Back to the Horsetooth Mountain Ride map.
If your ride at Horsetooth Mountain Park starts from the parking lot, you will begin by climbing up this service road. The singletrack trail that leaves from the lot is for hikers only, cyclists and equestrians are restricted to the service road. Frankly, the singletrack that leaves from the parking lot wouldn't be all that fun to ride, especially climbing. Please follow the park rules regarding trails that are set off-limits to riders--there's plenty of good, challenging singletrack that isn't off-limits.
This service road will hand you a grunt right away. From the parking/picnic area you'll have about a quarter mile of middle-chainring easy climbing, then you'll come to a right-turn switchback and a good, humbling grade. You'll be granny-gearing it for about 5 minutes, then you'll come to your first trail junction: the service road will jog left, and the Soderberg Trail will head roughly straight ahead. If you continue (left) on the service road, you'll be treated to about a quarter mile of relatively easy climbing, but then you'll come to a couple of sections that are probably a 10% grade. These sections are a good chance to find out if your bike is geared appropriately for offroading in the Rocky Mountains. The surface is no problem; slightly washboarded gravel, but the steepness will take some dedication if you intend to stay in the saddle.
The service road climb from the parking lot to the place where it rejoins the Horsetooth Rock Trail takes me a bit under 30 minutes normally, and it's just under 2 miles.