At least for me, GearSplit was a much more accurate and reliable software to determine gearing, time/distance/speed and tire size for LSR cars. No limits either. Only downside is it has not been updated to run on a modern OS. Win XP is it so if you have an old computer, you are in luck. Also, the developer, Dave Dahlgren, has not sold a copy in a while. Worth contacting him, however.
John