Quote:
Originally Posted by liljlandon
Thats factored in, the odo is off by 33%, so if i drive 20 on the odo im actually driving around 30. So i multiply my trip meter by 1.33 to get my actual mileage and divide by my gallons
usually i get 270-300ish off of 12-13gallons.
Also, once i factor in the difference of my original tire size it says my current axle ratio is 3.70
original 28
new 31
gears 4.10
new axle ratio 3.7032258064516123
Same as above using 4.88 gears
new axle ratio 4.4077419354838705
I actually come out a bit lower, which is what i want.
I dont think that the my tach is right, because according to that i should push 2800 rpm at 75 in 5th (.85) while i actually push more to the 3300 side.
4th (1:1) at 75 is 3332 while my tach says around 3800.
Can my tach be that far off?
Or have my gears been changed by the PO?
Ill check when ever my new seals get here from man-a-fre.
Thanks for all your help
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Doh, WDE beat me to it while i was looking for the color codes.
I'm confused by your math. With 31's, assuming you have a 4x4, you're not off by 1/3 on the spedo. Stock 235/75/15's are 28.9" so figure 29" to make the math easier. So one rotation of a 29" tire is 91". One rotation of a 31" tire is 97.34". So we're talking about a 9.3% difference. When you're spedo says 20, you're going 22mph, not 30. To get that far off you'd need 38.5" tall tires. I think that's why you think you're getting that good of mileage. Borrow a GPS and test it. I'm guessing you'll find your a lot closer to the spedo than you think.
If your engine is healthy, you should not have a problem with 31's.
I don't really care what you do, but I can tell you from experience that 5.29's work great for 35's and will be too low for 31's. That's what I had on my 84 pickup. And that's in Montana at 6,000 feet with mountain passes. I've also had 31's on my 84 stock with 4.10 gears and thought it was about right. I currently have 38's on my Landcruiser and 5.29's and they are actually a little low for highway cruising. It also had 4.11 stock gears.
Also, FYI, if you have stock gears you can check the ration by the color of the marking paint on pinion without pulling the 3rd members.
Table: Ring and Pinion ratios
Color
3.42 Purple
4.10 Pink
4.11 Orange
4.30 . . Blue . . .
4.37 Green
4.56 Yellow
4.88 White