[aardvarcus]

Big Dave,

As you compare inertias based on diameter, don’t forget that a larger diameter does not require the same angular velocity to achieve the same speed. Also the different diameters may also have different weights. I built an excel worksheet to compare wheel and tire combinations on my Tacoma. My goals were somewhat different, as I wanted the reduced gearing (jealous of your auxiliary overdrive) and wanted increased ground clearance.

What I ended up using to get accurate comparisons was the net kinetic energy stored in a wheel and tire combination at a given road speed. (I used 60 MPH) I believe this is the best and most accurate way to compare apples to apples when it comes to wheels and tires, as it accounts for the differences in weight, diameter, inertia, angular velocity, etcetera.

I went into my chart, which is based on the actual specs of Michelin LTX M/S 2 tires, and sorted it to show LT tires on 16” wheels in the sizes you were interested in, and a few other sizes for comparison that others may find interesting. I attached a screenshot of my chart, I couldn’t figure out how to paste a table without the formatting going bonkers. I would pay attention to the lines “Comparison Inertia” (which is actually Comparison Net Kinetic Energy) and Comparison Diameter which addresses gearing.

Note I have this set up to compare the other options to your current setup, 235/85R16s, which ironically is what I am running on my Tacoma. It looks like the 215/85R16s give you a 7.24% decrease in net kinetic energy while only reducing your diameter by 4.1%, so your gearing is not as affected. The 225s decrease your net kinetic energy 8.17% so slightly less, but they hit your diameter by 7.89% so your gearing is reduced more.