Happy Pi Day And How It Matters To Your Car

Happy Pi Day! A day which celebrates the never ending number, π or 3.14 (as commonly rounded to in math). Why does this matter? Well, π is the ratio of a circle’s circumference to its diameter. And as we all know circles are a pretty important shape when it comes to cars, think wheels and tires. Now imagine you are looking at changing out your current wheels and tires for something new and wondering if they will fit within the confines of your wheel well.

Pi Day

Reading Your Tire

Your tires will tell you everything you need to know. The tires on the Countach are 225/50/15

225 = the width of the tire in millimeters
50 = the height of the tire’s sidewall as a percentage of the width. In this case it would be 50% of 225mm or 112.5mm
15 = the diameter of the wheel in inches

Determining Your Radius

The diameter is the length across a circle and the radius will be half that. You will want the radius and not diameter because it will allow you to measure out in every direction from the wheels center to determine your clearance within the wheel well.

In this case the radius of the wheel is 7.5-inches; however, you now have to add the tire’s sidewall to the equation. After converting the 112.5mm to inches you will have a sidewall of 4.43-inches and an overall wheel/tire radius of 11.93-inches. Meaning you will need a clearance all directions from center of 11.93-inches or greater.

Bonus Math!

With the 11.93-inch radius of the wheel/tire you can now determine your whole circumference using C=2πr.


Your circumference (or distance around your whole tire) is 74.9-inches.

[Ed Note: We know the “Golden Ratio” isn’t directly linked to π, but rather just liked the way it looked with the Countach.]


  1. richard super show , also good eats at gmgrill dallas visted last time in dallas , also still have that pinto in yard ?

  2. Great show, wish I had the funds to get a car built by you. For now I can only wish and dream. Although I love watching and seeing the cars that are built in your garage. Keep up the good work.

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