Do people get bigger wheels just for the aesthetics? Is there a performance benefit?

[GTS_300_Coupe]

According to Mazda6tech (the man certainly *seems* to know what he's talking about) up-sizing your wheels is just for looks and you stand to lose in terms of handling and performance (especially acceleration and braking.)

Read here:
http://www.mazda6tech.com/index.php?...d=44&Itemid=50

Plus-sizing for Dummies

Larger diameter wheels:

Larger diameter wheels bring a more prominent aesthetic touch to the car. Many Mazda6 owners choose to change out their 16" wheels for 18's, or their 17" wheels out for 19's. These large wheels are attention-getting, and can make a statement about you and your car.
Care to know what that statement is?

Aside from looks, there is really only one great reason to change to a larger wheel size: to fit larger brakes. Do you need larger brakes? If, after a day of hard driving, you can still lock your brakes- then no. And even then, you should consider swapping your brake pads before your rotors.

There are, however, many compelling reasons not to plus-size your wheels that you should be aware of before purchasing new wheels:

1. Reduced braking distances. Larger wheels, even if they weigh the same as smaller wheels, are harder to slow down. [Further reading.]

2. Reduced brake pad life. Because of #1, the brakes must work harder. Expect them to wear more quickly, or in hard driving possibly overheat and fail.

3. Reduced steering feel. Due to gyroscopic effects, larger wheels are harder to turn left and right. Thus, a slipping wheel will not transmit as immediate nor as strong of a force to be felt through the steering wheel. Running a different wheel offset changes the car's scrub radius, which can multiply this effect.

4. Reduced acceleration. Larger wheels, even if they weigh the same as smaller wheels, are harder to speed up. [Further reading.]

5. Reduced gas mileage. Because of #4, your engine needs to work harder to accelerate the car. Highway mileage, where the car remains a constant speed, will be unaffected. However mileage in stop-and-go traffic will decrease.

6. Reduced integrity of the wheel mounts. Because of #1, #3, and #4, large wheels can actually put a dangerous load on the wheel mounts- the axle, hub, ball joints, bearings, and other load bearing parts.

7. Reduced integrity of the wheel. A larger wheel can be (be is not necessarily) more fragile. This is due to a manufacturer not increasing the spoke and rim strength proportional to the increased forces exerted on the wheel. This might be done to save cost or weight. To compensate, large wheels can be forged or pressure-cast, but this makes them expensive. Even forged 19" wheels are still heavier than most inexpensive, cast 17" wheels, and not necessarily as strong.

8. Increased ride harshness. Without much sidewall on the tire, the tire can no longer absorb bumps. It will try, however- low profile tires have very soft sidewalls to compensate. A soft sidewall will tend to deform, which is one of the reasons low-profile tires tend to require wider wheels.

9. Increased chance of tire bubbles, blowouts, and/or wheel damage. Since the low-profile tire cannot absorb as much impact, the entire combination becomes more delicate. This risk is increased by running a narrow tire.

10. Decreased ride quality. Larger wheels often (but not always) increase unsprung weight. Ride quality is largely determined by the car's sprung to unsprung weight ratio, where a larger ratio is better. A car with heavy wheels will need to run softer springs (hence increasing body roll and dive) to maintain the same ride quality.

11. Price. Large wheels are expensive. Since most 19" wheels need to be forged for reasons of reliability, they can cost two to four times as much as a 16-17 inch wheel.

12. Price. Large tires are expensive to continually replace. This can amount to roughly a $150-$300 savings ever few years- that adds up! All for the exact same width of tread.

Some plus-sized wheel combinations do give excellent grip, turn-in, braking, and overall handling improvements. This is not from the larger diameter of the wheel- it is despite the larger diameter. Those attributes are best improved by purchasing stickier rubber (more aggressive tires) on WIDER wheels.

Wider Wheels:
Moving to a wider wheel on the stock diameter (16" or 17" on the Mazda6) can provide great handling improvements.
It helps the tire's sidewall gain leverage in resisting cornering forces.

To achieve the same sidewall stiffness on a car with a skinnier wheel, the air pressure must be increased. Increasing air pressure has several undesirable effects, thus it is better to gain sidewall stiffness via a wider wheel.

The Mazda6 can accommodate an 8" wide wheel.
The benefits of a wide wheel are mostly limited to handling.
Acceleration and braking may degrade slightly if the wheel's weight has risen, though to a smaller extent than it would with a larger diameter wheel.

Much like large wheels look from the side, wide wheels look tremendously imposing from behind- so it's an aesthetic upgrade too.

The Real Upgrade: Tires!
Of course, the biggest upgrade for the Mazda6 is not the wheel- it's the tire. Upgrading to a tire with softer rubber will do wonders for improving cornering grip and braking distances.

A stiffer sidewall can drastically change the handling characteristics. In short, tires can make a world of difference and get you the performance you want- often without an expensive wheel upgrade. Tires are the single biggest upgrade you can buy for the car.

In fact, the most compelling reason to buy new wheels is to mount a second set of tires on them- have a set of winter and summer tires. Or all-season and competition tires. Either way- don't skimp on tires. Ever. [Further Reading.]

Next time you a car pulls up next to you with 19's catching your eye, enjoy how nice they look. In your rear-view mirror, that is, before they disappear in the next turn.