With regard to road bikes, are the sloping top tubes of compact frames just designed to decrease standover height or are there other reasons as well?

Are there tradeoffs to compact frames? I'm 5'7" with a long torso and short legs and find that many bikes that fit me well don't give me much, if any, standover room.

The sloping top tube of a compact frame makes it easier for the frame builder to make a small frame and keep the same angles. I ride an XS Look frame and the sloping top tube makes it work.

It was also thought back then that the sloping top tube tightened up the frame triangles making for a stiffer more responsive ride. There have been many arguments so take it for what it's worth. Plus with today's stiff materials, who knows if this applies.

I myself hated the look of a sloping top tube when they first came out. No after riding a few, I prefer it far more than the straight top tube. Easy Handling at stops etc. I'd much rather have a sloping tube because of it.

Yet another reason was to allow it to fit a wider range of people with a given size. Mid level to high range bike frames used to come in 2cm sizing increments which meant about ten different frames. Now they come in a maximum of 5... and most manufacturers only make three.

Aaron

I don't disagree with this except "most manufacturers only make three". Most? I know of hardly any that make only three. Ive seen a few that make maybe four, but most make 5 or more. I'd say "most" compact frame manufacturers make 2 cm incremental frames just like before. "Some" offer only 4 or 5.

Given Most Manufacturing is a limited number of companies Making Multiple Brands Under contract,
For a large number of Importing Distributors around the globe..

Generalizations are hard to quantify..

get out your tape measure and get the numbers..

Compact frames (i.e. sloping top tube frames) were created to tighten (i.e. make smaller) the frame triangles, particularly the rear, for less flexible, snappier frames.

It was Giant who popularized the compact frame (for industrial manufacturers) in the mid '90s with their TCR. The rethinking of classic road geometry grew out of the cycling milieu created by MTB demands and the rush to create lighter bikes and lighter tube sets, and the fascination with titanium. Lightweight tubes, at that time (i.e. late '80s) meant whippier frames, so MTB builders were forced to rethink traditional road frame construction. When Giant brought the philosophy to the road, roadies sneered because the frames looked like MTBs, but they were, of course, on the wrong side of history in that regard, first because MTBs didn't look like that for long, and the benefits of what came to be called 'compact geometry' were irresistible.

Those benefits, in addition to the driving frame stiffness gains, were weight reduction and production and stock economies. Whereas traditional geometry limited the range of people who could fit a given frame due to standover limitations, compact geo allowed a wider range of people with its lower standover heights. Add to that the rise of the Ahead set and stems and the associated ease of bar height and reach adjustments, one threadless fork could be produced, rather than a slew of threaded ones, and swapping stem lengths to adjust reach became fast and easy.

In other words, going compact was a no-brainer for manufacturers. Going back to Giant, if I remember right, that first TCR was only available in S, M, L, and XL. Most manufacturers up until that time were wrestling with how many of each of 10 or 12 sizing increments to produce and how to distribute them to dealers efficiently.

So, compact was really a boon for both manufacturers and consumers, in the sense that manufacturers gained efficiency, and consumers better performing bikes. Theoretically, consumers should have also gotten better availability of a bike that fits, and I think that's probably true (especially for women); it's common to see stems swapped, flipped, raised and lowered on the showroom floor as buyers go out on test rides now, where in years past, it just didn't happen. Bars up or down, that was about it!

Compact frames provide useful route for short-standover/long-torso riders to fit a frame since you fit by top tube length and can disregard standover requirements. Note the height of the head-tube and see if it works for you.
Giant compact frames also, originally, had a series of different seatposts to make fewer frame sizes fit more riders.
Compact frames do little to benefit small frames. They don't change any frame angles compared to trad style frames but they do make the small, stiff main traingle even smaller and stiffer. If you have luggage rack eyelets, they are placed too low, beneath the level of the wheel, requiring longer rack stays.
They do benefit XL frames, stiffening the frame nicely.
Compact frame can be harder to shoulder for portage , eg carrying up steps.