80 Series Gear Calculations

[ssssnake529]

I'm considering swapping out gears on my 80 Series. I did some calculations on the effects of 4.56 and 4.88 gears compared with stock gearing. I thought I would share for anyone else who is interested:


1st 2.95:1, 2nd 1.53:1, 3rd 1:1, Overdrive .765:1
High range ratio is 1:1 and low range ratio is 2.488:1
Tires: 285 75 R16 (32.83 inches)
Stock 4.11

Miles per hour (20mph to 75mph) plotted against RPM for each gear (Sorry, but I can't seem to make the columns line up right.

Stock 4.11

20 25 30 35 40 45 50 55 60 65 70 75
1st 2482 3102 3723 4343 4963 5584 6204 6825 7445 8066 8686 9306
2nd 1287 1609 1931 2252 2574 2896 3218 3540 3861 4183 4505 4827
3rd 841 1052 1262 1472 1683 1893 2103 2313 2524 2734 2944 3155
4th 644 804 965 1126 1287 1448 1609 1770 1931 2092 2252 2413



4.56
20 25 30 35 40 45 50 55 60 65 70 75
1st 2753 3442 4130 4819 5507 6195 6884 7572 8260 8949 9637 10325
2nd 1428 1785 2142 2499 2856 3213 3570 3927 4284 4641 4998 5355
3rd 933 1167 1400 1633 1867 2100 2333 2567 2800 3033 3267 3500
4th 714 893 1071 1250 1428 1607 1785 1964 2142 2321 2499 2678



4.88
20 25 30 35 40 45 50 55 60 65 70 75
1st 2947 3683 4420 5157 5893 6630 7367 8103 8840 9577
2nd 1528 1910 2292 2674 3057 3439 3821 4203 4585 4967 5349 3731
3rd 999 1249 1498 1748 1998 2247 2497 2747 2997 3246 3496 3746
4th 764 955 1146 1337 1528 1719 1910 2101 2292 2483 2674 2866

 

[Rallyroo]

So are you going with 4.56 or 4.88?

I have 4.56 gears with 255/85R16 tires to get back to near stock gearing.

 

[ssssnake529]

So are you going with 4.56 or 4.88?

I have 4.56 gears with 255/85R16 tires to get back to near stock gearing.

Probably 4.88. Lots of steep grades on the highways where I live, and being able to go uphill is perhaps more important to me than cruising at 75.

However, I still haven't made the decision, and may just do 4.56.

Do you like your 4.56 gears? Do you wish you had 4.88?

 

[Rallyroo]

Probably 4.88. Lots of steep grades on the highways where I live, and being able to go uphill is perhaps more important to me than cruising at 75.

However, I still haven't made the decision, and may just do 4.56.

Do you like your 4.56 gears? Do you wish you had 4.88?

-The Expo crowd will say 4.56 on 255/85R16 (33" tires).

-The IH8MUD crowd will say 4.88 since many of them run 35+" tires.

-Adventureduo will say 5.29 on 255/85R16 since the max speed he ever goes is 55 mph in his heavily loaded 80 plus he tows either a heavily loaded Adventure Trailer or Tear Drop all the time.


I like the 4.56. When I had the stock 4.11 there is this one grade that I'd have to take at 35-40 mph. Now with the 4.56 I can take it at 55-60 mph. I could of driven the grade at 60-65, but I like to take it easy on the grades. No need to burn fuel even faster. Offroad wise, in 4L I've driven up to 11,000' with ease. Perhaps my mind will change in the 12,000+' range.

On one of my trips I actually got 17.5 mpg (corrected mpg) while maintaining an average of 63 mph during the transit sections (as in highway and excluding offroad sections).

 

[taco2go]

Thanks so much for tabulating this information. I have been scouring the web for a similar comparision, for a while now, and never got around to asking for it here.

As a control for the stock grearing: Looks like you have bumpers and a roof rack, likely a suspension upgrade, other additions? and what tire size are you currently running ?

Edit- noted the tire size.