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Frame sizing. Is a 52cm a 52cm everywhere?(6 posts)

Frame sizing. Is a 52cm a 52cm everywhere?Nebuladds
Sep 8, 2003 4:41 AM
It seems that there's little standardization in frame sizes. I might want to invest in another frame, should I be unable to get my current bike fit correctly. The problem is, however, getting a frame that is actually 52 cm. Some manufacturers make a much bigger 52cm frame than others, if you know what I mean!

Moreover, if my LBS has the size I need, it's not the model I want, and if they have the model I want, they frequently don't have the size I need (i.e. the size I want to test for fit!).

So how do you get the right-sized frame?
no, not even in the same place :-) (nm)ET
Sep 8, 2003 5:09 AM
measure it or read geometry chart...C-40
Sep 8, 2003 5:23 AM
With few exceptions, every brand has a geometry chart on their website. The chart should (but sometimes doesn't) have a drawing that indicates whether the frame is measured center to center (c-c), center to top (c-t) or the oddest method, center to top of seat tube (Trek).

You have not stated how your "52" is measured. If you don't know, carefully measure from the center of the bottom bracket and see if the 52cm is to the top of the center of the top tube, top of the top tube, or top of the seat tube. Also measure the length of the top tube.

To really get a frame that fits the same (or differently) you need to know the seat tube angle also. This can be calculated by measuring the "setback". Setback is the distance from a vertical line through the BB to the center of the seat tube. A plumb bob can be used to create the vertical line intersecting the center of the BB. The seat tube angle is the inverse cosine of the setback divided by the c-c seat tube length.

The best way to get the right size frame is forget the LBS and buy mail order from someone who stocks all sizes or go to a better LBS. I haven't bought anything of significance from a LBS in the last 10 years.
about those geometry chartsET
Sep 8, 2003 6:18 AM
In general, even for official company web sites, the odds of the chart's indicated sizing method actually corresponding with reality are too low to rely on.
not true...C-40
Sep 8, 2003 6:51 AM
There are a few companies where the website pictures may not accurately indicate if the frame size is c-c or c-t but other than that, most companies have totally accurate geometry charts.

If you have a specific brand in mine, which one? I have not seen many errors in the charts.

The most often omitted dimension is the head tube length, which is very important.
re: Frame sizing.Chen2
Sep 8, 2003 6:42 AM
I agree with the others except that my local bike shops are usually willing to match and sometimes even beat catalog prices. Once I know what I want I usually order through a bike shop.
As for charts, Trek has good charts now but their previous charts showed a big mistake as to how they measure the seat tube height. A good way to compare bike sizing is to use a metric tape (I use my wife's fabric sewing tape). Measure and compare lots of frames, not only the seat tube length but especially the top tube length, and as C-40 says, the angles are also very important.