unterhausen

Would you say this route was particularly poor for the gravel bike? Hard to judge, but it sounds like it.

I have seen instances where a fellow rider on 44mm tires just rode away from me on really rough roads when I was riding on 32mm tires.

Lemond1985

Let's face it, the fastest human-powered thing on 2 wheels (recumbents notwithstanding) is your classic 15-17 lb road bike with 23 mm tires, as seen in the Tour de France and other races. That's the gold standard for achieving speed and distance on pavement. So the way I see it, any deviation you make from that design to accommodate off-road riding had damn well better be justified.

I think mixed courses are challenging, because on pavement is where the guy with 32 mm tires gains a real advantage over the one with 42's, especially if there's climbing involved.

Koyote

Horses for courses, as the Brits say. Gravel bikes are faster on gravel, road bikes are faster on pavement.

Lemond1985

But what of mixed courses, like say, Eroica California?

rosefarts

We'll there's always time trial bikes and speed record recumbents.

Toadmeister

If I ride a skinny tire 25mm high pressure road bike on rough gravel, would I be 20% slower than on my 40mm wide tire 35psi gravel bike?

you see where I’m going with this. The right tool for the job will always do a bit better. Cant say 15, 20, 25% better unless you do a direct comparison with the rider.

personally I went down maybe 10% in speed on the road going from a road bike to a gravel bike and I’m good with that.

DrIsotope

By poor for the gravel bike do you mean like... smooth pavement the whole way? Because no, definitely not that. This is the IE. There are places where riding the dirt shoulder is smoother than the pavement. That route includes a Strava segment simply entitled "Take my money and fix this road." I've done the exact same route on my not-light singlespeed on 700x37s, and averaged 17.2mph, about 3% slower than the CX bike. Not surprisingly, the engine is still the most important variable.

That's basically describes my Cervelo-- though the wide rims allow the 23s to mount to 25 wide. It's faster than the steel thing on 75% wider tires, but not that much faster. I mean... it's faster enough.

HTupolev

Totally different riders doing totally different rides doesn't tell you much of anything about the relative capabilities of two bikes.

"Pretty damn good shape" isn't very descriptive. The fastest people who ride road bikes are literally several times faster up hills than the slowest. Unless you compete at the pointy end of the climbers in professional WorldTour races, there are always people out there who can smoke you when the road points skyward.
A lot of people think I'm a decent climber, and on many gravel rides, I'm the strongest climber in the group. But if you stuck me on an ultra-fancy 9lb climbing bike, and you stuck Giulio Ciccone on a cheap 34lb comfort hybrid, and you had the two of us race up a hill, he'd make me look like I was rolling backwards.

Even with two riders of identical abilities riding the same bike, climbing speeds will differ dramatically on different rides. Someone racing to the top of a hill before a rest/regroup is likely to be putting in a much more intense effort than somebody climbing the hill in the middle of a semi-steady 50-mile effort. On one local hill where I recently grabbed the KOM, my all-out KOM effort was more than 30% faster than my typical efforts on that hill.

//============================

As to the what the performance difference between two bikes can "potentially" be, it depends on the specifics of the two bikes. It's always possible to make a bike slower.

"Gravel bike" is an extremely wide umbrella, and on one region of the spectrum, they don't necessarily give up much of anything to a traditional road bike. Some gravel bikes - many of the "allroad" sort - pretty much have road geometry and frequently get fit like road bikes. If their gearing remains suitable for road use, and the rider sticks a set of fast road wheels and tires on them, such a bike is pretty much a traditional road bike.

But if a gravel bike is fit with a more reclined posture, it will be harder to be aero at speed. If a gravel bike has tires have are beefy or have large knobs, they can roll poorly on pavement; supple wide tires can perform closer than most people expect to a fast skinny road setup, but you're still paying some aero and weight. If a gravel bike has low top-end gearing, it may be problematic for hanging with a paceline on shallow downhills. If various aspects of the gravel bike have been built particularly beefy, or obviously if you're carrying additional mass like bikepacking bags, it can add weight that reduces your speed on climbs.

20% would be an unusually large difference, although it's certainly doable if there are a lot of things about the gravel bike making it slow. Circumstance is important: 20% slower during what part of a ride is a relevant question. A bike that's 20% slower on a climb isn't necessarily 20% slower on the flats, and a bike that's 20% slower on the flats isn't necessarily 20% slower on a climb, for instance. A road bike is usually a lot faster than a faired velomobile on a steep climb, but on flat roads, a velomobile can absolutely destroy pretty much anything that doesn't have a motor.

