When you think performance, do you think engine, transmission and drivetrain? You should think again. Tyres affect not only the performance, but the handling and ride of the vehicle as well. Your tyres are literally where the rubber meets the road when it comes to performance. Here’s how your tyres can affect the performance of your car.
It doesn’t matter what tyre you mount on your ride, you must maintain the proper pressure. As simple as it may seem, proper tyre inflation has a tremendous impact on your car’s performance. Insufficient pressure doesn’t inflate the tread area properly. This means the blocks, ribs and groves can’t perform as designed. As a result, performance is degraded. Your handling on turns and even the ability of the grooves to channel away water, mud or snow is negatively impacted. This puts your car at a greater risk of hydroplaning. An under inflated tyre produces more friction. Friction equals heat; and heat is the nemesis of tyres. Your tyres won’t last as long if you don’t maintain proper tyre pressure.
Conversely, an over inflated tyre isn’t any better when it comes to performance. An over inflated tyre lacks flexibility necessary to handle potholes and other road hazards. Steering is compromised. Pirelli said it best, “Power is nothing without control”. Over inflated tyres may wear unevenly and fail prematurely.
Check your owner’s manual or the placard on the inside of the driver’s side door jamb for proper inflation rates. The inflation rate stamped on the tyre itself is the cold inflation rate and may be different from the vehicle manufacturer’s recommended pressure. Always follow the vehicle manufacturer’s rate if the two numbers differ.
Tyre and Wheel Size
You can’t talk about tyre size without discussing wheel size. Your gearing, ABS, traction control, speedometer and odometer were calibrated for the wheel and tire to cover a set distance with each revolution. To maintain the diameter of the wheel and tyre combination, if you increase wheel size you must decrease the tyre profile (height of the sidewall).
Minor changes in wheel and tyre size will not negatively impact performance and will make the car look better. But, a significant decrease in tyre profile to accommodate a significantly larger wheel will decrease performance.
As the wheel radius and mass changes, the amount of force to move the wheel changes as well. The amount of force on an object is equal to mass multiplied by acceleration. So, what Newton is telling you with his Second Law is that more wheel decreases the driving force from the wheels and the result is less acceleration. That bigger wheel requires a tyre with a smaller standing height. The lower standing height requires more rigidity in the sidewall. This decreases feedback to the driver and tangentially decreases performance.
Believe it or not, wider isn’t always better. If the vehicle weight and tire pressure stay the same, a wider tyre doesn’t create a wider patch (the area where the tyre touches the pavement). It will change the shape of the patch. The patch becomes wider but shorter, so the overall size stays the same. The width of the tyre should closely match the width of the wheel. For best performance, the tread width should be as wide as the wheel width. Note that the tread width and the tyre width are not the same. The tyre width is stamped on the side of the tyre and due to manufacturing variations may not be the exact width of the tyre. The tread width can be up to 1.27 cm less than the wheel width without affecting performance.
Deviate from this rule and performance and safety suffers. A tyre that is too narrow for the wheel is at risk of coming off the bead (refer to this guide to wheel anatomy if you aren’t familiar with the bead) during cornering manoeuvres. That’s unsafe at any speed. The strain on the sidewall will have a negative impact on grip and that affects performance as well. A tyre that is too wide for the wheel will have bulging sidewalls. This translates to sloppy steering, poor control and uneven pressure on the pavement.
The speed ratings for most tyres are useless. Unless you are going to hit the Autobahn on a regular basis you are never going to drive that fast. Grab those Zs if you are going over 270 km/h, but at lower speeds you aren’t going to see that big of a difference in performance over the S, T or U.
The Right Tyre for the Best Performance
Tyres affect your car’s performance. For the best performance, remember to make sure your tyres and wheels are properly sized for your car, that the tyre is the proper width for your wheel, and no matter what you drive check your tyre pressure regularly.
Chuck Krause is Wheelfire Blog’s managing editor. Since the early 2000’s, he has managed and owned a number of internet retail stores in the automotive parts industry. He is an especially enthusiastic owner of his off-road “monsterized” Jeep Wrangler. A fixture in every summer’s Jeep jamboree, (where his reputation for extreme mudding and trail riding are legendary) Chuck is well known for his infectious passion and knowledge about all things automotive.