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Comment by louthy | Hacker News Reader

If that were the case, surely Tour de France riders would use wider tyres to gain more grip going around corners, especially in time-trials or stages with sprint finishes.

Doesn’t a greater surface area touching the floor means more frictional effects when pushing against the road?

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Here's a pretty interesting article discussing Le Tour slowly getting wider and wider tires, compared to a decade ago [1]. Granted their use case is going to be at a very different scale than most rec/serious non-pro riders. But I know that most all my friends and I ride 28s on our road bikes these days compared to 23s a long time ago. More comfort and more forgiving.

My current road bike maxes out at 28, but I'd probably go a little wider if I could due to the nature of the roads around here (lots of potholes, chunks, crappy shoulders, etc...)

[1] https://www.businessinsider.com/tour-de-france-wider-tires-l...

You also have the theoretical perfect tire vs the actual best for the rider - the more comfortable tire may be better overall as it allows the rider to perform better and for longer.

From TFA: “ We tested our tires on smooth pavement at 29.5 km/h (18.3 mph), and found no speed difference between narrow and wide tires.”

A professional peloton rides at 28-30mph on the flat and significantly faster towards the end of a flat stage - I bet at higher speeds, for professionals where every percent matters, it does make a difference.

Certainly for my level (and I have ridden for an hour at 18mph average) it doesn’t.

It is worth noting that tires used by the pros have used slightly wide tyres over the years, and for events like Paris-Roubaix and Flanders, they absolutely use wider rubber on frames with more clearance.

"We tested our tires at the same speeds and found no speed difference". You don't say?

One thing every person has missed so far is that often the TDF riders are on rather narrow bikes with very little clearance.

This helps give an aerodynamic profile. Even at a few watts, this is considered worth it. You would likely have to do a lot of research to go with bigger wheels, as that would been wider fork, and thus throw off aerodynamics.

A bit daft, in my opinion, given that it's mainly the domestiques who are in the wind and the ones behind, and in the peloton, can be putting out significantly less energy. May even be better for recovery having a bit more comfort on the bike through wider tyres with a bit lower pressure.

Tour De France riders do use wider tires than they used to these days. At some point the width starts imparting aerodynamic drag penalties that are worse than the handling gains.

Static friction being constant regardless of contact surface presumes a uniform surface consistency (uniform frictional coefficient).

Large (an knobby) tyres are a statistical bet that there will be sufficient friction somewhere on the contact patch. When riding over nonuniform surfaces (dust, loose pebbles, twigs, mud, leaves, and embedded rock), that's a gamble the large and contoured tyre is far more likely to win.

On a velodrome deck, not so much, and cross-sectional area, thermal losses from compressive deformation, angular momentum, etc., favour thinner tyres and higher inflation pressures.

Is the static friction what is going on with wheels? Why do race cars (dragster, F1, etc) have wide, smooth (un-knobby) tires if it's so disadvantageous (no gain, but higher weight and moment of inertia)?

For your standard street-car tyres ... mostly, modulo variations in surface, rain, snow, mud, etc. On reasonably fresh dry clean tarmac though, yes.

For racing tyres ... you're getting into a differet set of circumstances and uncomfortably far from my knowledge and experience, though my understanding is that the rubbers are specifically engineered to be sticky, more so at high temperatures (hence why drag racers spin out, it warms the tyres). That's no longer the domain of static friction.

There's also the matter of thermal management, where tyres at high speeds generate a lot of heat. How much size affects and/or is determined by this, I don't know. I am aware that street-tyre speed ratings are based on thermal properties, however.

Knobby tyres are most effective on non-uniform surfaces: dirt/rock and mod most notably.

It is my understanding that race cars have wide tyres to shed more heat. Tyres melting is a problem at F1 speeds.

Softer tires give more grip but are less resistant to shearing forces. Having a wider tire helps with that.

When you're outputting on the order of 350 kiloWatt per wheel you want to have enough contact area not to spin through, the same goes for taking fast corners, where that width translates into grip.

You can't really rely on the Tour de France peloton for guidance. They're pretty conservative and, to a degree, ruled by fashion and sponsors.

I guarantee the masters of marginal gains, Sky (now Ineos Grenadiers), will have spent some resources on looking at which tyres are actually faster for them, regardless of fashion or sponsors.

I think it’s safe to say that whatever they ride on are the fastest options - and every other team would follow - or that within a certain set of parameters, it doesn’t matter.

I just tried to search to see if Ineos run different tyres on different race and stages, and found nothing conclusive.

According to eurosport commentary they do change wheels and tires based on the race. That said they use rim brakes so probably never go over 28m tires.

Cycling teams spend tens of millions each year, with Ineos going over € 50m some time ago. Are they conservative? They benchmark their material in wind tunnels. Sometimes they bend the rules with high-tech material[^1]. There's no way a team competing in Tour de France would choose fashion over performance.

