I've done a couple of triathlons this year, the longest being a mile swim, 25 mile bike and 5 mile run. It took me about 2 1/2 hours to complete.
There is a road race coming up that will take me about that long to complete. It's about 7 miles longer than I've been running, however.
Will running for 2 1/2 hours be very close to swimming, biking and running for 2 1/2 hours?