Why Wider Tires Corner Better

corner_adams

In our last post, readers noticed the image above and asked about cornering. How am I able to lean the bike so far?

Wider bicycle tires corner better than narrower ones. This may run counter to what many cyclists believe, but it’s easy to explain. The reason is the lower pressure at which you can run wider tires without risking pinch-flats. This has two effects:

1. Wider tires run at lower pressures and thus have a larger contact patch. This simply puts more rubber on the road and increases cornering grip. While simple physical theory suggests that friction should be independent of tire width – narrower tires are pushed onto the road with more pressure – in practice, wider tires provide more interlocking surfaces between road and tire, and thus provide more grip. If you don’t believe this – after all racing bikes use relatively narrow tires – look at racecars or racing motorcycles.

2. Wider tires absorb bumps better. This keeps the wheels on the road and provides more consistent adhesion. A narrow, high-pressure tire skips over the surface, which limits its grip. Even the smoothest asphalt is surprisingly rough. That is why race cars and racing motorbikes have suspension, and why they run their tires at 35-40 psi. If you inflate your tires to 90 psi or more, you are giving up a lot of cornering adhesion. (For the same reason, tires with stiff sidewalls don’t corner as well, because they don’t absorb the vibrations and bumps like tires with supple sidewalls.)

uphill_racer_rando

So much for the theory – how does it translate into the real world? A few years ago, we tested two titanium racing bikes against a 650B randonneur bike. We raced two bikes side-by-side up a steep hill (above), then turned around and rode back down the twisty descent.

I have talked about the uphill part of this test elsewhere, but the downhill part was equally surprising: In the corners, the racing bike with its 25 mm tires could not keep up with the randonneur bike on its 42 mm tires. The riders changed bikes, but it was always the randonneur bike that went down the hill faster. There were two corners, one extra-smooth with new pavement, the other bumpy. The wider tires were better in both corners. Not surprisingly, the advantage was magnified in the bumpy corner. And since the randonneur bike exited the corner faster, it also went faster on the straight that followed.

How did it feel riding the racing bike? I was one of the riders, and I consider myself a good descender, so I wasn’t happy when second tester Mark distanced me while he was on the randonneur bike. While I was riding the racing bike, I had to try hard to keep up. The first, smooth corner felt a bit unsettled, but then I really frightened myself in the second corner. I picked a good line that avoided the bumps, but my front wheel started skipping across the surface. I had to open the radius of my corner and went about a foot into the oncoming lane at the corner exit. In the same spot, the randonneur bike’s wide front tire simply keyed into the surface and rounded the corner without drama. (Both bikes were equipped with Compass tires, so the tread compound was the same.)

descent_blewitt

Of course, you can’t just slap wider tires onto any bike and expect it to corner like a machine custom-designed to optimize the handling. Here are some of the issues:

  • A wider tire’s larger contact patch stabilizes the bike. (This is called pneumatic trail.) If your bike’s geometry isn’t designed for wide tires, then your bike can feel sluggish in its response to steering inputs when you increase the tire size.
    Solution: Decrease the geometric trail to account for the pneumatic trail of the tires.
  • Wider tires tend to be a bit heavier, and thus have more rotational inertia. This makes the bike more reluctant to turn into a corner, or to change its line in mid-corner.
    Solution: Reduce the wheel size as the tire gets wider, to keep the rotational inertia within the range that gives the best handling.
  • Wide tires run at low pressures, but too low pressures can allow the tire sidewall to collapse under the cornering forces, which is not good at all.
    Solution: Make sure your tires are inflated enough to prevent sidewall collapse even under hard cornering. Especially supple tires don’t have much sidewall stiffness, and need a little more air pressure to hold them up.

Beyond that, technique can help. On bikes that are too stable because their tires are wider than is optimal, you may need to actively countersteer (that is, push the handlebars to the outside of the curve) to get the bike to lean. On optimized bikes, you do that, too, but you never notice it because the amount of countersteer is totally intuitive.

Overall, there is little doubt that wider tires corner better, all things being equal.

