I have seen a ride advertized up here in BC, Canada for a supported dirt ride on the Kettle Valley Railway. 3 days, 300 km, so 100 km per day. The max grade uphill would be 2-2.5% as it was used for trains at one time. So how much harder in % wise is dirt riding compared to riding on pavement? Sounds like it would be a fun ride. I have ridden 100km on pavement, took about 4 hours on a heavy steel touring bike and I am 69 years old. Plus this ride is 3 days doing 100km. What are your thoughts on this? Thanks, Cheers Roscoe

Dry, hardpacked dirt or fine gravel is probably about 85% as efficient as smooth pavement, assuming you're running slick road tires. With lightly treaded tires, you might approach 90% of smooth pavement efficiency (with same tires).

It depends.

If it's a smooth surface that's very well-maintained, it could potentially be better than a really crappy paved road.

If it's heavily potholed, you'll need to ride more cautiously than normal, but it won't necessarily make things much more tiring.

If the surface is rough or loose, you'll likely want more suspension and float from your tires than you need for paved roads. This means pumping your tires squishier. When pumping tires squishier, they can stay better-behaved by making them fatter too.
How badly nasty surfaces affect performance depends on how inadequate a bike is and in what ways. There are some loose dry gravel surfaces which the fat high-performance slicks on my gravel bike might manage at only a 5-10% penalty compared with paved road riding, but my speed could drop by tens of percent on one of my skinny-tired road bikes from the tires wallowing and dragging in the surface. But on good hardpack, they usually both perform well and do about the same as each other.

If there's going to be lots of mud, you'll want tires with some knobby-ish tread patterning.

All the rails to trails I've been on are pretty well taken care of but can't speak for them all. I'd still rate a little harder than any paved roads and depends on which oil and chip roads. But I've always enjoyed the Rails to Trails I've been on and sounds like a good time supported.

As an aside, doing 100km (62 miles) in 4 hours is fantastic for your age! Averaging 15.5 mph (or 25kph) for hours at a time is excellent, I can't do that at half your age.

I've been riding more gravel roads this past year and have been using my touring bike (Surly Disc Trucker) ... steel frame and quite heavy what with racks and fenders.

Couple of thoughts to consider:
1) Sounds like you've done 100k on pavement and survived. Have you ever done consecutive days of long rides? Especially as we get older (I'm about to turn 65), recovery time can take a bit longer. If you haven't already, may not hurt to try riding a couple of 100k rides back to back to see how you feel.
2) Find out what the course really looks like. I've joined a few "gravel grinder" or "dirt" rides and there can be a big difference in what the course looks like. As noted by another responder, if the course is largely hard-pack, well-maintained roads, you s/b fine (assuming you're able to manage 3 consecutive 100k days on the bike). If, on the other hand, by "dirt" they mean the whole range of loose gravel, single-track, unmaintained fire roads, then that can be a whole different story. Even with the optimal bike and tires, 100k can feel like 100 miles if the road/trail conditions are sketchy. From personal experience, I joined a gravel ride that ended up having miles of loose sand, off-road trail riding, a stream crossing, and more :-) ... out of my league in terms of skill and the bike I had and it was physically draining for me.

Good luck ... keep us posted on what you decide and how it goes.

FWIW, I have read some not so great things about parts of that trail. Very rough in places.

Edit: Heh. Who says the BF search function is useless? You just need to know how to massage it.

Kettle Valley River Trail

Kettle Valley Railway, BC. Canada

ACA write up, albeit a few years old: https://www.adventurecycling.org/res...ng/bc-ballast/

In short, I often prefer hardpack dirt/limestone to pavement. Can ride nearly as fast, often in better shape, and generally less people on it. As it goes downhill, though, it becomes much more difficult. Took us the better part of an hour to do about two miles on one particularly nasty road in Iceland.

When your eyes are telling you that you're on a flat road but your legs are telling you it's not, that's 2 1/2%

I'm 73 and I have ridden some 5,000 feet of climbing on road grades of 7% up to 12% over the last week or so on two days. I also have CX and full suspension bikes and off-road I do not find climbing more difficult. Since you are generally in a lower gear it may be easier.

I will say that 2.5% is not a climb - if is a rise. Now going up this for a long time will tire you out but in my judgement "climbing" doesn't start until 5%. Your mileage may vary of course.

Indeed. But perhaps we should address his doing three consecutive days of metric centuries. This is not that hard as long as you aren't riding hard. Rolling resistance of a CX bike, which is probably applicable if you are going to do the entire trip on dirt, is probably in the 30 watts area with 32 mm knobbies pumped to 70 psi. In general aerodynamic drag goes up pretty rapidly. At 12 mph you are generating perhaps 20 watts of drag and that doubles by 15 mph and that doubles again by 18 mph. So if you want to do three days of metrics you probably want to hold your speed between 15 and 17 mph.

Of the last two hard rides I've done, I've only averaged a little over 12 mph and a little over 11 mph. Two weeks ago I did a 50 miler and averaged a little over 15 mph. So that should give you a reference from someone that has about 1,500 miles in for the year. Hopefully that weather will improve and I'll be able to do longer rides.

OP, tires and bike you are using?

Well if I do it I have a choice of a Kona Sutra with Clement 40mm x 700c or a Kona Explosif hardtail with Maxxis 27.5 x 2.3 knobbies.

I climbed Crystal Mt. Road yesterday = 6 miles, ~1500ft elevation gain. Rise/Run = 4.7% avg. with a very consistent grade. It sure felt like climbing. Was glad to have granny along. YMMV.

Err - isn't that an average grade? I really doubt that if it has an average grade of 4.7% that you don't have 6% on it. Locally here we have Mt. Hamilton. At the top is an observatory that was installed in the 1900's. So all the components had to be trucked to the top in mule trains. Mules will not climb more than 6 or 7% but if you do the paved roads now you can find short 10% sections.

It's pretty steady, definitely no 10% and I'd bet 6 1/2% max because there is only one (maybe 2) spots where the grade lessened All the way up to the gondola loading area, so maybe closer to 6.5mi.

It was an early season practice run for Hurricane Ridge, Olympic Peninsula which from Downtown is 19 miles and 5200ft elevation gain.