I will say that it would be very surprising to see a gravel bike being 20% slower than a road bike on a climb, unless the gravel bike was loaded down with heavy cargo, or if it was something like a single-speed gravel bike where the rider has badly bottomed out their gearing. My gravel bike is only about 6-7% slower than my Emonda on paved climbs, and it's an extremely heavy vintage MTB drop-bar conversion with 2.1" tires and very floppy out-of-the-saddle steering:

Rides4Beer

Put road tires on your gravel bike and it's pretty much just as fast as a road bike (depending on your bike of course, mine has no problems). But I've also done A+/WBL type rides on the 40mm gravel tires (knobby, not slick), and kept up. Sure, there was def extra effort involved, just made for a good workout, that's just increased rolling resistance and aero from bigger tires, can't get around the physics.

Sy Reene

I'd think it's a strong "depends".. If you take 2 nearest neighbor bikes in a lineup (eg. Trek Checkpoint vs Domane?, Cervelo R3 vs Aspero?).. and use the same wheelset/tires on each, then I'd imagine the difference is very slight. Is the point of the question to evaluate how close can a gravel bike be relative to a road bike, on the road, by moving over the tires/wheels?

chas58

Very true. My "gravel" bike is faster than my road bikes (its also more expensive). I'm "sport" level, not elite. lol. Still, I'll do crits, CX, gravel, and even mix it up with hardtails. The only place I've felt the bike held me back is fast sweeping singletrack vs a hardtail. On the road, Maybe I would have gotten 1st instead of 3rd in my last crit on a road bike, lol. Doubt it though. ;-)
I'll never do 23mm again (well, outside of my track bike on the oval). Around here, my 32mm tires are needed for the crappy roads we have, and I'm convinced they are faster than the 23mm tires on the road bikes I ride with. Same tires work great on our gravel in the summer/fall. I'm not losing anything significant in the aero or weight battles.

Certainly I started getting a lot of PRs when I got my gravel bike - slow it ain't.

DrIsotope

Back to back Tuesdays. On the left, the Cervelo from my previous post, on the right, the very same Ritchey. Only on Tuesday #2 I decided to see what it would take to match the
Cervelo's time with the Ritchey-- which is 40% heavier, has 50% more tire, and half the gears. I mean, I came close-- I think I missed the embedded segment time by about
40 seconds, but the increased level of effort is... pretty small on paper, really. But when I hit the last of the hills at around the 20 mile mark, I felt it a whole lot more today.

The most fun bit for me? In the first two efforts (posted above) the speed differential was ~8%. In these two efforts, I went harder on the steel bike trying to make the time.
How much harder? 8%. That's almost like a result.

I do have another ride from about 3 weeks ago where I put in the same roughly 130 score effort on the lighter bike. As expected, it's faster, about 5%. As the average speed
continues to increase, I'm experiencing diminishing returns.

Cyclist0108

I think his data are rather compelling.

For me, as a less-able rider, the percentage is probably smaller on the road. (I'm actually reproducibly slower on my 1987 steel Bianchi than my 2014 steel custom "gravel" bike, but it probably has more to do with comfort and optimal fit, even though I "feel" less sluggish on the Bianchi.)

dwmckee

Aren't they riding even faster now on 25 & 28 mm tires in the Tour?

Craptacular8

Interesting. Your first side-by-side comparison showed slightly more effort/watts being used on the Cervelo. This seems to show more that you were having to work harder on the gravel bike to achieve the same speed. I know my carbon endurance bike is faster for the same effort than my Space horse over similar courses...but for the weight difference between the two, at least 6 pounds, and tire size roughly 28 versus 38....about 1 mph difference. Between my "gravel bike" and my endurance road, not much differences in geometry. Endurance bike is 72 HTA / 74 STA. SH is 71 / 73.5

mstateglfr 

Ironic that your screen name is LeMond, but you set your bike up Lance style.

IronM

IMHO opinion, it's not so much the bike as it is the terrain. Gravel just robs power; thus speed. Gravel speed depends greatly on conditions - loose, dry, wet, rocky. So on gravel, to me speed is irreverent.
Now on pavement - my gravel bike is a bit slower; but probably only because my road bike is an aero, lightweight race rig & my gravel bike is certainly not. The rotational weight of the heaver rims & dramatically heavier tires really slows things up; plus the higher rolling resistance of low-inflated knobby gravel tires.
As an average - I'd say that gravel multiplier is about 1.75 of that of road bike, per mile. So 40 miles of gravel is about the same effort (and time) as around 70 miles on my road bike.

Chuckles1

8% is close to what i'd estimate. I would have said 10% based on my avg speed at end of 20 mile "favorite" ride i do often on either gravel bike with disc brakes and 37c gravel tire on rear, 30c cyclocross tire on front: or road bike with 28c road tires and rim brakes. Gravel bike is way more capable and comfortable on gravel. Road bike way faster on paved road. Too bad I usually ride a mix of both!

daoswald

Differences that could have an impact:

• Frame & Component Weight: A heavier bike will accelerate more slowly, and will climb more slowly. On flat terrain in motion it won't be much different.
• Bike geometry: A more aggressive geometry optimizes power to the pedals, and rider aerodynamics. However, a more aggressive geometry may also inhibit deep breathing a little. There are trade-offs, but in general if your body can take it, more aggressive geometries will be a little faster. Rider aerodynamics become more important the faster you go.
• Bike aerodynamics: A bike with less aerodynamic drag will be faster. Or more accurately, will require fewer watts to maintain a given speed. This is more of a factor at speeds over 12mph, and increases in importance the faster you go.
• Tire rolling resistance: A tire that sucks down more watts to roll will be slower on smooth surfaces. On bumpy surfaces the tire that absorbs a little shock may be faster.
• Wheel/Tire rotational mass: A heavier wheel and tire will require more effort to accelerate.