[^1]: https://www.theguardian.com/sport/blog/2017/jul/03/vortex-su...

And quite a bit of the money they spend comes from companies trying to sell gear to hobbyists. It's a rather wild mix between ride what makes you fast and ride to pretend that it makes you fast.

Not sure what gear Inoes grenadiers is selling to hobbyists.

Pinarello bikes, Shimano groupsets, Fizik saddles, Kask helmets, Castelli kit, Oakley glasses, and all the other things you see surrounding the fat guy at the coffee shop on a Sunday morning ;)

None of them are the products of Ineos.

All of them, and many more than I managed to think of, are also sponsors of the team¹.

¹ https://en.wikipedia.org/wiki/Ineos_Grenadiers#Sponsorship_a...

"Man, you sure like Tide".

-Mitch Hedberg riding in a racecar

The whole thing is a fashion show with very narrow limits of what the UCI wants people to do. The rules that ban e.g. the famous Lotus bike were explicitly stated as being meant to discourage wind tunnel testing. Fairings and recumbents have been banned for nearly 100 years because they're too much faster than UCI-style bikes.

If you want fairings and recumbents, look up IHPVA. They have been arranging competitions where these are allowed for a long time, with very little popularity. I think the main reason is that time trials where the team with most money wins are boring, and UCI has more or less figured out what limitations make the race interesting.

Now compare the situation with mountain biking. UCI didn't adopt it at first either (IIRC the claimed reason was they already have cyclocross that is almost the same thing), but after it was popular enough they didn't really have a choice.

It's not about fashion, it's about maintaining an enjoyable and popular sport. 4D chess is probably more "interesting" than regular chess, but people play regular chess because it's a good game that people know and understand. They could start allowing funny looking bikes, maybe off-road sections and, heck, why not an army style assault course? But at that point it's just not the Tour de France any more.

> 4D chess is probably more "interesting" than regular chess, but people play regular chess because it's a good game that people know and understand. They could start allowing funny looking bikes, maybe off-road sections and, heck, why not an army style assault course?

That's an absurd comparison - it's not like we're talking about changing the course or the rules, and it's not like the UCI rules have people consistently using historical-style bikes (they rapidly adopted electric shifting, or novel frame materials, for example). In the world of fencing we have both sport fencing (try to win by whatever means within the rules) and historical fencing (trying to match historical materials, styles etc.) and both those are distinct and interesting disciplines. But adding ad-hoc rules to exclude some innovations but not others, as the UCI does, is the worst of both worlds.

You mentioned recumbent bikes. These would massively change the game as drafting wouldn't work any more. Riding in a peloton wasn't always a thing, of course, but it has been in recent years and it works well. The UCI do change the rules, but they are very conservative and that's a good thing, I think.

Drafting still helps for recumbents - less than for an upright since your drag is lower, but it's not like your drag is zero.

The UCI are conservative in some areas, but they're not conservative when it comes to something the big-name manufacturers want to sell (like electric shifting). It feels very artificial to me.

> Doesn’t a greater surface area touching the floor means more frictional effects when pushing against the road?

Good question because at first I thought it might be negligible due to the tire normally being in a state of static friction relative to the road. But some quick searches showed me that rolling resistance is related to how large the contact point is, like you suggest, along with a variety of other factors. https://en.wikipedia.org/wiki/Rolling_resistance

I don’t know how reliable this is, but googling brought me to this site which compares bicycle tire brands according to rolling resistance on their test machine. Apparently, some 25s have all the 23s beat. If true, the variability range for bicycle tires is a lot wider than I expected. https://www.bicyclerollingresistance.com/

I've bought a few tire models after researching at bicyclerollingresistance.com, and while I certainly don't have the means to do proper scientific research, I feel like I did buy the right stuff.

Same. I don't have any rational basis for it, but I've been happy with my tires. I think the best thing I learned from that site is even slightly larger sizes have a much bigger effect on puncture resistance than better construction.

I love brr.com and have used them a lot, but in the context of this thread, it's important to consider that the surface they test the tires against do not have the kind of imperfections you see on the road. This means lower pressure will always perform worse in their tests, which goes against the more recent consensus in that each road has an optimal pressure depending on its roughness.

> "If that were the case, surely Tour de France riders would..."

