You don't have to be on the Pro Tour to benefit from aero gains with narrower tires. Even moderately fit people usually can sustain 15 mph on flat, at which point aero gains start to matter. Even more for hilly terrain where you can easily pick up over 20 mph on descents. The wider tires roll more efficient at lower psi (when you have to air down for comfort). But roughness of pavement road usually doesn't require less than 60 psi, and above 60 psi the rolling resistance of wider tires is about the same as narrower tires, but watt savings from aero can be significant.
I got a gravel bike to replace my old road bike because everyone was raving about it, and I absolutely hated riding it. Sure, at slow recreational speeds, it was more comfortable, but when getting places, it just didn't roll as well down hills, making me having to pedal more over extended times to get uphill.
Now I ride an aero road bike with TT bars, with 28c tires, and even when running them at 60-70 psi for rough pavement, the aero gains from the narrower wheels are significant, as I can pick up speeds over 30 mph on some descents which carry me way further uphill.
It depends on what kinds of roads you ride on. If you're always riding nice smooth asphalt, then yes, high pressure narrow tires are going to be faster pretty much always. But if you're riding on really crappy asphalt, chipseal, or on dirt or gravel roads, then a wider more supple tire may be just as fast but a whole lot more comfortable due to the ability to run lower pressures.
The power losses on a perfectly smooth road are aero and rolling resistance. But once you get onto bumpy surfaces, now you also need to consider the power losses of the bumps on the bike AND on the rider because the rider is the one supplying the power, even the power which does not transmit through the cranks.
Although I do agree with you partially, if you're racing, ride what ever makes you fastest. Energy efficiency isn't paramount, getting to the finish first is. But if you're not racing, then really consider if the tradeoff of comfort is worth it.
The BRR website's test protocol uses a fairly smooth metal drum for testing. This is good for testing rolling resistance but not for testing total system losses over rough roads. So although BRR is a great resource, take it with a grain of salt.
The real eye-opener for me were that my kinda knobby MTB tires apparently have nearly the exact rolling resistance as my Schwalbe Marathon Plus on the Gravel Bike. So although they're a lot thinner, nothing is gained here at all. (If you assume enough pressure in the MTB tires on asphalt).
28 mm tires used to be huge tires. Pros didn't ride anything wider than 23 mm in the 90s. 25 mm would be for special occasions. 21 mm on tracks, sometimes even 19 mm.
I think than Valverde used a 28 mm in a Roubaix and at the end of the race said that it was too much and not worth of the extra weight and front section.
Every pro is riding on 30 or 32 mm now. Of course the rims are totally different and wrap those tires in a way that the old metallic rims could not do, hence the aerodynamic gains.
Edit: I've got a gravel bike with 42 mm tires and a 28 mm set. I use the 28 mm when going in the hills on asphalt. I'm with you on that: it's a day/night difference. On mixed mostly flat terrains the 42 mm tires are the best compromise.
Unfortunately you cannot discount the “sponsor effect” here. Wheel manufacturers have been pushing wider rims because it helps them sell another set of wheels to everyone.
In the days of rim brakes a wheel had a finite life (the length of time it took to wear down the braking surface). Then shimano and the frame builders pushed everyone to disc brakes, so the wheels now last for ever. What do you know, 2 years later all the wheel manufacturers are claiming “wide is better” and flogging everyone new wheels.
I’ve not seen any clear evidence that they’re right, and there’s lots of intuitive reasons to think that wider tyres will be slower (aerodynamics!). I remain sceptical, but genuinely hopeful that someone who thinks that wider is faster can provide me with some solid evidence…
I feel that any marketing strategy that relies on the niche of a niche formed of the people that would buy the cutting edge cycling gear just because it's presented as an improvement over the status quo, would hardly bring any benefits to any wheel maker.
I am 100% sure that in this age of "marginal gains", the pro tour teams would not go for anything that doesn't give them it unless severely hamstrung by sponsorship deals. And I doubt that the wheel sponsors don't have multiple sizes available.
And I think you're severely overestimating wheel life span for modern models, at least due to the fact that carbon is more brittle than more pedestrian materials. Just look for Pogacar's fall earlier last week in the Giro to see how a simple flat tire makes the whole wheel a risk.
>And I think you're severely overestimating wheel life span for modern models, at least due to the fact that carbon is more brittle than more pedestrian materials. Just look for Pogacar's fall earlier last week in the Giro to see how a simple flat tire makes the whole wheel a risk.
