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Bike Size - Confused.(13 posts)

Bike Size - Confused.Mart
Jun 10, 2001 10:42 AM
My inseam is about 83cm ( 29 3/4 inch). The bike size that is recommended for me is about 54cm (21 1/4 inch) centre to centre. When I ride one that size it always seems that I am stretching too far forward even with a 10 cm stem. Can anyone give me any advice, before I waste my money, rather than the sales staff who tell me all the bikes look okay.
Check your LBS's mathVelocipedio
Jun 10, 2001 11:04 AM
Your math, or more accurately, your LBS's math, seems to be off.

My math gives me 75.5 cm for 29.75 inches [1 inch = 2.54 cm]. Multiplying by 0.67 [the factor one USUALLY multiplies inseam by to get bike size], that'd give you a 50 cm bike. Multiplying by 0.65 [a factor used by some manufacturers], you get 49 cm.

We have roughly the same inseam length [I'm 5'8" male and have shortish legs... if you're normally proportioned, I suspect you're 5'7" or 5'6" if you're a man and 5'6" or 5'5" if you're a woman]. I take a 50 cm bike. The exception is Specialized and some other US-based manufacturers who make largish frames. I fit a 48 cm Specialized Allez.

I think you've been trying-out too-large frames. Try a 50 cm with a regular stem and see how it feels. The bottom line is that you should NOT buy a bike that doesn't feel quite right.
You ansewered my question too, thanks!SSgt Jeremy in Germany
Jun 10, 2001 11:18 AM
I can see by your ansewer to his question, you ansewered mine too, I am 5'7" just like you suspected for someone with a 29 3/4" inseam. I think the first LBS was right with their evaluation of a 50cm bike for me. And I suspect the second bike shop just wants to sell a bike, even if it is the wrong size.(I should have suspected as much from a shop owner that doesnt ride, grossly overweight) Thanks for the great advice, I am going to find a 50cm.
Check your LBS's mathsidley
Jun 10, 2001 11:23 AM
The only thing I could add to the above post is maybe its worth your while to schedule a fit at a different LBS. Any decent shop will put you on what looks like an exercise bike with movable parts to determine your ideal size. It will probably cost about $20-30.

I would have saved myself a lot of pain had I been fitted before buying my first road bike -- a 56 cm Allez -- which as indicated above, was way to big.
I have the exact same question!SSgt Jeremy in Germany
Jun 10, 2001 11:09 AM
My inseam is the exact same, 29 3/4, (I am 5'7") one LBS tells me I should ride a 50cm, another one says 56cm (they have a 56cm they are trying to sell me). What gives? I did feal stretched out a bit on the 56 too. I am lost, what do all of you think?
re: Bike Size - Confused.rpicayo
Jun 10, 2001 11:53 AM
I happen to be about the same size (at least inseam wise) and I'm a 5'7" male. I bought my first bike about a month and a half ago and got a 54" Trek 2300 that I am very happy with. I also looked at a 52" Specialized Allez Comp which was very close in size (Trek measures height differently that Specialized). I have a longish torso compared to my inseam, and I didn't feel right on a bike any smaller.

I hope I didn't just add to the confusion more as people seem to be steering you to a much smaller bike. I guess the bottom line is to test ride differents sizes, and get various opinions from various shops before settling on a bike.

R
What is a normal Torso to Legs ratio?SSgt Jeremy in Germany
Jun 10, 2001 12:10 PM
Now I am wondering what is normal, is there a ratio that is considered normal for your legs to torso? Should your legs be exactly 1/2 of your total hight? Or more like 40% of your hight? I guess what I am asking is what do the bike manufactures consider is normal when creating the geometry of their bike frames.
Typing error re original message.Mart
Jun 10, 2001 2:04 PM
Re original message: My brain was not in gear - My inseam is 83cm which is nearly 32 3/4 inches. This using the x .65 method means I should be looking at almost 54cm centre to centre but it makes me feel like I am on a rack. I may have to consider a Trek bike which I think seems to have a smaller length top tube or even a 54cm Cannondale which is measured centre to top.

