What gear to change to?

[RangerVet]

Fairly new here. I have a 3.0, stick shift, 2005 Ranger Edge 2wd with 65,000 miles. It has the 8.8 and a 4:10 gear without the limited slip. My goal is better gas mileage and less of a granny gear when taking off in first gear.
I swapped the stock 235 75R 15 tires and wheels for aftermarket black 15" X 8" wheels and BFG Radial TAs size 245 60 R 15s.
I have a decent size Pick n Pull in my Arizona town with many Fords to choose from and I have read through the info here about which ones to use as a donor. Mine is 8.8" with 28 spline axles.
I used a GPS this week that shows my speedometer is reading 10% high around 60mph. I don't remember the tach reading though.
Does anyone have some type of calculation to figure which axle ratio I should use to achieve a somewhat accurate speedometer reading? Also should I pull the donor truck's speedo gear and put it in my '05s transmission?
My Truck is used around town in stop and go traffic with the occasional 2-3 hour trip to Las Vegas or Phoenix. It runs out strong with no problems exceeding the speed limit at the sometime 75mph speed limit.
Excuse my ignorance on Ford products as I am a senior citizen-ex hot rodder who wasted(?) my youth on GM products and Corvettes.

 

[19Walt93]

While the 245/60 tires look better, they're a little smaller in diameter which is causing your speedometer to read high and actually hurting fuel mileage. Switching from 4.10's to 3.73's is about a 9% change that should pretty well correct the speedo error, 3.45's would be a 16% change that might help mileage as long as you have power enough to turn them. 3.45's would make your speedo read too slow. I got these numbers by dividing the new ratio by 4.10, for example: 3.73/4.10=.909. In the hills of NH a 3.0 struggles with 4.10's and has to be shifted down a lot, if you're in flat country 3.45's probably would help mileage. Tall, skinny tires would help,too, and could be cheaper than a rear end change. 245/60r15's turn 783 revs per mile and 265/75r15's turn 680 and would get you a 13% rpm reduction. I think you're unlikely to find a used rear end that doesn't have a lot more mileage on it than your truck has.
You didn't waste your youth on GM's, it's good training to work on something that breaks a lot.

 

[Dirtman]

If you do a lot of around town stop and go driving the higher gear may actually hurt fuel economy. The higher gear is better for fuel economy on the highway since it will allow you to maintain cruising speed at a lower rpm, but in stop and go traffic you're working the engine harder because the higher gears sacrifice your low end torque. Just food for thought.

 

[pjtoledo]

you mentioned a granny gear in first.
Ranger manual trannys come in 2 basic flavors, wide ratio for the 2.3 & 3.0, close ratio for the 4.0
the close ratio has the same 4th & 5th, 1-2-3 are the difference, first is not a granny.
unfortunately the trannys have an integrated bell housing, and the bell housing patterns are all engine specific/different.
that means you can't swap trannys.
however you can swap the innards.
check out the "how to tech" sections for all the ratios and write ups.

 

[Curious Hound]

With a 3.0L, I would definitely NOT go to 3:45's. 3.73 wouldn't be too bad since you have a manual tranny. You might be better off with different tires. Cheapest thing right now would be to change the speedo gear to get more accurate speed info. Once the speedo and odometer are reading correctly, you can get a more accurate picture of whether or not your mpg is really very far off. It might just appear that way because you have inaccurate info to calculate it.

 

[86merc5.0]

You may also try getting a bigger/taller ( larger overall diameter ) rear wheel/tire combo ( not crazy large ) but 255/50/20 is 30 inch diam & turns 691 ( factory 235/75/15--29 inch & turns 716 ) this would lower the overall ratio & still give compliant ride. I have used Tire Rack sizing/spec sections to find good combinations over the years.

 

[86merc5.0]

Note: taller side walls will effect handling, load & cornering.

 

[8thTon]

My ‘04 3.0/auto Edge has 4.10’s and I think it’s well matched to the power curve. They’re a little short at 75mph and that probably hurts milage, but I drive a lot of hills and it needs to rev to get to the powerband. Given the lack of aerodynamics it might not make much difference at speed though.

I don’t think there is a speedo gear, you have to reprogram the cluster to change the ratio.

The fundamental problem is the tire size you installed, and it seems silly to mod the truck to make up for that. Wait until they wear out and get something with the right diameter. In the meantime start in 2nd!

 

[4x4junkie]

I don’t think there is a speedo gear, you have to reprogram the cluster to change the ratio.

This.

Speedo gears went by the wayside for 1998. The speed signal instead comes via the rear ABS sensor & tone ring, which are parts not affected by gear ratio changes.

If you still want to change your ratio for performance reasons, I'd suggest 3.73, but I wouldn't expect a significant mileage gain. The 3.0L V6 is quite happy to sing along in the mid-high 2000s for cruising RPM, much more so than say, the 4.0L (or most V8s).

 

[RangerVet]

Thanks for the info folks. Extremely helpful! Especially the part about where the speedometer obtains its information.
I think I will adjust tire and wheel size as that looks to be much less expensive than doing a rear end swap - and laying my old arse on the ground trying to remove a possible worn 8.8 at the pick n pull does not sound like fun.
What Ford vehicle should I look for in order to purchase a set of 18" or 19" from at the pick n pull?

 

[Mike Tonon]

I’ve got your same setup and I took it easy on the throttle and kept my highway speed around 55, in 5th gear and today I filled my gas tank and checked my mileage. I git 20.17 mpg!