My experience is personal, but I get 50,000km out of a set of rim brake carbon wheels ridden in all terrains and conditions and through northern european winters. At that point you're also starting to lose spokes/nipples to corrosion, but the rim could be rebuilt with new spokes and a new hub if it didn't need a brake track. That riding includes racing, crashing, potholes, punctures.
Pogacar rides on Enve wheels, which are now hookless and therefore a puncture is much more likely to result in damage. Another innovation that makes life worse for the consumer and better for the manufacturer.
You're kidding yourself if you think Pogacar would run 30mm tires at 55 PSI at the detriment of speed to please his sponsors. Cyclists are notorious for re-badging stuff they don't want to use and being super finicky with their gear. You're talking about guys that hardly celebrate a win with a $250k purse because they want to make sure they stopped their ride right on the finish line on their headunit.
I don't share your optimism about the strength of the scientific method in pro-cycling :) It's not too long ago (admittedly in the pre-disc brake era) that climbers would have their bike built up to sub 6.8kg and then add weight to it to bring it up to the limit rather than use deeper wheels.
If you look at TT equipment all team members use the same helmet regardless of the fact that helmet performance varies massively from rider to rider.
The 2016 S-works Venge is 5w faster than both the SL7 and SL8, so on flat stages all specialized sponsored teams are riding it... aren't they?
Why is nobody wearing a TT Helmet and visor on a normal road stage?
> Why is nobody wearing a TT Helmet and visor on a normal road stage?
(1) weight is not always worth it, notably when there are lots of climbs
(2) riding with others, need to be able to turn your head. Further, you can't get as super low when in a big group. It also doesn't help as much because the group dynamic is more important than crouching extra low and/or helmet drag
To break away requires you to put out 30% more power than the person behind you, and then also means you need to put out 30% more power than the rest of the field. That is a good recipe to go out hard, overcook, and then get passed up by the entire peloton.
The 30% - Drafting is good for a 30% power increase. When in the middle if a peloton, even more. The breakaway plan can make sense, but not by fooling around in a TT helmet in the middle of a peloton for a few hours first.
> Why is nobody wearing a TT Helmet and visor on a normal road stage?
Because it doesn't work as much alone as in combination with specific aero body position. But you can't be in that position in a normal road stage because the aero handlebar extensions are forbidden in mass start stages.
Also there are less aero benefits to be had when you ride in the peloton behind other riders.
You don't need aero bars to have you arms forward and narrow. It's not particularly safe, but doable for a while.
The aero bar question (whether to have them or not) comes down to how long you will spend drafting and climbing. It's a more interesting decisions in Olympics and triathlons than most road bike racing (the latter it makes no sense because people are drafting as much as possible).
The aero drag of wider tire is not a lot. It is more the wider tires are not slower. Wider tires allow: more air volume in tire, lower PSI. In turn those help ride quality.
The aero drag is the elephant in the room here. By this study’s measurements there wasn’t much difference, but what was the width of the rim they used with the narrow tyre?
A narrow tyre on a wide rim is a wide tyre. They don’t explain or address this issue. I suspect they would have used a wide rim with all the tyres, which is notionally a sensible thing to do, but in reality it’s completely flawed.
What are the results if you used a narrower rim with the narrower tyre so that the frontal area was actually reduced as much as it could have been?
Rene herse has been doing those tests since 2006 "back when go-fast tires were 23mm." They covered a lot of variety and their conclusion is the aerial drag is tiny and real world conditions are more important than the idealized condition of tests on a steel drum.
The tests in the reference were done with a 21mm inner rim width. I believe that is neither super wide nor narrow. Arguably a good test bed rim to isolate the difference in tire.
Though, wide rim equates to a wide tire I do not think is true (at least, unsupported). The deep dish rims are only aero if the width is close to that of the tire. Reducing the ratio of tire width to rim width is aero! If anything, a wider deep rim on a skinny tire is increasing are dynamics. The aero dynamics of a wheel is not just a function of the tire alone. A deeper dish of more equal width to the tire helps that teardrop shape you want for aerodynamics.
The reference does go into some more detail why wide rim is desirable to reduce drag. I won't paraphrase further here other than to conclude a wider rim would actually be favorable for the skinny tire.Regardless, a middle of the road rim width was used in that data sample.
> Wheel manufacturers have been pushing wider rims because it helps them sell another set of wheels to everyone.
