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Are gravel bikes slower than road bikes?

The euphoria about gravel bikes is hitting a snag: Many riders feel that their gravel bikes are slower than their road bikes. For example, James Huang, the technical expert from CyclingTips.com, posted:

“I’ve been spending too much time on gravel and mountain bikes lately. Good to be reminded what real speed actually feels like.”

Global Cycling Networks even did some – admittedly unscientific – testing:

They ran a set of racing tires and a set of gravel tires. They did three tests: on a roller, on the road and on gravel. The result: The racing tires were faster on all surfaces.

Is it true? Are gravel bikes slower than racing bikes? The answer is: ‘It depends.’ There are a few things that can make a gravel tire slower:

Aerodynamics of the bike: Wider tires catch a tiny bit more wind, but a 10 mm increase in frontal area doesn’t make a huge difference. Otherwise, steel frames with skinny tubes would be faster than carbon bikes with large-diameter down tubes.

Differences in airflow over tire and rim can be measured in the wind tunnel, but the effect is very small compared to the overall wind resistance of bike and rider.

(Bicycle Quarterly’s wind tunnel tests found no significant difference in the wind resistance with a 25 and a 31 mm tire.)

Aerodynamics of the rider: The rider is responsible for most of the wind resistance. Many gravel bikes have a more upright riding position, which is less aero. There is no reason why a gravel bike couldn’t use the same riding position as a racing bike (above). After all, gravel roads are roads, and there is no need to change the position just because the ground is a bit rougher.

(The more upright position may be more comfortable, especially for long rides, but this applies to road bikes just as much as it does to gravel bikes.)

Rolling resistance: Most gravel tires today are built like mountain bike tires, with stiff casings that absorb more energy and transmit more shocks than supple racing tires. GCN’s testing (above) shows what happens when you compare apples to oranges: The supple racing tire requires far less power than the stiff gravel tire – not just on pavement, but also on gravel.

The higher rolling resistance is due to the tire’s casing, not its width. We know that with the same casing and tread rubber, wide Rene Herse tires roll as fast as their narrow cousins (at 22 mph/35 km/h). The (very small) increase in wind resistance of the wider tires is compensated by a (very small) decrease in rolling resistance.

(GCN’s table also shows that high pressures roll faster – that is only true on rollers, where the convex roller digs deeper into the softer tire.)

Weight: Wider tires are heavier than narrow ones, but not by much. A 650B x 48 mm Rene Herse Switchback Hill Extralights tips the scales at just 413 g. Still, a set of Switchback Hills will weigh about 450 g more than our featherweight 700C x 26 Cayuse Pass (183 g each) – but that difference is little more than half a water bottle.

The Rene Herse Cayuse Pass is one of the lightest tires you can buy. If you are running a more standard racing tire, like the Continental GP 5000 (221 g), the difference shrinks to just 384 g. And you get some of that weight back, because the smaller 650B rims and shorter spokes weigh a bit less.

(If you are the type who notices whether your water bottle is half-full or totally empty, then the weight difference may matter to you. For the rest of us, bikes like the sub-17-pound Open U.P.P.E.R. above are plenty light.)

Q factor: Many ‘gravel’ cranks are very wide (above). Road cranks rarely have Q factors of more than 150 mm. For many cyclists, a wide Q factor makes the cranks harder to spin. However, the wide Q isn’t necessary: Many modern gravel and all-road bikes are designed to accept standard road cranks.

(Due to carbon’s lower density, you need wider chainstays on a carbon bike. However, the dropped chainstays pioneered by Open have solved the problem of fitting wide tires between narrow cranks.)

Cornering feel: The rotational inertia of wider (and usually heavier) tires makes many gravel bikes feel sluggish compared to a good racing bike, especially when climbing or sprinting out of the saddle. The solution is simple: Use smaller wheels and lightweight tires, so the rotational inertia is the same as on a good racing bike.

(Some riders prefer the more stable feel of bigger wheels and tires. For them, ultra-wide 700C tires are a great choice.)

So we’ve seen that gravel bikes don’t need to be slower than racing bikes, if they are built to the same specs. Why does the industry insist that racing bikes are faster?

