is it? Would a diameter difference of a few mm really make a difference on the roads we have in this country?
Not on the wind up - just genuinely curious if this would make a difference as I've never read anything to say you must have the same tread depth on both tyres on the same axle.
Taken from a website:
Why does this matter for tyre replacement?
Okay, so imagine wearing a new shoe on your left foot and a heavily worn shoe on your right foot. Not only would the right shoe lack grip and support, but over time, it could cause injury to your leg, foot or ankle.
It’s a similar story with your car’s tyres. If one tyre in the axle pair is heavily worn or has less pressure, it puts extra weight onto the axle shaft and hub bearings. Short-term, you’ll have less grip. And it can also throw off your wheel alignment and cause new tyres to wear out quicker. Because of this, your car’s performance will suffer.
The long-term effects are more serious, mind. The uneven tread will cause different parts of the axle system to wear down to a point that it will need replacing. Which, if you didn’t know, is a lot more expensive than buying two new tyres.
Having the same tyre tread matters
Your tyres are the only point of contact between you and the road. So as well as making sure they’re in good condition, you must have equal tread depth across the axle pairs. (Or, across all four tyres if you have an all-wheel-drive car, but more on that later.)
The tyre’s tread has many jobs, and one of the most important is to channel surface water. If the tread depth is too low, the tyre won’t be able to channel water, and you’ll experience what’s known as aquaplaning.
This also happens if two or more tyres have a different tread depth or pattern. In this instance, they’ll still channel water, but at different rates. As well as affecting performance in the wet, it will also lead to uneven pressure on the axle shaft.
Oh, and remember, never combine summer, winter and all-season tyres. This will put even more pressure on the axle shaft as your tyres fight one another for grip.
The benefits of changing tyres in axle pairs
Replacing your tyres in axle pairs improves braking performance and control. And as you’ve just learned, they’ll channel water more efficiently too.
The benefits aren’t entirely performance-led, though. Changing your tyres in axle pairs will also save you money. Okay, not initially, but long-term. Your new tyres will last longer and prevent damage to your car’s axle shaft. What’s more, the chances of you needing to splash out for performance-enhancing fixes like wheel alignment adjustments are less too.
What about four-wheel-drive vehicles?
It’s a slightly different story if you have an all-wheel-drive car. Here, you might need to replace all four tyres when they wear out, or if you get a puncture. This is because all four wheels drive the car — rather than two.
If you’re replacing all four tyres, make sure the maximum load rating doesn’t exceed the number in the manufacturer’s handbook. Ignoring this could damage the axle shaft and cause the tyres to wear out quicker.
