Question:
Recently when buying two new tires for my
front-wheel-drive car, I was told the company policy is
to put the two new tires on the rear. Their rationale:
In a skid they would have more traction and tend to
straighten the car out. In theory, this is correct if no
other control action is taken.
I watched a video showing a car with
the newer tires on the front going into a skid and
spinning out. Watching the front wheels, I could see no
action to steer out of the skid. Conclusion: The
recommendation is valid for dead people driving cars.
In a front-wheel-drive car, the front
tires steer, drive and provide most of the braking, thus
it makes sense to me to put the best tires on the front.
I suspect that the tire companies expect to sell more
tires by having the worn tires on the front that will
need replacement sooner. What's your opinion?
Answer: You are correct, and you've
already answered the question: Brain-dead people drive
cars. The mandate from tire companies require tire
dealers, when a customer purchases just two new tires,
to install the new tires on the rear axle, regardless of
which end drives the vehicle. The reason, I strongly
suspect, is motivated by liability concerns rather than
available traction. I also suspect that this policy is
the result of lawsuits rather than real-world tire
testing.
You've identified the pertinent facts.
The front tires on any vehicle do all the steering and
most of the braking. On a front-wheel-drive vehicle, the
percentage of braking is even higher, and these same
tires also provide all of the acceleration. Logically,
the best tires should be on the front.
Tires with significantly less tread
are far more prone to losing traction in slippery
conditions. When traction is lost, the tires with the
least grip will try to "lead" the car. In
other words, if the front tires lose traction first, the
vehicle would "understeer" — it would tend
to continue straight ahead in the direction of travel.
At least you see what you are about to hit! What's the
fix for this? Ease back the power or modulate braking to
allow the front tires to regain traction and begin to
steer the vehicle again.
If the rear tires lose traction first,
the back end of the vehicle will try to pass the front
— the vehicle will rotate around the front tires.
What's the fix for oversteer? Look where you need the
vehicle to go, ease back the throttle or brake to help
the rear tires regain traction — hopefully — turn
the steering wheel in the direction the rear end is
trying to go — instantly and exactly the right amount
— then anticipate the rear end hooking back in the
opposite direction like a pendulum if and when the rear
tires regain traction, requiring you to steer back in
that direction — instantly and exactly the right
amount.
Obviously, loss of traction in the
rear is far more difficult to correct than loss of front
tire traction. That's why modern antilock brake,
traction and stability control systems are effective in
reducing loss of control. These systems react more
quickly, correctly and far more precisely than drivers.
And that's why tire companies and
dealers require that two new tires be mounted on the
rear of the vehicle.
What's the safest and best answer?
Install four new tires for equal and excellent overall
traction on all four corners of the vehicle. And, of
course, drive carefully.