So if a gravel bike has wider tires, worse aerodynamics, and heavier wheels/tires, it will be a little slower. But it won't be 20% slower because it still puts the rider in a road-bike position; it still has most of the aerodynamic advantages of a dedicated road bike. Not all, but most.

It's hard to assign a percentage difference to a given set of bikes. But 20% is pretty extreme; I would expect that 20% when comparing an upright-geometry adventure bike or beach cruiser to a road bike. I would expect 10-15% going from a decent hybrid with knobby tires to a road bike. I would expect 5-10% going from a gravel bike with gravel tires to a road bike. And if you put road bike tires on the gravel bike, I would expect less than 5% difference for most riders.

Even the difference between a fairly run-of-the-mill road bike and a true racing road bike would probably be less than 5%. But races are won on narrow margins; 5% counts there. However, nobody's counting for your typical fitness/enjoyment rides.

20% is a big number. Putting it in perspective, if you were riding 20 miles on the road bike and averaging 15 MPH, you would complete the same course averaging 12 MPH on the gravel bike if there were a 20% difference, and you were putting out the same effort. That's huge. That's the difference between a cruiser and a road bike, not a gravel vs road bike. And yet you would finish the ride in 1h 20m on the road bike, or 1h 40m on the 20% slower bike. Now if the gravel bike came in at a more modest 7% slower, you would average about 14 MPH. And that same ride would take 1h 25m. I think this is a lot more reasonable; for every 20 miles add 5 minutes, or 2.5 minutes every ten miles. Or four minutes for every hour of riding to reach the same distance. That's really not much.

Put slick tires on a gravel bike and you'll hang with the road bikes just fine. Most of what makes a gravel bike a gravel bike is a slightly sturdier frame that can accommodate big tires, more lower-range gearing, and big gravel tires. Most people don't need the higher-range gearing for normal rides, and tires can be swapped. The only thing you can't change is the slightly heavier duty frame. That's just fine.

Tomm Willians

On a flat paved road I can hit 30mph on my Wilier, on the same surface I can only do 22 on my Ridley X-Fire. I guess in that limited example yes my road bike is faster than my gravel.

Metieval

well my Scalpel MTB on WTB Exiwolf 2.35 is like 20% faster (sustained) than my Gravel bike (Trek crossrip) on a 38 slick. that was pavement. I am 100% positive that that spread got worse on gravel, and even farther apart on mtb trails.

so which road bike, which gravel bike, and what tires are we talking about here?

The only debate I have now on a new Gravel bike is do I want 1 tire 700x44 snoqualmie all the time , or do I want 2 wheel sets, one with a GP5000 32 tubless + a wheelset with a 700x42 WTB resolute.

mikehuangsd

The difference is A LOT more than 20%, according to GCN:




Here's the video link if you want:

You Tube

.

HTupolev

They neither tested for, nor calculated, the speed difference between the two tires.

The roller test (sort of) implies a ~50% increase to hysteretic rolling resistance. But for a typical fit road cyclist doing 20mph on flat ground with fast road tires, this implies somewhere in the neighborhood of a 4% cost in speed. Even if we account for the added aerodynamic drag of the gravel tires, it'll only bump that by a few percent. This is because, at cruising speeds, the vast majority of resistance to your forward motion comes from aerodynamic drag on your body.
Results on a climb will similarly be much smaller than the measured "50%" difference, since the vast majority of drag on steep hills is gravity, not rolling resistance.

The rolldown test was also not a direct measure of cyclist speed. There are ways to process rolldown data to produce useful results, but GCN did not perform them. How far you roll after reaching a few kph on near-level pavement does not have a very proportional relationship with any reasonable performance-oriented use case.

Gravel tires are also an extremely wide umbrella. Testing just one of them tells you very little about the spectrum.

Cyclist0108

Jan Heine had a good article on this:

Are gravel bikes slower than road bikes?

https://www.renehersecycles.com/are-...an-road-bikes/

It discusses the GCN video posted above.

aaronmcd

I don't ride my gravel bike when speed is a priority. Like in a road race.
20% is 16mph vs 20 mph. It's not THAT slow. Maybe 18 vs 20? Idk, and idc really. I ride my gravel bike when I'm just chilling, or if I wanna do some fun dirt s***.