Assuming there are no studs, would a wider tire be safer on tarmac with pockets of ice? How does also the profile or other features of the tire impact this?
Add a comment
|
5 Answers
On a smooth sheet of ice only studded tyres provide real grip. With all other tyres you can only hope to stay upright if you go as straight and steady as possible. Even the tiniest turn or braking is likely to result in a crash.
If there is some surface roughness wider, softer tyres with small knobs help and should be run at the lowest pressure possible. There are some special winter tyres like the Continental Top CONTACT Winter II Premium (what a mouthful) which promise improved grip thanks to a soft rubber compound optimized for cold temperatures.
For snow and slush bigger knobs can help.
If the snow or slush is not too deep narrower tyres could be beneficial if they can dig through to tarmac, though I’m always surprised how slippery even a thin layer of slush is with road tyres. You’d think they’d just press through to the ground and behave like you were riding on wet tarmac, but it’s not the case.
There's no significant difference in grip on ice between different tyre widths or thread pattern. Only steel studs can really help. Tyre compound can perhaps make a small contribution, but not enough to save you if the front wheel ever breaks out.
Wide tyres at low pressure do however avoid another problem: if there are patches of ice of different thickness, they don't “deflect” off them as much and as unpredictably as narrow tyres do, nor do they follow grooves as horribly (refrozen slush with cycle tracks in it is the worst!)
I spent a couple of december days with a (studless) fat bike in Tromsø, Norway, and survived... at least the fat tyres could be relied on to keep rolling straight forward, even on uneven ice or on a frozen stream. But steering or braking was still almost impossible. Just about any bike with studded tyres would have worked better.
And this point really plays out only with very wide tyres / low pressures. Even downhill MTB tyres cope with grooves in ice hardly better than road/gravel tyres do.
An entirely different story is of course snow. Here tyre width makes a huge difference – wide contact patch at low pressure is your only chance in deep snow, but narrow tyres can actually be better on shallow, loose or crumbly snow because they cut through better. Intermediate-width hybrid/MTB tyres give in some sense the worst of both worlds, because they neither float on top nor cut through to the bottom, although I would still say that studs make up for that. Studded MTB tyres at low pressure also work really well on compressed snow with icy patches.
Yes. On clean ice the width doesn't make much difference but on frozen tarmac the larger contact surface increases the chances that there is something the tire can grip.
Note that the area and shape of the contact patch do not depend only on the pressure but also the width and construction of the tire carcass and the tread pattern.
Source: Dressel, Sadaukas: Characterization and Modelling of Various Sized Mountain Bike Tires and the Effects of Tire Tread Knobs and Inflation Pressure under CC-BY
-
7To clarify, what helps is having a large contact patch, which is a function of tire pressure, not tire width. However, running low pressures is more feasible on wide tires than narrow ones, so tire width is an indirect measure of "ice-worthiness." Jan 20 at 14:42
-
4@njzk2: No, pressure (N/m²) multiplied with area (m²) results in a force which counteracts the force of gravity. With the same pressure you need the same area to get the same force.– MichaelJan 20 at 19:22
-
2Michael/njzk2: you both have a point. Michael's description is pretty spot on for a normal range of pressures, and the laws of physics do apply. However, njzk2 is taking things to the extreme where the laws of physics still apply, but the tire is now so deflated that it deforms in a way that appears to defy the laws of physics. At this point tire does not have an equal force across its contact patch, likely lower toward the center as the tire deforms. The laws of physics are not broken. Still, more contact area provides additional opportunities for traction.– Ted HohlJan 20 at 19:58
-
2Thank you for the comments. I do value pedantry, so I have to point out that the width of the tire does limit the size of the contact patch. So, while the wildly theoretical contact patch can be calculated from the formula A=F/P, the actual contact area doesn't approach infinity when pressure goes to zero but instead reaches the physical width of the tire and then goes effectively to rim width because the tire is not supported by air pressure any more. Second, the thread structure of the tire limits its flexibility so the contact force is indeed not constant through the contact patch.– ojsJan 20 at 23:34
-
2With bicycles and a rolling tire, it is also not necessary to have grip all the time. So a wide tire at high pressure can still have a wider and shorter contact patch, more likely to catch some grip every now and then as it rolls along.– jpaJan 21 at 6:42
Wider tires may have more edges, increasing their grip (including on ice).
Grip is not a direct function of tire width. Instead, the shear force required to drag all contacting edges over the top of each other, causes surfaces with more edges to grip each other better. The more edges, the more grip. More force pressing those edges against each other, also grants more grip.
The reason a "slick" racing tire can get good grip on dry asphalt, is that it isn't actually slick: Its soft rubber surface deforms enough to contact more edges on the rough asphalt, than does the stiffer rubber of an "All Terrain" tire.
"Siping" & "lugs" each increase the surface area of a tire. Lugs are the large knobs which protrude from a tire, creating extra edges to interleave among the edges on the ground. Siping is the hair-thin slits which create even more edges along the surface of a tire (or its lugs).
Lugs are helpful on loose surfaces; while siping increases grip on all surfaces (but increases drag & reduces tire lifespan).
On firm asphalt, tall & widely spaced lugs tend to lift the rest of a tire's surface away from the ground, reducing the edges available to grip; while on looser ground, lugs dig in until the recessed portion of a tire's surface also contacts, with the combination creating much more grip than a "slick" tire with its very very small edges. This is why road tires lack big lugs, while All Terrain tires rely on them heavily.
Although lugs work great on loose snow, they contact smooth ice along even fewer edges than a "slick" racing tire; if the "slick" lugless tire remained soft at low temperature, it would grip ice relatively well compared to the tall stiff lugs of a long-wear All Terrain tire.
A smooth surface of ice presents very few edges, which are also weak & self-lubricating under pressure.
To overcome this, a studded tire adds additional edges by penetrating the ice, the same way lugs penetrate loose ground. By punching into the otherwise smooth ice, more edges are created, granting more grip.
Ironically, a narrower tire will sometimes achieve more grip than a wide tire, in conditions where the narrower tire is able to penetrate far enough to bury its studs &/or lugs: A wider tire distributes the vehicle's weight, resulting in less force per inch to press the edges of the tire & ground surfaces together. In sloppy conditions where a wide tire may lose grip, a narrow tire sometimes retains grip by digging deeper, due to carrying the same weight on less area.
Conversely, a fat tire may "float" across extremely loose ground such as deep sand or snow, where a narrower tire digs in so deep it gets stuck.
In short:
- The more edges a tire can keep pressed across the ground, the better it grips.
- Smooth ice presents so few rough edges, puncturing it with studs can be the only way to obtain enough edges to grip.
- An especially wide tire may not press down with enough force per square inch, to dig its edges into a smooth hard surface (such as ice).
For maximum grip on smooth ice, use the widest tire which fully buries its studs, at a given vehicle weight.
If studded tires are unavailable, just remember that the quantity of contacting edges pertains to grip more than width alone.
-
1
-
A wider tire may provide more surface area in contact with the road, which could potentially increase traction on tarmac with pockets of ice. However, the tread pattern and overall design of the tire also play an important role in determining its performance on ice. Tires with a more aggressive tread pattern and/or specialized ice-gripping technology will generally provide better traction on ice than a tire with a smooth tread. Additionally, tires with lower profile will have less surface area in contact with the road, which may lead to less traction on tarmac with pockets of ice.