Modern vs older geometry
 

An older, 70s or earlier, Olmo bike I have. 56cm seatube, and 54cm toptube with an adjustable stem that goes up or down 9cm, and is angled so only adds 6cm forward reach to the bars.

A 56cm seattube trek1000 has 56cm toptube +12cm of stem. That's effectively 8cm longer than it used to be. I have some 80s bikes that are in between these 2 measurements. In fact, I'm very happy with the fit of an 80s 50cm seattube, 55cm toptube bike (I guess 8cm stem).

Why have bikes stretched out over the years? Is there an advantage to a longer reach beyond knee clearance?

I don't understand your math. One bike has a 54cm top tube and the other is 56cm. How is that an 8cm difference?

There are lots of choices out there; buy whatever fits you best. Trek tends to be longer than most of the big brands.

Real bike fit includes the stem reach.

counting the stock stem that comes with the bike... the reach difference to the bars is much longer (8cm) on the recent bikes.

Are you supposed to just pick the smaller and lighter bike instead of the size you were used to getting, because its not obvious that reaching forward so much is a good idea for long ride comfort, seems like there would be more stress in holding yourself up in a weaker position for a long time.

On a short test ride, the longer trek 1000 felt a bit weird, but it was a comfortable nice ride. It occurs to me that keeping weight off the hands could be useful in marketing aluminum frames, and explain why they have longer reach.

Have any of you found speed or ride differences between long and short reach geometries?

Changing stem lengths on modern bikes is trivial. A good shop will do that for you for free. They may even swap out stems as part of the test ride.

Hell, I do stem swaps before test rides on our cheapest hybrids. There's no sense sending someone out on a test ride if the bike's going to fit them awkwardly.

Seems like a much better design to have adjustable stems. Even if moving forward is somehow a "better" (athletically) position than moving down. Ride fitness would probably change over time, and so being able to lower the stem gradually, and raise it back up after winters, seems like a good idea.

Also, mail order/bike mfgs don't even spec stem length.

How are you measuring the seat tube on your Olmo? It used to be that most bikes were measured from the center of the bottom bracket to the center of the top tube. Nowadays most bikes are measured from the center of the bottom bracket to the top of the top tube. Trek bikes are measured from center to top. A 56cm Trek may be closest in measurement to a 53 or 54cm "old" bike.

I'm measuring center BB to top of seat tube for all the bikes.

Another reason why not to buy mail order bikes, or at least plan on replacing the stem with one that fits you. Retail bikes don't spec stem length because most shops will help you pick a stem that fits.

that, of course, is not the case. main traingle geometry has varied a bit with fashion, same with BB height. But ultimately, for general road bikes, and depending on intended rider size, square to slight over-square designs are still the mainstay. TT and TRI bikes being for a very specific discipline have gone thru quite some important design changes, based on positional changes for the rider.
Stems, disposable and intended to be fit to suit the necessary adjustment for position.

A lot to consider when deciding on 'reach' to the bars. Too much to really be succinct here, but I will say I see more riders scrunched on their machines than at any time in my past. A lot of victims of fashion out there...

I think that's part of your problem. Seventies and most Eighties bikes, especially lugged steel, were square or even under square. Square is when the seat tube and top tube are identical. Under square is when the top tube is shorter than the seat tube. Though I've never heard it used, you could call present day bikes "over square" because the top tube is longer than the seat tube. Terminology aside, visit Rivendell's site for an explanation on old school fitting.

This is a subject that's almost as caustic as Campy VS Shimano or steel VS everything else. Most modern geometry is an attempt by manufacturers to sell high performance to the consumer. Long top tubes and high seat posts give the allusion of a high performance racing bike. That appeals to a lot of riders.


Tim