Further reading:

About Jan Heine, Editor, Bicycle Quarterly

Spirited rides that zig-zag across mountain ranges. Bicycle Quarterly magazine and its sister company, Compass Cycles, that turns our research into high-performance components for real-world riders.
This entry was posted in Testing and Tech, Tires. Bookmark the permalink.

41 Responses to Why Wider Tires Corner Better

  1. Tran says:

    I completely agree with your claim. I have never reviewed a product before, but must say that the Compass Elk Pass have been a game-changer for me. I increased my personal best average speed on my Peter Johnson randonneur on the maiden ride with them. Now only if they were a bit wider – so as to corner better – they would be just perfect.

  2. phr3dly says:

    Obligatory Jobst Brandt picture:

    Skinny tires can handle a lean too.

  3. Visko says:

    Racing cars and motorbikes use big tyres to dissipate the heat that the extremely soft rubber compounds they use generate under big forces, specially acceleration (but cornering too). Also because the shape of the rubber patch on the tarmac affects traction (although only very little compared to rubber compound and tyre pressure).

    Also…what’s the point of the file thread on Compass tires? Makes no sense…

  4. DavidM says:

    Here in Ireland I rarely encounter corners dry, clean, well-cambered enough to enjoy leaning in hard. Nonetheless, I still get huge extra confidence through rougher, gritty and often damp/wet corners with GB Hetres or even better, Compass Extralight 42mm tyres. I’m around 165lb/ 75kg, and inflate about 36f/40r.

    Just no comparison to 700c 28mm Conti GP 4Seasons I used previously.

  5. Dan Michael says:

    I have been impressed with the wonderful cornering afforded by low pressure 650B x 42 tires.
    Although tire construction is obviously different from bicycle tires, Formula 1 tire pressures run 17 – 21 psi and teams often attempt to use the lowest permitted tire pressures, and drag slicks run as low as 5 or 6 psi.

    • How is that even possible, when ground-level atmospheric pressure is 14-something psi?

      • Dan Michael says:

        Tire pressure is measured in “gauge pressure” (e.g.: psig) rather than absolute pressure (psia). Gauge pressure is relative to atmospheric pressure. When your tube is punctured and your pressure gauge reads 0, the tube does not contain a perfect vacuum. 🙂

      • Daniel W says:

        Tire PSI measurements are PSI above atmospheric pressure, otherwise it wouldn’t be PSI, it’d be PSIA (Pounds per Square Inch Absolute). PSI is above atmospheric pressure, PSIA is in reference to a vacuum. It’s perfectly possible to inflate something to under 1 PSI.

  6. Chad says:

    I prefer my steel randonneur bike with 42mm wide Compass Babyshoe pass tires over my carbon fiber road bike with 23mm Michelins for a twisting descent any day. I really enjoy aspects of both bikes, but the wider tires instill much more confidence in that case. Before I had a bike with wide tires, I didn’t put a lot of stock in their use on smooth roads, but to my surprise, the performance advantage was very apparent. Thank you for bringing these tires to the market. I look forward to trying the extra supple version.

    I am not affiliated with Compass or Bicycle Quarterly in any way (though if Jan ever wanted to send some parts a few miles north to Everett for road testing I wouldn’t turn him down). Just a very satisfied customer.

  7. Eric Hansen says:

    The article is not consistent with physics. The maximum force of friction is the coefficient of friction multiplied by the normal force. It is completely independent of area. Area goes up, but normal force per unit area decreases.

    This is complicated in that tires don’t have a constant coefficient of friction for some arbitrary pressure and loading. Tire blocks, and the carcass itself, deform as more cornering load is placed on them, increasing their coefficient of friction.

    Friction also doesn’t work in the classical sense you describe. It’s not the jagginess of the two respective compounds hooking on each other. If you took two pieces of glass and ground them to optical perfection, like a reflecting mirror on a space telescope, then put them face to face, they’d optically weld together, and would be hard to slide against each other.

