Bicycle Rolling Resistance: Tire Rolling Resistance Tests and More
bicyclerollingresistance.com
bicyclerollingresistance.com
They are also a testament to the dazzling amount of options that mature industries seem to produce.
> The Schwalbe Racing Ray is optimized for front tire use and is a bit less aggressive than the Schwalbe Rocket Ron, […] Schwalbe suggests pairing the Racing Ray with the Racing Ralph (read review), which is optimized for use on the rear wheel.
> The Racing Ray used to be only available with the Addix SpeedGrip compound, which [is] grippier than their Addix Speed compound. We just noticed Schwalbe also released a Super Race version with the Addix Speed compound somewhere in the last few years, and we're not sure about the front wheel claims for that version.
It's a bit like obsessing over the lightest frame possible. Yeah, we can get a 1lb frame made of space materials but at the end of the day it's basically something that will reduce a cyclist's average speed by like 0.1mph.
For anyone doing anything other than competitive cycling, comfort is far more important than anything else and fat wheel bikes with steel frames are damn comfortable to ride on.
A relatively heavy bike with giant wheels might take your average speed down .5 or even 1 mph. You almost certainly won't notice it.
I race on a carbon frame with 30mm tires, and commute on a steel frame with 38mm tires for what it's worth.
Bike weight is irrelevant on flat roads. We should be obsessing over Watts/gram of drag, not Watts/kg if you're not a climber
Also see https://www.renehersecycles.com/12-myths-in-cycling-1-wider-... for a related myth-debunking of the impact of tire width (which contributes to rolling resistance) on speed.
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.
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.
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.
https://www.hambini.com/cycling-aerodynamics-wider-tires-and...
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.
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.
> 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.
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.
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.
Tongue in cheek, but isn’t fitness the point?
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)
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.
...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.
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.
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?
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.
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 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.
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.
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?
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.
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).
https://www.cyclingweekly.com/news/racing/uci-publishes-imag...
(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
(3) out of the saddle sprints.
Nobody ever has…
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.
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
It's always: this is the latest model, it has these features, thanks.
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.
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)
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 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.
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?
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.
My knowledge of tire/rim ratio comes from conversations primarily. References for that ratio being important are not hard to come by, eg: https://silca.cc/blogs/silca/part-5-tire-pressure-and-aerody...
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.
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.
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.
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.
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.
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.
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?
Then look at the methodology:
> The total rolling resistance of an average rider with a total bike + rider weight of 85 kg / 188 lbs that averages 28.8 km/h / 18 mph will be double the rolling resistance you can find on our website. If you're heavier than that or average higher speeds, the total rolling resistance will increase roughly linearly with the increase in weight or speed.
All I can say is that I am a lot heavier than 85kg with my bike and that I am usually riding at 20-25 km/h.
So let's say the lower bound they mention would 2x15 and the upper bound 2x25. Let's assume 127kg with luggage, that scales linearly to 3x15 - 3x25, but the speed is only 2/3, so we can dial it back. My napkin math now says the difference between a good pair of tires and a bad one is 30 vs 50.
And I'm still not sure if that translates 1:1 to the assumed typical 100 Watts of an average rider..
I found https://www.gribble.org/cycling/power_v_speed.html though and if I plug in my numbers, the coefficient of rolling resistance is our variable, and
0.00465 -> Rolling resistance is working against you with 5.79 (N) of force, or 50.15 watts of power.
0.00273 -> Rolling resistance is working against you with 3.40 (N) of force, or 30.01 watts of power.
So the tires make about 2-3 kph, which fits what most people have posted when I was researching this.
I let both of my kids try things and choose, both choose tires with fairly low resistance. One more so than the other, but both clearly regarded high pressure as somehow comfortable: Apply pressure to pedal, feel bike move. Responsiveness.
Edit: after browsing the site, the Marathons are the lowest rolling resistance touring tires too! Double bonus for an excellent tire, which I can now recommend without reservations.
Happily, this is also more comfortable.
There are other trade offs than rolling resistance. Like puncture resistance, grip/cornering ability, aerodynamics, weight etc. that also comes into account when choosing a tire setup.
Not quite. You can air down narrower road tires for this. The difference is that a wider tire (i.e a tire with more volume) is going to be more efficient at lower psi, because of a wider contact patch that ends up spreading the load out more and deflecting the tread less.
This effect definitely is pronounced for gravel riding when you have to run pressures lower than 60 psi, and a wider tire is better. However for on road riding, even on rough roads, a narrower tire is going to usually be better, because you gain the aerodynamic advantage, even if you run at lower psi. If you can sustain above 20 mph, running a 28c tire vs a 38c will save you 20 watts, which is noticeable.
>Then bytul vs latex vs tpu tubes.
This matters extremely little for most people. Maybe like 4 watts at most. For racing, when you are optimizing everything, its worth it, but generally tubes matter way less then tire selection. That being said, there really isn't any reason not to run TPU tubes because they are a lot more pliable and puncture resistant.
Generally asking bike industry to do actual engineering is an impossible task, but for optimal design there is no reason why even road bikes should not have suspension that doesn't rely on tire compliance. You can do carbon leaf springs with very small dampers. The best we get is suspension stems and seatposts, which suck because you still have all that unsprung mass of the entire bike bouncing around.
For the rear same idea, make the seat stay and chainstay meet earlier and mount the axle mounting dropouts on carbon leaf springs in the same way.
