What is the 3% rule for tires?
The 3% tire rule is a guideline for upsizing tires. It recommends keeping the new tire’s diameter within 3% of the original to avoid affecting performance and safety. 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.
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. 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.