[Bongobyll]

Howdy,

I sadly realized that it makes more sense to buy her a minivan than me a new truck. In keeping my truck, I want to be happier with it and was debating on swapping out my gears to 3.9something's or 4.10's.

I have stock gears and 33" tires. I drive 90+% around town with a 4 mile commute to work and too many traffic lights and pull a trailer here and there. Bunch of trips to Home Depot and what not.

I'm unhappy with the driving characteristics (power) when I'm at 45-55, which is my most common speed minus the stop and go. I regularly turn the OD off in town to cure this, but at and over 50mph the rpm's climb higher than I like and I feel like I am racing the engine.

Even though many people claim that they have plenty of power with the 3.55's and 33's, I think that makes me a prime candidate for swapping the gears.

I don't mind spending the money on the gears, just want to make sure it is a sound decision. Figuring going to 3.9something's is only a 10% change in RPM, right? I'd drop a couple miles off of my sweet spot while cruising the highway, but nothing big? 4.10's would be about 15% change in RPM at any given speed?

4.10's and 33's are probably the equivalent of a truck coming with 3.73's and stock tires?

If my logic is correct, I'm going to start staring at the tach and speedo while I'm driving and try to avoid the people on there cell phones. Do some mental math and figure out where I'd be with any given RPM. I know where the engine is happy and I'll just choose the gears that are the best compromise.

I am capable, but have never swapped gears, so I don't know how good/bad the improvement feels. Got a vote or have you made a similar swap?

I guess I can do something silly like a 2500 axle swap for not a ton more money and even get manual hubs, but have never tried to hunt down a part that big.


.... hope you're still reading

 

[t00tall10169]

basically the rule is every tire size you go up ex 31' to 33' you go down one gear set. so if you have 3.73 now go to 3.90 for the same power as stock. if you want a little more get up then 4.10 are fine, they just use a little more fuel which isnt a big deal if you have a short commute. i wouldnt bother with a HD axle swap, to much weight and it gets complicated fast if you dont have have all the tools a fab shop would have. trust me its not impossible but unless you are planning off road adventures every weekend, dont bother, spend the money on 4.10 gears and take a saturday and put them in yourself, its no hard thing, just take the time and do it right. happy modding and im subscribing to see how this turns out for you

 

[Bongobyll]

Thanks. I'm still working on figuring out which ones. The subscription makes me feel obligated to follow through, I like it.

Based off of the door sticker, I had 225/75/16 (29.25") with 3.55's. Doing math problems, I would need 3.93's or whatever is closest to get back to an equivalent final gearing with 285/75/16's (33"). I was considering the 4.10's also, I just don't want to be screaming at 65mph when I do make road trips.


3.93's are a 10% change from 3.55's and 4.10's are a 15% change from 3.55's. Does that mean my RPM's would change by these percentages at any given speed AND that my MPH would change by the same percentages at any given RPM?

If my math works, I will drive around for a while and do the mental math to see which gear set would be better for me.

Side note, what RPM do you guys like to run on the highways. I was going to use this to help decide. Currently, I shoot for 1800-2250 and I will do some short highway driving to see where my speed would be with a R/P change.

 

[Okiespaniels]

This chart should help you.'
Don't forget to take the listed rpm and multiply by .85 to get your OD rpm for highway driving.
4:10s should be perfect for 33s.

http://www.jeep4x4center.com/jeep-tires/tire-gear-ratio-chart.htm

 

[Bongobyll]

Don't remember if it was your post or not, but I saw that link in another post. Love that I can compare everything at a glance.

That specific link is why I was asking about what highway rpm's people like to run on the highway. I think those jeeps like to be rev'ed a bit more than my engine does.

ALSO... I got off my lazy butt and found the sticker under the hood that gives a few details about my truck and it says my ratio is 3.9, does that mean 3.90's?... HOWEVER, doing this crazy math problem with figuring I had 3.55's... =SUM(5280*12/(32.83*3.14)*65/60*3.55*0.85).... seems to match up to the RPM's I'm currently running at 65. So, the math says I have 3.55's and the sticker seems to say 3.90's. I guess I'll craw under the truck and check for a tag on the rear and hope it doesn't say 3.73's...

I want to do gears, replace the cat and y pipe(pretty sure the internals of mine are broken up), upgrade the plenum and possibly have a look-see at the trans and try my hands at a rebuild and address some of the notorious problem areas.

With all that work and money, I might just want to sell the truck and put the modification money towards trying to find a 3/4 ton Ford (I'm in love with the V10) or Dodge of a similar year or hopefully a few newer... decisions decisions

 

[Bongobyll]

If this is useful to anyone, you can substitute any number you want and paste it into excel...

=SUM(5280*12/(32.83*3.14)*65/60*3.55*0.85)


5280*12 converts feet to inches in a mile
32.83 * 3.14 converts tire diameter to circumference in inches
65/60 is 65 miles in 60 minutes (65mph)
3.55*.85 is gearing times the .85 recommended for OD above

 

[Minihandcuffclub]

I'm having kinda the same problem you are I'm trying to get the best gears to help with towing I have 33's on now 285 75 16 and my truck has stock 4.10 gears but it sucks at towing so what would be a better gear ratio for towing with 33's