Frame comparison help

[tjk23]

So I'm looking at buying a new, to me, frame and hoping for some help. I currently have a BMC GF 54 and looking at a Specialized Tarmac 56 and wondering how close they would be in sizing. I have a 130m stem on the BMC and thought maybe with a 56 a could use a 120 or 110 and be pretty close. I found a good price on the 56 Tarmac is the main reason I am thinking about changing frame sizes.

[Black Dog]

What is the difference in the effective top tube lengths? You can generally subtract the difference between the two to figure out your new stem length. Also if your stem is as low as it will go the compare the head tube length on both frames.

[oldpotatoe]

So I'm looking at buying a new, to me, frame and hoping for some help. I currently have a BMC GF 54 and looking at a Specialized Tarmac 56 and wondering how close they would be in sizing. I have a 130m stem on the BMC and thought maybe with a 56 a could use a 120 or 110 and be pretty close. I found a good price on the 56 Tarmac is the main reason I am thinking about changing frame sizes.

I would write down all the particulars of each..top tube length, seat tube angle, headtube length, head tube angle. Then show to fit guy, have them determine if the BMC fits ya..then have them see if the Spec-fits ya. it's what good ones do.

[lhuerta]

Brush up on STACK vs REACH and then compare figures (posted on BMC and Specialized websites). Top tube length means nothing unless you know STA, not to mention HTA, BB drop, etc.

[soulspinner]

brush up on stack vs reach and then compare figures (posted on bmc and specialized websites). Top tube length means nothing unless you know sta, not to mention hta, bb drop, etc.

+1...dont forget bars. The reach on each is different..........