Pirate4x4.Com : 4x4 and Off-Road Forum - View Single Post - *FAQ*What tcase gears should I (or you) buy?
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Old 02-08-2019, 12:36 PM   #22 (permalink)
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Originally Posted by Gwagensteve View Post
The speedo drive is on the output of the transfer case that means itís unaffected by anything upstream of the speedo drive- what gear the gearbox is in, what range the transfer is in, or transfer case reduction.

Itís only affected by whatís downstream of the speedo drive- axle ratio and tyre size.

Put bigger tyres on and the speedo becomes inaccurate. Change the axle ratio and speedo becomes inaccurate. Put the transfer case in low range and the speedo doesnít become inaccurate.

I canít explain it any more clearly.
I guess I just cannot wrap my head around this. If it's on the output of the transfer case, then putting lower gears in the case will slow the rotation of the output shaft. That should cause the speedo to read faster than you are actually going if all else is stock. Adding a larger diameter tire without changing transfer case gears would cause the speedo to read slower than actual speed is all else is stock. But if I slow the output shaft with TC gears AND increase the tire diameter with 33" vs 27" stock to go further on 1 revolution of the tires, they counter-act and I get a closer to accurate speedo reading. What part am I missing?
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