What is the purpose of a tread pattern on city/road tyres?

Question

What is the purpose of tread patterns on city/road tyres?

I think I've understood (perhaps wrongly) from this site that they're unnecessary on paved roads:

Grip (friction) is more-or-less contant, or perhaps a question of the material
Racing tyres for example are "slicks" made without grooves
Grooves are needed on other tyres (e.g. for cars) to prevent aquaplaning; but that bike tyres are too narrow and too slow to ever aquaplane

Schwalbe say:

When is a tire worn out?

In bicycle tires the tread is far less important than for instance in car tires. So using a tire with a worn out tread is less of a problem that is of course with the exception of MTB tires.

When the puncture protection belt or the carcass threads can be seen through the tread the tire has reached its wear limit and must be replaced. As puncture resistance also depends on the thickness of the tread layer, it may be useful to replace the tire sooner.

The sidewalls of tires often fail before the tread is worn out. In most cases, this premature wear is due to prolonged use of the tire with insufficient pressure. Checking and re-pumping the inflation pressure at least once a month with a pressure gauge is most important.

Is it only a matter of puncture-resistence?

The bike shop called mine "dead", saying I should change, because the tread is worn (like the photo in this answer).

Not all roads in cities are paved, in particular not all bicycle roads. — gerrit, Jun 20 '22 at 09:45
To start with, most urban cyclists do not ride exclusively on paved roads. When cycling around town myself, I regularly have to deal with sections of road/sidewalk that are about equivalent to a gravel trail, and I occasionally have to ride through sections of poorly kept grass. I would not even consider a racing or velodrome style for this simply because it would not give enough traction on those areas (especially if the grass is wet) to be able to safely turn when moving at otherwise reasonable speeds. — Austin Hemmelgarn, Jun 20 '22 at 12:10
Do you really think tyres show no different performance on wet or dry roads? — Robbie Goodwin, Jun 20 '22 at 21:41
@RobbieGoodwin If your comment was meant for me, of course I know that roads (and certain parts of roads e.g. paint and metal) can be more slippery when wet. What I don't know is whether treads on tires help with that, at all. — ChrisW, Jun 21 '22 at 03:17
@ChrisW Sorry, I should have asked whether you thought all tyres showed the same performance on dry roads or wet. Do they? — Robbie Goodwin, Jun 22 '22 at 22:05
@RobbieGoodwin I don't know, I've only used one kind of tire (Marathon Plus). Three times I've fallen were on sheet ice, on mud, and on braking while turning on a grit-covered paving. A consensus on this site seems to be that people continue to use Marathon Plus tires after the tread is worn, so I wanted to see why that contradicts the advice from the bike shop. — ChrisW, Jun 23 '22 at 06:36

score 17 · Answer 1 · answered Jun 19 '22 at 08:03

Schwalbe has another page on this - https://schwalbetires.com/technology-faq/tread/#:~:text=On%20a%20normal%2C%20smooth%20road%2C%20the%20tread%20has,smaller%20and%20the%20contact%20pressure%20is%20much%20higher.

On smooth road, slick tires perform best in all conditions (unless you doing over 200km/h), however in rough roads tread provides predictability, which is far more important than absolute grip on a bicycle. Choice of tire you use should be based on the types of road you ride (and in some countries, tread is a legal requirement). Keep in mind that few of us are in the luxurious position of riding perfectly smooth roads all the time.

This is different to what you have, which is a worn out tire. The tire shop has to advise you based on lots of factors - but the liability and reputation precludes them advising a worn out tire is safe to ride. If the country you requires tires to have tread, they would probably be legally bound to advise you to replace the tire.

Given all this, IMHO they are being professional and have advised you correctly.

You still have a choice, the liability of your decision not to replace the tire lies with you. The real risk of running worn tires (as long as you keep an eye on them) is they are more vulnerable to punctures. Riding once the chords show though can lead to catastrophic tire failure, which can cause crashes, but you really need to ride well past the chords just showing in one spot. The loss of predictability of a worn tire in adverse conditions can be mitigated with riding style.