I suspect the reason is simple: The industry wants to sell more bikes. The thinking seems to go like this: Now that many riders have bought a gravel bike, let’s convince them that they need a new road bike. Of course, most already have a road bike, but that one has outdated rim brakes. It’ll be easy to convince them that they need a disc road bike with tubeless tires.

(You don’t want to get dropped on your Sunday morning ride!)

Perhaps that will work for some riders. The rest of us know that swapping the heavy, stiff ‘gravel’ tires for a set of supple, fast-rolling tires will make your gravel bike as fast as a road bike. That is why we coined the term all-road bikes and don’t call them ‘gravel’ bikes.

(As speeds increase, wind resistance matters more, so it’s possible that at time trial speeds, narrow tires are a little faster. On the other hand, if you ride slower than 22 mph, you’re probably faster on wider tires.)

Many non-cyclists are excited about the idea of the all-road bike. They want a bike – one bike – that combines speed with comfort and the ability to go off the beaten path. They view these new bikes with a level of excitement that I haven’t seen since the mountain bike boom.

I’m surprised that the bike industry is turning its back on these would-be cyclists. Instead, they keep trying the old strategy of selling bikes to those who already have plenty. Rather than trying to fill the garages of those who already ride, we should bring potential cyclists into the sport. Let’s put them on all-road bikes, where they’ll have more fun than on (slow) mountain or (uncomfortable) road bikes. They’ll be more likely to stay engaged and become life-long cyclists. And that is good for everybody – even for the bike industry!

16 Responses to Are gravel bikes slower than road bikes?

  1. Larry T December 3, 2019 at 7:42 am #

    Your take on the bike biz is refreshing. The push on e-bikes was the first clue gravel had already peaked, just as ‘cross had a few years earlier. My guess is it’s just easier to sell another bike to someone who already has one (three) than trying to create a new customer? Why the bike biz folks don’t create a “Got milk?” type of marketing scheme to appeal to potential new customers is a mystery to me. There was also the “RVing” TV campaign – were neither of those effective?

  2. Alex December 3, 2019 at 8:06 am #

    One of the most obsolete post in your great blog!
    Yes heavier bike is slower. Yes less aerodynamic steel bike with round tubes and wider tires IS slower than proper carbon aero bike with aero shaped tubes, aero wheels and 28mm tires.

    I have several bikes including my loved and very versalite 10,5+ kg Cannondale slate with 650b 42mm tires and dropper and 7kg carbon race bike.

    • Jan Heine December 3, 2019 at 12:06 pm #

      Physics are physics, but the question is ‘how much slower.’ And on the other hand, a bike that vibrates less is faster. So you trade some aero and weight for improvements in rolling resistance/suspension losses. All our testing indicates it comes out to the same in the end.

      Believe me, if I thought a racing bike on 28 mm tires was faster than my randonneur bike with 42s, I’d have ridden that in Paris-Brest-Paris. Fortunately, you can choose – Rene Herse makes tires for both 😉

  3. Ford Bailey December 3, 2019 at 9:02 am #

    As you’ve mentioned before, skinny high pressure tires feel faster because they don’t deform over every bump and transmit every vibration to the rider. this sensation feels faster to the rider.

    Drum rollers seem to deform tires more, making less supple tires appear slower (less efficient) The casing is pushed into a more extreme shape by the diameter of the roller.

    The GCN tests are merely reinforcing conventional wisdom, and uses flawed assumptions. Too bad.

    I don’t feel slow on my Rat Trap Pass tires ! And I know I’m faster on a lot of rough descents, passing people on 40mm tires pumped up to 85 psi because they want low rolling resistance…

  4. Dr J December 3, 2019 at 9:42 am #

    Bike industry loves to compare numbers and sell speed as the ultimate metric for success. For most of us, mortals, speed on bike is secondary.

    Plus, we all know that the fastest bikes out there are neither gravel nor road bikes, but velomobiles.

  5. Timothy December 3, 2019 at 10:29 am #

    Here we go again. What about rider fatigue? Paris Roubaix is out of my league, but that said, my local roads aren’t getting any better.

