What makes a tire corner well?


Like many cyclists, we love climbs, but we live for twisty downhills. The feeling of the bike leaning deep into a turn is something that is hard to explain, yet easy to enjoy.
[youtube https://youtu.be/mvGv9IEiDzY?rel=0&w=640&h=360]
This video clip was taken on a short descent toward Lake Washington. We know this road well, and even though we aren’t taking any risks, it’s always fun.
Obviously, one key component in making descents fun and safe are good tires. What makes a tire corner well? Here are some factors that determine cornering grip on pavement.

Most important is a round profile. That way, the tire’s behavior is always the same, no matter how far you lean the bike.
Some older tires were taller in the center – I believe the idea was that you’d roll on a narrower portion of the tire, which was thought to be faster. This caused strange transitions as the effective radius of the tire changed as you leaned the bike. Some tires have a squared-off profile. That is even worse, as amount of rubber on the road decreases dramatically as you lean the bike into the corner. Fortunately, most ‘road’ tires today are round.

Next in the order of importance is the rubber compound. A grippy rubber compound will make the tire stick better to the road surface.
In the past, we had to choose between grippy rubber that wore out quickly, or durable tires that provided heart-stopping moments when they suddenly lost traction and skipped sideways.
Today, the best rubber compounds combine excellent grip with long life, giving us the best of both worlds.

The width of the tire is also very important. More rubber on the road provides more grip – that is why racing motorbikes use wide tires.
On bicycles, there are two reasons why wider tires grip better. They run at lower pressures. This allows them to stay in contact with the road surface better. When a narrow tire skips over a bump, it loses traction. The suppleness of the casing plays a role, too: A tire that absorbs bumps better also has more traction.
Reason 2 why wide tires have more grip: The tread rubber interlocks with the irregularities of the road surface. A wider tires can interlock with more surface irregularities, so it has more grip. (No. 2 appears to be the main reason why racing motorbikes have wide tires.)

Tread patterns also contribute to the grip of a tire, or reduce it. Micro-knobs that squirm under cornering loads should be avoided. The most grippy treads are designed to provide as many interlocking edges as possible. This is especially important on wet roads, where the pure friction between rubber and asphalt is much reduced. But you’ll notice the effect even in dry corners.
Why do racing motorbikes use slick tires? Motorbikes are too heavy and too powerful to use fine ribs – they’d wear off immediately. Instead, they use very soft rubber compounds. The heavy weight and high speed of the motorbike pushes the tire into the road, thus creating the interlock with the road surface. The downside is that racing motorbike tires wear out very quickly.

Tire pressure is important, too. It’s a compromise: Pump up your tires too hard, and they’ll skip over bumps and lose traction. Run the pressure too low, and the tire can collapse during hard cornering. If your pressure is just a bit too low, you’ll just notice that the bike is running wide. If it’s much too low, the sidewall can suddenly collapse, which isn’t a good feeling at all. Fortunately, there is a wide range of ‘OK’ pressures between these extremes.

Temperature is important, too. Rubber becomes more sticky when it’s warm. On a cold day, the grip from your tires will be much reduced – even if you don’t run into ice.
Racing motorbikes warm up their tires for optimum grip, but cyclists are too light to generate significant heat when cornering.

At least as important as the outright grip of your tires is the feedback they provide as you corner. Narrow tires provide very little, but wide tires with good tread patterns give you feedback of how much grip you have in reserve. It’s subtle, but once you know what it feels like, you can sense whether you have a lot of grip in reserve, or whether you are approaching the limit. The best way to learn what this feels like is to ride on slippery surfaces – mud or snow – where you can slide at low speeds and (usually) recover from the slide. But that is a topic for another post…
In summary, to corner with confidence, you want a tire that is round, wide, supple, with a tread pattern that interlocks with the road surface, a rubber compound that grips well – and ideally, you’ll ride on a warm or hot day.

At Rene Herse Cycles, we love descending, so we’ve optimized our tires for all these factors – except the weather. You’ll have to provide that yourself.
Click here for more information about Rene Herse tires.
 

14 Responses to What makes a tire corner well?

  1. Richard Kaufman May 16, 2019 at 5:00 am #

    Good article. (FYI, small typo in third to last paragraph: “wether” should be “whether”.) 👍

    • Jan Heine May 16, 2019 at 9:54 am #

      Thank you. It’s fixed!

  2. Alan Rutherford May 16, 2019 at 7:57 am #

    I’ve never been clear what ‘collapse’ means. It sounds catastrophic. What does it mean for an underinflated tire to collapse when cornering?

