Any recommendations for tires or wheelsets to plush up a stiff ride. An option could be 25c tires, if they fit. Is there a tire you can use at lower pressure?

are standard recommendations. The "Other RBR" roadbikerider.com is a strong proponent of lower pressure and larger section tires. Spend a little time on the website and get on their free subscription list.

Any recommendations for tires or wheelsets to plush up a stiff ride. An option could be 25c tires, if they fit. Is there a tire you can use at lower pressure?

Any wheel will flex less than half a mm vertically, so I wouldn't look for much comfort there. Supple, larger size tires would be your best bet... and you can lower the pressure down as low as you dare. The only thing you need to watch for is getting pinch flats.

Any recommendations for tires or wheelsets to plush up a stiff ride. An option could be 25c tires, if they fit. Is there a tire you can use at lower pressure?
yep, as wide a tire as you can fit (ie higher volume)... really depends upon your frame & brakes what'll fit. for most road bikes & brakes 28 is as wide as will fit before you either run out of room in either the tire rubbing the frame or tire rubbing the brakes.

also, one manufacturer's 28 is another's 25, so what's written on the side isn't necessarily the actual tire specifications.

I never noticed one iota of difference between a 23, a 28 and a 32 tire. All I can say is that the 32 made the bike a little harder to pedal. Lowering the pressure, though, does do wonders, especially if you're brave and lower it to about 60 psi. If you have tubulars, you don't even have to be brave about it. The new tubless clinchers supposedly can get way low down, too.

I also recently found to my shock and pleasure that when I went from 70's-80's era 36 hole/three-cross/high-flange hub/semi-aero rimmed wheels to 70's-80's era 36 hole/three-cross/ low-flange/box-rimmed wheels, the comfort increased remarkably. (This is on my retro-bike.) Who'd a thunk it?

I never noticed one iota of difference between a 23, a 28 and a 32 tire. All I can say is that the 32 made the bike a little harder to pedal.

That's funny, because if you run them all at the same pressure, repeated tests have shown that the wider tires are faster (assuming same construction). Of course, you'll have a hard time finding a 32 and a 23 with the same construction because the 32 will be a touring tire. Apples and oranges, anyone? :)

before i switched to continental contacts id have to say that the one set of Serfas Seca's that i had were super plush compared to the conti ultrasport and gatorskins that i used before, unfortunetaly they didnt last very long before the back tire had a bunch of mr tuffy sticking out and i blew up the front on a chunk of misplaced road.

i havent tried the 28's but i fit a set of 32's(closer to a 28 really) conti contacts on my pista and theyre the **** i can run them at around 65 psi and have beat the snot out of them for at least 2k miles and no flats yet if you can fit them and speed isnt your number once concern (although i dont notice much difference) theyre worth a shot

Kerry - I can't give a direct comparison between the 23's and the wider tires because they were on different bicycles but I can say that, whatever those reapeated tests may have concluded, I personally found the 32's to be harder to push than the 28's. I used both 28's and the 32's on my late, unlamented Rambouillet. Both sets were Panaracers of the same model. To put it in a nutshell, I was slower, angrier and more frustrated with the Rambo after I switched to the wider tires. My wife and fellow rider can attest to my being slower with the 32's as well. She was always happy when I rode my Rambo instead of my Colnago. She could keep up with me! When I switched to the 32's in an attempt to attain the cushy ride the Rambo was supposedly famous for, she became happier still.

... if you run them all at the same pressure, repeated tests have shown that the wider tires are faster (assuming same construction).
Really? I've never heard that. Does it have something to do with distributing the load over a wider area? Do you have links to any of the studies? I'm not being sarcastic here, I'm genuinely curious.

Does it have something to do with distributing the load over a wider area?

With a wider tire the contact patch is shorter, which results in less distortion of the casing... ie less rolling resistance. The wider tires are usually made from less supple materials though (sometimes even the same model), so the comparison ends up being apples to oranges. You also need to consider that vibration on rough roads will favor wider tires run at lower pressures. If you have deeper rims with some aero benefit, you need to consider that as well to determine which tire is "fastest".

Really? I've never heard that. Does it have something to do with distributing the load over a wider area? Do you have links to any of the studies? I'm not being sarcastic here, I'm genuinely curious.

Well, sort of. With wider tires, the casing has to deform less to form the contact patch. Casing deformation is where rolling resistance comes from. Specifically rolling resistance is the result of hysteresis in a cycle of casing deformation. So if the casing deforms less, there is less rolling resistance, and so the tire is a bit faster.

Of course as the tire gets wider, the aero drag on the tire gets larger. Allegedly there is a sweet spot w.r.t. rolling resistance and aero drag, and it's said that a 23mm tire comes close to hitting that sweet spot.