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bike size ??(3 posts)

bike size ??dcr915
Jul 7, 2001 11:35 PM
Im looking to buy a bike frame at a great deal. The possible problem is that the frame has a 1 inch longer top tube than the bike I have now. Im 5'7' and Im riding a 54. The frame Im looking at is at least 1" longer in the top tube. Any hard fast rules out there for buying the right size frame??? Is there any leway in frame size?
Some one let me know anything you might know or have experienced with sizing.
Thanks
Dennis
Ride hard and have a blast
re: bike size ??PsyDoc
Jul 8, 2001 7:45 AM
How do you like the length of the toptube on the 54cm bike? What is the length of the toptube? What is the length of stem are you using? So, the new frame you are looking at has a toptube length that is 2.54cm longer than your current bike. I would have to say that this is quite a jump and would require a much shorter stem than you are currently using, unless of course you are very flexible.

There are not any hard and fast rules out there for buying the right size frame, only general recommendations. This is a standard reply as questions of frame sizing often present themselves on this board. This information should be used as a good starting point for frame sizing. Frames differ not only in their size, but also in the angles that are used which may influence your choice of frame size.

A typical solution is to take your inseam measurement from your pubic bone to the floor in bare feet about 6 inches apart. Place a book with a 1 1/2" or so binding between your legs and pull up until you cannot pull up any further. In other words, you want to measure to the pubic bone so pull up hard. Make sure the book is level. Have a friend measure from the floor to the top of the book binding.

Then, take that number and convert it to "cm" by multiplying it by 2.54. Next, take the converted measurement and multiply by .67. That will give you a good estimate of the frame size (measured center of bottom bracket to the top of the top tube; commonly referred to as c-t) you would need to get. But, someone commented that this could put riders over 6-feet on a frame that is too small (c-t) and they may be best served by subtracting 27-28cm from their inseam length for a c-t frame size.

In order to find the frame size you would need from a manufacture that measures frame size from the center of bottom bracket to the center of the top tube (commonly referred to as c-c), you would multiply your inseam by .65 or you can subtract 1 - 1.5cm from the c-t value.

Once you have a good starting point, then you really need to go out and ride a few different sizes to see which one fits you most comfortably. I found that the more I knew about frame sizing, the more confused I became. Here are a few links on sizing information that will benefit you.

http://www.bsn.com/Cycling/

Note: click on "Ergobike: Competition Bicycle Size/ Proportions
Analysis" and at the bottom of the new page that opens, you can choose your inseam measurement. The program then calculates all the other measurements that are "average" for someone with your inseam. You will get a plethora of information back. BUT, keep in mind this is a "Competition Bicycle Size" analysis and the size you choose to buy may be a size larger or smaller than the size recommended.

http://www.coloradocyclist.com/BikeFit/index.cfm

http://www.huberbikes.com/production_bike_fit.htm

Chris Huber advocates finding your frame by taking your inseam measurement x .66. This value represents a center-to-center frame size. You would need to add another 1.5 - 1.8cm to that value to get your center-to-top frame size.

http://www.wrenchscience.com/WS1/guest1.asp
This is a pretty good sizing program.

http://www.electriciti.com/~bikelane/sizing.html

http://www.rivendellbicycles.com/frameinfo/Frame_Sizing.htm

http://www.sheldonbrown.com/frame_sizing.html

http://www.PeterWhiteCycles.com/fitting.htm

http://www.huberbikes.com/production_bike_fit.htm
no way! post the specifics...C-40
Jul 8, 2001 5:41 PM
Unless you're considering a much larger frame size, (which you shouldn't at your height), there's not a frame out there that varies that much in top tube length. You also have to consider the seat tube angle to determine the "effective" top tube length. The top tube length rarely varies more than 1cm in a given size. Maybe you're looking at an odd custom built?