such a market for custom frames , vanity ? if you can afford it that´s the way to go but otherwise just mix and match and learn from experience - and don´t experiment with expensive stems etc until you know it´s the right size .
 

boudreaux

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Oct 16, 2003
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Conniebiker said:
I am 5' 9" and 32" inseam. My frames are 17 and 20 inches(mtb). The 20" being the nicer fit.
Just another example of how lame 'internet fitting' can be. I'm 6' with a 35.25 bike inseam and ride a 18-20' mtb....lol... :rolleyes:
 

Gonzo Bob

New Member
Feb 13, 2004
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tonttu said:
Hi everybody! I would like to know what a regular height to inseam ratio is. Being 5'9" with an inseam of 33" I always feel that my 56 frame is way too
long for me. To be really comfortable I would need 50 or 60mm short stem
which doesn't exist. How do height, inseam, top tube and stem length really relate?
Thanks for your input!

I'm close to your proportions. 5'9" height and 33.5" "cycling" inseam. My road bike is a 55cm c-to-c (about 56.5cm c-to-t) with a 56cm top tube and a 100mm stem. Maybe the top tube on your bike is too long.

Another thing to watch out for - once you get the correct stem and top tube length for comfortable riding, you could have problems with knee clearance when you stand to sprint or climb. On my bike, my knees sometimes come pretty close to back of the handlebars. To work-around this, you may be better off on a frame with a steeper angled seat tube - i.e. 74 or 75 deg instead of 72 or 73 deg. My bike is 74 deg. This essentially moves the bottom bracket further away from the handlebars giving more knee clearance.
 

tonttu

New Member
Apr 18, 2005
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Gonzo Bob said:
Another thing to watch out for - once you get the correct stem and top tube length for comfortable riding, you could have problems with knee clearance when you stand to sprint or climb.
I had that experience already with my computer mount.... OUTCH!! :eek: But thanks for reminding me.. ;) I actually found another used frame, a 55 c-c with a rather short top tube. I am gonna give that a try. It should be close enough. The rest of the discomfort I will have to make up for with more neck muscle..
 

LioNiNoiL

New Member
Sep 29, 2004
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tonttu said:
I would like to know what a regular height to inseam ratio is. Being 5'9" with an inseam of 33" I always feel that my 56 frame is way too long for me. To be really comfortable I would need 50 or 60mm short stem which doesn't exist. How do height, inseam, top tube and stem length really relate?
There is at best only a very crude relationship among height, inseam, and bike dimensions due to the lack of a "standard physique" among bicyclists. The best guide to fit is your own body, which seems to be telling you that you should get a frame with a shorter top tube, or maybe a smaller frame entirely.