New tyre position
Your non-diagnostic vehicle-related problems solved by Steve Rothwell
A relative needs two new tyres for her front-wheel drive diesel supermini. The worn tyres are at the back, but the current budget front tyres are good, with 6mm tread on each. Logic would say to swap the new tyres to the front, where braking, steering and acceleration forces are greatest. However, there has been conflicting advice from a main dealer (who says put the new tyres at the front) and a tyre dealer (who says keep the new ones on the back). Incidentally, neither the owner nor myself agrees with changing wheels/tyres round at service time unless all four tyres are the same brand and age, as it could upset the vehicle handling. Current pick of replacement tyre would be a pair of new Goodyear Efficientgrip Performance 185/65 R15 H (88), rated at A for wet grip, B for economy and 68db. To which axle would you suggest fitting the new tyres? Stuart King Before I start, I will point out that this advice is applicable only to vehicles which have four tyres of the same size. Some vehicles run differentsized tyres on the front and rear, making any thought of swapping tyres impossible. Even so, there have been many heated discussions on this subject, so in order to present a balanced view I will start with the comments from a tyre manufacturer, who recommends new tyres should be fitted to the rear: "The rationale behind putting the new tyres on the rear is that understeer is easier to control than oversteer for the average driver. It’s the lesser of two evils. Added to this, if a tyre was to suffer a puncture or premature failure it is again preferable that this happens on the front axle because again it is more controllable."
Going back a few years, all vehicles had crossply tyres until a new innovation came onto the market in the form of radial tyres. Radial tyres are far superior to the earlier crossplies and they do have different handling characteristics. Because of this, if you were mixing radials and crossplies, it was only legal to fit radial tyres at the rear of the vehicle. This has embedded a sense in many motorists that the better tyres should be fitted to the rear. It also brings me to a point I learned at a road safety training course many years ago: a skidding tyre will always overtake a braking tyre. So if your rear tyres lose grip and skid, they will overtake the front of the vehicle, spinning it round.
Today, we are dealing only with radial tyres. On a front-wheel drive vehicle, the driving and steering forces are transmitted via the front wheels, wearing out the front tyres at a greater rate than the rears. For this reason, many motorists place the new tyres on the front and leave the partworn tyres to run out at the rear. Although this seems to make sense in many ways, it has been proven by tyre manufacturers and is recommended by the AA that new tyres should be fitted at the rear.
It should also be noted that we are not talking about fitting different types of tyre, such as winter and summer ones. In such circumstances, the different break-away point of the tyres may allow one pair of tyres to lose contact at a different rate from the other set. For this reason, summer (or normal) tyres should not be mixed with winter or mud and snow tyres.
Something else to consider is that, these days, we have another innovation in the form of ESP (electronic stability programme). According to some Mercedes-benz handbooks, this has negated the need for drivers to fit new tyres to the rear for reasons of driving stability and safety. The reason for this is because, in an unforeseen emergency involving a tyre losing traction, the system simply takes over.