Plus sizing is the practice of replacing an automotive wheel with one of a larger diameter fitted with a new tire of lower

aspect ratio The aspect ratio of a geometry, geometric shape is the ratio of its sizes in different dimensions. For example, the aspect ratio of a rectangle is the ratio of its longer side to its shorter side—the ratio of width to height, when the rectangl ...

so that the new tire has close to the same diameter and circumference as the original tire to minimize any changes in

speedometer A speedometer or speed meter is a gauge (instrument), gauge that measures and displays the instantaneous speed of a vehicle. Now universally fitted to motor vehicles, they started to be available as options in the early 20th century, and as ...

accuracy, torque and

traction control A traction control system (TCS), is typically (but not necessarily) a secondary function of the electronic stability control (ESC) on production motor vehicles, designed to prevent loss of traction (i.e., wheelspin) of the driven road wheels. TCS ...

, while reducing sidewall flex and (generally) increasing cornering ability. The number following the "plus" describes the number of

inch The inch (symbol: in or prime (symbol), ) is a Units of measurement, unit of length in the imperial units, British Imperial and the United States customary units, United States customary System of measurement, systems of measurement. It is eq ...

es which is added to the diameter of the

rim Rim may refer to: *Rim (basketball), the hoop through which the ball must pass **Breakaway rim, a sprung basketball rim * Rim (coin), the raised edge which surrounds the coin design * Rim (crater), extending above the local surface *Rim (firearms) ...

. For example, ''plus one'' sizing means increasing the wheel by – i.e. from a rim size. A "plus zero" upgrade means changing to a wider tire size while using the same diameter wheel. Changing to a wider tire requires reducing the aspect ratio (the second number in the sequence of numbers that describes the tire's size). Since the aspect ratio is a percentage which is used to calculate the height of the tire's sidewall, if follows that is a larger number is used for the width, a smaller number must be substituted if the final result is to remain the same—which is the objective of Plus sizing.

Plus sizing example

These are simply examples and do not represent all the possible combinations which could achieve the same result. For an R16 tire, 195/65, 205/60, 215/55, 225/55, 235/50, 245/50, 255/45, 265/45, 275/45 and 285/40. width/aspect ratio tires have essentially the same diameter. The exact dimensions of tires in the same size might differ slightly depending on tire brand, model, etc.

Advantages

* Larger tires improve handling and cornering, due to wider tread faces and stiffer sidewalls. * Wider tires may decrease

braking distance A brake is a mechanical device that inhibits motion by absorbing energy from a moving system. It is used for slowing or stopping a moving vehicle, wheel, axle, or to prevent its motion, most often accomplished by means of friction. Background ...

s on dry pavement. * Wider tires may also increase acceleration, especially in very powerful vehicles such as muscle cars. * Larger wheels with lower profile tires are sometimes aesthetically desirable.

Disadvantages

* Larger wheels typically cost more. Wider tires tend to be more expensive because they are less common, and there is less competition between brands. * Performance improvements beyond what is achieved in a Plus One sizing are often minimal. * Lower profile tires tend to have stiffer sidewalls, which might decrease riding comfort. * Low profile tires are likely to sustain more damage to tires and wheel rims when encountering

road debris Road debris, a form of road hazard, is debris that accumulates on or off a road. Road debris includes substances, materials, and objects that are foreign to the normal roadway environment. Debris may be produced by vehicular or non-vehicular sour ...

and

pothole A pothole is a pot-shaped depression in a road surface, usually asphalt pavement, where traffic has removed broken pieces of the pavement. It is usually the result of water in the underlying soil structure and traffic passing over the affecte ...

s. * Larger and wider wheels decrease

fuel efficiency Fuel efficiency (or fuel economy) is a form of thermal efficiency, meaning the ratio of effort to result of a process that converts chemical energy, chemical potential energy contained in a carrier (fuel) into kinetic energy or Mechanical work, w ...

and increase consumption. A test done on Volkswagen Golf 2.5 saw a 10% decrease in

from 23.3 to 21.1 U.S. miles per gallon (from 10.1 to 11.2 liters per 100 km) in a Plus Four sizing. * Larger and wider wheels may also degrade acceleration on many everyday vehicles. The test done on a Volkswagen Golf 2.5 saw a 0.3 second degradation in acceleration from 7.6 seconds to 7.9 seconds in a Plus Four sizing. Although this is likely caused by the weight difference, per corner, in "unsprung weight". * A larger tire-footprint can increase the time taken for "return to center" (steering) after taking a sharp turn.

Controversial issues

Some people claim larger wheels wear faster. Wheels with reduced sidewall heights may increase risk of damaged rims, breaking the bead, and/or damaged sidewalls. The increased width of the contact patch of wider tires may increase the risk of hydroplaning. Plus sizing tires may enhance the vehicle's value. Improving the vehicle from the factory specifications may increase value. The additional height and weight of plus-sized wheels may reduce vulnerability to rollovers, particularly by changing the center of gravity. During rapid tire deflation at speed, reduced sidewall height may decrease rollovers. Total wheel weight (tyre & rim) represents ”unsprung“ weight. Standard fit wheels and tyres tend to have less unsprung weight than oversized rims and tyres. With less unsprung weight, the shock absorbers and dampers are much better able to control the lower inertia and consequently, the vertical “bounce“ of a wheel over a bumpy road surface, resulting in better and more consistent tyre contact with the road surface.

External links

Effects of Upsized Wheels and Tires Tested, Car and Driver, April, 2010

Compare Two Tire Sizes

Wheel Tech, Part III:Wheel Diameter's Effect on Performance, Tuner University.com

References