    That said, all my tires are fatter than the norm for several reasons, some of which you mentioned. Stability over bumps is crucial to riding quickly, and going up 3mm in sectional width increases air volume by something like 26%, allowing a reduction in racing pressure of 25PSI per tire. Also, the lower air pressure greatly reduces maintenance required on wheels, and requirements to ‘pay attention’ for obstacles in your path.

    • The article is not consistent with physics. The maximum force of friction is the coefficient of friction multiplied by the normal force. It is completely independent of area.

      The fact that race cars use wide tires shows that there is more to cornering than simple coefficient of friction. Your analysis overlooks the interlocking between road surface and tire tread pattern. That depends greatly on area, softness of rubber, tire pressure and tread pattern.

      • John Clay says:

        I believe that, in the context of the tires we’re discussing, wide tires “corner better” but I’m not convinced your race car or interlocking rationales are correct. Can you cite any tire company or other technical research? It doesn’t make sense to me so I’d like to understand it.The suspension effects make lots of sense and are, I think, the entire reason that better cornering and speed performance are available and more easily exploited by any given rider, all else being the same.

        Modern race vehicles, and their tires, are concerned with more than merely maximizing ultimate lateral g force capability. Engine and brake power are enormous, rubber compounds are far stickier than in years past and tire temperatures are of major concern. All of that affects wear rate, tire behavior and all aspects of performance. Those are huge, make or break, issues in modern racing. Apply F1 power through a skinny version of whatever they’re using and the rubber/road shear stresses would go through the roof. Temperature would skyrocket and the tire would be useless in short order, if not immediately.

        While I definitely buy your general conclusion wrt wider tires and handling/speed improvements on bicycles I’m not sure all of the logic sticks. If it does, I’d sure like to read your sources.

      • Can you cite any tire company or other technical research?

        I first saw the interlocking effect mentioned by a Michelin engineer in the long-defunct Bicycle Science newsletter. Interestingly, when the article was published, Michelin was promoting slick tires!

        Research: It’s easy to test this. All you need is a set of standard Grand Bois Hetres, a set of shaved Hetres and a set of Babyshoe Pass tires.

        I have done that experiment. I crashed on the shaved tires as soon as the road got wet. I almost hit the inside curb on my first ride on the Babyshoe Pass, since I was used to the bike on standard Hetres. The difference in cornering grip was surprising even for me.

        Finally, I’d like to point out that the Compass thread pattern isn’t our invention. For decades, virtually all high-performance road tires used this tread. I suspect the superior grip was the reason for so much conformity when tire tread patterns are pretty much the only way to distinguish your tires from those of the competition.

      • John Clay says:

        Thanks Jan. Interlocking varying as a function of tread, compound and casing makes (and made) sense to me. It was really the “race cars use wide tires so wide tires must make bicycles corner better” that seems a bit of a theory stretch to me. Wide racecar/cycle tires are a strong function of dealing with all forms of the enormous power transmitted through them (engine, braking, cornering) and the results of that (temp, wear). And like you I was using “wide” as a proxy for low pressure. The suspension effects of wider tires operated at lower pressures (and with more supple design/materials details) and the fact that they are less disturbed by and better conform to surface imperfections, not falling into cracks and the like, would seem to encapsulate like the reasons for the cornering improvement they offer and the reduction in skill required to use it.

        Regardless, thanks for introducing the performance offered by wider, supple tires operated at lower pressures to the mainstream. That opened a huge door to the benefit of many.

    • Eric Hansen says:

      http://physics.stackexchange.com/questions/218145/why-friction-between-two-smooth-surfaces-is-high

      We don’t yet have a model describing how friction actually works, because there are just too many variables. We can only empirically test and iteratively experiment. Testing the same tire carcass with tread polished off is not a great way to compare the performance of tread adhesion. Each type of tread is going to require a different carcass design to perform equally in the first place.

      • Most tire carcasses are designed for performance and puncture resistance. I am not familiar with any manufacturer who considers the interplay between tread pattern and carcass. What would that look like?

        The reality is that you can vary only a few things: thread material, thread diameter, how fine you weave it (TPI), and how much rubber you put on it. The tread rubber can be designed for a smoother transition from tread to sidewall, and that is about it. You can add extra layers and belts, but that will always reduce your performance and feel.

