What is the 3% rule on tires?
The 3% rule states that when replacing tires, the new tire’s diameter should not differ from the original by more than 3%. This guideline helps maintain proper vehicle performance, safety system functionality, and speedometer accuracy. Only tire sizes recommended and approved for the specific rim size and/or vehicle year, make and model can be safely used. If in your circumstance a shop incorrectly specified tires for your vehicle they are obligated to take the tires back and offer a full refund.It’s highly recommended to use the exact tire size recommended for your car. However, in a pinch the tire width and aspect ratio can be changed slightly and still fit on your rim. Although this will still work, keep in mind it may have adverse effects on the performance of your car.
What is the 105% rule on tires?
A common guideline is the “105% Rule”: The external rim width should be at least 105% of the tire’s actual inflated width. This ensures that the rim controls airflow better than the tire, maintaining laminar flow. For example, if your 28mm tire inflates to 30mm, the rim should be at least 31. The Rule of 105 states that for a wheel-tire system to be aerodynamic, the rim’s external width should be at least 105% of the tire’s measured width. In other words, the rim needs to be wider than the tire to reduce drag and improve airflow.