MTB miles vs. road miles

One thing I've heard, and heck -- I've done it -- is comparing miles ridden on a mountain bike to miles ridden on the road. Just this morning, talking with a friend, he mentioned someone who did 14 miles in Wissahickon, and said "the guys say that's like 40 miles on the road". So, this got me wondering. Obviously, there are far too many variables, such as terrain and exertion to come up with a hard and fast number, but we could come up with an estimate, right?

Thankfully, I didn't have to wonder too much. With the Garmin bike computer, I've got detailed information on most of my rides this year. So, I decided to compare a road ride to a mountain bike ride in Wissahickon. I had to keep something consistent, so I looked for two rides which were approximately the same time duration. I wound up with a 11 mile ride in Wissahickon, and a 21 mile road ride from home. For the mountain ride, I covered 11.94 miles in 1:12:23, and burned 1660 calories. For the road ride, I covered 21.32 miles in 1:13:48, and burned 1751 calories. That works out to 139 cal/mile on the MTB, and 82 cal/mile road... but this is exactly what we expect. Riding the MTB is tougher, so you burn more calories per mile than on the road. However, the really interesting math is the calories per minute. The mountain bike burns up 22.93 calories/min, but the road bike burns 22.73 calories per minute. Almost the same!

So, based on these two rides, the conversion from MTB miles to road miles is 1.78x... so a 14 mile MTB ride in Wissahickon is about 25 miles on the road.

However, while I was writing this up, I noticed a couple problems. My Wissahickon ride isn't a round trip -- I forgot to start the computer, so if you look at the map, you can see I started it well into the ride. This way, I was "starting" the Wissahickon ride already warmed up. And, although I had 1000 feet of climbing in the road ride, it's probably the flattest ride in our area. So, I took a look for other comparable length rides and found the PMBA Rally in the Valley and my commute from work to home last week.

	MTB	Road
Time	2:05:40	2:04:25
Distance	15.65	33.44
Calories	2764	3082
Cal/mi	176	92
Cal/min	22.0	24.78

So again we have a calorie per minute number averaging around 23! This would give us a conversion factor of 2.1.

So, based on two far from scientific comparisons, you can ballpark MTB miles as 2x road miles. Funny, too, since I have used 2x in the past.