When you start looking for the best car tyres, the first thing you'll need to do is check what tyre size and specification you need for your car. This information is specified in your car's handbook, or on the sidewall of the tyre itself. Only when you know which size tyres you need can you start thinking about what you want in terms of capabilities.
Here are some of the main things to consider when comparing tyres.
Car tyre grip
How well a tyre grips the road surface depends primarily on its rubber compound and the grooves that form the tread pattern.
Remember, it's the tyre surface that's in direct contact with the road that does all the hard work.
Before we start testing, Which? runs in our tyres on normal roads to ensure accurate, consistent results.
Wet grip
In wet conditions, water lessens the contact between the tyre and the road, reducing grip. Taken to extremes, the result is aquaplaning – when there is no direct contact between rubber and road, resulting in a loss of control.
The tread grooves are designed to expel water from between the tyre and the road. Each manufacturer designs its own tread pattern to achieve this.
The more efficiently the grooves expel the water, the better the tyre will be at maintaining grip in wet conditions.
If you've ever skidded on a wet road, you'll know just how frightening it can be. That's why we painstakingly measure the exact point at which each tyre begins to lose grip in the wet, so that you know which tyre brands are the worst for losing it in the rain.
To do the wet grip test, we accelerate the car on a road surface covered with 7mm of water and note the speed at which the tyres start to lose traction. We accelerate to 80kph (50mph) and brake, measuring the distance required for the car to slow down to 20kph (12mph).
To test lateral wet grip, we drive the car on a fixed radius circular track, driving into a stretch of water 4mm deep. We repeat the test between speeds of 70 – 100kph, in 5kph steps, until the tyres lose grip.
Dry grip
In dry conditions, the friction between tyre and road is the main factor in maintaining grip. If you brake harshly, accelerate rapidly or take a corner too fast, this tends to overcome the frictional forces, in which case the tyre will slip and tyre wear will be accelerated.
On dry roads, we accelerate on an asphalt surface to 100kph (62mph) then brake to a halt.
Wet and dry handling
We also compare how well each tyre grips on a series of demanding corners, both wet and dry. This tests how well the tyres maintain grip, when the car's weight is shifting and the tyre walls are working hard to resist this load transfer.
Car tyre noise and wear rate
Most tyre noise comes from the tread as it comes into contact with the road.
So the hardness of the rubber, the shape of the tread and the squareness of the tyre's shoulders (the edges of the tread in contact with the road) influence the noise. Two assessments can be made - pass-by noise, where the noise is measured from the roadside as the car coasts past, and interior noise, considered from the position of the driver's ear.
All noise generation varies depending on the road surface (course concrete surfaces will generally be much noisier than smoother tarmac or asphalt surfaces. But the noise transmission is via two media - airborne noise and conducted noise.
Interior noise is a combination of air-borne noise and structure-borne noise, and will vary between vehicles depending on sound insulation (to restrict air-borne noise) and attenuation - design of the vehicle components to resist transmission of noise and vibration into the cabin.
How well a tyre wears depends on a whole host of factors, including driving style, road and climate conditions, and how well you look after your tyres and maintain your car.
Car tyre rolling resistance
Rolling resistance affects your car's fuel economy. This can make a significant difference to fuel bills over the life of the tyres.
Some tyres have words like 'fuel saver', 'eco' and 'energy' in their names, which imply low rolling resistance, but this isn't necessarily the case.
Wear
We run every tyre for 5,000km, measuring the tread depth throughout. We then rate the tyres against each other to show which ones will last longest under the same driving conditions.