I’ve been racing BMX for a long time now (18 years give or take).
I was ready to go out and start hunting for a new longer frame to race.
But, when I talked to people from club, they started talking about rider area,
rather than top tube length, as a way to compare different frames.
What is this measurement, and what does it mean to me?
I have only found a few frames manufactures that give you this measurement
(eg; Chase, Crupi and Yess).
Down under in New Zealand
“Rider area” is a measurement that was suggested by Yess, who also used to make Crupi frames, which is why you find those two brands in the same boat measurement wise. Chase came on board to offer this measurement as well because many people do like to cross reference this measurement.
To start, here is how the measurements differ; “Top tube length” is measured from the center of the head tube to the center of the seat tube, along the side of the top tube, while “Rider Area” is measured from the bottom center of the headtube to the bottom center of the bottom bracket and does not follow the down tube. Now, why the RA measurement? TTL is not constant, if you have a frame like the Yess with a unique, or steeply angled top tube, and/or a seat tube angle that is not the typical 71-72 degrees, then this measurement can vary by up to half an inch. Rider area on the other hand is less effected by top tube and seat tube angles so it is more consistent.
Why they are both right? They both give you a clear line of measurement to help you gauge and compare the sizes of a frames.
Why they are both wrong? They are both subject to variation based on headtube or seat tube angle, so they are both marginally flawed measurements.
Our advice is to compare frames size based first on geometry. If you are comparing two frames with 74-degree headtubes and 71-degree seat tube angles. Then your top tube lengths should be relatively close. On the flip side, if you do have a frame with unique angles, like the Yess with a 68-degree seat tube angle, or a funky top tube, like that on the Yess or the Phoenix, then rider area is a great alternative to gauge length.
Hope that helps Alex. If you swing by the http://www.yessbmx.com they have some clear visuals on their Rider Area measurement system side by side with projected top tube lengths so you can compare.
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