It's the rear tire that wears first (perhaps because it has more weight on it, or because it is the one that's being driven). But I expect the rear tire to skid easily even when it's new, so, I think the front tire is more important and is the one I use more for braking. — ChrisW, Jun 19 '22 at 09:25
On smooth clean* road*, slicks grip better. But gravel, a thin layer of mud, or wet leaves seem to handle better with a little tread - I swap on my Marathon Mondials in winter (instead of Gatorskins or Marathon Supreme, which have a little bit of a pattern but nothing more) for that reason. — Chris H, Jun 21 '22 at 14:02
It doesn't take anything more than a fine mist of rain on a painted line to make the road exceptionally slick for a bike. I rode slicks all through college. A group of us were stopped at a light in town, track-standing. Light turned green, we went, I looked back to be sure everyone was with us and one guy was down on the other side of the intersection - he'd just started moving when his (treaded) tire hit a wet line and over he went. We all laughed once he got up & moving again. I continued to ride slicks, but was careful to avoid lines in the rain... — FreeMan, Jun 21 '22 at 15:24

Criggie · Answer 2 · 2022-06-19T02:38:30.763

In my experience, smooth or treadless tyres are perfectly good in the dry, and on smooth/good roads.

Smooth tyres are adequate on wet smooth roads.

Wet AND oily roads, or wet AND gritty roads is where tread starts to becomes useful. When the road surface is not firm and cohesive, tread allows spaces for those particles to be such that they're not a ball-bearing.

Have you seen occasional islands or moraines of fine dirt or sand or stones that accumulate where cars don't drive? In the corners of intersections and between lanes.

^{Example island of loose gravel, in thew middle of the green cycle lane.
Fine to roll over, but if you were hard-braking for the red light then it might be different.}

These are okay to ride straight over, but exacerbates slidiness when turning or manoevering or braking. Tread may reduce the "ball bearing" effect of turning while on loose rolly gravel. If its hard-packed like cement then its just bumpy and not relevant here.

Ice is another matter completely - tread helps not-at-all when turning on hard ice. In this case you want spiked tyres.

Snow - I can't speak for riding in snow etc, because there's not enough of it here for me to have experience.

The two main reasons for changing a worn tyre are:

if there's a sudden increase in the frequency of punctures (this means the rubber is too thin for your riding conditions)
there's damage where you can
- see the tube inside at any time, or
- see a lot of threads, or
- if the tyre is bulging in weird ways.
  In these cases, you're asking for a blowout which is never wise. Booting may help, but only to get you home.

Personally I'd ride either pictured tyre until the frequency of punctures increases or significant damage happens to the tyre.

In my experience riding in snow is fine without spikes if the rubber doesn’t harden in cold and tread grooves don’t get packed with snow. My first MTB was quite bad with both of these. — ojs, Jun 19 '22 at 09:18
@ojs depends on your snow. In the mild winters here (when we even get any) it often gets partially melted and forms a crust. Sometimes there's only crust. So if I get a snow ride I take my hybrid with spiked tyres, rather than my MTB with knobblies, though the latter would handle soft snow better (I nearly said "deep" but deep snow near here is 10cm) — Chris H, Jun 21 '22 at 14:07
@ChrisH True, I thought the partially melted and frozen snow counts as ice. It certainly needs spikes. In my inland hometown one could ride through the winter without spike tires, but where I live now it's a bit risky. Not that people do it anyway. — ojs, Jun 21 '22 at 15:22

score 7 · Answer 3 · answered Jun 19 '22 at 10:15

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Few users of bicycles will be riding utterly exclusively on good tarmac.