Apologies for appearing to pick you out here, but your comment is representative of a number of eminently "logical" comments made here (as well as many analagous comments on HN in general). So, modern professional cycling is a sport with a 100+ year history, and in 2021 represents a bizarre fusion of the sports entertainment industry, the romantisation/revival of the past, celebrity culture, global cycling manufacturers, the mid-life crises of Wonka-esque team owners, the aestheticisation/fetishisation of the working class, the 'Olympics industry', lurking labour disputes, the fast fashion sector, the ad-hoc application of modern sports psychology, a looming confrontation with its historical emphasis on (mostly horrifically underpaid) white males, neoliberal economics, petty and bountiful financial corruption, widespread pharmaceutical corruption, and the influence of petrochemical money from several ex-Soviet states... All mostly filtered through the celluloid lens of France and Italy, two European nations that have an extremely complicated relationship towards their own history which comes out as a muted pageant of lukewarm national pseudopopulism that is not only is confused within its own borders, but is more-or-less unintelligible to those in the Anglosphere. To imply in any way that a kind of efficient market analysis can apply to decisions made within this sport (that has, if I remember correctly, strict rules about sock length), suggests an insufficient engagement with the background.

Tour riders are EXTREMELY conservative, well they were back when Lemond pushed clipless pedals, more helmets, and aerobars.

The nameless scapegoat who was totally the only person using EPO pushed more thorough full-system wind tunnel testing/aerodynamics and a lot more scientific testing, and even (gasp) clincher tires.

Euro riders for a long time worshipped Eddy Merckx (who was totally clean and never doped) and thought you basically only needed an italian bike and nothing else and were culturally averse to change.

Also, keep in mind the Tour riders are basically showcasing industry products, and those products aren't really that diverse in their sourcing, especially with globalization. They all run on whatever they are getting for free or at a vast discount from the two or three providers in each equipment category.

The problem is that wide tyres tend to eat lots of momentum in corners.

When going mainly straight and/or on uneven ground, use wide tyres. When cornering a lot, use narrow tyres.

Also, they have higher raw weight, so thinner is better uphill.

This is actually not really true. Competition bikes have a minimum weight nowadays, and technology is that advanced that it wouldn't be a problem to add some weight here or there because the bike would stay the same weight in total as they have so much margin else to keep in track with the minimum weight. This is why most teams have switched to disk brakes btw, and that they can have all the electronics onboard with power meter, bike computer etc.

But there's rolling "sprung" vs. static "unsprung" weight (the examples you listed). You care a lot more about rolling weight as that affects the acceleration characteristics of the wheel - that's really important at the limits.

If you bother to do the math, but simplify things so that all the mass of wheels is at the contact patch, you'll end up that rotating mass has twice the kinetic energy and takes 2x effort to accelerate and decelerate. Now if you check how large fraction of the mass of rider and bike the wheels are and how fast bikes accelerate, it's kind of insignificant.

Technology was advanced to routinely end up with bikes beneath the minimum, but those days are over. With wider tires, disc brakes, excessive focus on aerodynamics and even wider gear ranges they are usually racing considerably above the limit. These days you'll find bikes in the range of 5000 euros advertised that are considerably heavier than what you would have got for 1500 ten years ago.

They're already using wider tyres than a decade ago.

Yes. Much, much wider.

I nearly passed by this comments section because i assumed everyone already knew this was true.

I think you're exaggerating a bit.

From 2018:

https://www.businessinsider.com/tour-de-france-wider-tires-l...

"It depends on the road surface, but 10 years ago the standard was 23mm tires at 8 or 8.5 bar, or 115, 120 psi," Brown said. "And now it's 25mm for regular road racing and 7 to 7.5 bar for front and rear, so a little less than 100 to 110 max on the bikes."

2mm and 10psi less is not that huge a difference.

It's pretty big when you take into account whole context. Stuck up "socks size is a rule" UCI, historical norms, technical limitations (25mm is a limit for caliper brakes), tire tech (wider tires used to be heavy)....

My prediction is 27mm being the norm in next 5 years.

Currently I'm riding a decade-old road bike. It was fancy at the time because it fit 25mm tires without issues. People would give me shit for "slow" tires on group rides. But 25mm tyres improved a lot in that time. Now I wish it could take 27mm :(

25mm is not a limit for caliper brakes? No idea why you claim that. One of my bikes has calipers and can fit 33mm tires.

Also 28mm is extremely common; 27mm doesn't exist.

There are definitely calipers that can't take a 28. And the mounting bolt position isn't a precise norm, there are frames that put the brake considerably closer to the rim than others. And not without reason, the effective length of the caliper arms has an obvious influence in brake leverage.

Classic road bike caliper breaks don't >25mm. 33mm would be cantilever CX brakes. Or a weird type of caliper.

Nit-picking, but 27mm is very common as the "actual width" of tyres branded 25mm.

8% width and 13% pressure is significant.

True. And these days, "wider is faster" is the cycling myth in need of getting corrected. Because is mostly a tie, with a very soft optimum between clearly worse extremes (neither 10 mm nor 10 inch would be fast). And people who feel in the mood for "overthrowing the old" will often do comparisons were they lower pressure on the wider tires, but don't really lower then adequately, they compare a narrow tire at the lowest and of its useable pressure range to a wider tire at the high end of its range and, surprise, with these conditions the wide one rolls easier. The assumed optimum has shifted, but it hasn't run away.

