would aggresive tires relly take from gas mileage? i went from 235/75 sidewinders to 31x10.50 cooper discoverer stt (mud tires) to get a better "look" for my bronco and to help bring the revs down on the highway.

 

mine didn't when i went from 31 to 33 (firestone destination m/t)...no noticable change at all...road noise actually got quieter

 

Superman, I'd say that it could... You'd not get enough fuel, so would be low on power, so in turn, would push harder on the gas pedal... Bottom line, is to make sure your truck (or any vehicle for that matter) is tuned and in tip-top running condition.

Muscletruck & Tylus, between two tires of the same size, I'd say that the one that's easiest to roll would produce better gas mileage. That one would ussually be the less aggressive tread design, i.e. street tire.

 

"I'm at 4 city, no highway driving, and I put about 30 bucks in gas every 3 days."

That is not right. Either you have a gas leak or your carb or EFI is hosed bad. IK once had a truck and the rebuilt fuel pump that I put in had a leak, it sprayed gas while I was driving but I never saw any or smelled any when it was turned off. I drove it like that for a while before I got lucky and noticed it spraying one day when I had the hood up and the motor running.

I also once had a Maverick with a 302 that started getting about 3-4 mpg with no gas leaks. It was carbureted and was a total dog off the line after the mpg problem started. The tranny went out and I scrapped the car so I never figured it out, but I am pretty sure that it had something to do with the carb.

Broncos are gas hogs, but 4 mpg is not normal by any means.

 

We just drove to New Orleans and back (about 1100 miles) and got 12 mpg overall...

 

Somethings probably way wrong! However, my Friend has a 351W in a 89 F250 that's getting 5mpg city. So it may be just that all your driving is city. He gets about 12mpg highway. His solution is no city driving.

Heres some tips for better MPG's:

Check your fuel pressure if it's EFI. You want no more than 37psi at idle with the vacum hose disconnected from the regulator.

If it's got a carb then read the plugs, and determine if leaner jets can be used.

Don't use platinum plugs. I swear they cost 1.5mpgs-don't know why????

Use a hotter range plug if it doesnt ping, and use a bit more plug gap. For example if it calls for .052" run .060".

Run as much intial timing you can get away with, without pinging. A 302 or 351 runs best at 14* BTDC intial. If your running EFI, this will cause your check engine light come on, but you know why. This usually causes a noticable mpg improvement.

Make sure the cat isn't 1/2 plugged up.

My friend hasn't done any of this to his 351 yet because he's planning an overhaul soon.

 

well, my 7 mpg might be due to the tranny going out. It went out the last thursday, so I'll see what i get after the new tranny is in

 

Ha. This is funny. I also have a big lifted Jeep Wrangler in addition to my '90 Bronco, lifted with 35's. This exact subject comes up on the Jeep boards when gas climbs toward $2.00/gal. When gas goes up everybody starts crying about gas milage. A friend of mine says it best:

"You're driving a brick with a pup tent set up on top, and you're asking about gas mileage?" hahahahahahahahahaha

Now, I understand that the Bronco doesn't have the soft top that the Jeep does, but the same principle applies. PLUS add a big displacement engine (hey, my Jeep has a 242, anything with 2 extra cylinders is big...LOL). My Jeep gets 13 mpg, downhill, with a tail wind. The Bronco gets around 12. When I'm towing the Jeep, that falls dramatically. I don't even bother to check. I don't expect the Bronco to get good gas milage. If I wanted a vehicle with good milage, I'd go buy a Toyota Prius.

 

I know there are other MPG threads running around the Forum somewhere, but thought I'd toss the last tank results out on my '94. After a major tune, fuel pump change out and tank evap valve change she's now doing 15.3 on general driving around, to and from work.

FWIW, that commute is 17 miles (one way) in 'rush' hour into and out of Seattle proper on I-90 and I-405 mostly. It can be okay or it can be a slow parking lot... it varies.

Bronco is very much a stock '94: 5.8, E4OD, auto hubs, 31 10.5 15 Big O AT tires..

at 15.3 I don't feel too bad. Will probably try to tweak that some, but for now, it will make a good baseline.

Swit

 

My 94 Bronco has a 302/E4od. I took it on a 300 mile trip a few months ago with 4people in the truck with luggage. I checked the gas mileage when we got back with 32's and 355 gears and various eng. mods I got 17.7 with the cruise set at 65mph and dropping back to 35mph for little towns along the way. On the interstate I can easily get over 18. Around town with some interstate added in I get 13.8

 

remember with larger then stock tires your milage will be inaccurate especially with 32's and a 3.55 gear still nice numbers though.

Swit, take an set your timing to 12btdc , this will give you a little extra mileage to.

late

 

My milage figures were after calibrating my speedometer for the 32" tires.
I've also got my timing at 12 degrees before top dead center its all I can give her without spark knocking on mid grade gas.

 

Thanks i am gona try some of what you suggested.

 

I got a 1990 351 all stock except a k&n, single flowmaster and shift kit. Its got 3.55 gears and 31 tires. I have gotten 15.2 mpg driving between 60 and 65. If I run over 65 the mileage starts dropping off fast. Also I try to start off real easy, if I drive it like I wont to I probably get about 10 mpg.

 

The advertised mileage for the 302 is about 13City -17highway, so your figures are good, no need to change anything just yet...