28s would work OK; 32s would be better. When it comes to trails though, nothing flies quite like my 650X42b Grand Bois Hetres.

Make sure you have enough clearance though, especially if you want to run fenders.

27" x 1 1/4", or 32-630.

I'm still running a Specialized Armadillo in the front, but the rear and my spare (and any in the future, if I can still find them) are Continental Gatorskins.

I'm a recent convert and fan of the Panaracer T-Serv 25's. I take it through gravel, trails, what have you on my commute. 90% pavement, but not at all afraid to take it off road.

One of my old bikes came with 19's, and I commuted on those for a few weeks before swapping them out for Vittoria Randos at 28c. Only reason I changed was the sidewalls were cracking from dry rot. Had no problems with the 19s, but that was also in late summer, and my commute is purely paved.
Been riding on 27's for a couple months, I believe they are 1 1/8 due to clearance issues. (couldn't fit 1/4 under a fender)

My favorite are all around tires are ritchey speedmax by far , but for commuting I really love 32 slicks because the occasional gravel path just doesent make up for the sketchy road cornering with off road with tread. The major difference will be cornering, tires with knobbies will give you better offroad cornering slicks will give you better road cornering it's really a trade off that only you can decide. A thin cross tire with tread you might be intrested in is kenda kwicks 30s, a buddy of mine fit those on his old road bike but it was a tight fit.

Love them, and run them on my cross bike for commuting. Found out the Speedmax Comps are a LOT lighter than the Speedmax Pros when I replaced them. They last about 3k miles for me before the rear is smooth

But to answer the OP's original question, road bike I run 28's, Cross bike 32's for commuting

700x23 and 35. The 23s are harsher but I keep them at 120psi (they are also armadillos). For my next commuter I am going to go for 700x35 Marathon Supremes.

I've got 25s on my commuter and most road bikes. However, if my route included crushed gravel, I would use at least 28s. The roads are all paved on my route with few potholes or bad pavement. I'm getting some new wheels (Velocity Dyads) built for my commuter-tourer that can handle larger tires, so I will probably install 28s on them. Not that I need them for my route, but the Dyad rims are designed for tires 28 mm and larger.

23s on the Raleigh, 27 x 1-1/4s on the Miyata. Pavement all the way, but not necessarily smooth pavement!

love my 25 RiBMo's.

All Condition Armadillo 700x25 on a 2000 Litespeed Vortex frame.

Switched out Reynolds Uzo Pro fork for a Surly Cross fork for those wet, muddy occasions. (no rear brake to worry about getting clogged up.)

Much of my daily commute is on natural paths, and (touch wood) so far no flats as a result--the flats come from debris picked up on pavement (like industrial staples). Daily air-pressure checks keep the snake bites well at bay.

If you have gravel 32's are the way to go and they won't slow you down on smooth pavement if you get a nice tire like Jack Browns or Paselas. I was on a populated bike tour a couple of years ago that hit a 2 mile section of freshly graveled road. It was like someone hit the Slo-Mo button on all the other riders as they slowed down or got off their bikes while I tore past them at my normal speed.

Funny I have been running pros until just recently I put a set of comps on they do last a really long time for a cross tire though no flat protection which is normal for a cross tire.

700x23 is all I can get under the fenders, and even that took some serious effort. Speedium 2 on the front, Gatorskin on the back.

was using 700 x 38c hybrid tires = too slow
switched to 700 x 35 smoothish commuting tires but on;y went up to 85 psi
fell in love with 700 x 28 at 120 psi!!!
got studs for the winter at 700 x 35 and been playing with their pressure depending on the day

I agree.

Also consider this article.

23s Conti 4000s, commute 20 miles, each way. Love them.

The chart only goes up to 70kg. Many of us weigh more than that!

I run 28's in the summer and 35's (cross tyres) in the winter... winter riding is akin to off roading here as the roads can be extremely rough and the 35's are more plush and offer better traction.

When it gets really ugly I ride mtbs with 26 by 2.0 tyres and use studs as well.

23's

I currently use 23s on my Tarmac but I'd like to put a larger tire on my other set of wheels and use those for winter commutes. Anyone have any idea how large a tire I can put on a Specialized Tarmac?

That's per tire. Most of us are probably under 120 - 140 kg.

As Emily Litella said, "Oh, that's different! Never mind!"

Actually, I'll take a look again in that case.