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Frame size in relation to top tube length
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What is the relationship between frame size and top tube length? How does one determine which frame size one ought to purchase in a given model of bike? I have looked at the tribike fit section and I've yet to uncover this information. If I'm missing something that has already been posted on the site, please direct me to the right place.

The reason I ask is that I am considering a new tribike, and my bike woes of late have all been related to fit. I live in a bike fit wasteland, so I will have to figure everything out (to the best of my ability) on my own. If I knew what size frame I should start with, I think the rest of the tribike fit section would make more sense.

I have tried inseam x .67 and I'm not comfortable with the figure I'm coming up with. My inseam is 33, so I come up with a 56cm frame. I'm 6'2", and I know I don't fit on a 56cm bike. (I've had a 57cm QR Kilo that was too small. I was too scrunched up on the bike; a 57cm Kilo carries a 55cm top tube, according to the website.)

Am I correct in my belief that there is more to frame size than just frame size; that it is also frame size in relation to top tube length?

RP
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Re: Frame size in relation to top tube length [rhpreston] [ In reply to ]
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You may want to start with a tool such as this to see how your 'typical' recommended frame might be dimensioned.

http://www.competitivecyclist.com/...FIT_CALCULATOR_INTRO

If memory serves me, the calculator's output includes total reach and recommended top tube / stem combinations.
Last edited by: JustCurious: Sep 5, 03 13:04
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Re: Frame size in relation to top tube length [rhpreston] [ In reply to ]
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IMO, top tube length is more important than is seat tube length. Unfortunately there is no formula for determining top tube length. I have three road bikes with 55.5 cm top tubes - a medium size Giant TCR, 57 cm Bianchi and 53 cm Sekine. All fit me fine in the top tube measurement.
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Re: Frame size in relation to top tube length [cerveloguy] [ In reply to ]
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Top tube length seems to me to be the missing ingredient in my quest for the perfect bike fit. For example, two knowledgeable people told me that the 57 cm QR would fit me. However, they did not take into account the top tube length. For example, one of the bikes I have looked at is a Litespeed Saber (don't know that I have a chance of getting one, but I'm I'm looking at it!). Just for kicks, I compared the top tube lengths of the 57 cm Saber and a 57 Kilo. The Saber sports a 56.5 cm top tube length in that size, whereas the Kilo has a 55 com top tube. So by virtue of these figures, a 57 cm Saber would not fit the same as a 57 cm Kilo. It seems that the top tube length is the key, but I don't know exactly how. If I knew that, I would know where to start in the search for what I hope to be my new bike.

RP
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Re: Frame size in relation to top tube length [rhpreston] [ In reply to ]
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Even frame size can be misleading. A 58cm from one manufacturer can be different than a 58cm from another. One may be center to center and another center to top,ect...I had to get my measurements first then go into shops with a tape measure(or look at geometry,online ect.)to find what fit. Example: I needed a seat tube of 61cm with a seat post of 12.4. and a top tube of58.5. My Klein gave a seat tube of 59.8(on a 58cm bike) with a 13.6 seat post and a 58.7top tube. Seat post adjustment gave me the perfect saddle to peddle distance and nothing I could find here in Montana came as close to the .2cm difference my Klein did. Hope this helps
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