Just recently bought a 96 f150, 300 i6, 2.73 gears 2wd, single cab long box, 5OD standard trans. I’m looking to put 30.5”x10.5” tires on it and wanna know how much of a hit I’m going to see on fuel milage I do mostly highway driving so will be happy with anything above 15mpg

 

What does it get now?

 

not sure what it gets as of now since I just purchased it and hasn’t been driven my myself yet was just hoping for a rough idea of others with same tire size currently

 

2.73 Gears with a 30.5X10.5 Tire? You'll be lucky if you can even pull fifth gear. It's going to be a complete dog, and I would bet that the mileage is going to be awful.

 

with the research I’ve done 2.73 gears aren’t bad for milage but you are correct with it being a dog and not being able to tow much with such a tall gear I just didn’t think a 30.5” tire would affect it that much to not be able to pull through 5th. I don’t expect this truck to be fast I just need it for daily driving which is highway and country roads with the odd scrap run

 

Not being funny, but I dont think you can tow anything with those gears, and that manual trans, legally, I seen it somewhere on here, in another thread , dangit!

 

2.73's are only good for mileage, if they're in a vehicle that has an engine with the right torque curve, and enough torque to maintain speed, without having to hammer on the throttle to maintain speed. This isn't one of those cases. The 300 makes pretty good torque, but not enough in something the size and weight of an F150 that you're not going to have your foot in it every time you're headed uphill, or have anything in the truck. It's not an apples to apples comparision, but I had an AOD behind a mild 302 in my hotrod at one point, with 3.00:1 gears in the rear end ('41 Ford Pickup, 2WD, rough weight as I recall at the time was about 2700 lbs, so quite a bit lighter than your F150), the AOD has a 33% overdrive, and at 65 MPH, I was in the 4bbl's just to maintain speed, because it kicked the engine down to around 1600 RPM-ish, and was out of the torque curve for that engine. And with that setup, I never saw better than about 12MPG. I regeared it at a later date, to 3.80:1, and that made the Overdrive actually useful, putting my cruise RPM at around 2100 as I recall (This was 20 years ago, so my memory could be a bit faulty)

Now, your F150 is heavier than my setup was by a pretty fair penny, and I guarantee that the stock 300 in your pickup makes less torque than the 302 in my hotrod had. Regardless, your M5OD has a 20% overdrive, which makes the 2.73's a little more palatable, but with a 30.5" tall tire, you're going to be looking at roughly 1500 rpm at 65 MPH. I don't have a dyno sheet in front of me, but most of the 300's are going to be making peak torque right around 2000 rpm somewhere, so you're out of the torque curve, and going to have to be hammering it. Even if you're cruising around at 65 in 4th gear, you're going to be at 1900 rpm, which is better, but still a but under the curve.

If this is a truck you care about, and want to keep, and want to get what mileage you can out of it, I'd recommend regearing it. If you changed to a 3.55, which is a very common ratio, in the OBS F150's, and you can usually get a complete rear end pretty cheaply out of the boneyards, you'd be looking at roughly 2050 RPM at 65 in fifth gear, which is going to put your cruise RPM right in the sweet spot of the torque curve, and going to make it far more driveable everywhere else.

 

I bought a '79 Ford pickup new with a manual transmission and 2.73 gears. A total dog for power. My '87 has 3.08 and a 4 speed direct transmission with 30x9.50 tires. Just going from 235s to this one size larger I saw a good sized decrease in takeoff and pulling power.

You won't see 15 MPG in that truck empty with stock 235 tires. They just won't do it at highway speeds. What you will do is become an expert at changing between 4th and 5th gear, as you will need to on every small hill.

 

thank you for the generous advice I had planned on getting a limited slip for it as I have pretty decent winters here and would like more than an open diff on a 2wd truck and was leaning towards either a 3.08 or 3.55 whatever I can find locally I guess. I was planing to do that in the future but if I need different gears to not destroy the milage it gets then larger tires will have to wait

 

Read this thread
https://www.ford-trucks.com/forums/1...4-10-gear.html

he had an auto with a better overdrive than the five speed, so a 3.55 should be ok for you.

 

My '91 came from the factory with a 4.9L I6 mated to a M5OD, with 2.73:1 rear gears... It was a DOG.
I swapped gears to 3.27:1 and was much happier with it and it actually improved MPG slightly, but I think 3.55 would be a good fit too..especially if you're going to a taller tire.

Now I've swapped to a 351 and I want some 3.73 gears!

 

I have that truck with 3.55's and it's a good match-
accelerates pretty well, cruises at lower revs, and there aren't any huge gaps
in the gearing. It won't tow uphill in 5th, but 4th keeps up with traffic ok.

15mpg is about the best I've seen- but it's also usually about the worst, too.

2.7 diff would make 5th pretty useless, period.

t

 

Those gears may have been good for gas mileage in previous generations with out overdrive, but with overdrive not so much even with the low reving 300. I would want at the minimum 3.08 gears with stock 235 75 15 tires for that engine. For 31 10.50 I would want no worse than 3.55 with that engine. I'm not sure about 30 10.50 but there was a 30x9.50 that used to be available but haven't seen that size in several years. It would be a better size for the gearing. Years ago a friend had this combination and it was bad even with the 235 75 15 stock size tires. I have no idea why Ford even offered this configuration. I seriously doubt it had any benefit at all.

 

Torq'ta pretty sure ur spot on. I remember seeing probably the same post you did. Tow rating on the 2.73 manual trans trucks is a WHOPPING 0lbs and I think you could only carry 500 lbs in the bed or something like that!

 

I had 31s, 3.50 gears and the 4 speed OD. Total pooch. Maybe 19 mpg highway, never really kept track around town, but iirc I also got about 13 on one tank, probably mixed driving. YMMV but tall gears and tall tires are not a winning combo in this case.