Tire size

It depends, how wide is your rim? (IW or OW) How much space is between the top of the forks and the tyre?

I used to have 28mm tires front/back. The last 1500 miles I've had 28mm front, 32mm back. I thought the 32mm would be good for better supporting fully loaded touring and better handling on dirt roads. I think this is as wide as I can get without buying wider fenders.

Now it's time for new tires and I'm going back to 28mm front/back because I just no longer seem to take my bike on bad enough roads to want the extra traction.

Truthfully I could hardly tell the difference.

Sorry, I didn't quite answer your question, maybe I should go into politics!

I think 28mm is too narrow if you're doing a lot of miles on dirt/gravel. For me 32mm is a minimum to get decent traction on a good dirt/gravel road. For worse roads, especially a little sandy or looser gravel I would want wider than that. Most importantly I'd get a grippy tire like a Continental Twister.

700 by 32.

I'm using Specialized Nimbus 38's and like them very much. They handle gravel very well and still have pretty minimal rolling resistance on hard surfaces. I did note however that they have decreased the psi max from 100 to 80 on the last one and I'm thinking of going with 32mm at least for the front next time.

Something To Bear In Mind Is Different Tyre Manufactures Tyre Sizes Are Different To Others.

A Good Example Is Vittoria And Swalbe Tyres

Mark