M_S

Yesteray during my evening ride I did about 20 on road miles and the same number on a rutted dirt road. I've been cycling sans computer lately, but I got to thinking what was the speed difference per amount of effort? I've been tossing around in my head the idea of doing an off road century for a change, but assuming all other variables (weather, elevation gain) are the same, how much more effort might I be putting out off road than no? And then is doing 70 miles of dirt roads like doing 100 on?

If any of you have experience doing distance events off road I'd love to hear about it. Since I've moved to Missoula I'm finding the best rides and roads often turn to gravel or dirt without warning but keep going for a ways afterwards, so much of my riding is a mix.

Anyways, this post is kind of inchoherent, but hopefully some of you will have a bit of insight.

spokenword

From my experience, it's highly dependent on 'how dirty' said dirt roads might be and how much rolling terrain one might expect.

My girlfriend and I have a tradition of taking a long weekend to camp in Acadia National Park and ride our bikes on the carriage trails that are laced through the park. Those are fairly wide roads with loose gravel and generally easy gradients (though my girlfriend will contend that statement while climbing Cadillac Mountain) and I'd say that, there, 35 miles of carriage tracks is probably like 50 miles on tarmac.

The Deerfield Dirt Road Randonee, by comparison, includes several 18% and 20% grade climbs on narrow roads that are strewn with rocks and bumps. Tackling that ride on a conventional road bike without shocks or suspension can be tough because you can't really rest on the descents, and you have to work even harder on the climbs. A lot of people refer to the D2R2 as a 200k that rides like a 400K, and I'd agree with that sentiment.

Hezz

100 miles of easy flat dirt road would be easier than 100 miles of mountain road passes. But generally the road 100 is a lot easier than100 mile off roads because the road bike is lighter and rolls easier. I'm going to say that if both courses are flat and the dirt road is good it would be about 50-60 dirt miles would equal pitch road miles. Also, the road speed would be a little faster for the same amount of wattage expended.

M_S

Thanks. For what it's worth I've been switching between a touring bike and cyclocross bike, which seem pretty ideal for a mix of pavement and light off road. The roads around here vary. Some of the logging roads are extremely steep with some sketchy surfaces (rocks/gravel) though alot of the lowland dirt roads are, well, dirt. So smooth in places but often bumpy due to ruts which form when it's wet and stay when it's dry.

I'm really enjoying mixing up the terrain though. It adds another dimension to longer rides.

Richard Cranium

Yeah, essentially, you disregard distance as a measure - and think in terms of intensity and time.

Typically riding 15 miles on gravel with bumps might be like riding 20 on perfect pavement. If both rides take the same amount of time. But if 15 dirt miles takes 1.5 hours and 20 road miles only takes 1.2 - well figure it out, the road ride was probably easier.....

C Law

Well put. Definately not all dirt is equal. Not only the friction/traction loss at the surface, but getting beat up on the bike takes a toll after a while. And then throw in the weather, extremely dry or extremely wet conditions would make it (more of a) a slog for sure.

I would have to say that the D2R2 at 200% road mileage feels a bit high to me. Maybe more like 180%

It felt to me like a 100 mile mountain bike race. I think it had to do more with the climbing than the road surface though.

Rowan

There is another issue -- the concentration required to navigate a rutted gravel or dirt road/trail compared with a smooth asphalt shoulder or country road. The constant decision-making on which line to take around potholes or avoid loose gravel, or ride a thin, firm strip next to a ditch, plus the traction issues while climbing loose surfaces, then equally braking on loose surfaces downhill... can all have an effect on how you perceive the ride.

In Australia, the Audax organisation has an off-road series that covers 35km, 70km and 100km leading to a Dirt Series award. I'm really not sure how the distances are supposed to equate to their road event equivalents, but I suspect 35 = 50km, 70 = 100km, and 100 = 200km.

chadfbrown

Comparing a dirty century to a regular road century is tough; the former is sooo much harder and requires usually about 2 times as long. While most roadies can crank out a century in 5 hours, a dirty century with climbing can take anywhere from 10-13 hours. As an example, the Coconino Dirty Century usually takes around 10+ hours and has 9-12k of climbing.