Gear ratio for dummies

[99z28monster]

Stole this link from 4wheel parts figured it can help give folks a baseline idea on what gears to run.
http://www.4wheelparts.com/aux_incl/gear_ratio.html

 

[Greg]

looks like im good with 3.73s and 33s

 

[JohnnyRingo]

that chart is dumb 4.88s and 33s. says my chart.

 

[99z28monster]

how are yall getting such low numbers? I based a 31 inch tire with 3.73s stock, and came up with 4.56-4.88 for 35s

 

[Cajun4x4]

i got some plans coming that involve 4.88s and 35s

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[99z28monster]

i got some plans coming that involve 4.88s and 35s

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As do I. Gonna make low gears and small tires the new cool thing to do.

 

[Aloicious]

that chart is extremely dumbed down, it doesn't take into account anything from the transmission or transfer case, he says it assumes a 1:1 ratio. unless you're towing or something, who just straight up drives around in 3rd or 4th gear? and the transmission gear plays as big a role as the rear gears do. no to mention different setups will change the desireable RPM range by a ways, so simply stating that lower RPMs equal better gas mileage or that higher RPMs mean more power is completely false and totally setup dependant. if you know how your truck runs and where it makes its power you can figure out what gears to use much more efficiently than that chart.

for example, in my setup 3.73's are undergeared, but I've only got 28.8" tires, its because I've got a T56 with a .74 5th gear, and .5 6th gear. I barely turn 1400 rpm going 65 mph in 6th, which is too low and the truck just bogs in 6th anywhere below like 75ish rpm. and even at like 80mph where I'm at around 1750 rpm, it still isn't able to climb small inclines without being under pretty heavy engine load. so in my case, with 28.8" tires, 4.56 or 4.88's would be a much better choice. which is what I'm working on, 4.88's.

The correct formula to use for determining speed at a given RPM would be:
(RPM*Tire Diameter)/(differential ratio*Trans ratio*transfer case ratio*336)=mph

I've been looking at different gearing ratios and made a small spreadsheet to simultaneously compare several gears along with transmission setup. it won't let me attach a spreadsheet so I zipped it into a .zip file, if anyone is interested it may help out and is much more in depth than that graph from 4wheelparts. I have a 2wd, so none of the calculations include a transfercase ratio, so the spreadsheet wouldn't be accurate in like 4 low or something. but its could still be useful in 2wd or 4 high where the tcase ratio is 1:1

 

[Giiventofly]

this makes me want 4.88s baaad.

 

[6chevy9]

with my 5 speed im running the stock 373 gears and 33 inch tires and im pretty happy with it for the most part. it will break both rears loose into 2nd and still does awesome on the freeway.

 

[Cajun4x4]

As do I. Gonna make low gears and small tires the new cool thing to do.

werd...


dont fear the gear

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