Which frame is bigger?
 

Frame A: 54.3cm top tube, 54cm seat tube, 135mm head tube, 405mm, 74* STA

Frame B: 55cm top, 53.5cm seat, 152mm head, 394mm chain stay, 73.5* STA

With these numbers can anyone tell which frame is larger?

I'd say it isn't as much a question of the difference in the two sizes as it is between the two geometries. If you can, compare the bikes side by side, taking time to sit on and ride each.

I cant sit on one of them cause it's just a frame. I don't wanna waste time building it if it's going to be larger than the one I have right now.

Not enough information but B is seemingly bigger if they have the seat angle.

Are the top tube measurements given horizontal/effective TT length?

You're looking at a half cm or so difference in top tube and seat tube measurements. Assuming the TT measurement is for a horizontal tube or effective length of a sloped or curved tube, there isn't going to be much difference in overall size, but there might be a noticable difference in geometry. I have two hybrids right now. One has a 21.5" seat tube and the other 22" but the standover is almost identical and the bike with the 21.5" seat tube actually feels "bigger" because of a slightly longer top tube.

Frame B is bigger but without the seat tube angles I couldn't tell you if it fits bigger.

I added the seat tube angle.

They are effectively the same. Frame B is bigger but by such a small amount that you won't notice the difference. If they both use the same type of headset then B is roughly 1.5cm higher stack (front) depending on forks, headset stack, BB drop, etc.

Thanks. Is there some sort of formula for all this? The thing that was throwing me off was that one had a longer TT while the other had a longer seat tube.

You should try some of the online fit calculators, they all give slightly different numbers for recommended geometry....and these are just guidelines not gospel.

Asking which frame is "bigger" is like asking which person is bigger, the 6 foot 145 pounder (me) or the 5 foot 8 220 pounder (my dad).

youre dad is bigger and you are taller.

yeah i know about online calculators...i wasnt looking for the best fit for me. i was trying to compare to frames and hope that they were about the same size, geometry or what not.

There is, a few trig formulas are used. You want to compare the stack and reach between different frames. You also have to account for the different head tube lengths when the other values are equal. There are a few stack/reach calculators on the web that get you close enough for comparisons. There are also many stack/reach articles out there that explain the concept.

http://velonews.competitor.com/2011/...ndustry_154565

http://www.slowtwitch.com/Bike_Fit/C...er_One_95.html

Your frames practically have the same reach. Frame B has a higher stack.

The answer is simple. The second frame has a 17mm taller head tube, so it's vertically larger, IF the type of headset used is the same on both frames. If not, then you need to specify if one uses a conventional press-fit headset and the other an integrated model. It make a significant difference. Because you list the out-dated seat tube dimension, I assume that both are traditional horizontal TT frames.

Horizontally, the 74 degree STA adds about 5mm to the reach of the first frame, so it's only about 2mm shorter in reach.