Reader question: What do I do when only changing two tyres?
We get a lot of questions on tyres which is no surprise as they’re important and wear out quickly. Here’s another question about uneven wear.
QUESTION: I have a theoretical question that has been bugging me: “If you have two bald tyres on your 4WD and two with decent tread and they are factory highways. If you want to replace the two bald tyres with a same size more, but a more aggressive all-terrain (say Cooper ST-Maxx), would you put the new ATs on the front axle or the rear axle?”
This is theoretical because you should rotate your tyres, and a reasonable person would relace all 5 tyres. Normally, best practice is to put the tyres with the most grip on the rear, thus promoting safer understeer and vehicle stability (which is normally the new tyres) … but the change in tyre type really thows a curve ball – haha.
ANSWER: The answer isn’t theoretical and while not ideal, many have had to deal with exactly this situation. The answer depends a little on the nature of the vehicle, but the default is the front wheels as those do the steering and most of the braking in any vehicle regardless of drivetrain.
This situation is far from perfect – it’s much better to have all four tyres of the same size, make, model and wear on a given car unless it’s specifically designed for differences front/rear, such as some high performance sports cars. The reason is consistency of handling and therefore safety. The car’s braking systems expects the same grip from front and rear axles, and the engineers also set up the handling (over/understeer characterisitcs for example) with that in mind. Then there’s the effect of different rolling diameters on drivetrain, and the inability to swap a spare wheel to any other wheel.
If you must replace one set of tyres on an axle then try and keep them as close as possible to the other axle, for example not fitting mud terrains on one axle and passenger tyres on the other.
Tyres are just about the most important bit of equipment on the car for handling and safety – all the suspension, brakes and power in the world don’t help if the tyres aren’t up to the mark.
We have explored this a bit further in the What Happens If One Tyre Is Replaced reader help.