Crossing verges, cutting a corner across dirt, taking avoiding action off the tarmac, riding through a region where the tarmac has been temporarily removed or where the road surface has degraded to little better than dirt, crossing a bit of garden or gravel to a shed at the back, and even short distances across parkland are all very common for riders who use their bicycles in the city or for commuting. A tyre with a bit of tread is much better at handling these circumstances than a slick tyre particularly in damp conditions, while a tyre with tread is not much worse at riding on normal roads than a slick tyre.

Since the majority of riders aren't going near the mechanical limits of their bikes, the advantages of extra flexibility of a treaded tyre easily outweigh the performance advantages of a slick tyre.

answered Jun 19 '22 at 10:15

Jack Aidley

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On gravel and dirt low tyre pressure and a flexible carcass is more important than tread. The more “blocky” city bike treads like on the Schwalbe Marathon Plus Tour might provide some extra grip on mud or (firm) sand. But really don’t expect much, especially since these tyres are stiff, should be run at high pressures and usually have some hard (long lasting) rubber compounds. – Michael Jun 19 '22 at 16:16
@Michael: they're not off road tyres, no, but they're still significantly better than slick tyres for occasional use. – Jack Aidley Jun 19 '22 at 16:26
@Michael the MP tour look pretty similar to the Marathon Mondial. They're far far grippier than slicks or even regular MP on mud and gravel - I've done enough of both on my tourer to know. On dry gravel Marathon Mondial handle almost as well as MTB tyres, unless it's very coarse – Chris H Jun 21 '22 at 14:10
@ChrisH: Have you really compared like-for-like at similar pressure and until you truly lose traction? I’m often surprised how well slicks work on gravel if you lower the pressure far enough. – Michael Jun 21 '22 at 14:20
@Michael I run tubes so I'm wary of going too low, but I do take the slicks on gravel as well. It depends on the shape and depth as well as the size of the gravel. I had fun sliding around on wet, very rounded stuff (like beach pebbles) but wouldn't have fancied trying to stop in a hurry, or steer precisely – Chris H Jun 21 '22 at 14:30

Andy P · Answer 4 · 2022-06-20T09:13:16.920

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On tarmac/roads the tread has virtually no purpose. Two small uses it has are:

The extra thickness of rubber provides more puncture protection
Possibly a little extra grip in the tiny beads of gravel often found around junctions.

In my experience the bigger issue with extremely worn tyres is they tend to get very squared off and then have very strange handling (and probably less grip) when you lean the bike over in corners.

In the case of a 'normal' tyre, i'd usually replace it if it was in the condition of the one you linked. However in the case of a touring tyre with an extra rubber layer under the tread there's probably no need.

Edit: Here are some links from tyre manufacturers expressing they believe that on a road tyre the rubber compound is what counts.

https://www.michelin.co.uk/bicycle/tips-and-advice/tips-and-advice-bicycle/what-is-grip

