In between frame Sizes
 

The Roubaix Comp has what I would call recreational geometry, with a short reach and tall stack, to produce a more upright riding position.

Here's a link to the geometry chart. https://www.specialized.com/us/en/ro...=240093-129154

The smaller size has 6mm less reach and a 10mm shorter stem, so total reach to the bars is 16mm shorter. The stack on the larger frame is 21mm taller, so the bars should sit significantly higher. Whether that's good or bad depends on your body proportions. To get an idea of your proportioning you need to determine an accurate saddle height.

There's a big 41mm difference in seat tube length, which makes saddle height more important to know.

Cycling inseam is measured from the floor to firm crotch contact, in bare feet. As an example of an extreme, I'm only 5'-6.5" tall, but my cycling inseam is 32-5/8" or 83cm and my saddle height is 73cm. I've seen people who are 6" tall post the same cycling inseam.

Unless you have very long legs, like mine, I'd lean toward the smaller size, because the bike has such a tall stack height. Even then, there's no reason you can't put a 120mm stem on it to increase the reach.

Consider your leg length and how that might affect your ability to vary the seat position which in turn affects many other aspects of your fit.

If you don't feel significantly better on one vs the other then it's probably not going to matter much. I'd however want to do an actual ride of a mile or so on both. That way I can figure out which might give me more or less confidence when maneuvering fast turns and slow turns. As well did I feel like I was going over the handle bars on one when I braked hard, particularly when going downhill?

A fairly wide range of frames can be set up to fit your body, IMO. So don't let the 1-1/2 inches of difference between the 58 and 61 cm frame bother you too much. Providing of course that your leg length doesn't suggest that you should favor smaller or bigger. Even with that some might ask "how 'bout your reach?" That might throw everything back the opposite way.

So if your gut instincts and any insight the people at the shop give you as to which way to go, then go for it. Getting bogged down in the mathematics of the perfect fit will not have you on a bike very quick.

I agree. You really should take each bike for a real test ride outfitted with the shoes and pedals you intend to use and the saddle adjusted for height and setback to give you the position over the cranks that you prefer. One bike will then no doubt feel better in reach and body position than the other with the stock cockpit setup.

I have a similar issue. I'm exactly 5'10" with a 32.5" PBH, and a saddle height of a little over 29" (74cm) from the BB. These measurements are usually right between the sizing of a typical "54" or "M" and "56" or "M/L" road frame. This is actually a good thing in that multiple options will work for me depending on what I'm looking for. On the other hand, I do like to test ride bikes before buying to ensure I'm picking the right option.

The great news about being this size is that I really have two options: generally more aggressive (54) or generally less aggressive (56). As long as I get the relative position of the saddle and bars where I want them for the given type of riding, either will work. With a 56 you usually get longer head tube and longer effective top tube which means I need to run less/no spacers, run a slightly shorter stem and run bars with a shallower drop. In contrast, with a 54 I need to run 1-2cm more stem, deeper drops and maybe a spacer or two. The main difference is that on the smaller frame I can get a lower front end by removing spacers and adding stem length. Doing the same thing on a 56 is not always as easy as I start getting into negative angle stems and the like.

One other factor is the amount of exposed seatpost, but this is also influenced by the slope of the top tube.

At the end of the day, I can get the saddle and bars into the position I prefer on either the 56 or 54 and the decision becomes an aesthetic choice. In general, if I'm looking for a road race bike, I go with a 54 and a 110-120 stem and a maybe few spacers. For gravel and endurance frames, I'd go with a 56 and a slammed 90-100 stem. I actually prefer the look of the 56 with the slammed stem, but it's really a question of aesthetics only.

Side note: frame size used to be far more of an issue decades ago when I first started racing. Stems/bars/seatposts only came in a couple of sizes and frames generally had 2" increments between sizes. Also, frames were not "proportional" back then, they'd just make a longer seat tube and head tube and leave the top tube/angles/trail/wheelbase about the same. As a result, getting the right fit was a pain and most anyone serious about racing went custom back then. Neither issue is really a problem these days, we've got it easy.

This sets aside MTB sizing, which is yet another can of worms...

Yeah, I heard the same general rule, if in between sizes...size down for a more aggressive riding style, size up for a more upright/relaxed position.

The Higher End ones do CM by CM size increases, like Pro Italian Steel ..