Gearing Vs Tyre sizes.

[mike_nofx]

Just trying to work something out here. Are tyre sizes proportional to t/case gearing?

I tried searching sierra bible, but the "tcase info" link no longer works.
From memory (and im probably totally wrong here) the stock low range transfer case gearing is 2.5ish:1 ratio.

So for stock 26" (2075mm circumfrence) tyres, 2.5ish:1 is the correct low range gearing.

I have 33" tyres, with an actual circumfrence of 2541mm. This means they are roughly 25% larger. Would this mean that t/case gearing would only need to be 25% lower to be equal to stock?

I'd like to know, because when i bought my sierra it already had 4.2:1 Low range gears (not sure what kit, i only know its about 4.2:1 because ive counted the turns from input/output shafts)
Just want to make sure its at least equal to, or lower than stock gearing.

Feel free to correct any mathematical errors.

Thanks
Mike

[Gwagensteve]

Yes, you gearing is lower than stock, even taking the tyres into account.

Sierras need lower than stock gearing anyway, and when you add a larger tyre you are not just making the gearing taller, you are also adding traction and increasing rolling resistance, which is why it's never wise to aim to just correct the diameter increase.

Steve.

[GRPABT1]

And even if you do want the low range to be equal to be stock the high range is going to suck badly then.