I have tried to make it a point to understand everything I can about road bikes, yet next to someone who works in the field, I know just enough to be dangerous. That’s usually a bad thing.
That said, there are several simple things that a noob should know when considering the purchase of a road bike. Let’s face it, they’re anything but cheap. In this post I’ll try to cover what is important, without getting too deep into the intricacies. My goal is simply to help one make an informed decision rather than try to cram a 5-year apprenticeship in frame geometry into one post.
Giant came out with the sloped top tube compact frame TCR about two decades ago and it revolutionized bicycle frame building. With the standard (horizontal) frameset, sizing a person to a bike was a very intricate process requiring precise sizing. For instance, on my iconic Trek 5200 (1999), I must have a 58-60 cm bike at 6’0″ tall. The bike relies on stretch to get into an aerodynamic position:
With the advent of the compact frame, the geometry was vastly simpler to fit a cyclist to a bicycle while negating the need for so many frame sizes. My Specialized Venge is of the compact variety:
My Compact Frame Venge is a 56 cm frame and I’m told I could have been fitted to a 54. I picked the 56 for a specific reason though. I purchased the bike when I was 43 years old. I knew the 56 would give me a more aggressive posture on the bike when viewed against my 5200 but wouldn’t be so aggressive that I wouldn’t be able to ride it 20 years down the road at a crisp 63. The 54 would have meant a much greater drop to the handlebar and either more spacers under the stem or an egregiously sloped stem.
My 58 cm Traditional Frame Trek 5200 is about as small as I’d want to go, though with some tinkering and special parts I could have probably gone with a 56, but a 54 was absolutely out of the question. How do I know this? I’m glad you asked. I bought 54 cm Cannondale SR-400 on Craigslist (scroll down to the last bike). It was advertised as a 56 cm frame but once tape measure was put to frame we came to find out it was indeed a 54. I’ve ridden the bike for fun, on our annual night ride, but trying to fit my big butt on that little bike isn’t all that much fun. You should have seen how the owner of our local bike shop reacted when I wheeled that Cannondale in. It was priceless. He knew it was too small without me ever throwing a leg over the top tube.
In any event, having put more than 10,000 miles on each of the Venge and Trek, I can say unequivocally, the Compact Venge simply fits better. It feels better, rides better and is vastly more comfortable and more stable – and this is with the same wheels on either bike (I regularly ride the Trek with my good wheels on it, it only takes a swap out of the cassette).
I am not an authority on frame style though. There are plenty of people out there who still swear by the old standard frame. Choosing a bike and frame style is a highly personal thing so investigate prior to purchase. Just know, going in, if you pick a bike with the standard frame, you must get the proper size. With a compact frame you’ve got a little more room to play around.
There is no right or wrong when it comes to which style one prefers, there is only “like”. I like my compact Venge because the geometry feels vastly more comfortable to me. This doesn’t mean I don’t like my 5200, I just prefer the compact geometry over standard. I truly believe the compact suits my riding style a little better.
Now, what I won’t do is feed into conspiracy theories about the industry forcing everyone into compact framesets because it’s cheaper for manufacturers to make the frames (they don’t need to make as many sizes, it is cheaper). As I’ve been told about both, the advent of the compact frame, and its acceptance as pure awesome, it was a cycling team (Oncè) who pleaded the case for them to not be banned by the UCI, then rode the frames to glorious victory.
The nature of the conspiracy is that it’s industry driven, the move to the compact frame, because the manufacturers save money by not having to produce as many frame sizes.
Let’s say I look at a Specialized Venge, the 2017 version of my bike. 49, 52, 54, 56, 58 and 61…. The same frame sizes one would expect in a standard frame. However, let’s look at this differently, rather from a defensive posture; My undersized (by one size) Venge is vastly more comfortable (vastly) than my perfectly sized 5200 – and I am talking about the position of my body, not the way the different frames react to the road. I can ride more aerodynamically (lower), yet more comfortably, on the compact frame that the standard.
In other words, the compact frame benefits me, the cyclist, just as much (if not more) than it might the manufacturers (if they bothered to make fewer sizes I’m the first place). So forgive me if I roll my eyes when people complain that the industry is skewed. The way I see it, they’re skewed in my favor, and that’s a good thing.
What’s important
What is important here, beyond the hoopla, is what is best for the cycling noob, who understands the words I wrote but not exactly what they mean.
I didn’t understand “sizing” five years ago, and that ignorance led to a poor choice and a waste of money. When dealing with a standard frame, size is incredibly important. If you don’t know what size bike you need, there are online calculators. Work strictly within the sizes recommended, the geometry matters.
When looking at a compact frame with a sloping top tube, if you want a smaller frame so you can ride lower, this is possible, though it’ll likely cost you money in replacement parts if you’re not ordering a new bike (a new, longer stem, and new crankset with longer crank arms for example).
In both cases, don’t buy a bike larger than your recommended size. I’ve never seen a credible reason to do that.
Fit Recovery 
Interesting article…I though that the original TCR frames were developed because the provided a stiffer rear triangle with all the benefits that gave. Sizing a frame is surely based on the three contact points of bottom, feet and hands – and the optimal relationship of the thee points to each other with the riding you intend to do. These can all be achieved with a smaller stiffer frame but usually at the loss of something else – slow steering because of the oh so popular long stem, front wheel/foot contact problems with longer cranks, over long seat posts that have to be stiffer than usual – hence adding back the weight that the TCR frame apparently loses through the use of less material than a ‘standard’ frame. The most difficult thing is that no matter what size frame we ride, we all have the same size wheels….which means that the largest and smallest frame sizes are genuinely compromised. Yes, there are smaller wheels but their use is still very low (costs again).
The stiffer frame was a part of it, as was the weight savings (the original TCR Aluminum weighed just 900 grams). Now, it’s interesting you mention the longer stem and slower steering because you get that with a stretched out standard frame as well, in a longer wheel base. Also, I’ve never run into a situation where I felt my steering was compromised in any way due to my 110 mm stem – everything feels too right.
Great comment!