mine is 30x32 is 24.7", and mtb is 22x34 at 17"
However I'd like to throw a spanner in the works, over the last couple of weeks I did notice something, I set my garmin speed/cadence sensor to automatic wheel size setting, initially I had it set to manual input of 2096mm (from a cateye wheel chart I had) On automatic wheel size the kellogg's bike came out 2068mm and the TDF came out at 2067mm, both identical make/model of tyres both running 120psi, the tdf tyre had more mileage wear on it on top of which I am a heavy old lump. The distance it took to calculate was approx GPS 0.5mile, So what's the difference in real terms of the tyre settings, on the manual setting on a 50 mile route I knew the exact point where my half way point was when I would turn around as I had done it several occasions, on automatic setting I noticed that the usual halfway point was now 24.8 miles so in effect my 50 miles on automatic size setting was 0.4miles longer than on manual size, would tend to take the automatic setting as gospel due to the fact it calculates wheel revolutions (including tyre wear/tyre pressure and rider weight) over distance, with an accuracy difference of 0.8% over manual input setting.
When you think the circumference difference is 28mm between auto and manual input it screws up the gear inches a bit, 
