Ideally, all four tires on your car should be identical. It's a matter of safety; with identical tires on all four wheels, the car will handle more consistently and predictably in a variety of situations and weather conditions.

But in reality, where people rarely rotate their tires or check air pressure and potholes can cause immediate tire failure, buying 1 or 2 tires only may be necessary.

Today there are more tire manufacturers designing more types of tires and tire models than ever before. Unfortunately, few tire stores understand the differences between tires, and even fewer are as interested in your safety as they are selling what they have in stock. The result is often potentially dangerous.

Given that a professional driver would have difficulty adapting to a car so equipped, are you certain your skills are up to the challenge?

Below you'll find a few examples of the hundreds of cars we've encountered equipped with tires of different categories, speed ratings, and design intent. Someday cars will be able to adapt for tires that are not meant to be used together. In the meantime, there are many cars on the road that are quite literally accidents waiting to happen.

Exhibit A

 

 

Walking past this Mercedes-Benz late last fall, something hazardous caught our eye.

 

 

The front tires were the same 'three-season' tires that Mercedes-Benz - like many other manufacturers today - includes as part of the optional "sport package."

Unlike 'all-season' tires, 'three season' tires lose their grip when the temperature drops below about 40° F, and are designed under the assumption that the owner would never try to use them in the snow.

 

What's hazardous about this particular car is that the rear tires are 'all-season' tires (designated by the "M&S" on a tire's sidewall) which don't grip as well when the roads are dry.

The unfortunate driver of this vehicle would likely experience 'fishtailing' when it is hot and dry and lack steering and braking ability when it is cold or snowy.

The fact that the front tires are 'H' speed rated and the rears 'V' speed rated only complicates matters.

We tried to tell them all of this, but they were in too much of a rush to listen.

We just hope no one in or around the car is hurt when they experience the inevitable loss of control.

 

Exhibit B

 

 

This Acura Integra has a similar problem. In this case, the front tires are the same "all-season" tires the car came equipped with from the factory.

 

The rear tires, however, are "three-season" design.

In this case, the car's front end would 'run wide' during spirited driving in the dry, exacerbating an inherent handling weakness. If any snow were on the road, the driver would be lucky to not spin. His tire store has effectively rendered the car ineffective in any season.

We left a note, but although we walk by this car a few times each week, we haven't seen any signs of intelligence to date.

 

Exhibit C

One day after over 20" of snow fell on the Boston area, we caught a Honda Civic EX Sedan equipped with one High Performance unidirectional tire and three Original Equipment Firestones (a standard all-season passenger tire).

Incidentally, the unidirectional tire was also mounted backwards. We're not quite sure how the driver had managed to avoid an accident. Neither was he.

Exhibit D

With the proliferation of large wheels and low profile tires, it's become increasingly common for tires to fail due to 'road damage'.

Today we encountered an Acura that was less than 2 months old with one of it's four Michelns replaced by a Goodyear, apparently due to road damage - typical of todays stylish, low profile designs. It's never a good idea to replace a single tire with a different type, but in this case more than just the brand of tire was changed.

The replacement Goodyear's load index was 90, well short of the 93V - Extra Load rating of the Original Equipment Michelins. Both are clearly marked on the tire's sidewall.

Translation: the replacement tire is more likely to fail than the one it replaced, which we can only assume is the tire installer's way of bringing in repeat customers...

Exhibit E
Date: July 21, 2003
Car: Ford Focus ZTS sedan
Rear tires: well-worn Original Equipment Firestone Firehawk GTA 02 all season tires
Front tires: fairly new Michelin Arctic Alpin winter tires.

Danger: tricky and unpredictable handling, particularly in winter conditions. accelerated tire wear

Reason: For reasons of safety, tire manufacturers now stress the need to put winter tires on all four wheels, not just the driven wheels.

Why? Because while winter tires on just two wheels may help get you going, they'll also dramatically change the handling characteristics of the car once you're in motion. The Focus is a very easy car to spin in slippery conditions when all four tires are identical due to the engineers' desire to make the Focus feel more like a rear drive car (i.e. more balanced in its handling). By fitting winter tires on the front wheels only, the car will be more difficult to drive in winter conditions, with a tendency to 'fishtail' with little provocation.

Conversely, when it's not slippery out the front will lose traction earlier than expected, making for handling properties that are very difficult to predict - never a desireable trait.

The winter tires will also wear prematurely when driven in warmer weather (something the tire installer will not mind as much as the owner).

Exhibit F

Date: July 29, 2003
Car: Mazda Protege 5
Problem: Tire installer replaced the right rear Original Equipment Dunlop SP Sport 5000 all-seasons with a Dunlop FM901 summer tire.


Potential danger: Had we not told him, the driver would have remained unaware of the difference in traction until trying to make their first left turn on a slippery surface, at which time they'd be likely to leave the road backwards.
Here are a few additional tips for those of you that have read this far:

•Tires should be replaced in pairs

•If only one tire needs replacing and you have a full size spare, use it (and keep the new, mismatched tire as the spare).

•The replacement tire should have the same speed and load ratings as the factory installed tire. If tires with different speed ratings are used, the low-rated tires should go on front to prevent unpredictable oversteer (fishtailing).