Cyclocross - Sizing question, looking for opinions

I'm looking at picking up a BD bike, though not sure what size. I ride a 52 road bike with a 53cm TT. I think I should get a 49 from BD, which according to the website has a 52.5cm TT and a standover of 29.6". The 52 size has a 52.9cm TT and a standover of 30.3". My inseam is ~30".

I think I would be better off with the 49. What do you all think? Thanks.

I'm looking at picking up a BD bike, though not sure what size. I ride a 52 road bike with a 53cm TT. I think I should get a 49 from BD, which according to the website has a 52.5cm TT and a standover of 29.6". The 52 size has a 52.9cm TT and a standover of 30.3". My inseam is ~30".

I think I would be better off with the 49. What do you all think? Thanks.You said your road bike is a 52 with 53 TT, so why do you think the 49 cross bike would be better than the 52?

I was pretty much going by standover. The difference between the toptube lenghts is almost nil. Is the standover not that important?

I was pretty much going by standover. The difference between the toptube lenghts is almost nil. Is the standover not that important?Standover is irrelevant, on a road or cross bike at least. Standover is relevant on a mountain bike where you are picking your way through boulders and such, but mountain bikes are built with tons of standover anyway. In other words, standover is irrelevant.

What is relevant is the spatial relationship between the five contact points (two hands, two feet, and arse).

There is only 4mm difference in TT between the 49 and 52. But there is a roughly 30mm difference in head tube length. (They don't publish exact HT numbers, I am inferring 3cm from the seat tube numbers). That means the handlebars are going to be over an inch lower on the 49 than on the 52, while saddle height stays the same. In other words, your butt-to-bars reach would actually be longer on the smaller bike.

Another way of visualizing this, is that when you move to a smaller frame, you will be using that much more seatpost, which moves your butt up and away from the handlebars. Most people don't quite grok this.

Sure, you can make up for the lower handlebars with a riser stem, or more spacers, or both, but at a certain point the handling of the bike changes, and you might as well get the correct frame to begin with.

Allright then, thanks for the help!