Running larger size wheels or wider tires is the best way to get the additional traction you need for your car or improve vehicle aesthetics. It may seem intimidating to run something different from a factory setup, however, once you understand how the mechanics work, it’s very simple and straightforward. Let’s look at the below and understand what to consider when running larger-size wheels and tires. If you are just learning about tires, it is recommended to read this article to understand the basics of tire size.
First and foremost, the new tires need to physically fit within wheel wells. For example, a 285 wide 20” tire can fit on the front of a Nissan GTR, however, it will not fit the front of a Toyota Corolla. The wheel well on a Corolla physically does not have space to fit a 285 wide 20” tire. Therefore, depending on what car you have, the tire size selection is different. At Forgelite Wheels, we will recommend tire sizes to work with our recommended wheel sizes for a worry-free fitment.
This is important to consider if you are running a staggered setup (different size front and rear wheels and tires. Read more about it here). Let me explain why. But first, we need to understand what tire rotational circumference is.
The rotational circumference is the circular length of the outer edge of a tire. It is calculated using the overall diameter of the tire including sidewall thickness. It determines the distance traveled when the tire is rotated one round. The same diameter and width tires with a different sidewall profiles can have different circumferences. For example, between 255/30/R20 and 255/35/R20 tires, the 30 profile tire has a side wall thickness of 3” (255*0.3=76.5mm=3”), and the 35 profile tire has a side wall thickness of 3.5” (255*0.35=89.3mm=3.5”). After some math we will find that the one with a 30 profile has a circumference of 2075mm/81.7”, and the one with a 35 profile has a circumference of 2156mm/84.9”.
Modern cars have sophisticated traction control systems, which help drivers to regain control when cars lose traction on the road by reading speed differences on each wheel. When there is a difference in the traveling speed of the front and rear wheels (like in the case mentioned above), the car might think some of the wheels have no traction and start intervening and cutting power to the wheels. Therefore, it is recommended to stay close to the factory rotational circumference difference to avoid any issues with traction control systems. Different manufacturers and car models have different tolerance limits when traction control will kick in. However as long the new wheel and tire sizes are within the system limit, you will have no issues. The best way to know what tires will work is to browse car forums and see what’s working for other people.
BMW’s Xdrive has a tolerance of 1% which means as long as the difference in tire circumferences in the front and back is within 1% difference, the Xdrive system will not detect traction loss and will not kick in. For example, a 2022 G80 M3 has a factory tire size of 275/35/R19 and rear 285/30/R20. The front tire circumference is 83.5” and the rear is 83.9”, the overall difference is 0.4%. It’s possible to upsize to front 285/30/R20 and rear 295/25/R21. The new setup has a circumference difference of 0.4% (83.9” vs 84.2”) which is within the limit and the same as the factory, therefore these sizes will work well. A handy website to use is Tiresize.com (https://tiresize.com/comparison/) which the calculator can show you all the calculation results by simply typing in tire sizes
