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Customizing Your Vehicle Can Help or Hurt Performance

Automobile enthusiasts have always been on the lookout for ways to customize their vehicles, but these days, it’s not just “tuners” or car lovers who are looking for a way to set their car apart. Now that your average consumer has become accustomed to customizing everything from a coffee beverage to blue jeans, they are also taking an interest in personalizing their vehicles.

One of the easiest ways to customize your vehicle is changing the size and look or tires and wheels. When done properly, changing tires and wheels is one of the easiest ways to improve the looks and performance of your vehicle. When performed incorrectly, however, it can cause undesired changes to the speedometer and odometer, anti-lock brake reaction, braking distances, acceleration, suspension wear and fuel consumption.

In this article, we’ll explain the appeal of increasing tire size and share some tips that can help you end up with the best results for the look and performance of your vehicle.

First of all, why size up? Is bigger always better? The term “Inch Up” is the process of mounting tires that are wider and have a shorter sidewall. The result is a wider contact patch and a sportier appearance. In addition, “inching up” can help improve your car’s steering response, handling and cornering.

Inching up works by increasing the rim size of your wheels by one inch, and then adding a tire with a lower aspect ratio or side profile so that the overall diameter of the tire is maintained. This creates a wider contact patch with the road and a shorter sidewall, yet allows the speedometer to read accurately and your vehicle to perform as well or better than originally designed.

Inching up provides a lot of bang for the buck if you’re looking to improve the performance of your vehicle and if you’re after a sportier look. Because the wheels and tires are relatively easy to switch out and are among the most visible parts of a car, inching up offers the consumer a quick change that yields a big impact both in looks and drive feel.

How much is too much?

It’s important to remember that a lot of engineering went into the original design of your vehicle. The weight and size of your rims and tires were carefully calculated in regards to how it affected suspension, braking, acceleration, gearing, and more. So, drastic changes could result in lost performance. Mounting a set of heavy rims and tires on your vehicle would be like swapping running shoes for hiking boots before running a marathon. It can add stress everywhere and significantly hinder performance.

More specifically, consider how tire and wheel weight affect on your vehicle’s unsprung weight. Sprung weight is the weight supported by the springs (that is, the vehicle's body, frame, motor, transmission, interior, fuel, and passengers). Unsprung weight is that portion of a vehicle that is not supported by the suspension (i.e. wheels, tires and brakes). Unsprung weight is most susceptible to road shock and cornering forces and, as a result, is one of the most critical factors affecting a vehicle's road holding ability.

Heavy rims, such as the popular spinning rims that continue to spin even when the car is not moving, add weight that not only slows acceleration, but also diminishes steering responsiveness and handling. Since rims are part of the "unsprung" weight of the car, reducing unsprung weight minimizes the load placed on controlling the motion of the wheels and tires. This means that suspension springs and shock absorbers will have a greater reserve capacity to control body motion, resulting in better vehicle handling. So while you’re upsizing your tires, don’t forget that no matter how great your tires look, it’s their function that’s paramount.

The standard plus sizing ratios are the following:

Plus 1 - increases the rim size by one inch, in conjunction with a tire with increased section width (tire width from side wall to sidewall) and lower aspect ratio (the ratio of the tire’s section height to it’s section width). A tire with a lower aspect ratio will have a lower side profile. Note: that this may require a replacement wheel to maintain proper rim width for the new tire. This option is best for those who want better handling and cornering without losing much fowl-weather grip. Ride comfort may suffer and costs for tires and wheels are significant even at this level.

Plus 2 - increases the rim size by two inches, in conjunction with a tire with increased section width and two-step lower aspect ratio. This option is best for those who value style and dry-weather grip over all-weather performance. Ride comfort and all-weather grip decline and you also run a greater risk of damage from potholes and curbs.

Plus 3 - increases the rim size by three inches, in conjunction with a tire with increased section width and three-step lower aspect ratio. This option is best for warm weather drivers who want even more style and are willing to pay for it. With this upgrade drivers needs to be especially careful through puddles and potholes and curbs are potential sources of tire and rim damage.

In all cases, the original diameter of the replacement tire must be equal to or less than the original equipment tire for your vehicle. Also, the load capacity must be equal to or greater than the original equipment tire for your vehicle. Consult with your tire service provider to make sure these requirements are satisfied.

Should you decide to go with plus upgrades 1 through 3, be aware that these upgrades always require a replacement wheel. With any upgrade, make certain that there is enough clearance within the wheel well to accommodate the new tire. All vehicles often vary in clearance measurements. Over time, the suspension may sag causing a change in tire clearance. Make sure you visually inspect tire and fender clearance when the steering wheel is in it’s fully locked position. Tire clearance should also be examined when the suspension system is in its fully compressed position.

The safest route is to replace tires originally installed by the vehicle manufacturer with the same or comparable tires. Speed ratings should always be equal to or greater than the original equipment tires for your vehicle. However, if you choose to significantly change the size, follow the guidelines of this article and consult with your local tire service provider your same old car will feel like a brand new ride.