We get a lot of questions about tire sizing, and we always want to make all those numbers on the sidewall make a little more sense. A tire's aspect ratio determines the height of the sidewall, which ultimately determines the overall diameter of the tire. The aspect ratio is a percentage of the section width. So if you have a 70-series tire, that means the sidewall height is 70 percent of the tire's overall width. Aspect ratio for most bias ply tires is somewhere around 80 or 90 percent. Numeric sized tires (such as 6.00-16 or 6.70-15) that end in zero feature a 90-series aspect ratio, while numeric sizes that end in five (such as 6.95-14) feature an 80-series aspect ratio. Alpha numeric sizes (such as F70-15 or G78-14) have the aspect ratio clearly stated in the size. Aspect Ratio Radial tires also have the aspect ratio clearly stated in the size. Here's an example: 205/75R15. The "75" is the aspect ratio, and it indicates that the tire's sidewall height is 75 percent of the claimed 205mm section width. For classic cars, high aspect ratios are common, but some muscle cars and custom applications feature a lower aspect ratio to stiffen the tire and provide better handling characteristics. 60-Series tires are popular for many '60s, '70s and '80s applications. Many modern cars have very low profile tires, but these modern tire and wheel combinations tend to be out of place on a collector vehicle. Figure out the correct aspect ration for your ride, and choose from our incredible product lineup! Aspect Ratio