22re, 1 tons, 43s, and 4.56?

It's going to suck. I drove my Xtra Cab around Boone with a 22r on pane, 42's and 4.56's. I would start with the front case in low then shift 1-2-front case to high-3-4 never use 5th
 
Croatan_Kid said:
The speedo being off isn't constant. At some point, it's reading slow. Somewhere in the spectrum, it's actually correct. Eventually, it reads fast.

You absolutely can NOT trust your speedometer. However, your tachometer and math don't lie. Gear ratios are constants.

Gear ratio x speed x 336 (a given constant) = a number
Divide that by the tire size
Multiply by .85 (that's your overdrive ratio)

This gives you an RPM at whatever speed you plugged in to start with while you're in 5th gear.

7.17 x 78 x 336 = 187,911.36
187,911.36 / 42.5 = 4,421.444
4,421.444 x .85 = 3758.23

So, again: 78 MPH, 5th gear, 42.5" tire gives you 3758 RPM.


Your tires are rated for 62 MPH :driver:
Click to expand...
Actually, its always off a constant percentage, and if you can do simple percentages, it will be pretty darn close. The math is correct, but the first three statements are not. If your speedometer is showing 65mph, and you're actually going 78mph, its 78/65=1.2, so you are going 20% faster than your speedometer shows, whether it shows 1mph, 10mph, or 100mph (dream big :D)
 
You could both be right depending on what has been changed.
If youve just changed rear end gears or tire sizes Matt is dead on. Its a straight % deal.
However if youve changed the T-Case or Speedo gear and have a total different tooth count set Croatan would be right.
 
Ron said:
You could both be right depending on what has been changed.
If youve just changed rear end gears or tire sizes Matt is dead on. Its a straight % deal.
However if youve changed the T-Case or Speedo gear and have a total different tooth count set Croatan would be right.
Click to expand...
No, gears are gears are gears. They only know how to work linearly. Its measuring rotation rate of the t-case output via a gear or sensor. We're talking mechanical stuff here, not electronics :D
 
My old K30 reads all three.... slow, fast, and correct and one speed or another. It must be something in the speedometer itself...the magnet or something could be dragging :driver: It's a factory one, so it's not exactly a calibrated instrument :D I've noticed the same thing in my S10. Maybe it's a Chevy thing? I used a GPS speedometer to verify those readings. I just went 65 via GPS and whatever the speedo showed, that's what I always run in traffic.
 
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