The steepest paved road in Boulder.
Length: 4.47 miles (7.19km)
Average Grade: 9.8%
Maximum Grade: 14.75%
Vertical Gain: 2162 ft (659m)
Summit: 8250 ft (2515m)
Tour de France Category: N/A
Tour de France analogue: To my knowledge, there are no climbs longer than 3k approaching 10% regularly included in the TdF.
I can’t believe after living my entire life in Boulder County I had not ridden what is rumored to be the steepest paved road in the county, Magnolia Road. Perhaps because I was scared of it… or maybe just coincidence… Anyway, the base of the climb is across Boulder Canyon from Sugarloaf Road, and is similarly dangerous to access due to traffic.
The bottom of the climb is the most impressive. Viewed from across the canyon on Sugarloaf road, the switchbacks are unfathomably steep. Unlike the gently graded switchbacks in Europe, these are incredibly tight and steep on the inside. If you were to ride the first switchback on the white line, be prepared for a bike length of 43% grade (approximately a 23 degree angle)! There are plenty of skidmarks on the insides of the corners from cars losing traction ascending the road. The average grade of the bottom 1/4 mile is 14.75%, the bottom 1/2 mile averages 13.8%, and the bottom mile averages 12% grade.
The climb is quite punchy with constant variation in grade as it climbs, including four 1/10 mile sections of flat or gentle downhill. The last set of switchbacks around mile 4 will leave you crying for mommy, and you’ll be glad the last half mile is ‘only’ 5%.
From the top you can continue the ~5 miles further on the dirt road to peak to peak highway and then continue to your destination of choice (Ward, Allenspark, or Coal Creek Canyon). Many of the local elite will combine this ride with Sugarloaf and then Flagstaff. If each is ridden to the dirt, it is called Where the Sidewalk Ends.