I think the push to wider tires and lower pressures on road setups is actually because hookless carbon rims are much easier to manufacture than clinchers, and hookless tires can't handle 80+ psi.
Clincher carbon wheels are basically considered a niche product by big manufacturers
I think you might be transposing the cause and effect. Mechanical rim brakes had been limiting the wheel width because of physics of leverage, disc brakes opened demand for wheels of any width and users naturally migrated to the wider wheels.
It can't work like that in the world of mass produced equipment. You can only buy what the manufacturers are making, and as far as I'm aware there haven't been any wheels that are offered in different widths that the consumer can choose from.
It's always: this is the latest model, it has these features, thanks.
I don't think this is a realistic world picture: if this was true then the wheel manufacturers would just keep making rim brake wheels, which a apparently more profitable in your view. In real world a wheel supplier will make wheels for the specs their customers, bike manufacturers and bike shops, order. And those order what their customers, cyclists, demand.
I hear what you're saying and that would normally make sense, but there are reasons why I don't think its true in the bike industry. It comes down to the same arguments that you often see on HN about whether or not a free market works.
Shimano can decide to stop manufacturing rim brake groupsets and spares for existing rim brake groupsets unilaterally. It doesn't matter if the customer wants it or not. The rest of the bike industry supply side won't object to it, because it pushes people towards replacing whole bicycles which benefits all of them.
Other component manufacturers can play the same games in the areas that they can control. Wheel manufacturers can start pushing to wider rims, and then increasing profitability with hookless. Benefits the frame manufacturer (oh no, you need a frame with more clearance!), the tyre manufacturer, doesn't negatively affect any other the other players who aren't directly affected, spin a marketing story about how great this new thing is based on dubious test results and claims, and off it goes.
Repeat that cycle a few times in a few different areas and you have the situation we are now currently in:
The price of a mid/high end bike has doubled in the last 5 years.
The bikes have got heavier and more complicated and harder to maintain.
The consumers are all pissed off with it and start leaving the sport.
Sales suddenly fall off a cliff.
I'm not saying this as a conspiracy theory nut, but rather that there are a set of dynamics at play in this industry that mean that this kind of thing can happen.
If shimano stopped making rim brakes, no tour de France athlete would use shimano groupsets. Rim brakes are lighter, that is why.
Would shimano ever give that up? No. All these companies pride themselves for being what the elites run. Dura ace would become a joke if no elites used it. The dura ace groupo upgrade is thousands of dollars (2k to be exact, it's the most expensive 100g you can pay for), & dura ace is high profi. So mo, too much brand risk. I mean, why haven't they stopped selling rim brakes already? It makes zero sense for shimano to do that.
Further, there are plenty of bike tire manufacturers making a variety of rim sizes. Some bikes can only do 25s max, makes no sense to only have a 28mm rim.
What's more, there's millions, probably hundreds of millions of older bikes that all need new rims every few years. For what you're saying to be accurate, no company would seize that demand and instead some sort of duopoly would instead opt for forced obsolescence. I don't see that as being the case (it is for thing like iPhones/cell phones, but the bike industry is very different)
Your points about the zillions of rim brakes bikes sold at 100-300 Euro price points are definitely on spot. They don't need performance, those brakes are very cheap, they are easy to maintain, they'll last forever in the market IMHO.
However I'm not sure I understood your first point about disc vs rim brakes.
Rim brakes are lighter but disc brakes brake better, in a shorter span and under any circumstance, even in the rain when the rim is wet and a rim brake takes a little to warm up and make friction on the rim. Furthermore wheels and bikes are at 6.8 kg even with disc brakes now. That's why every pro rider started using them when they had a choice. There was a short while when they were kept at hold because of concerns that the disc could hurt riders in group crashes (they don't have that problem in cyclocross or MTB,) then concerns about weight and aero, but given the average speeds they are doing at the Giro in these days I'd say that it is all well in the past.
I'm no tour de France rider but on a steep and long slope I rather use my disc brakes than the rim brakes of my previous bicycle. It was a good bike with much better brakes than the vbrakes of the bike I use for touring with bags but disc brakes are on a different level.
The 28 wheel feels immediately faster. It's lighter, so it accelerates faster than the 42 one and there are a lot of accelerations from low speed in a ride, especially for slow riders like me. On the other side the 42 wheel should be better at keeping the speed because of the higher mass and inertia. Unfortunately that's wasted each time I use the brakes or I slow down.
