Need some confirmation on frame sizing from all city owners for the thunderdome or big block (same geo). I am 5'9" or 5'8" barefoot and about to order the 49cm. For those of you who have never researched their geometry a 49cm has a 53.5 cm top tube. My 54cm caad10 road bike has a 54.5cm top tube but its a bit big. Had to drop to a 90mm stem. So i think i am making a good choice here but any confirmation or argument against would really help. What size is your frame and how tall are you?

Although my All City is a nature boy, I went with a 49cm. All their frames have a healthy top tube length. I'm also 5'8.5" and have a 54cm CAAD10 with a 90mm stem. I think you'd be making a good decision on size.

Wow what are the odds someone has same bike, same size, and replied in like 5 minutes. I f'n love the internet. Thanks man!

I've been wondering about this as well. Due to a long top tube to seat tube ratio, I feel like I'd need to get a bizarrely small size in a lot of the frames I'm seeing, like the All-City frames.

Is the point that these frames are meant to stretch the rider out over a standard height (standard seat tube, long top tube), or is it that they're supposed to crouch the rider way down (short seat tube, standard top tube)?

In any event, I despise an overly long top tube, so to ride one of these frames I'd either need to accept a big saddle to handle drop, or else jack the handlebars way up, right? Or am I missing something about the geometry?

Well, after studying the geometry for many days converting mm and cm to inches, measuring my current bike, rinse, repeat, etc etc...... I think what it boils down to is that you just cant get hung up on the numbers. The 49cm all city big block for example has almost identicle geo to the 52cm caad10. So after all that measuring and worry when i compare the caad10 54 to the all city 49cm i will have approx 15mm shorter reach and 22mm more seatpost sticking up. So from here i am just going to assume moving back 15mm cancels out moving my arse up 15mm and once its all said and done my ass is a quarter inch higher than it was before in relation to the bars. Cut the fork tube long, add an extra spacer and back to same riding position with a more comfy reach.

I passed math with a D- though so better not listen to me. Think i will order the 49 though and hope it all works out

A short cut to all this is to look at the stack measurement. Thats a verticle measurement from bb to head tube effective base height. That in my opinion gives you the seat to bar height relationship assuming crank length is the same

Yeah, I hear a lot of people lately using stack and reach to size frames rather than TT length. I thought a 49 sounded way small until I looked at the geo chart and saw that their size labels come from the seat-tube length. Still don't understand why companies do that.

This seriously baffles me too, especially when 1) it ignores seat tube angle and 2) always measures center-top, which is highly arbitrary. It might have made sense when frames tended to use the same angles and the seat tube stuck up a standard height above the top tube, but these days it's totally unworkable. I can see why it's a useful measurement for the builder, but not for the consumer.

In fact, I'm shocked in general that a more sensible and standardized system of measurement and spec presentation hasn't caught on.

I am ~178cm with ~33-33.5 real inseam. I have Space Horse, Big Block and Nature Boy disc all in 52 and have been riding them quite comfortably for a while (90-100mm stems on all of them). I recently bought Nature Boy in Reynolds 853 and Mr Pink, both in 55 and they are way more comfortable for me, fit like a glove with 100 mm stem.
Now looking at getting either Big Block again but in 55 or Wabi Special (I rebuilt SH and Big Block for my wife so need to backfill the gap :-)). Still keeping my first Nature Boy for myself though, just gonna build it as another winter ride with 110mm stem and different bar setup

All City labels their sizes based on the Seat Tube, they build their bikes long and low so while its called a 49 it really fits closer to a traditionally labelled 53 except with better stand over height. I love this since I have short legs. I'm 5'10 and ride a big block 52 (fits like a 55). You're probably making the right choice with the 49.

What made the 55 more comfortable for you? The higher stack? The difference in reach looks very minor on the geometry chart - is that what you found in riding it? Going through a similar debate - thanks for the help.

Did you ultimately decide on the 49cm here? How's it working out? Girlfriend is your size and having a similar debate (albeit on the Space Horse).

On 52 I felt a bit cramped, tons of seat post exposed, lots of spacers (not that it is a bad thing on Surly or All-City frame) or pretty deep saddle to bars drop for non-race setup Plus I do like my frame bags and 55 has a bit more space to fit half-bag and two water bottles
Long story short - I switched Space Horse 52 to Mr Pink in 55, Nature Boy from 52 to 55 and very happy. I also switched from Big Block in 52 to 55 Wabi. All fit like a glove with 100mm stem and compact drops.
My friend has Space Horse in 55 and I started switching after I rode his.
And yes, I like higher stack

I'm slightly taller than 6'2" and the 61 was way too big for me. The 59 is just right.

Go for the 49. I have a 52 Big Block and it's a hair too big for me at 5'10.

i'm 6'1" and ride 58s in all-citys.

im 5'8 and my tube top on my Nature Boy is 21 inch not sure of the actual size but its 53cm give or take a few mm.
seems to fit me fine. i have noticed i have to play with the height of the seat and dial in the distance on the saddle but fits like a glove.