I'm interested in seeing how much of a difference, if any, tire size has on final drive ratio

NOTE: I did numerous searches without much luck, so if this has been covered already, sorry

I am going to be switching from stock size tires (195/55-15) to 195/50-15 Yoko ES100's.

Overall tire circumference with stock tires is 73.654 inches. The new tires will have a 71.242 in. circumference. Which equates to a 3.27% reduction in overall diameter.

What % will this change my final drive ratio (4.40) ? Is it a likewise 3.27% change?

It is my understanding that decreasing the tire circumference will lead to an increase in final drive ratio. Is this correct?

Basically, my question is what will the final drive be equivalent to now with the smaller tires? Something noticable, like 4.5-4.6, or not as much?

Thanks in advance

 

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Multiply the drive ratio by the amount of change. 4.40 x 1.0327 gives about 4.54. Don't forget that your speedo will read the same amount high. If 60 was really 60, then 62 will now be 60.

 

Right on the arithmetic, but not on the terminology. The 'final drive' ratio doesn't change. It's still the gear ratio for the differential gearset. What changes is just the tire diameter. Gearing & final drive simply say how many rpm your wheels are turning - you haven't changed that.