gears and tires

[Pipanski]

So I'm trying to figure out a good gear size for when I ever get to put 33's on my truck and I was looking at this

I have 29 inch tires and 3.55 gears on my truck now and this chart says that in 4th gear I should be turning about 2674 rpm at 65 mph. I was on the interstate the other day and stayed in 4th gear till about 50 mph....and was already turning 3000 rpm! Something doesn't seem right. I don't understand. Is the chart incorrect? I just got the truck a little over a month ago and I don't believe the gears have been changed. If they were judging by this chart I would have probably 4.56 or even higher gears!

If anybody can straighten this out for me I would appreciate it!

 

[rickcdewitt]

my 91 is like that.the tach is a little off.also if you run 4.10 gears(you can get whole 4.10 axles at the junk yard) with 33's your speedo will be plus or minus 1mph from dead on with your factory 3.55 speedo gear.

 

[Pipanski]

Thats not a little off....thats a whole hell of a lot off...

If the tach is off by any amount....I would have to say maybe 200-300 rpms...not 2000ish lol

 

[Hjcraver]

You say you were checking in 4th gear . Your Transmission is a 5 speed . What is the ratio of you tranny in 4th gear ? How does that ratio compare to the chart you have?

 

[Pipanski]

This chart is based on 65 MPH and a gear ratio of 1:1, on a manual transmission in 4th gear.

I was going off of this which is on the page with the chart. Even in 5th gear at 65 IIRC my rpm's are higher than what they should be compared to this chart in 4th gear.

This is just all really confusing because I am new to the whole RWD gearing deal and am trying to figure out which gears to get when/if I ever get my 33 inch tires. I think I've narrowed it down to 3.73-4.10...but I still need to sell my escort in order to buy the $1600 SL and not be completely broke lol.

 

[4byRANGER]

if your still thikin about 4.56 gears, ill tell you first hand it was absloutely the best investment so far for my truck with 33inch nitto grapplers
on the freeway at 65-70mph my engine turns at 2000-2200 rpms
and offroad the extra tourqe helps so much

hope this helps!

 

[kunar]

ill tell you the same thing i tell everybody else. i have 4.10 gears with ~28" tires. i have no problems at all and i get better mileage than my other truck with the same engine and trans, 3.73 geared. go 4.10's atleast. your indecision should really be between 4.56 gears and 4.88 gears. go lower if you arent sure. if you decide you want bigger tires in the future, you will be happy you took my advice. on top of that, im pretty sure linuxman had 4.56 gears with stock tires before he sold his truck, and he commented on better mileage.

 

[Ranger44]

With the 4.0 I'd say either 4.10's or 4.56's. You can find 4.10's in junyards, but if you want plenty of offroad power and on-road get up I'd go 4.56's. I'd go 4.56's personally, because there is always that chance you may want to go to a slightly bigger tire some day and you don't want to pay again to get a lower gearset.

 

[Hahnsb2]

4.56 for 33s if I was going to bother re-gearing but if your looking for whole axles to swap then 4.10s.

 

[4x4junkie]

It sounds to me like the tach is off also.

One way to check your gears is to jack up ONE rear tire, and give it TWO complete revolutions while counting how many turns the driveshaft spins. 3-1/2 turns = 3.55 gears, 3-3/4 turns = 3.73, 4.1 turns = 4.10 and so on.
(the above method won't work if you have a locking diff, in this case, jack up both tires and give it one turn while counting the driveshaft turns)

Another is to pull the diff cover and count the teeth on the ring & pinion gears and divide by the pinion teeth. 41 ring / 11 pinion = 3.73, 41 ring / 10 pinion = 4.10 and so on.

I agree with the others, go with 4.56 with 33" tires on your 4.0L.

 

[94rangerxlt]

same situation

Figured this would be a good spot to ask...
what would be a good brand and from where?
also, what price could i expect for front and rear?
I'll be running 33's on a 4.0L auto.


thanks

 

[linuxman2003]

ill tell you the same thing i tell everybody else. i have 4.10 gears with ~28" tires. i have no problems at all and i get better mileage than my other truck with the same engine and trans, 3.73 geared. go 4.10's atleast. your indecision should really be between 4.56 gears and 4.88 gears. go lower if you arent sure. if you decide you want bigger tires in the future, you will be happy you took my advice. on top of that, im pretty sure linuxman had 4.56 gears with stock tires before he sold his truck, and he commented on better mileage.

Indeed I did 4.56 gears with 235/75 tires, ran about 3200rpm's at 70 mph and fuel mileage went UP from 20 to about 22mpg.