Mart
The right size...Velocipedio
Jun 10, 2001 3:05 PM
RE: "I should be looking at almost 54cm centre to centre but it makes me feel like I am on a rack."

Indeed. What all of this boils down to is that sizing a bike is as much art as science. As another poster pointed out, there are a whole number of other variables involved, including trunk length/top tube and the actual design of the bike.

I don't know if you're a man or a woman, but if you're a woman, you've hit upon one of the fundamental truths of bike sizing: they're sized for men. Women tend to have longer legs and shorter trunks than men, so a frame that fits them in terms of standover, may not fit them in terms of top tube. That's why some manufacturers, like Trek and Bianchi, have bikes with femal-specific geometries.

The other thing is that, even within genders, there is considerable variation of body type, and many manufacturers don't even bother to try to design for the average...

The only thing to do is to TRY the bikes in a given range -- say, two centimetres more or less than your mathematical [theoretical size].
I'm the same size rangezelig1
Jun 11, 2001 7:14 AM
AT 67" with a 30" inseam I have 5 frames which run from 50.5-52 ctc including a custom Marinoni. The top tubes run from 52.5-53.4. So to MeloVelo's point, there are a lot of variables. My 51 ctc custom has a 73.5 seat angle, 53 top tube and I run a 100 quill stem. My Vortex is about 50 ctc, 74 seat tube angle, 52.5 top tube and use a 100 threadless stem. Both fit the same with the shorter top tube versus the custom being mitigated by the lower bar height from the threadless setup. Confusing enough? Regardless, the 54 size sounds much too large, primarily the result of the related top tube length. If you feel like you're on a rack, the top tube's too long.

I would try bikes in the 50-52 ctc range if your body is of 'normal' proportion. The .6667x inseam is just a guide and not a rule. If they insist on the 54 frame and you're not comfortable on the bike, I'd find another store/salesman.
All these rules are starting points.....Len J
Jun 10, 2001 4:05 PM
Not hard rules. I have short legs and a long torso, so I have what appears to be the opposite problem as you, I get a smaller frame that I have to "Streach out" with a longer stem. It sounds like you may have a short torso compared to you leg length (vs. the average). This would mean that a frame that fits your legs may be to long for your torso. Three Suggestions:

1. Try different bike Manufacturers. Not all bike builders use the same geometry. (eg.Lemonds have a longish top tube.)

2. Try a smaller frame with a longer seatpost. One possible problem with this has to do with the height of the threadless fork. you may need to change out the stem for one with some rise in order to get comfortable.

3. Go custom.

The idea above to try a fitting from a different LBS is not a bad one. I would find someone certified by Serrotta and pay them for it. ($50 to $75) Seems like a lot until you consider that the most important thing about the bike is the fit. You are doing exactly the right thing so far in questioning the fit. Its a pain, but unless you have an average body (which very few have) its worth the effort once you get the bike. The better it fits you the more comfortable & efficient you will be. & the more you will ride.

Good luck.
Try these sizing sitesKerry Irons
Jun 10, 2001 6:48 PM
http://www.bsn.com/cycling/ergobike.html
http://www.coloradocyclist.com/BikeFit/index.cfm
http://www.sheldonbrown.com/harart-frames.html
http://www.electriciti.com/~bikelane/sizing.html
http://www.rivendellbicycles.com/frameinfo/Frame_Sizing.htm
http://www.peterwhitecycles.com/fitting.htm
re: Bike Size - Confused.BrianU
Jun 10, 2001 11:12 PM
You sound like you are about the same size as me. I am 5'6" and after doing a week long tour last year, decided that my old Cannondale SR800 was too big. I found a 2000 Cannondale that had my name all over it. White with the stars and stripes on it. However, even though it was supposed to be my size, a 54cm, I still felt stretched out on it. I eventually ended up with a LeMond from a different shop. Its a 51cm and feels right. Definitely get a fitting done if possible and do not buy something that doesn't feel right, regardless of what the sales staff says.