Gear Logic...someone check me up on this and make sure I'm right

[BobCarter]

Allright. I am currently running 265/75/16...(31.6"'s) with 3.73 gears. My old tires were 235/75/15's...(28.8"'s). So...my new tires are about 10% larger. If i take my gear ratio and multiply it by 1.10 (for 10% more gears) I get 4.10...which tells me that 4.10 gears would be perfect for my X.....here in which lies my question. When I switch gears....theoretically wont that fix my speedometer error...b/c right now its off by 10% obviously. Also, wouldn't the new gears put my highway rpm's right back where they started when it was stock? I hope this makes sense to someone. I just wanted to check my bases before I did anything. Thanks, Bob

 

[Crankcase]

Simple answer:

If you put on bigger tires, 4.10 is perfect for you, the RPM's will be alot closer to original......

 

[Okrazie1]

Regearing will help put your truck back to its original RPM range, but it will NOT correct your speedo error. Your '99 uses the RABS sensor for speed data. The toothed ring used to activate the sensor is mounted to the differential. Changing the gearing does not affect the speed at which this ring rotates. I recently changed from 3.27 gears to 4.10's, and it did not affect the speedometer.

Earlier Explorers which use a cable driven speedo or a gear driven VSS attached to the transmission will have their speedo reading affected by a gearing change.

 

[Texan01]

You are correct in that changing the R&P won't affect the speedo reading on the new systems.

However bigger tires WILL change the speed at which the axleshafts and carrier spin at. So he'd have to get it re-calibrated to read correctly (assuming that it can be recalibrated) The shafts and carrier will spin slower, thus the slower speedo reading.

Changing gears changes how fast the driveshaft spins at a given speed/rpm ie. 4.10 gearset spins the driveshaft 4.10 times for each turn of the axleshaft.

Just my take on the situation.