Are your 28 and 42 tires the same type (e.g., the Rene Herse standard tires are the same construction across the entire size lineup), or is the 28 a road tire and the 42 a gravel tire?
I've got a road bike and a gravel bike. A while ago, I did the same workout, 12 reps of a local hill, 2.5 hours or so, once on each bike, separated by a week.
The road bike is 8kg and 25mm tires, the gravel is 12kg and 650bx42 or 48 tires. (might have been either, as I switched tires around then). The difference in time was 6 seconds.
The gravel bike doesn't feel as fast. It doesn't reward spinning, and the gearing jumps are just a little big for me (1x11). The road bike beats me up with vibrations, but it feels better climbing and standing. It's got closer gear ratios, so it's just a bit better matching. Now, to be fair, the gravel bike is running far better tires, so there's less resistance there. (and, that's basically why I bought it) But overall, they are basically the same speed, even on a hilly climbing workout.
Narrow will feel faster, and lighter accelerates faster - but the perception is often over perceived.
So, the weight difference of 28 vs 42 is going to be 100g maybe. It's not a lot. Weight vs aero experiments have found conclusions like weight over 100 miles is tiny small compared to any aero gains (talking like +3 lbs having a few minute difference over hours). Which is to say, the effects you describe are pretty small when measured.
Moreover, the choice of 28 vs 42 is rare, feels like is more choosing 25, 28 or 32; or choosing something in low 30s compared to 40s. Meaning, the weight delta is even less in real world choices. What's more, you can go to 650b and have the exact same tire weights with much bigger widths.
You cant really pump up 42c tires to 100 psi safely, so no.
Remember that the wider tires are more efficient at lower pressures than narrower tires. However as the pressures go up, the difference becomes smaller. Even without aero gains, the narrower tire will be faster provided its a smooth surface.
On descents you can also pick up a lot of speed by getting a heavier bike and supersizing your meals at McDonalds.
Speed on descents isn't really that relevant - you're descending, so unless you're racing it's practically effort-less. What matters for people biking normally (i.e., not recreational road bike racing) is assistance in the 10-15mph regime, on flat terrain or climbing.
Large changes in rolling resistance matters here, like going from an almost 40W tire to a 20W tire. But aerodynamics have a very minimal effect here, and going below 20W tires won't really make a meaningful difference in biking effort compared to the effect on your butt and wrists.
Going from 20W tire to 10W tires is going to be massive even more so for recreational not so fit riders. Such a rider may output 120-150W on average. Getting 20W free (there are two tires) results in a difference comparable to installing a small motor on your bike.
No: A 20W tire is a 20W tire at 18 mph. At 10 mph, it's roughly a 10W tire (rolling resistance should be mostly linear at these speeds). Going from 20W to 10W tires therefore only saves you 10W total at those speeds.
At 120W, you are idle pedalling. You do not really pedal lighter, so saving a few watts mean an increase in speed, but as both rolling resistance and aerodynamic drag goes up with speed the gain becomes small.
At normal climbs - the time where you'd wish pedalling was easier - you're either 1. spend in the area of 200-300W maintaining the same speed without increasing rolling resistance, making rolling resistance a smaller part of the load, or 2. drop to a granny gear, going very slow to maintain your 120W and thus making the rolling resistance negligible with any tire. In either case, rolling resistance matters much less in climbs.
Yes if you bike slowly, wider tires are better. However I mentioned that in my post. A lot of people who are into biking are in the fitness zone where they are going into speeds where aero starts to matter way more. This is especially true when you consider wind.
> The German magazine TOUR built a sophisticated setup with a motorized dummy rider and found that a 28 mm-wide tire had the same wind resistance as a 25 mm tire when the wind was coming from straight ahead. With a crosswind, the wider tire was very slightly less aerodynamic. Even then, the wider tires required only 5 watt more – on real roads, the reduced suspension losses make up for that.
> To summarize all this research: Narrow tires (<25 mm) are slow. Above 25 mm, the width of your tires are won't change your speed on smooth pavement (at least up to 54 mm wide tires). On rough surfaces, wider tires are faster. That doesn't mean you can just slap any wide tires on your bike and expect it to go fast.
25 and 28 are basically same width. Also wind tunnel testing is not really representative of real world condition given real world turbulence, but I dunno if that would really affect results.
Im just against the general saying that wider tires are faster. This implies that fat bike smooth tires are the fastest, but we know that this is ridiculous. 25 to 35c probably doesn't matter too much aero wise at regular cycling speeds, but going all the way into 40-50c does.