    • Jan Heine May 16, 2019 at 9:53 am #

      When you have too little air, the tire sidewall holds up the tire, with little help from the air pressure. The sidewall doesn’t resist the sideways forces of cornering well, so the rim will suddenly move sideways. I haven’t seen a crash caused by this, but I am sure it could happen.

    • alexanderluthier May 16, 2019 at 7:43 pm #

      Underinflated tires can collapse in cars as well, it usually happens when taking curves at higher speeds: lateral G forces make the wall of the tire to flex, and if there is not enough pressure to push the tire bead into the rim, air will escape suddenly.
      Sometimes drivers forget they have to increase their tire’s pressure when loading the vehicle, and a collapse can happen even tough the pressure was “normal”. So remember: tire pressure should be adjusted to the current payload of the vehicle.

      • Mike M May 18, 2019 at 2:42 pm #

        That’s a lesson that I learned the hard way with my bike trailer. I was loading some concrete pavers into the trailer when I noticed that it’s tires were bottoming out. The same tries, at roughly the same pressure, were fine when hauling home the groceries the day prior. At that pressure they were not up to the task of hauling home some ~200 lbs of concrete!

  3. Kurt Sperry May 16, 2019 at 3:28 pm #

    Have you ever done any objective empirical testing of smooth versus treaded tires’ lateral grip on pavement? My anecdotal experience is that smooth aka slick tires work as well or better than any treaded designs, even in the wet — at least at the relatively high inflation pressures (>~50 PSI) I’ve tried.

    • Jan Heine May 16, 2019 at 5:55 pm #

      I just talked to a number of engineers from other tire companies about this. Here is how they test tire grip: They suit up a rider in motorcycle gear for protection and then have them ride on a known course with different tires. The testers grade the tires based on what they feel. This is highly subjective, so the difficult part is finding riders whose observations are reliable and repeatable. It’s sort of like the race car drivers who set up the suspension of the cars based on feel. Many people have tried to quantify grip on two-wheelers, but nobody appears to have been successful.
      Along those lines, I’ve fallen twice in corners during the last 10 years. Both falls were in the wet, and both were on tires that didn’t have tread. One was a corner I know well, and the only discernible difference to my normal rides around the same corner (also in the wet) was that I was riding a set of prototype tires that had a smooth center section.

      • Brian May 17, 2019 at 3:58 am #

        Maybe to make the testing more scientific it could be done blindfolded… 😀

  4. Frank Toman May 16, 2019 at 7:28 pm #

    Hi Jan.
    Thanks for your article/s.
    I have a related question from a previous post …
    You said one of your favourite rim/tyre combinations was a carbon rim with your 650b 48 tyres.
    Can you please let me know a shortlist of your preferred carbon rims (650b and 700c)? I’m having a hard time finding a model with your recommended hooks … they all seem to be hookless.
    Best. Frank

    • Jan Heine May 17, 2019 at 11:51 am #

      Rim models are changing rapidly. I don’t have any experience with the latest models. In the past, we’ve used Enve’s rims (which had hooks then), Reynolds and a few others. If we get a test bike with hookless rims, we run the tires with tubes, which greatly increases the margin of safety against blow-offs.

  5. John Duval May 16, 2019 at 9:31 pm #

    How do these variables affect something like sand on smooth concrete or hardpack? I used to ride my 23mm tires on the beach bike paths, and learned to ride like I was on ice. I have been riding such paths since going wide, but the careful habit is ingrained. My impression is that it makes an even bigger difference.

    • Jan Heine May 17, 2019 at 11:52 am #

      Sand on pavement or hardpack is tricky. In my experience, a wider tires works better, probably because you have more rubber touching the hard surface in between and because the lower pressure means the tire doesn’t just ‘skate’ on top of the sand particles. Still, traction inevitably is reduced, and you’ve got to be extra-careful on those surfaces.

    • Craig Lloyd May 17, 2019 at 10:51 pm #

      Loose over hard is one of the most difficult conditions for any tire. It depends so much on the size of the aggregate and the density on the surface, that picking an effective tyre is very condition specific. If you were on something a little larger than sand a hard 23mm tyre may actually work ok, because it will slide a bit but cut through to the solid surface underneath. Unfortunately, even a 23 is too blunt to cut sand.
      As an n=1 anecdote, I joined an adventurous gravel ride yesterday riding 38mm Barlow Pass EL with a good 7000km on them. There were a few sharp climbs that had thin volcanic dust (a surface dusting) over concrete and I was able to clear them without spinning out. The same for sparse litter of small stones… but a friend on 2.1in treaded tyres was losing traction because they were pumped rock hard and couldn’t deform to the surface and were riding on top of each stone.