This wasnt me personally, but a friend who also plays LFS.
He was playing a le man game on the PSX, decided to do a whole 24hour race non-stop by himself, (think it took 25hours with food and toilet breaks) {and gentlefoot, just incase you're wondering, hes one of your team mates lol}

Longest race with no breaks was about 3hrs, 90 laps at BL1 in the GTT, an event the Australasian League ran on the updated S2 alpha demo. Had my team mate rots on my tail almost the whole way
Those road tyres last a long time, only changed them once.

200 laps @ michigan in NR2002 for ESCORS... Took about 3 hours.

My longest race was the Master of Endu 24h Aston GP Event. Puted in hours I have done approx. 5 and a half hour.