The second number, that has been noted already, is the width of the tyre. A wider tyre will ride smoother and last longer....depends on what you want. I've ridden for about 55 years and got really tired of flats here in the New Mexico desert. I finally found a tyre that is nearly impervious to flats...the Armadillo. Don't know about its availability on the continent but here in the colonies its easy to find, even on ebay. It's not a race tyre but it runs well on 50 mph descents here in the mountains...and NO flats.