The issue is that narrow tires have a very, very inefficient suspension behavior, and road surface and rider movement causes it to be constantly exercised. That does not mean that you gain anything from going nuts - there are diminishing returns just like there is for slimming the tire for aerodynamics.
What tire is best depends on the surface, the rider and the speed. On a perfectly paved road at high speed and with a light, stable rider, 25 might be right. On regular roads, 35 might be faster. On a bumpy mess, "smooth fat bike" tires would indeed be faster still - assuming you can stay upright without the tread. There's a reason you don't take a road bike with 25mm tires to do downhill mountain racing.
Gravel bikes are going to transform in coming years as now they are neither very comfortable nor fast. It turns out that wider MTB tires are both faster (when it comes to rolling resistance) and way more comfortable and safer than gravel tires even on tarmac, let alone any kind of terrain.
The reason is that soft casing is way more important than knobs when it comes to rolling resistance and MTB tires can be made soft because all the additional rubber coming with width while gravel tires are usually harder and thus slower (and less grippy and less comfotable). Notable exception is Continental Terra Speed but it's still not as good as Race King and way more puncture prone.
The problem with most current gravel frames is that they don't fit wide and fast MTB tires so you are stuck with the worst of both worlds - slow, not comfortable and still not grippy/soft enough to go fast off-road unless it's a very well maintained road.
Gravel bikes are much more comfortable and fast than road bikes on unpaved roads, which is what they are designed for. Wider wheels will add more weight and more angular momentum, making it harder to climb and harder to steer so you might need to replace the drop bar with the MTB flat bar and without the drops you can move the saddle into a more comfortable position as well... ending with a hardtail w/o the suspension fork.
Kenda booster & rush. Continental race king. Maxxis Aspen & Aspen ST. Schwalbe RRs, Vittoria Mezcal, S-works Renegade & fast track, Pirelli Scorpion. Basically every MTB tire manufacturer makes an XC race tire in the 600g range. Some are below 600g, some are above 600g (but below 700g). Just look at the list on the website this thread is under.
But these do not show amazing rolling resistance on that site either. Only Race King approaches top RR numbers of the gravel tires. There are plenty of sub 400g gravel tires with less RR than these. As far as I understood my correspondent, he predicts that riders will add angular momentum (when and MTB riders already complain about steering on gravel bikes) and, apparently, won't win any rolling resistance. What for? Riding at even lower pressure? To do what?
Salsa cut-throat is a gravel bike, fits 2 inch tires. Personally, I find having drops to be more comfortable because you can change hand position. Look to tour divide bikes for gravel bikes optimized for comfort and fatter tires. I don't understand your prediction for an imminent transformation.
My prediction is that gravel bikes will have wider forks and people will put MTB tires in them instead of 40mm "gravel" tires they do today. It will be faster, more comfortable and safer. Drop bars are great, they will stay. You don't need an MTB bar for your typical light off-road terrain.
Gravel bikes with wide forks and MTB tires already exist. That was my point with the salsa cutty example.
Classic gravel tires do not have very aggressive knobs, but there are some that do.
Gravel is odd as that can be hard packed dirt, small rocks, larger, up to mountain road (babyheads). For some of those conditions, the sidewall of a MTB is overkill and there is a stronger desire for a supplier, faster tire. Basically a cross country MTB tread.
So, there are already wide forked gravel bikes, and there are conditions where a 38 tire is plenty. To fit a 2 inch or 3 inch tire also requires trade offs for the down tube. Which is to say, it's arguably different bikes you want fir some Kansas gravel compared to northwest mountain passes.
As well, the upper limit will probably be at 2.5 inches.
Last, a lot of MTB tires are designed for folks that drive up to a trailhead and then ride down a trail. Those tires need to be solid, and just solid. So, I think it will be the variety of tires that change. More tires suitable for "light" cross-country MTB and ranging in between the spectrums.
I absolutely love my Lauf with their weird suspension front fork. Bike is super comfortable to ride. Also has plenty of width room for wider tires. I run WTB Nano 40c, which are a great mix for road/gravel.
>It turns out that wider MTB tires are both faster (when it comes to rolling resistance) and way more comfortable and safer than gravel tires even on tarmac, let alone any kind of terrain.
...except when you are going fast. But I do agree that honestly, full on XC MTB are better than any gravel bike for mixed terrain. Modern race XC bikes are not only lightweight, but have enough suspension travel front and rear to tackle super rough trails, which means you don't have to rely on tire pressure for compliance (although QC on the carbon frames is questionable even from the bigger brands).