  8. Charlie says:

    “Wide tires run at low pressures, but too low pressures can allow the tire sidewall to collapse under the cornering forces, which is not good at all.”

    Narrow rims can exacerbate this problem. With tires beyond 30mm or so, this can be an issue with rims of outside width <20mm.

    • With very supple tires, there is little sidewall stiffness to hold up the tire, so rim width is less important.

      The extreme are tubular tires, which are not at all supported by the rim sidewalls. You simply run supple tires at higher pressures, to make up for the less-stiff sidewalls. Fortunately, supple tires ride, perform and corner better than stiffer tires, no matter which pressure you ride.

  9. Bob says:

    Only slightly OT, I was sorry no Compass tires were used in Zinn’s recent VeloNews article. Can you make an educated guess where some of your tires might rank?

  10. Eric says:

    One thing I experience when riding my bike with 650bX42 wheels/tires is what was explained to me as “off-axis” steering. When you lean a bike with wide tires the contact patch will be more off-center than with narrow tires. This gives you the feeling that the bike wants to continue steering more into the turn. I’ve ridden the same bike with 700cX23mm tires which have the same approximate diameter so the geometry isn’t really different in any other way. Have you made similar comparisons?

    • I think Jan’s experience is similar in finding differences in the line the bike takes due to the tire/wheel combination, as well as differences in the required level of adjustment from the rider. The difference may be that he’d flip it: he finds the line of travel of the 650B wheels to be more natural for him, which is to say that when the bike does continue to steer into the turn, he finds that to be an intuitive response that does not require conscious inputs.
      -Barbara
      Compass Staff

      • Eric says:

        It’s something that I adapt to in a ride or two. It’s just worth noting if someone is trying it out for the first time.

    • Eric Hansen says:

      I call that ‘power steering’, or a positive feedback loop (which is bad). My fatbike does it like CARAAAZY when I run the front tire at 5PSI.

  11. Michael says:

    Was wondering about tire profile shape and a tire’s reluctance/willingness to carve into a corner?

    I noticed on my old 42mm egg-shaped tire profile (shoulders low and center of tread pointy) I had a hard time carving into corners, but with round profile 42’s and 38’s (having a very round profile) the tires just carved right in.

    Of course there were other vastly different characteristics of the egg vs. round profile tires, but was wondering how much the profile has to do with it.

  12. Skynet says:

    Is pneumatic trail a geometric measurement? Or a term for the trail-like stabilizing effect of a lager contact patch, due to friction.

    I imagine that the contact patch would still be centered under the front hub, so the ‘trail’ would be caused by increased resistance to turning from the added area

  13. John Duval says:

    Here is an article explaining why wide rims are better for wide tires at lower pressures. It is pretty convincing.
    http://www.pinkbike.com/news/Tech-Tuesday–Wider-Rims-Are-Better-and-Why-Tubeless-Tires-Burp-.html

    • Thank you for linking that interesting article.

      They talk about tubeless tires, and “relatively stiff” tires. I don’t know enough about burping tubeless tires, but cornering on supple tires is almost independent on rim width. Otherwise, no cyclocross racer would run tubular tires on rims that are effectively just a few millimeters wide – they don’t support the tires’ sidewalls at all.

  14. “Wider tires have a larger contact patch”

    No. Lower-pressure tires have a larger contact patch, and (as you say), wider tires are easier to run at lower pressures. But a tire at 80 psi with 80 pounds on it will have a 1 square inch contact patch, skinny or fat.

