Which frame geometry would be bigger?

[jckid]

I have a Moots Rigormootis frame with the following specs:

ST: 16"
TT: 22"
HT: 10.4cm (standard threadless headset)
ST Angle: 73.5
HT Angle: 70.8

I am looking at a frame with the following specs:

ST: 16"
TT: 22.1"
HT: 4.7" (internal headset)
ST Angle: 72.5
HT Angle: 71.5

I'm guessing that the frame I'm looking at would feel slightly longer than my Moots, based on the differences in ST and HT angles. Am I correct in my thinking?

[avalonracing]

Seems that way to me. But I don't build bikes or like math.

[djg]

I'm not sure we have all the variables we might want here, but it seems to me like it would tend to go the other way. If the new frame has a seat tube angle that's one degree less than that on the old frame, and you use the same post and saddle, and want the saddle in the same position in relation to the bb as before, then you need to scoot the saddle forward a bit on the new bike to get that saddle position you had on the old one, which would effectively -- or apparently -- shorten the top tube (although the actual length of the top tube just is what it is of course, and it might not be the case that all else is equal). The head tube angle change would work in the same way, although it would make less of a difference, and although here too other things could be going on. I don' t know which bike would feel or seem larger overall, but I'd guess that you'd use a slightly longer stem on the new one. No?

Oh yeah, the head tube is a little longer, but then I'm guessing that the stack height of the internal headset is less than that of the regular headset. Seems like about the right ballpark.

[PacNW2Ford]

The steeper seat tube angle is going to more than compensate for the 0.1" shorter top tube. Assuming that all of the measurements are made in the same manner, the Moots is going to have more reach.

[David Kirk]

Bigger in what way?

Dave

[labratmatt]

djg is right.

The bike with the slacker seat tube is going to be shorter in the top tube even though the two bikes have similar top tube lengths. So, the bike with the seat tube angle of 72.5 is going to be shorter.

[jmewkill]

Bigger in what way?

Dave

You know, bigger in "that" way

[Dave]

The slack STA will shorten the reach by about 1cm, with the saddle in the same position relative to the BB, so you'll need one size longer stem.

The front-center on the new frame should be shorter, due to the slack STA and steeper HTA.

The 12cm HT on the new frame is longer, but internal headsets have less stack height, so there will be little difference there.

The steeper HTA will increase the reach, but the amount will be too small to worry about.