That being said, when it comes to road, ultimately, aero bikes are still king for efficiency if you are least moderately fit.
it's always wild to me hearing what pressure people use.
on my road bike with 28c and inner tubes, 60 psi is what i use on _good_ road surface. maybe the roads are just shit here, but even 55 psi feel rough. i usually run on around 50 psi, 40 in winter.
there was a time i lost my track pump and i just pump the tyres using a mini pump without a guage. later i discovered i was running on something as low as 30 psi.
i have never had a pinch flat. i don't think i'm particularly light. full load when doing groceries is probably 85 kg. is it just that my pressure juage is woefully inaccurate?
28 to 32 is negligible aero wise for most people, I don't disagree. 30 mph (or slower into the headwind for an air speed of 30 mph) will start to matter a little bit though, math doesn't lie.
But saying wider tires are better as a blanket statement implies that you can run like 45c gravel tires and still have the same aero drag, which is by far not the case.
All that aero is probably not working so well for you. Even on my mountain bike with grippy and wide tires I get over 40 mph. On my gravel I can hit over 50 mph, and thats with 45mm tires.
I can get close to 50 mph (safely) downhill on my 30 year old steel framed 8 speed bike with 20mm tubular tires pumped to 120 psi. No problem with riding at 20 mph on the flats and I'm close to 60 years of age. My "aero" CF bikes with deep carbon rims are minimally faster. Speed is irrelevant unless you are racing. Enjoy the ride and stop relying on equipment for minimal performance gains.
Its totally possible to hit over 40 mph on steep hills on an MTB, especially if you weigh more. I was more referring to slight grades with just pure rolling without pedaling.
Im in Austin so I frequent COTA Bike nights on Tuesdays on the track. Coming down the hill from turn 1 with other riders is a very good test of aero efficiency, because there is a slight uphill after the bend. Couple of my friends ride gravel bikes, one of them is heavier than me, and its pretty clear that that my bike is more efficient.
Shout-out to Violet Crown, PHENOM, Breakfast Club, UNITED, Night Owls, and all the other great cycling clubs in Austin! Wonderful community that I still miss.
Have you tried swapping bikes with your buddy? Are you two the same height/weight? Who has the more flexible spine? It would be fascinating to measure aerodynamic efficiency for two riders on the same bike. Is the more variation within populations, or between populations?
While it's certainly possible to have a throttle most electric bikes require pedaling and therefore some degree of exercise. In many cases it gets people riding that would not be riding otherwise. For people that are actually interested in fitness it's a lot easier to maintain zone 2 on real roads with electric assist without the impulse to push it a bit up the hills. I did far more aggressive rides when I had access to my electric road bike than I do on other bikes because I knew I had a bail out if I pushed too far. Nobody's going to congratulate an e-bike rider on their feats of endurance or power but there are lots of points between a normal cycling effort and no effort at all.
Sometimes people riding bikes are in a rush (eg: morning meetings and commuting. [And no, drinking is not always a solution, in my situation it's a 30 minute drive or bike ride either way, and driving then costs $30/day and the time to find parking makes it slower. The drive Honda will be usually faster but has to be after 6pm, otherwise it is an hour to get home. This is a 10 mile commute I'm describing, and fir about 6 hours out if the day it's a traffic jam half of the way)
Lots of factors. For example, i get way less tired riding a road bike in the heat than a mountain bike, because the airflow at speed helps me keep cool.
You don't have to be on the Pro Tour to benefit from aero gains with narrower tires. Even moderately fit people usually can sustain 15 mph on flat, at which point aero gains start to matter. Even more for hilly terrain where you can easily pick up over 20 mph on descents. The wider tires roll more efficient at lower psi (when you have to air down for comfort). But roughness of pavement road usually doesn't require less than 60 psi, and above 60 psi the rolling resistance of wider tires is about the same as narrower tires, but watt savings from aero can be significant.
I got a gravel bike to replace my old road bike because everyone was raving about it, and I absolutely hated riding it. Sure, at slow recreational speeds, it was more comfortable, but when getting places, it just didn't roll as well down hills, making me having to pedal more over extended times to get uphill.
Now I ride an aero road bike with TT bars, with 28c tires, and even when running them at 60-70 psi for rough pavement, the aero gains from the narrower wheels are significant, as I can pick up speeds over 30 mph on some descents which carry me way further uphill.