Regardless of whether it is the case or not, Tour de France riders would not use wider tires to gain more grip around corners because ... wider tires do not add more grip.

You get a larger contact patch from a wider tire, but that patch has less pressure.

Grip (static friction) is coefficient of friction, times weight. The coefficient of friction is a constant which depends on the materials. Rubber on road is no exception.

That’s the first order effects, however substances deform under pressure which is just one of many complexities involved. For car tires on dry pavement you get maximum grip from racing slicks. Unfortunately they need to swap in the rain.

First order effects are the only effects which matter in cycling. This isn't aerospace.

Racing slicks are a different material.

In Formula 1 racing, you go through multiple tires in one race.

In consumer driving, tires are expected to last 100,000 km or more.

There is even the practice, in racing, of using chemicals to attack the rubber to soften it.

> In Formula 1 racing, you go through multiple tires in one race.

They could easily make a tyre which lasts the length of a race, but they mandate pit stops and two different tyre compounds to add interest - teams can use the mandatory pit stop to “undercut” or “overcut” competitors.

In fact, IIRC, for the 2005 season, changing tyres mid race for anything other than safety reasons was banned.

> In consumer driving, tires are expected to last 100,000 km or more.

This is much closer to 25,000-50,000km, and peaking at 70,000km. Source: https://www.pirelli.com/global/en-ww/road/how-many-kilometre...

Using a different material is in effect irrelevant, they still get maximum grip from maximizing contact area because of how rough roads are. Ultra narrow tries need higher internal pressures, which limits how much the deform and thus reduces grip.

Also, F1 cars are going up to 246 mph and doing heavy acceleration and breaking throughout the races, which seriously heats up the tires. Normal road tires would actually die sooner under those conditions. Just read up on who long tires last when people are doing street racing, burnouts, etc.

I might be missing something here but I believe slick tire compounds are geared toward longevity at the expense of lower grip. Unless you are referring to racing tires in general which are grippier than their street equivalents.

Racing slicks are a type of flat tire designed for maximizing grip in dry conditions. https://en.wikipedia.org/wiki/Racing_slick

Slick tyres are not suitable for use on common road vehicles, which must be able to operate in all weather conditions. They are used in auto racing where competitors can choose different tyres based on the weather conditions and can often change tyres during a race. Slick tyres provide far more traction than grooved tyres on dry roads, due to their greater contact area but typically have far less traction than grooved tyres under wet conditions. Wet roads severely diminish the traction because of aquaplaning due to water trapped between the tyre contact area and the road surface. Grooved tyres are designed to remove water from the contact area through the grooves, thereby maintaining traction even in wet conditions.

Ah, so that terminology refers to the absence of tread. Thanks for the link.

> The coefficient of friction is a constant which depends on the materials.

This is an approximation. It holds here, but it doesn't hold for (say) figure skates on road.

That is false; you might be thinking of figure skates on ice. Steel on road obeys coefficient of friction.

(I promise I will keep that in mind the next time I attach skates to a bicycle frame.)

Steel on road obeys the coefficient of friction… until it starts cutting into the road. Unless you're very light, that's going to happen if you're going an appreciable speed wearing figure skates and then try to stop.

Yes; anything cuts into anything else if you concentrate enough weight into enough of a small area, or there are other extreme factors involved like things melting.

E.g. A carbide bit milling a stainless steel object is clearly not following carbide-on-stainless coefficient of friction.

Rubber tires does not generate grip through simple static friction. They stick to the road in two different ways, adhesion and deformation. The adhesion is weak molecular forces that stick the rubber to the road like sticky tape, a larger area will have more adhesion. The deformation deforms the tire to follow the surface and dig into it. Because rubber is viscoelastic, the force is greater on the lagging side of a bumb when the tire is slipping.

The adhesion is greatest in the front of the contact patch where there is less slip and a wide tire has a wider but shorter contact patch, so it has more grip from adhesion.

If you keep the pressure in two tires the same, a wider tire will have the same contact patch area as a narrow tire since they will carry the same force and force is pressure multiplied with the area.

Path Less Pedalled recently had a great discussion on this with Josh Poertner, the owner and president of Silca, the tire pump company:

https://www.pathlesspedaled.com/2020/01/09/your-tires-are-ly...

The one caveat this article doesn't mention is worse handling but they replied in the comments about it. And handling matters way more at higher speeds, plus they commented the extra weight matters more for steep climbs too.

This, and a wider tire also has a larger front surface, resulting in more aerodynamic resistance. As every watt counts in the pro peloton, this is an important factor. For us amateur riders, probably not so much.

I was a little surprised: the weight difference isn't huge. It is about +27% between Conti 5k 25mm and 32mm, or 60 grams per tire.

Aerodynamics are the only real reason, I think.

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