Quantifying Speedo Difference for Tire Differences

[moshe_levy]

All-

 

I recently replaced my car's OWM 195/55-16 tires with more readily available and much less expensive 205/55-16 models. I know tis has some extremely small impact on the accuracy of my speedo / odo. I was wondering if someone out there knows how to accurately compute exactly what this difference would be. I'm not sure of the formula to use and math ain't my thang.

 

-MKL

[Paul Mihalka]

It is quite simple if you know what the numbers mean. The "16" is the diameter of the wheel in inches. The "195" is the width of the tire in millimeters - I know it does not make sense. The "55" means the percentage of the height of the tire in relation of the width. So the total height of the tire is: radius (1/2 of diameter) of the wheel 8" = 203.2 mm, height of the tire is 195x.55 = 107.25 mm, total height = 203.2 + 107.25 = 310.45 mm. Changing to a tire 205/55x16 adds 10 mm to the width and 10x.55 = 5.5 mm to the height. So the total height changes from 310.45 mm to 315.95 mm. That is a increase of 1.77% in size, = nothing. You get much more difference between a new and used tire, or brand of tires.

I know I gave details most of you know, but I wanted to make it clear just in case.

[moshe_levy]

Hi Paul-

 

Yes, I knew thee basic numbers. I just wanted a saninty check that this ~1.77% difference is a direct +1.77% translation to the speedo / odo reading. You think that's the case?

 

-MKL

[Paul Mihalka]

Hi Paul-

 

Yes, I knew thee basic numbers. I just wanted a saninty check that this ~1.77% difference is a direct +1.77% translation to the speedo / odo reading. You think that's the case?

 

-MKL

That is the case, and I consider it insignificant. You don't worry what you speedo difference is between a new and worn tire... A worn 205 will be smaller than a new 195...

[chrisd]

This might help. Can't attest to its accuracy.

[moshe_levy]

Thanks guys!

 

-MKL