I never run the day before or after a long run, with the exception of when I was training to do back-to-back half marathons last year.
However, as a couple others have suggested, you can incorporate the race into your mileage. Run 10 miles and then do the race (or if the race is in the morning you can do the race and then run 10 miles later in the day).
But, unless you're seasoned for this type of running, I would not do that type of mileage on back-to-back days.
In fact, next month I have a 10k planned on a Saturday which is usually a rest day. So, that means I have 5 miles scheduled the day before and 8 miles scheduled the day after. Since I have a scheduled off-day on Thursday, I'm going to push my Friday run back a day to Thursday so I will have Friday off. Then I will push my scheduled 8 miles back from Sunday to Saturday and use the race as 6 miles of it and then run the extra 2 miles as a cool down after the race. Then Sunday will be an off-day of recovery.
It takes a bit of re-jiggering, but if you can be flexible with the rest of your running days, you can account for anything without forcing yourself to do difficult runs on back-to-back days.
Edited by: TYKXBOY at: 8/21/2013 (17:10)
"One machine can do the work of fifty ordinary men. No machine can do the work of one extraordinary man." ~ Elbert Hubbard (1856 - 1915)