Tires Part 1: The Basics

For a suspension tuner, the first question to ask is almost always this: “What kind of tires?” Tires have a major influence on a car’s ideal suspension set up, including spring rates and alignment settings. Maximizing what you get out of your tires is the key to going fast.

And yet...tires are one of the most overlooked parts of the average "build." If you want to improve handling, those baller-status forged wheels wrapped in generic all-season tires won’t do you much good, even if they’re mega-wide and meaty.

Tires might seem simple, but there are arguably more secrets and protected data about tires than any other part on your car. The science moves fast and is one of the main reasons that records continue to be broken at every level of motorsport. When it comes to discussing specific tire models…by the time I finish writing this, it’ll be out of date.

But there are some things that don’t change, and that’s what we’re going to focus on in this article. So let's talk about size first. Yes, it does matter, but maybe not as much as you thought.

Overall tire diameter is not printed on a tire but is crucial info that’s easy to find online. For example, going to a wider 245/45/17 from a 215/45/17 adds over an inch in diameter. A bad decision. A 245/40/17 is within 0.1 inches and can work well.

Too tall can cause rubbing and gearing issues. Too wide can also cause rubbing.

The tire below is a 225/40/18 size.

 225 – Tire width in millimeters.

   40 – Aspect ratio of the tire sidewall. Relates sidewall height to tire width.

   18 – Wheel diameter in inches.

A wider tire doesn't really mean more tire on the ground, but a change in the shape of the contact patch. Keeping it simple for now, a wider contact patch is generally a good thing for grip as long as the wheel is wide enough to support the tire. We’ll talk more about that later.

But for grip and lap times, tire model or compound is far more important than width. For example, a Subaru BRZ with factory size 215 width tires but in sticky Michelin Pilot Cup 2 spec will be much faster around the track than the same car with wider 245 width all-season tires.

So race tires for all? If you're racing, sure...but they're not for everyone and not the best choice for the street. At the track, a lower grip tire is often easier to drive and a good learning tool…as long as it can take some heat. An all-season tire can’t do that. Meanwhile, sticky summer (or track focused) tires do a poor job in colder temperatures.

The right tire for the job is the answer. Every tire has a unique character and there are huge differences even within a category. Grip, stiffness, noise, and breakaway can all be very different.\

Tire categories explained

Winter – Intended for cold weather, ice, slush, and snow.

Touring and all-season– Designed for comfort and low noise in different climates.

Summer – More dry grip and response, but only in warmer temperatures.

Extreme summer– Sportier tires for auto-x and track days. Loud and uncomfortable.

Track – Dedicated track tires for dedicated track and race cars. Not for street use.

A good summer tire in the right size will be great for backroads fun and still be fairly comfortable. Some can put down quick laps or crush an autocross course if you ask them to. But the step up to more serious tires is a big one and is an easy way to cut seconds off lap times.

That’s why race series often use the tire as a primary component for classing vehicles or require a spec tire. For the street, tire choice can transform the character of a car and drastically improve handling. But a good car with the wrong tires is definitely a bad car.