You can also add a cable tensioning system to both suspension, which can be used as a lockout to make the bike more efficient.
Suspension weighs like 2 lbs (_very_ heavy) and can fail/needs maintenance, and for small bumps the shock absorber moving around loses a lot of power transfer. Nicer suspensions have lock outs so you can disable the suspension on roads and flip it back on when you're back in the mountains.
Fir road only, I don't think suspension ever would make sense. Fatter tires and a (for road) dropper seat post will likely give you all the suspension you need with little penalty
Testing has shown this to not be true. Width is less important than overall shape of the tyre/wheel/bicycle interface when it comes to aerodynamics.
Per 10mm tire width increase, you are getting 10 watts more aero drag at 25 mph.
32 also happens to be the biggest tire that fits in his Canyon race bike.
Aero drag is just not that simple. You can’t, without testing, make the claim you’re making. Also, you can’t make the claim outside of the exact setup you tested. A different rider, wheels or bike could test faster on 40mm because aerodynamic drag is that difficult to predict.
Consider that from a programming perspective, imagine using no tech newer than 2004.
The transition to 28s took a long time itself
> Per 10mm tire width increase, you are getting 10 watts more aero drag at 25 mph.
Interseting, where can I read more about this? I don't think this conclusion lines up with either the article, or the research from rene herse. Travel surfaced also matters quite a it, I could see that maybe being true in an idealized setting.
There is more to it. Tire needs to be in contact with ground to transfer power. A skinny high PSI tire will spend a lot of time bouncing. Just one example of how other real world factors can be more significant.
Then the wheel rim bounces over every rock and pebble, but the axle doesn't.
Also if your spokes are too slack, they can move in the hub, cause wear, and are likely to snap at the elbow.
Wheels are a prestressed linear superposition of overall tension and a compressive load at the bottom. Generally, you'll see ~4 spokes at the bottom of the wheel relaxing to take the vertical load. (in a properly built wheel)
This is due to rims not being completely rigid, but being a somewhat flexible beam. Rims are nowhere near rigid enough to do the "hang from the top" thing.
Spokes will break at the elbow, but generally due to fatigue, which is made much worse when there are stress reversals. Fatigue is when cyclic loads cause small imperfections to grow into cracks, and eventually failure. If you have stress reversals under rolling loads (where the stress goes from tension to compression, anywhere in the spoke elbow) you should expect to see spike failures in ~1000 miles. A stress reversal doesn't necessarily mean that a spoke is slack, because there are some interesting stress patterns in the elbow in poorly built wheels.
You wouldn't want berd spokes to go slack any more than you'd want steel spokes to go slack.
It's even more difficult with off-road tyres, as it's not really the rubber compound providing the grip.
Also on 2 wheels going fast around corners doesn't only involve grip but confidence. This is partly personal/psychological and partly based on feedback from the tire that comes on how the carcass of the tire deform while you are leaning the bike. It could be that a tire with more grip doesn't give you as much confidence as a tire with less grip on which you are closing in much closer to the limit.
Off the road the grip is so dependent on surface that it is even more difficult. There are tire for dry, mud or mixed surfaces and what you will encounter on the trail might be somewhere in between all of these.
For example if you run an MTB tyre hard it will bounce around on a rocky surface and roll less efficiently than if you run it at lower pressure that allows the tyre to deform and bounce around less.
Interesting site nonetheless and a useful data point to compare tyres in a systematic way.
The only tests which BRR does which are likely applicable to mountain bike tires mounted to mountain bikes ridden on trails are the puncture tests, as you're likely to find sharp objects even on trails. Maybe the wet grip tests matter, if you often encounter wet large rock that you ride on.
"One-time payment, no auto-renewal"
[5 lines further down]
"From $ 0.79 / month"
There's no auto-renewal, you get an email telling you your membership is expiring and asks you to pay again.
What you've posted implies they're lying and they are verifiably not.
How do you pay a single one-time payment at a per month rate? How many months do they charge for the one-time payment?
Usually a 'single one-time payment' would be a payment for life. Typically for apps they're <$10 for the lifetime of the buyer (or app if that dies first; there are issues around this sort of pricing, but people are expecting a minimum of several years).
What you appear to be describing would be a pre- payment plan at 80¢/mo.
I really don't understand how this is confusing for you.
This is not what I would call a one-time payment. If you wish to continue to use the website you pay again. That's just not what "one-time" means to me.
It's not confusing, it's just annoying marketing-speak in the sense that (paraphrasing) 'a simple one-time payment' is what customers like when purchasing something. Whereas the offer is not that, the term has been used in any case.
What is offered is 'a subscription without auto-renewal'.
If you really wish to understand my thinking I can elucidate you at length, but it seems we've spent way too long already discussing understanding of a particular piece of marketese.
They're not lying as such but it's at least accidentally misleading. "It's a subscription" should be up front, then go into how it's prepay and well behaved.
Tire rolling resistance comes from effectively the rebound damping on the tread. As the tire rolls, the tread on the backside of the contact patch takes some time to rebound, so the tire is effectively always rolling over a bump that is the uncompressed tread the front of the contact patch
The lighter the tire, the less sidewall and puncture material there is, which means that the rebound damping on the tire is going to be less.
Indeed based on your explanation the stiffness of the tread is going to be as much of a cause as anything.
Compare continental gatorskins in 28c vs continental gp5000 in 28c. Gatorskins have more casing to prevent puncture, so they are heavier, but that casing also takes away from the rolling efficiency.