Originally Posted by base2

Frame geometry has always been variable in accordance with a bikes purpose & design objectives.

If anything, road bikes are shorter in the 2020's than in previous generations, chainstays shorter than 16 inches are common. Short bikes feel faster & the faster feeling bike tends to get the sale.

But with gravel becoming popular (again,) the longer chainstays & slacker head tube angles & wider 32+mm-ish tires found on many bike-boom 1970's era road bikes (& their 1980's rigid mountain bike progeny) designed at a time when America had less paved roads are now making a come back return as current paved roads are no longer important enough to maintain. Americas return to the good ol' dirt road continues, & America (& bike design) unlikely to change course any time soon.

I think we hit peak infrastructure in about the mid-1980's when 19mm tires at 140psi was a totally reasonable & popular set up to have. You can't do that now outside of a new MUP or a velodrome, even if you wanted to...Race bikes are being designed around 25 or 28 or wider tires to compensate for poor road surface & poor infrastructure. It's no wonder the return to bike-boom geometries, tire width & pressures only with savvy gravel marketing this time around is the latest trend.

If anything, slope-ier top tubes help with the vertical compliance, so I think we'll see that trend continue for a while. What'll be different is the terms "girls bike" or "Womens specific design" will not be used. Nor will the terms "mixte" or "step through." The trend for sloped top tubes will continue though at least as long as unnecessarily stiff, low spoke count highly tensioned carbon wheels remain in fashion, especially so long as the above mentioned infrastructure erosion trend continues.

Sloped top tubes also allow for fewer frame sizes to manufacture. Less SKU's make for simpler manufacturing & more generic bike frames. All of humanity will continue to be on 1 of 5 sizes. 52, 54, 56, 58, 61 & it'll be big-bike & their shareholders that will decide this.

Internal frame dampeners (ie. Zertz) or other suspension devices such as shock absorbing seatposts, stems, or intentionally flexible thin "aero" carbon handlebars will continue their rise in popularity under the banner of "comfort." Where as in the 1970's bikes were just made with shock absorbing gas pipe & flexible singlewalled steel rims galvanized spokes.

The hoods of modern bikes are where the drops used to be. Bikes aren't designed for the drops to be the primary riding position anymore. The position of the rider hasn't changed much though.

On a related note: I feel that handlebars tend to be a bit wider than they used to be, but that may be just the bikes I've experienced.

These are just random thoughts. Feel free to "correct" my wrongthink.