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Jun 4, 2003 12:30 AM
Can anyone tell me how to determine what frame size my bike is. Not sure where I take the measurements to make this determination. Thanks
2 answers:Alexx
Jun 4, 2003 3:11 AM
The old method is this:center of the BB to center of the top tube.
The new method is this: center of the BB to the top of the seat tube.
Both standards are used-it depends on the manufacturer.
2 answers:fredstaple
Jun 4, 2003 3:58 AM
Thanks, any idea what trek uses?
1 answer:filtersweep
Jun 4, 2003 4:24 AM
Trek sort of measures center to top, which is why they run small.
Jun 4, 2003 8:26 AM
My understanding is that Trek measures center of bb to top of the seat tube collar, not the top of the top tube like other "center to top" manufacturers.

THAT is why Trek runs small, because the seat tube collar is higher than the top of the top tube.

Now, Say that three times fast!
hence "sort of"filtersweep
Jun 4, 2003 8:48 AM
Did I miss something?TNSquared
Jun 4, 2003 9:21 AM
If there is a "sort of" somewhere, I missed it. Sorry about that.

Not that I really wanted to put to fine a point on it (cliche alert!), but I just spent months trying to determine the proper size Trek frame for me with no LBS help and no prior experience. It was a nightmare.

Tarwheel is absolutely right. THERE SHOULD BE A STANDARD!

The best thing to do is probably to go to Trek's website and see if the geometry charts describe exactly how they measure each dimension. I know it's in the catalog, but I don't have it with me.
a third answer...ClydeTri
Jun 4, 2003 4:30 AM
I have seen some who measure from center of BB to top of the top tube...
unfortunately, there is no standardtarwheel
Jun 4, 2003 5:08 AM
One of the ridiculous things about the bike industry is there is no standard for measuring frame sizes. Some manufacturers measure center-center, others center-top, others center-to-the very top of seat tube, others center-seat tube binder bolt. What brand of bike do you have? That would help in determining your frame size.

Top tube is another matter. To my knowledge, most manufacturers measure top tubes the same way, that is center-center. However, with sloping top tubes, this gets a little tricky. Most bikes with sloping top tubes also give a "virtual" top tube length -- that is, what is would measure if c-c if parallel.

To complicate matters further, top tube measurements mean nothing without knowing the seat tube angle. A steeper seat tube angle (74 and up) makes the top fit longer; a slacker seat tube angle (eg 72.5) makes it fit shorter across the top.

Perhaps the only consistency in bike measurements is that they are usually done in centimeters (cm).
mtbikes are in inches... nmClydeTri
Jun 4, 2003 6:39 AM
Always go with manufacturer's method of measurementelviento
Jun 4, 2003 6:48 AM
If you are selling a bike and use YOUR measurement method, you will only get into trouble. In fact a frame I ordered from a dealer turned out to be the wrong size because the dealer measured it without checking manufacturer's official size label.

Of course that's how to determine what frame size your bike is, not how to determine what frame size you need.