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Factors to Consider
Moving to a larger wheel is a simple way to improve the look of your automobile, especially now that low-profile tires are all the rage. It can also help with performance: a shorter sidewall flexes less during turns, keeping grip, while a wider tire enhances lateral stability. Switching to a larger wheel might provide you access to a wider range of tire options, especially for performance versions.
There are, however, certain tradeoffs. Because tires are lighter than wheels, weight increases as wheel size increases. This has a detrimental influence on fuel efficiency and acceleration and makes steering more difficult. The car's ride is additionally rougher due to the shorter sidewall, which provides less cushioning.
When making tight bends or when the suspension bottoms out, the tires may rub against the fender well if the replacement wheels and tires are larger than the originals. Because speedometers measure speed by calculating the distance traveled for each wheel spin, a change in size might result in an erroneous readout. The factory diameter and breadth of the wheels and tires must be maintained to keep the suspension and speedometer working properly.
It's safe to put a tire up that's 20mm wider than the original rim’s stock as a general rule of thumb. The rim width will determine the actual width of the tire. For every half-inch increase in rim width, the tire will expand 5 millimeters.
Tire sizes are a combination of percentage and metric system measurements, but wheel sizes are in Imperial standards; therefore, switching to a new rim becomes a little trickier, which is another reason why you should stick to your OEM rims. Also, if the rims are wider than the stock, it might not have enough clearance for the steering arm or ball joint for that additional width and could possibly rub the fender as well.
While you can get wider tires on stock rims, as mentioned earlier, there are certain factors that you will need to consider, which can be confusing for first-time car owners. Here, we will break down the entire process of getting wider tires on stock rims the right way.
The speed category at which a tire can carry a load under defined service circumstances is indicated by its speed rating. The current speed rating system was created in Europe in response to the necessity to regulate tire performance at uniform speeds.
A tire's official speed rating ranges from 3mph to over 186 mph and is represented by a letter from A to Z. This rating system describes the highest speed at which a tire is approved. It does not represent a tire's overall performance capabilities. The Unlimited V category of over 130 mph was the greatest speed rating a tire could obtain when this speed rating system was first introduced.
As additional tires that did not fall into this category were produced, it became important to effectively control performance at specific speeds to maintain safety. The Limited V category was formed, with a peak speed of 155 mph, and the Z speed rating was considered the highest speed that a tire could attain. As higher speed categories, the W and Y limited symbols were introduced.
You should always check Unlimited Z tires’ maximum speed with the manufacturer. The tire's speed rating is listed as part of the size or service description. All grades except Unlimited ZR combine the speed symbol as well as the load index in the tire's service description in the most recent attempt to standardize tire designations. When you decide to get wider tires, it is important to keep this factor in mind to get the most bang for your buck.
Tire Rolling Resistance
Traditionally, rolling resistance has been assessed using the SAE (Society of Automotive Engineers) test technique J1269. It determines how much force is necessary to roll a tire against a dynamometer at a constant speed of 50 miles per hour. There are almost 1,300 truck products in the Bridgestone brand alone, with each one potentially having a variable rolling resistance. The tread compound is important, but so are the structure, size, and even tread pattern.
To get a decent average, at least three tires must be run in each combination. This translates to 3,900 hours — or more than six months — simply to run the Bridgestone brand, assuming one hour each rolling resistance test. This explains why these figures are based on guesswork. We do have some information, but it seldom corresponds to the sizes or patterns requested. As a result, an estimate is necessary. These figures are based on estimations from non-profit groups. Rolling resistance is not measured by many tire outlets, so make sure you find out the rolling resistance of the tires you will purchase.
How Much is Too Much?
The contact patch — specifically, how much of the tire meets the ground at any given time — is one of the reasons why people choose bigger wheels and tires. Perhaps you've updated your engine for more power, and now your tires are bursting at the seams simply by staring at them funny. To use that more power for something other than crazy burnouts, you'll need greater contact with the ground (and hence more grip).
The contact patch of a tire may be made larger in two ways: making it longer or broader. The total diameter of the tire grows as the tread patch lengthens. This works better on a four-wheel-drive vehicle, but most passenger automobiles will benefit from the increased tire diameter. This works better on a four-wheel-drive vehicle, but most passenger cars will have issues if the tire diameter is increased. First and foremost, there's the obvious problem. The tire may rub against other sections of the vehicle, such as the wheel well.
Second, when the total tire radius increases, the car's effective gearing increases, robbing it of acceleration. In most cases, gear ratios are expressed as "4.10:1." The greater the first number, the more the gear multiplies the input torque, which eventually spins your wheels. The problem is that rotating a tire with a greater diameter takes longer.
On a four-wheel-drive vehicle, this works well, but most passenger cars will have issues if the tire diameter is increased. The first problem is self-evident. Other elements of the vehicle, such as the wheel well, may be rubbed by the tire.
Second, the car's effective gearing becomes taller as the entire tire radius increases, robbing it of acceleration. "4.10:1" is a common format for gear ratios. The greater the first number, the more the gear doubles the input torque that turns your wheels. On the other hand, a wider diameter tire takes longer to rotate.
About The Author
I've spent many years selling cars, working with auto detailers, mechanics, dealership service teams, quoting and researching car insurance, modding my own cars, and much more.Read More About Charles Redding