Inseam and Frame Size
 

Seems there has been a few threads recently (OK, all the time) about "that frame size is to small" or "Whoa...your frame is way to big". So I was curious as to what size frame everyone is riding and their corresponding inseam.

31" inseam
54 cm

Someone ran a similar thread a few months back and got a bunch of replies. The problem is, many newer road bikes don't follow traditional geomentry, with a top tube that is horizontal to the ground, and the seatpost clamp just above the top tube. So, a guy would post to say "My inseam is 32 inches, and I ride a size 52 bike." Quite unlikely that guy was riding a tradional bike, as his correct frame size (if his slack's inseam is 32 inches) is more likely to be around size 56 (for racing) or size 60 (for touring or commuting).

The second problem in the thread was that some people were referring to inseam as being the inseam on their slacks (32 inches) and the next guy, who also wears 32 inch slacks, was using inseam to mean leg length from the pubic bone done to the floor (35 inches). Without a shared understanding of what "inseam" means, the posted measurements were not very helpful.

The Rivendell website is helpful in relating leg length to frame size. They explain how to measure total leg length from the public bone to the floor. And, they have a chart suggesting frames sizes. Rivendell's chart assumes that their customers are not buying their bikes to race, and so their suggested sizes are about an inch higher than what many bike shops would suggest (many bike shop clerks fit bikes as if every customer will be racing in the Tour de France next July).

32" / 54cm

31.5" inseam
54cm (or 53cm) frame

38"

Small trek 63cm frame

30' inseam

53cm Lemond (proper fit)

49 or 50 cm Trek 2300 (sold to me by an overenthusiastic salesman before I knew about proper fitting - but I bought a long stem to compenstate)

60 cm Nishiki (knew it was a bit too big - but mainly use it for leisurely rides)

+1

30 inch inseam
56 Trek

Giant TCR's are sized with letters (i.e. S,M,L). For a rider who is 5'8" 160 and has a 30" inseam which of the Giants would you choose? (2005 sizes)
S = 44cm
M = 50cm
L = 55.5cm

Thanks in advance
Josh

35 inch inseam, 61 cm frame, 175mm cranks (yes, it matters).

34.5" inseam
58cm cannondale six13 , perfect fit for me,with a 120mm stem and 175mm crank.

33 inseam, 55cm Bianchi and a 57cm Orbea

~29in inseam, 52cm Felt (90 stem, sloping), 51cm Basso (120 stem, traditional)

32 in inseam, 56 Trek

alan is so right about this, look at the variances in the replies, they are all over the place. It's all about measuring your inseam PROPERLY, then gauging frame size from there.

Here is a start -Giant Compact Sizing BUT please visit a Giant dealer and get properly sized.

34.5 inseam riding 63 cm trek 1000. it may be a tad too big. later.

32" inseam..............56 Trek Pilot 2.1

Inseam only puts an upper bound on the seatpost dimension and really isn't the most important dimension for me. I'm 6' 2" with a "pants size" 32" inseam, hence I have very short legs for someone of my height. Since I haven't won a Lotto I need to get as large a frame "off the rack" as possible without risking some "vital organs" because of my long torso. Maybe someday I'll get a custon frame, but currently there are other priorities in my life that need the $'s more. As of now I have an old (1986) Cannondale 58 cm (c-t-t) and a newish (2002) Lemond Zurich 57 cm (c-t-c) as my road bikes. Both are OK in terms of fit, but I sure would like the top tubes to be just a little bit longer.

Ditto...we agree. Must not be a national thing. ;)
George

34" inseam (32" pant size)

58cm Trek 1500 (not a compact frame)

34" inseam, 57cm LeMond, could have went with either a 56 or 58 Cannondale with proper stem.

36"
58cm van dessel kermis

32" on a 54cm felt

34" (pant size)

56cm Miyata 610
58cm Mercier Serpens
58cm Trek 2120

Az

30" inseam, 54cm. I would have preferred a 53cm frame but I couldn't find one in my price range at the time but the 54 feels really comfortable.

Same size as mollusk. Just bought a Cannondale Synapse... 60cm. The fit appears to be just right using a short stem.

+1 I switched to a 110mm stem with 6 degree rise and it fits perfectly. Of course, this is a prime example of what is wrong with this thread. You have to go to the specs of every bike to find out how the seatpost is measured. The center to center measurement on my bike is actually 60cm. On the other hand, I have a steel bike that is a size 60, but the actual length is 59cm. I am convinced that the seattube measurement is pretty worthless, by itself. The virtual toptube and standover height have a lot more relevence. I wish I knew why the manufacturers on one hand use this as the main measurement and then make it as confusing as possible. Trek and Lemond are made by the same company but they measure their bikes differently. Why?

I'm still a bit confused.

I based my measurements on this page: http://www.coloradocyclist.com/BikeFit/index.cfm
My inseam is 32-inches or 81.28cm. Multiply that by 0.67 for "C-T" and I get 54.45cm. (call it "54cm")

Here's where I've got questions.

What that number basically tells me is, if I buy a frame labelled "54cm", the manufacturer will PROBABLY have spec'd the geometry such that I, with a 32inch inseam, can reach the pedals.

Similarly, if I tried, say, a 65cm frame, I would, in all likelihood, NOT be able to reach the pedals. (and the top tube would be long enough I'd probably feel pretty stretched out anyway)

Really though, I could probably get away with, say, a 50 or 52cm frame and raise the seat so I had proper extension or a 56cm frame with the seat appropriately low. The smaller frame would have a shorter top tube so I'd be less stretched out, the opposite being true of the larger frame.

Missing anything?

EDIT: with ANY bike, using "0.883 * inseam" my 32inch/81.28cm inseam tells me to make sure the distance between the top of my saddle and the center of the bottom bracket is 28.25in or 71.77cm (call it 72cm)

As long as I can get that distance out of a given bike, I'll have appropriate leg extension to not be causing me knee problems...?

EDIT2: Mollusk, if you had, say, a 54cm frame as your inseam suggests, I understand how it would be too "cramped" for you.

Could this be alleviated with a HUGE stem or are there other issues I'm missing? These ones from Yellow Jersey seem like they add 4 inches of rise and extension: http://www.yellowjersey.org/photosfr...t/823STEMZ.JPG