I know thinner is faster, but I’m not into comp racing, I just like covering a lot of ground.
I noticed BD sells Mercier bikes that tout 28mm tires.
Can a road bike that comes with a 23mm tire take a larger tire, or does it have to be designed for it? I haven’t seen any rims widths listed anywhere.
How often do 23mm tires blowout? Is a 28mm any more durable?

A 23 mm designed rim will most certainly accommodate a 25, but a 28 may cause issues, depending on your bike type. It would be best to ask your shop about that.

Blowouts really shouldn't happen at all unless you hit a blunt object at a high rate of speed. Pinch flats, where the tube is "pinched" as a result of its form being changed as a result of hitting an object. Pinch flats can almost always be avoided by having the correct pressure. You'll see a lot here about lower pressures being more comfortable, and they are, but you need to take your weight and road conditions into account too.

A 28 mm tire can be run at lower pressure, which will make for a more comfortable ride, but again ask your shop. You may only be able to go up to 25 without issues.

Yep, do a search on specs for your bike. The limiting road bike factor for tire width is usually fork clearance.

Also thinner isn't necessarily faster. Speed is dependent on rolling resistance and the ability of the tire to maintain smooth contact with road surface is affected by tire width, construction, and air pressure. So a wider tire that maintains contact might be faster than hold that bounces.

I just bought a Mercier Aquila AL from Bikes Direct to use for running errands and it takes up to 40mm tires. My Specialized Roubaix will fit 28mm tires. Many road bikes will struggle to fit anything bigger than 25mm tires (quite a few fit only 23mm tires too.) One other thing to remember is that many tires run narrow so don't just a assume one 28mm tire is going to be wider than another brands 25mm.

One thing I've realized is that there is a chicken-and-egg problem when it comes to wider tires that have a low(er) rolling resistance and good puncture resistance. The demand for those tires is almost all in the road bike space so you only find them in 23 and 25mm sizes. If Continental made a GP4000S in a 28mm size I'd buy it in a heartbeat but until that happens I'm stuck riding them in 25mm.

Thanks for the info.

Ha, the Aquila is one of the bikes I’m considering. I’d really wanted a 20spd, but BD is sold out of my size in everything except the Dawes 2300. Nashbar has a 20 spd / shimano 105 something for 900. Looks like a GT?
I’m coming from a fat tire hybrid so I guess I’m not sure what I want, other than something more aggressive. I'll usually ride solo, an hour or 2 at the time.

This. "Thinner is faster" is largely a myth, and fatter is certainly more comfortable and secure.
As others have said, your wheels should be fine with 28s. I've run tires from 19 to 41mm on the same wheels with no problems. But you'll be limited by fork clearance or (maybe) the brake arch. The figures are probably published somewhere, but it might be more accurate to go to a bike shop and tell them you need to try some tires and you'll buy them if they fit. But then if they fit, you have to buy them. No ordering off the net.

https://janheine.wordpress.com/2012/0...ance-of-tires/

Not sure what size you're looking for, but I just ordered one of these. 20 speed SRAM Apex groupset on a chromoly frame, $800 https://www.bikesdirect.com/products/...fantom_cxx.htm

All my bikes can fit at least a 28.

Most of the "aero" frames are limited to 23mm. For example, the Ridley Noah and Cervelo s5. I don't think it is worth it.

Most jamis bikes can have larger tires, my Zenith endura can accomodate a 35mm tire / wheel, very unique for road bikes, came with 25mm stock.