After you’ve selected the style and material for your fenders, you need to pick the correct size for your specific setup. The perfect size is something that will “hug” your tires relatively closely while maintaining enough space to prevent any contact.
You need to have a minimum of 1.5” space on top and at least 0.5” on the sides. Anything less than that and you run the risk of your tires making contact with the product during normal operation of the vehicle.
First check the manufacturers recommended tire size for that specific model. Then you can confirm by checking your overall tire diameter against the manufacturers recommendations (if available).
When choosing the specific model, consider how much spray protection you need and how accessible you want your wheels and tires to be.
Don’t forget that the ‘lip’ on the side of the truck fender is great for blocking road spray but a larger lip will make it a bit more difficult to remove your tires.