https://www.schwalbe.com/en/profil

edited Jun 20 '22 at 09:13

answered Jun 18 '22 at 20:10

Andy P

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The tread on a tire is an important factor in maintaining traction on wet and/or oily roads. This is even more important on paved roads than on gravel. – Daniel R Hicks Jun 18 '22 at 23:52
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https://www.schwalbe.com/en/profil - not according to the people that actually make tyres and are well known to do various research projects – Andy P Jun 19 '22 at 06:27
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@DanielRHicks That is definitely true for car tires. As the answer points out though, significant tread is not needed on a bicycle tire. – MaplePanda Jun 19 '22 at 07:10
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@MaplePanda - I once neglected to change out a worn rear tire -- one with virtually no tread left in the center. Then we went through a rainy spell, and I had the tire slide out from under me several times while making turns on slick asphalt pavement. – Daniel R Hicks Jun 19 '22 at 13:09
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@DanielRHicks That had nothing to do with tread - wet causes loss of traction for all tires, and thread won't help on a bicycle because you simply can not go fast enough on a bicycle to hydroplane. If you were strong enough to get a bicycle to hydroplane, you could win the Tour de France just using one leg. Hydroplaning is extremely well understood - the speeds needed to get a bicycle tire to hydroplane generally have three digits, even for slicks. IIRC it's related to the tire pressure - higher pressure needs higher speeds. If you could go that fast, yeah tread would help... – Andrew Henle Jun 19 '22 at 14:13
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@AndrewHenle - It's not about hydroplaning, it's about getting a grip on the asphalt. – Daniel R Hicks Jun 19 '22 at 14:21
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@DanielRHicks Tread still doesn't help on asphalt. If it did, racing motorcycles would use treaded tires. In fact, tread is likely to hurt traction in turns, as any significant thread can lead to the tire squirming under side load and breaking free sooner than a slick would. – Andrew Henle Jun 19 '22 at 14:47
In my experience the bigger issue with extremely worn tyres... And a much higher propensity for flats. – Andrew Henle Jun 19 '22 at 14:48
@AndrewHenle: From my understanding of physics I agree that tread indeed shouldn’t really help on wet roads. But then why do special winter tyres have this tread with tiny channels? https://www.bike-components.de/en/Continental/Top-Contact-Winter-II-28-Folding-Tyre-p33190/?v=24707-black-reflective – Michael Jun 19 '22 at 16:36
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@Michael That tyre is designed to be ridden on snow (and hence shares design features you see on a car snow tyre). To quote the Conti website: "Hundreds of biting edges across all tread lugs help interlock with snowy terrain" – Andy P Jun 19 '22 at 17:20

Michael · Answer 5 · 2022-06-19T08:23:52.570

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Tyre tread won’t improve grip on hard surfaces, even when wet. On soft surfaces (like grass, mud or snow) the treads of city bike tyres are pretty much ineffective. You’d really need knobs with proper spacing.

So why do city bike tyres often have treads like these:

(photos show Schwalbe Marathon and Continental GP4Seasons tyres)

I can see several possible reasons:

Marketing and customer expectations. Tread just looks … grippier. I’m pretty sure that’s the reason why even road bike tyres often have tiny, useless treads on the rubber surface. Doesn’t increase costs and doesn’t have any other disadvantages, so they just do it.
For thick rubber having those “cuts” (negative tread) probably allows the rubber to flex without cracking and maybe reduces rolling resistance.
Maybe some weight savings without sacrificing too much puncture protection.

edited Jun 19 '22 at 08:23

answered Jun 19 '22 at 07:05

Michael

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Thanks, that was part of the reason why I asked -- i.e. if they're truly ineffective, why are they even manufactured? – ChrisW Jun 19 '22 at 07:10
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In my experience the flex groove effect is significant for tires with thick tread. There are thick completely slick tires, but I won’t be buying them again. – ojs Jun 19 '22 at 09:15
City tyres promise robust operation in commuting conditions (ie, whatever the weather, you are riding home from work). Some minor tread deals with a small amount of snow, mush and mud. – vk5tu Jun 20 '22 at 15:31
I think that treads are good if you hit a level difference or small ledge or crack etc., e.g. between bike path and sidewalk, or adjacent concrete slabs that have shifted. A momentary lack of attention, an evasive maneuver: Suddenly you are happy that the wheel can climb that obstacle at a steep angle, possibly because of the treads (note how the tread is often more pronounced on the sides!). – Peter - Reinstate Monica Jun 20 '22 at 16:27

score 3 · Answer 6 · answered Jun 19 '22 at 09:51

(Assuming that by tread you refer to a patterned tread; in some other contexts tread is the area of the tire that gets worn whether patterned or not.)

They're there because most bicycle buyers are familiar with car tires and are aware that car tires absolutely do require a patterned tread or else they'll hydroplane.

If you attempt to sell tires without patterned tread, you will go out of business because you will lose N% of potential buyers. Even if the tires are intended for bikes, because bike tire buyers are not aware that the danger of hydroplaning doesn't apply to bike tires.

For this reason, even tires such as Continental GP 5000 that are supposed to have the absolute lowest rolling resistance, and therefore from an engineering point of view should have completely slick tread with no patterns, do have a tread pattern.

