Last I checked you can't drink the water at the rest area at Thornton Gap (E-coli). So be sure to fill up at Elk Wallow (MP 24) if you're coming from Front Royal.
If you start too early you might get to Elk Wallow before the Wayside and the restrooms are open, but you can fill your water bottles from the spigot behind the restrooms.
If you're going farther than Elk Wallow, but not as far as Big Meadows (MP 51) for the turnaround, a really good goal to go for is:
- Entrance to Elk Wallow (24 miles)
- Elk Wallow past Thornton Gap (rest area but no water)
- ride through the tunnel and about 4 more miles to "The Pinnacles" overlook, and then turnaround.
- or you can ride a bit further to Skyland (highest point in the park), but you have some down and then back up between Pinnacles and Skyland
The downhill from The Pinnacles to Thornton Gap is about as fun as riding gets -- fresh pavement, beautiful curves, 6% grades. Wheee!
Also when figuring miles, I never count the last six from Dickey Ridge back to Front Royal, since it's all downhill
Have fun!