2009 Mercedes Benz C350 Using Non-Stagger (width) Setup

The "average" driver doesn't drive on a race track so they can't tell the difference between most tires. What is strikingly important though, if your vehicle has anti-lock brakes, as most do now, is all four tires must have exactly the same outer circumference. On some car models you can even run into problems when all four tires are the proper size but they were purchased at different times. Tires of the same brand, model, and size can have different circumferences if they were made from different molds or at different times, even a week apart. Same-size tires from two different manufacturers are even more likely to be different. Year-old tires can have enough miles on them to have significantly different circumferences than identical new tires.

Some vehicles are more forgiving with tires of slightly different sizes. Anti-lock Brake Computers monitor wheel speeds during braking. They look for one wheel that's slowing down more than the others, then modulate brake pressure to that wheel. You typically will not notice a problem while driving but false, or unneeded activation of the system can result, especially at lower speeds when you approach a stop. Most systems will not set a fault code during normal driving when one wheel is spinning a little slower or faster than the rest because they can tolerate those differences when going around a corner. Some systems will set a fault code related to mismatched wheel speeds after a mile or more because it knows by that time you're no longer going around a corner.

You also have to be concerned with the spare tire size when you have anti-lock brakes. It must match the rest of the tires to prevent false activation.

It sounds like you pay a lot more attention to your car's handling than most people. That makes YOU the expert on what you like. When a tire is taken to the limits of its abilities you will notice what you like and don't like about its performance, and that will dictate your future buying decisions. You can get a general idea of how a tire will perform by looking at the tread wear rating and traction rating. Higher tread wear means the tire is made from a harder rubber compound that lasts longer but usually doesn't stick to the road as well. High traction can mean a softer rubber compound that wears out faster, but it can also relate to how aggressively the tread pattern grabs in dirt and snow.

Some tires have softer sidewalls to provide a more comfortable ride, but you're usually giving up control on hard cornering. Tires with harder sidewalls may require lower air pressure to remain safe. If your vehicle has tire pressure monitors you'll need to go by what was programmed in at the factory with factory-installed tires, not by a lower pressure that might be recommended by the replacement tire manufacturer.

Keep in mind too that the manufacturer chose a specific tire for your model to meet the needs of the largest number of owners. They have to balance ride quality with noise, traction, handling, and braking. When one of those things has a higher priority to you, that's when you go shopping for a tire with different characteristics, and only you can decide what pleases you.

I don't think you're looking at a performance issue. You're after ride quality. Wider tires provide more contact area with the ground. With more internal area to hold up a given amount of weight, you need less air pressure than with a skinnier tire. Lower air pressure allows the tire to squat more and flatten out, thereby increasing the contact patch even more. That's fine for the rear.

There's two problems with doing that on the front. First of all you're physically turning those tires with the steering system and the tires have to scrub across the road surface. Turning becomes very difficult at lower speeds. On the race track that isn't a problem at higher speeds, plus the tires lean to the left for oval-track racing so they're only riding on one edge most of the time. Still, ask those guys why they're worn out after a 500 mile race. All they did for a few hours is push a few pedals and turn the steering wheel. Wider tires on the front have the same affect on a passenger car. You don't need the same extreme cornering ability as a race car. All wider front tires would do is make your arms tired.

The second problem is ride quality. Even though people like to think they're driving a race car on the road, they still demand comfort. As the front tires get wider you start to feel more and more twigs, pebbles, and other bumps in the road. Those jar the steering system enough for you to feel in the steering wheel. My first experience with wide front tires was test-driving a late '70s Pontiac Firebird after performing an alignment on it. That was the most miserable handling car I had ever driven and I couldn't imagine having to drive it for long distances. Years later I put fat wheels and tires on my Plymouth Barracuda. That car also become no fun to drive.

As a side note, the engineers are also concerned with lowering weight for better fuel mileage. In the late '70s Chrysler started making their brake master cylinders out of aluminum instead of cast iron to save weight. It was that big of a deal to them. Since then all manufacturers are using thinner sheet metal, styrofoam bumper forms, alloy wheels, and considerably lighter suspension components. A heavy front tire and wheel will get thrown around more when they don't have the old, heavy control arms to help dampen that bouncing. You may feel the added reaction to road bumps with wider tires on the front and interpret that is "better road feel". Other people might interpret that as a busy steering system that is not enjoyable to drive.

The automotive business is extremely competitive. If a manufacturer can claim one extra horsepower, one more inch of leg room, or one more mile per gallon, they are going to do whatever they need to so they can do that. Styling and perception also account for a lot of sales. If wider rear tires are appealing they will offer a car model with wider rear tires.

With skinnier tires on the rear you may want to experiment with air pressure to see how it affects handling. The average driver wouldn't notice "decreased over steer" because that is not part of a normal driving condition. Over steer is a product of rear tires slipping. You changed the front tires and went back to what the engineers designed the car to use. Unless you're running a timed obstacle course, it's doubtful anyone is going to notice the difference. You're the one driving the car before and after the tire change, so you're the one who would notice the difference in handling. Where and how are you driving that you need to reach the limits of the car's handling abilities?