Eyedrop

I'm and amateur road and MTB cycling enthusiast. I've been spectating the competitive bikepacking scene (indipac, inca divide, etc..) for a couple years and noticed pretty much everyone runs these road bikes but with very wide tires and knobbies on them. Literally looks like XC MTB style tires.

But it seems like most of the racing is done on either pavement, or on paved dirt roads that cars are still able to drive on. Nothing too gnarly at all. Wouldn't running such an aggressive setup for an endurance event would be a huge waste of energy?

Surely you could get away with some fast rolling 700c cyclocross style tires? Or dual purpose, traditional type touring tires with a little bit of tread?

Ive entertained racing at one of these events with my road bike (which does fine on basic dirt paths), just because I feel like I would have an advantage over everyone riding their DH MTB's (joking).

What gives?

TenGrainBread 

They choose the tires that will suit the worst terrain they'll encounter. It's better to go a little slower on pavement and to have a good tire for riding dirt and mud than to go a little faster on pavement and have to hike-a-bike through miles of rough terrain. Plus higher-volume tires are way more comfortable over long distances, and provide better handling and traction, which is important when you are sleep-deprived and exhausted.

kingston 

Ted King: Gravel Racing on Rene Herse Tires

rhm

If you believe Jan Heine (https://www.renehersecycles.com/wide_tire/), there really isn't such a great disadvantage to running fat tires, or even fat knobby tires. The important variable in tire efficiency is the flexibility of the sidewall, rather than the size. A high quality 2" tire rolls just as fast as a 1" tire. Now, I don't really want to get into arguing about whether Heine is right, or what his motivations are (he is the only one selling the tires he recommends, after all); but there's no denying that he sells some pretty expensive tires, and a lot of people are using them for long distances.

Last season I rode a lot of miles on 53 mm tires-- a whole SR series, two fleches, a 1200 km brevet, etc-- and if the tires slowed me down, it wasn't by much. With such fat tires, you don't hesitate to ride on rough or even unpaved roads. While the fat tires seem to have a distinct advantage on rough roads, they don't seem to have any disadvantage on smooth pavement. Seem, I say-- because it is hard to tell what's slowing you down. More readily apparent is the overall comfort of fatter tires. After last Saturday's brevet, a friend remarked that he felt like he'd been pummeled in a bar fight. I didn't; and I weigh more than he does.

unterhausen

I was pretty happy the year I rode all my brevets on 38mm tires. And those tires are relatively crummy, not RH quality. I don't have that much experience with knobby tires, but a lot of them have a tread pattern that rolls fairly well on the road. There is a lot of riding on relatively smooth roads in mountain biking too. The downside to fat tires is weight, if acceleration matters at all. But generally it doesn't.

Fat tires are a no-brainer for gravel, they are definitely faster than narrow tires, even disregarding the lower likelihood of flats. That's not inconsequential around here, the gravel roads are built with a base layer of really sharp rocks somewhere between softball and football size. There are inevitably some of those rocks poking up through the top layer, and bikes are attracted to them like a supermagnet. I use gravelking small knob for gravel. They are a bit more robust than slicks, but they still roll really well on pavement.

atwl77

One of the more renowned randonneurs in my local audax scene rides on a Santa Cruz Stigmata with 38mm tires. We once tried lifting it and it was heavy A.F. Yet he is often among the earliest to finish (or he gets tons of time to sleep, depending on how he feels like riding), so yeah, weight and fat tires don't really matter (at least in the context of randonneuring and ultra long distance cycling).

gif4445

Sorry if I'm detouring the thread a bit, but I recently put some gravel king slicks on my Diverge. Went with 32mm for comfort and wanting a little wider tire for a race this June that will include some limestone trails and gravel (only about 6% of the ride). Really liked how they rolled, but a few weeks ago hit some loose rock while riding on chip seal in the Texas Hill Country and slide on my arm/leg/shoulder/hand. I'm wondering if I made the wrong tire choice. May have lost control if I was using my regular tire (Armadillo all-purpose), but it is obvious to me that the slicks are not as stable on the road. Maybe the small knob? Your thoughts.

Steamer

Pilot error. Accumulations of fine loose gravel from a tar and chip repaving is dangerous stuff. It needs to be avoided when possible and ridden with great care if not.

gif4445

Of course it was my fault. I was alone and I crashed. However, I'm betting it would have caught you too, unless you tend to keep your speeds at 10mph or under on a century ride. Downhill, a jag in the road, and rock, the same color and texture as those that were part of the road, laying on the surface. Perfect set-up. I didn't mention, however, that I had a couple of skids/lockups on the tires going downhill (12-14% grade) in the 300 +/- miles that I have on the GK slicks. That had never happened with my Armidillos. Who knows, I may have ran over something similar with the Armadillos and remained upright. Just weighing the benefit/cost of reduced rolling vs stability and attempting to get input from those that have experience with such.

kingston 

Tire selection is all about trade-offs. I use knobby tires on my gravel bike, but I'm not racing either. If I were a competitive racer, I would use something faster.

unterhausen

a pile of small rocks like from chip seal are going to steer a smaller tire. Bigger tires will float. 32mm is not big enough to float on most such gravel. Your only hope is to ride it out. Small knob tires will dig in just like a slick tire