So I had my Edge booklet but my smart girlfriend threw out the box for my Edge which also included my booklet. I have 306/65/18 BFG's if anyone knows it off by heart. Is it 3682mm? If not could someone post it!!

 

Using 305/65-18 as you provided in the example...

(Width x Aspect Ratio) x 2
(305 x .65) x 2 = 396.5 mm (this is total sidewall height)

Rim Diam. x mm per inch
18 x 25.4 = 457.2 mm (this is the diameter of the rim)

Sidewalls + Rim = Total Diameter
396.5 + 457.2 = 853.7 mm

Diameter x PI = Circumference
853.7 x 3.14159265 = 2682 mm

I have found that most tires will require what I call a "squish" factor to accurately correct for diameter change where the tire is squished from ground contact. This is usually about 3%.

2682 mm x .97 = 2602 mm

So for 305/65-18 tires, your should be at 2602 mm.

Take care.

Bill

 

hmm, squish factor. That's a new one - have to adds that to my vocabulary! :-)

Other than that - x2 on the calculation.

 

hmm, well since so much math was involved - perhaps I should clarify that by 'x2', I mean I agree - don't multiply anything by 2! :-)~

 

Thanks Bill!

LOL to be honest I suck at math and the first time I did that. I had to do the question like 6 times to get that answer.

 

Yeah, the math can get obnoxious. That's why I wrote this handy utility to do all the hard work for you. Just punch in the tire size off the side of the tire and you're good to go!

http://www.powerhungryperformance.co....htm#utilities

Right-Click and select [Save As], save to your hard drive and then install.

Enjoy.

Bill