"Minus One" and "Minus Two" Conversions

For cars with low profile tires, it is often a good idea to downsize the diameter of the wheels by an inch or two when the time comes to fit winter tires. Low profile winter tires are not only hard to find and expensive, they're also less effective and facilitate the buildup of snow inside the wheels.

Wheels of a smaller diameter should always be shod with taller (higher profile) tires to keep the rolling diameter, the diameter of the wheel / tire combination, constant for the following reasons:

  • to allow the speedometer and odometer readings to remain accurate;
  • to prevent the engine from running at too high an RPM at a given speed;
  • to ensure that suspension operation is not adversely affected.

Making a "minus one" conversion means fitting a one inch smaller wheel with a suitably higher profile tire to keep the correct rolling diameter, while a "minus two" conversion involves a two inch smaller wheel with an even higher profile tire.

One clue: the easiest way to fit smaller winter wheels to your car is to go to the smallest (usually the standard) wheel offered by the manufacturer as original equipment for your vehicle.

IMPORTANT NOTE: Making a "minus one" or "minus two" conversion is not to be taken lightly. You should consult a specialist and / or your dealership before fitting wheels or tires of a different size to your car. Also, you should always follow the recommendations made by the manufacturer of your car. Fitting improper wheels to your automobile could cause mechanical problems and could result in an accident.

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Buying Larger Wheels: "Plus One" and "Plus Two" Conversions

If you intend to fit winter tires to your car, have a look at minus one and minus two conversions.

If you are planning to fit wheels of a larger diameter to your car, you must equip them with lower profile tires. And if you are thinking about buying lower profile tires, you will also have to buy larger wheels. Why? Simply because the rolling diameter, the diameter of the wheel / tire combination, must remain the same for the following reasons:

  • to allow the speedometer and odometer readings to remain accurate;
  • to prevent the engine from running at too low an RPM at a given speed;
  • to prevent the tires from rubbing in the fender wells;
  • to ensure that suspension operation is not adversely affected.

Making a "plus one" conversion means fitting a one inch larger wheel with a suitably lower profile tire to keep the correct rolling diameter, while a "plus two" conversion involves a two inch larger wheel with an even lower profile tire.

IMPORTANT NOTE: Making a "plus one" or "plus two" conversion is not to be taken lightly. You should consult a specialist and / or your dealership before fitting wheels or tires of a different size to your car. Also, you should always follow the recommendations made by the manufacturer of your car. Fitting improper wheels to your automobile could cause mechanical problems and could result in an accident.

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Conversion Applet

Plus one conversion? Minus One? Plus two, or minus two? Here is an applet that takes the hassle out of calculating the aspect ratio of the tires to be fitted on wheels of a different size to keep the same rolling diameter.

Simply input the diameter of the old and new wheels, the tread width of the old and new tires, the aspect ratio of the old tires and voilà! the aspect ratio of the tires you need will be revealed.

ONLINE SOON!

DISCLAIMER: You should always consult a specialist and / or your dealership before mounting wheels or tires of a different size on your car and you should always adhere to the manufacturer's recommendations. Fitting improper wheels or tires to your automobile could cause mechanical problems and could result in an accident.

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