The fear of bicycle tires hydroplaning won't happen. To hydroplane, you need:

A tread that is flat, not curved
A tread that is wide, not narrow
A tire that is filled to low pressure, not high pressure
So much speed that bicycles don't regularly attain such speeds

Even if you manage to ride 80 km/h on a downhill, bicycle tires don't hydroplane.

More about hydroplaning and slick tires on bikes.

As for worn tires, the time to replace a tire is when you see the first casing cords below the worn out tread.

There are plenty of other reasons to have tread on bike tires. Just read the other answers. — ojs, Jun 19 '22 at 09:56
very good point about the marketing - i nearly included that in my answer. in the case of the GP5000 you mentioned, the tread pattern is actually there for aerodynamics - it was discovered by accident (i think by aerocoach if memory serves correctly) that one reason the GP4000SII gave such good results was due to aerodynamics, so conti actually kept/improved this feature for the GP5000 — Andy P, Jun 19 '22 at 15:46
Cars also have their weight spread out among 4 wheels. A better comparison might be between a bike and a motorcycle. These have wider tires (and only 2 of them), travel at much faster speeds (comparable to cars if not faster), and you'll see that these are also generally slick. — Darrel Hoffman, Jun 20 '22 at 19:05

MaplePanda · Answer 7 · 2022-06-20T20:53:20.890

EDIT: Upon further discussion with Andy P and referring to some manufacturer publications, I have found that the macroscopic tread pattern is likely insignificant regarding increasing grip. What matters more for road tires is a good rubber compound that can better interlock with the road on a microscopic level. Hence, we can find very grippy road tires on the market without any sort of tread pattern whatsoever. I'll leave up the answer as bathroom reading if you'd like still.

I'll discuss the "micro-tread" sometimes found on high-performance road tires in this answer. In the comments on Juhist's answer, Andy P cites aerodynamics as one reason for these tires to have a micro-tread pattern. While I do not have a background in aerodynamics, I could imagine the tread pattern acting like the dimples on a golf ball, which serve to create a boundary layer of air around the ball. That helps reduce the wake generated by the moving ball and ultimately reduces drag. [Citation] At high speed, this could have a meaningful effect.

Another reason for these tread patterns (which I understand better) is the mechanical friction aspect. Commonly, friction is just modeled as the product of the normal force and the coefficient of friction, but this is a simplification that doesn't always work too well in real life. A good analogy for how micro-tread interacts with the road surface is a group of interlocked Lego blocks:

The peaks and troughs (known as asperities) interlock to provide a mechanical bonding effect. Since the surface of even a very smooth asphalt road has lots of little nooks and crannies, it actually makes sense to have a micro-tread pattern which can interlock with these imperfections. Of course, the "micro" prefix inherently means these tread patterns don't last very long as the tire wears down.

Some examples of these tread patterns can be seen on the Continental GP5000, Vittoria Corsa, and Bontrager R4, shown in order:

score 0 · Answer 8 · answered Jun 21 '22 at 11:54

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A minor improvement I noticed when replacing a worn tyre with one with more tread: you get less spray when riding in the wet, as the tread clears more of the water to the sides near the bottom, rather than having water stick to a smooth tyre and end up spraying vertically onto you. Not such a big deal if you have decent mudguards though.

answered Jun 21 '22 at 11:54

sqek

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I kind of doubt this. On the contrary: the more tread there is the more water can cling on to it long enough to spray up- and forwards. I think you rather experienced the result from another effect: tyre rubber is pretty hydrophobic on the surface, so fresh tyres don't have much water clinging to them regardless of tread. Only after some use, the surface gets contaminated with lots of tiny dust etc.. particles sticking to and/or embedded into the surface, and those particles are hydrophilic, so you get higher spray. – leftaroundabout Jun 22 '22 at 16:32

What is the purpose of a tread pattern on city/road tyres?

8 Answers8