  6. Steve December 3, 2019 at 12:16 pm #

    It is great that road bikes and gravel bikes are good at different things.

    My long&low road bike with aero wheels and 28mm (Compass) tires is materially faster than my gravel bike with a more relaxed riding position, low gearing and 700×42 (Compass) tires, but they are both great at what they are designed to do and without trying to perform like the other.

  7. Jacob Musha December 3, 2019 at 12:58 pm #

    Gravel bikes are better for most riders than road racing bikes, but it’s still baby steps.

    Can the bike industry please make the randonneur their next big thing? Mine is as fast or faster than my road racing bike, better on gravel than any “gravel” bike, and also makes a better commuter than any “commuter” bike. With two bags on a low-rider front rack it can even go camping, filling the long lost “sport touring” role.

    Five bikes in one! They could market it to everyone. It’s the bike I tried to cobble together for years (before I knew it existed) but was always let down by geometry, tubing selection, tire clearance, decent fender/rack mounts, or all of the above. Unfortunately, full custom or a small number of low-production frames is the only way to get a bike like this.

  8. RickH December 3, 2019 at 1:36 pm #

    Aero? Oh Dear where do we start… Never have I seen or read where aero is measured with a rider on the bike in a wind tunnel. I’m sure you’re aware of this Jan.
    Aero is VERY IMPORTANT for an aeroplane flying at 500 kilometres an hour, not your average cyclist riding between 20-35 kph. Then when the wind is blowing around you on the bike, in the real world, there will be eddies and flurries of wind that has changes in direction and causes a dislodgement of laminar flow over your super duper aero frame and wheels which renders the design useless. For example, have you ever seen a wind vane stay totally steady in any kind of breeze?
    I would tend to concentrate more on proper handling geometry with comfort high on the design list.

    • Jan Heine December 3, 2019 at 1:54 pm #

      BQ’s wind tunnel tests measured the rider, too. As you mention, cyclists are an incredibly un-aero shape, so all that really matters is frontal area. That is why aero bars and the aero tuck work so well, and why even just lowering your stem by 20 mm does more than a set of aero wheels.

  9. Peter M December 3, 2019 at 3:03 pm #

    A heartfelt thank you for your efforts to communicate the benefits of wider tires!

    I only took up cycling in my mid-60’s – and came across your early posts on the benefits of wider tires and became a convert running the widest possible tires on my Synapse.

    A couple of years ago I treated myself to a 70th birthday present –> a Ti ‘7’ built to a design by Steve Hogg based on measurements by his Canadian fitter (Mark Dwyer) – my input being it had to allow for wider tires even when mudguards are installed.

    Perhaps this was a relatively early ‘all-road’ bike

    I have two sets of wheels:
    ~ Hed SL+ where I installed your superlative Barlow Pass Ultralights running at some 50 PSI. Really smooth out the poor road surfaces up in Ontario, and I have not noticed any diminution in speed on my rides.
    ~ ENVE 4.5ARs where unfortunately I cannot use your tires so run 30mm nominal Schwalbe Pro Ones Tubeless (actual 32mm mounted) which I run at about 60 PSI

    I love riding my bike (I have completed 200 miles in one day) – likely primarily due to design / construction, but also partly due to benefits of the wider tires.

  10. Craig Lloyd December 3, 2019 at 7:07 pm #

    The particular gravel bike I had was too long and slack. It was uninspiring to ride and didn’t even have useful mounts, but it was only when the speed went over about 35 km/h that I went backwards compared to my ride buddies on top road machines. Below that, my 38mm Extralights rolled great.

    I changed it for a road frame with the opposite geometry (Trek Emonda – very steep and short) as an experiment. I run moderate aero wheels with 28mm tyres. The position is identical.

    The new frame handles much more responsively (fun) and responds better to accelerations… but this is due to the extreme geometry differences. A Specialized Crux would probably have felt massively better also, but allowed wider tyres (still no useful mounts). Here in Bali, you can be pedalling fast downhill for 40-60 minutes so the wheels noticeably help there. The 2kg weight saving isn’t even worth 5 minutes on the longest climb (2.5 hours).