  15. The Jobst Brandt article discusses a lot of the physics, but doesn’t really get down to actual cornering technique. Plus the notion of countersteering by moving the bars slightly in the opposite direction to initiate the lean in the proper direction has never resonated with me. I think a much simpler way to set up countersteering is to use downhill ski technique on your bike. The biggest improvement in my cornering/descending skills came when I began to “steer with my hips” and let the rest of my body take care of itself. This usually results in the bike leaning into the turn and the upper body remaining upright or leaning away from the turn. This also puts you into a position where you’re suddenly more comfortable dealing with the bike “drifting.” Compared with just leaning the bike with my body centered along the bike’s vertical plane (the way most people corner), I was able to increase cornering speed at one tight bend on my commute from a max 27 kmh to a comfortable 33-34 kmh on dry pavement..
    One thing that I find truly maddening (and that I’m glad is not seen here) is the oft-expressed notion that “putting all your body weight on the outside pedal will lower your center of gravity,” espoused by more than one pro rider in the most popular bicycle magazines (as well as by the director of Seattle’s Cycle U, whom I tried to correct, but he just ignored me). This shows a marked ignorance of how center of mass is calculated. Lifting your body weight off the saddle will actually raise your center of mass slightly, BUT it also reduces the unsprung weight of the bike/rider system (which on a bicycle is far more important), since your legs are now the springs and the bike is free to pivot around the outside pedal axle. This reduces the effect of the road’s bumpiness in the turn, like a good suspension system.

    • There are a lot of misconceptions about how bikes steer. The fact is that whether you steer “from the hips” or actively countersteer the bars to the outside of the turn, you always have to move the wheels to the outside of the curve to unbalance the rider and initiate the lean. And the only way to do this is by countersteering.

      There are different techniques on how to initiate that countersteer. For example, when you ride no-hands, you must use your hips to tilt the bike, which then causes a reaction from the front-end geometry that gets you the countersteer. Most of the time, on a bike with good geometry, countersteering is so intuitive that you don’t notice it at all, just like don’t notice it when you walk around a corner. Without leaning, you’d fall over, but you don’t actively think about leaning…

  16. Michael Arciero says:

    Regarding steering-recommendations like putting your weight on the outside pedal can be effective for some riders more because they create a mental image for the rider or create secondary movements that affect the necessary countersteer. These are like “swing thoughts” in golf. Pointing your knee in the direction you want to turn is another that comes to mind. Also leaning the bike rather than body, or vice-versa. Regarding counter-steer itself as a technique-it’s pretty striking how quickly you can make a bike dive into a turn when you consciously do this. I usually dont think at all about turning but sometimes it’s fun just to try different techniques.

    • I agree that different ways of visualizing the countersteering process can help. I think once you become a very experienced rider, you get very attuned to the balance of your bike, and cornering becomes just an extension of balancing your bike. The only difference is that your bike is leaning over instead of upright.

      “Active” countersteering is very useful on bikes that have too much stability and “corner like on rails”. If you need to change the line of such a bike in mid-corner, pushing the handlebars to the outside of the turn is pretty much your only option.

  17. DDDDer Pedersen biker says:

    It’s quite fun riding a sporty bike like an E. Merckx through difficult descents, since the countersteering force required is so low.

    Recently, in a news article about a rider who collided with an oncoming car, it was reported that the rider had tried to “lay the bike down” in the moment before head-on inpact, but of course his action was confused by witnesses with his actual counter-steering in an attempt to steer away from the car.

    One thing about lower tire pressures is that the tire can roll over larger pieces of un-seen gravel without the entire contact patch being lifted clear of the pavement, so traction is better maintained.

    Larger tires run at the same pressure as narrower tires will have proportionally more tension stress in the casing, so lower pressures are needed to maintain a supple conformity with rough surfaces.

  18. Bill Gobie says:

    Regarding sidewall collapse at low pressure: Has anyone photographed this happening? Some other possibilities occur to me: Since the contact patch is wider at low pressure, as the bike leans the tire may develop camber thrust more rapidly than the rider can react, resulting in a sort of shimmy as the rider reacts belatedly. Another possibility is the tire is reacting more sensitively to irregularities in the road surface. Something I have noticed with a large low pressure front tire is the tire’s eagerness to suddenly climb small irregularities like a thick paint stripe. Countersteering results as the contact patch moves from underneath the center gravity and the bike steers off the stripe, only to repeat the process until I can edge the bike away from the stripe. Something similar might happen when cornering, except that an irregular road surface would not provoke such a well defined oscillation.

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