    Am I keeping it? Probably not for long. This bike handles great but is not at all versatile. I may keep the wheels; they will cut through a muddy CX course if nothing else, but when I return to the twisty, undulating terrain of the UK/Ireland with unpredictable weather I will be going back to bigger tyres and mudguards! The length of time ‘pedalling’ above 35 km/h will be a small percentage of most rides.

  11. Steve December 4, 2019 at 12:10 am #

    Hi
    I love riding on babyshoe pass 42mm tyres, and I don’t notice any difference in speed for solo riding. However, if I am riding in a fast group at my limit I find I am much more likely to get dropped when it gets hard. Could it be that the little accelerations needed to grab the wheel after being on the front are a tiny bit harder than on a bike with narrow light tyres and at the limit this is enough to mean you are dropped, which then makes a big difference to your speed.

    I guess that problem would be solved if everyone rode on 42mm tyres, and then the groups would go faster too…

    • Jan Heine December 4, 2019 at 2:24 pm #

      Thank you for sharing the observation. Are you using different wheels on the same bike? Or different bikes? In my experience, even in fast group rides – like the early stages of this year’s PBP – I have no problems keeping up on my Rene Herse with 650B x 42s. Certainly, I’m no faster when I ride a test bike with narrower tires.

  12. Mark December 4, 2019 at 6:31 pm #

    Since 2012, I’ve had a Lynskey ProCross CX bike on 32 or 35 mm tyres, and a 2016 Trek Domane on 32 mm (before that I had steel touring bikes). All 700c. Often but not always with ‘guards & lights. Used for commuting, brevets, and bike packing tours on rough & gravelly roads.

    Lynskey: rigid, rugged, manœuvrable. Rode well on any tyres, but best on 35 mm BJP XLs. Fast on rough/deep gravel, but pretty harsh. No difference to speed or handling when I changed fork from carbon to steel.

    Domane: very comfortable—even on rough dirt. Handling felt cumbersome. Fun, but a handful, to ride on deep gravel. Surprisingly good loaded with bike packing gear. Light; but, as I found, carbon is fragile.

    My fastest brevets were on the Domane (not by much). But my overall average speeds on these bikes on commutes, brevets, tours, &c on asphalt & gravel, were more or less the same.

    For two months now, I’ve had a custom steel bike built for brevets & gravel—thin tubes, low trail, mudguards, c/p brakes &c. And 38 mm Barlow Pass XL tyres (700c is easier to replace far from home than 650b—everything is a compromise).

    I’m still learning how to ride this bike. I notice the extra weight of wheels and frame. The big diameter wheels feel a bit ponderous, hard to accelerate (650b would alleviate this). I diesel rather than zip up hills. Comfort is somwehere between Lynskey & Domane until on rough, wet, or gravel roads where it’s in a different league. I regularly come home thinking I feel much fresher than I expected to. The cornering is quick, precise, and great in the wet. However, the bike feels slow, slow, slow. Up hill I feel like I’m going backwards. In a group I find it hard to move with any surges.

    But, but, but … my overall average speed is more or less the same, and my times on the few Strava segments I check are too. Some of the climbing segments are faster.

    I need more data before I can be definitive, but, despite my perceptions, it seems that a steel bike with fat tyres, heavier than my carbon and titanium bikes, and with a big box under the handlebars, has made no difference to my overall speed, and may have increased it.

    I clearly have to adjust my perceptions. I look forward to running 42 mm tyres when I know I’ll always be on gravel.

  13. Chris V. December 5, 2019 at 3:14 pm #

    I have been running the 700×35 Compass/Herse tires on my bike for multiple years. I really like the tires very much. And I intend to go to the 700×44 Snoqualmie Pass tires in the future.

    I recently put the Standard casing Snoqualmie Pass tires on my wife’s aluminium Trek hybrid. She instantly could tell the ride difference.

    I’m curious about others experiences. I personally feel like being above 6 foot tall that 700c wheels are much better than 650b.