100lbs on a truck in reality not do much at all. As for smaller stock tire it will be more for your own needs.
When it comes to these trucks fuel economy seems to be some thing we try to get from them but they will never achieve.
I noticed here that gas mileage dropped when we were forced into using gasohol. My new jeep was getting 21 mpg and dropped to 18 after the forced usage. The truck even when new would only go just under 17 mpg hiway (65-70mph) and winter city 11 mpg.
I did some changes by putting in a manual and city went up to 12.5 mpg and hiway still around 16. This 10% alchahol gas dropped it to 10 and now 13 mpg. I personally just gave up on trying to achieve economy on the truck.
Hell come to think, my motorcycle, which used to get 54 mpg, now only gets 47mpg, can’t win.
Want fuel economy go with a diesel, but the price of diesel offsets the price of gas here. So who knows.

 

Just to clarify.....

Knew the mpg's would suck before I bought the truck.

What I'm looking for is better fuel economy, not good fuel economy. I would have kept my 2wd Ford Escape.

Basically meaning that I'm just trying to maximize my mpg's on the truck and if one thing over another will help, I would go that route.

I.e. I have to replace my tires anyway, would going with a shorter diameter tires help with fuel economy no matter how small that number may be?

 

Yes and no. If you go very low then your RPM's will be much higher on the highway causing you to loose mpg's but around town you'll gain some. 245/75's are still decently tall and skinny so I think you'll definitely pick up some MPG's with them.

 

Essentially, you are going down to a 30.48 or so diameter tire. Similarly you can change the differentials to a higher numerically higher gear ratio. Or a simple test is to “not” use your overdrive in the transmission. This will allow a (I am guessing your truck comes with a 3.55 rear and the over drive of the auto is .62-1) leaving it off will give a 3rd gear of 1 to 1 and you can see if your fuel economy increases. This would be the same as, or close to putting on smaller diameter tires.

 

To clarify.....

Not questioning your knowledge, I truly don't know.

Driving with O/D off will give better fuel economy????

I thought overdrive was to not make the engine work as hard at higher speeds?

 

Driving around town and under 60mph, yes using the 1:1 ratio in the transmission will help mpg because there is less load on the engine.

Pass the coffee, it's donut time!!!!!!! 245s are TINYYYYYYYYYYYY man! They came stock on mine and many 2nd gens with 3.5 gearing. My best all around power/mpg/driveability came with the 265/75s. I could still get up and go decently in town but if kept under 65mph on hwy, achieved much better mpg than the 245s. Of course, I did have the deathflash with the 245s so who knows. And I have a manual so my 1:1 is 4th. You know what? I'm no help at all, sorry!

 

Actually...that was pretty helpful.

I was looking for some real world experience. 265's sound like a good compromise as I really didn't want to go that small, but would for mpg's!

By the way, what is the 'deathflash'?

Thanks to everyone!!

 

The death flash was a computer strategy used on the magnum engines which lowers power and mpg's by modifying the timing advance in order to preserve the engine's plenum gasket. Get a tuner, get rid of it and feel the HUGE DIFFERENCE! Think it only applies to 98 and newer though.

 

245/70's are what came stock I'm assuming, not 245/75's. A 245/75 will be the same height as a 265/70 tire, a 265/75 tire will be taller and very close to a 305/70 tire. Thats what sucks about metric sized tires, they are confusing since the first number is the width of the tire (245,265,285,305,315, etc) and the second number is basically the "ratio" or percentage of the width that is the height of the tire. So a 245/70/16 tire =

245 wide, 70 or 70% of that 245 width equals the height from the rim to the edge of the tire.

I really hope I'm not confusing you but basically a 245/75 tire will be tall and skinny, whereas a 265/70 will pretty much be the same height but just a tad wider.

 

A 265/75/16 is a very good compramise tire, its 31 1/2 inches tall instead of the 33" tires your running but another thing that will be noticed is that you will be going from a 12" wide tire to one thats 10 1/2" wide.

Less rolling resistance better mileage, the 265/75/16 will keep you in good efficiency standings which will help fuel economy.

I think the 245/75/16's are to skinny and to small for a fullsize truck, my truck had them from the factory and on a 2wd truck they still looked a little small, and the ability to spin the tires when going 40 on wet roads could be very scary

 

Actually, the deathflash is just a web monicker for the "update" Dodge flashed in many later magnum pcms to alleviate "ping" or heat detonation. Dodge, in all its infinite knowledge, never installed knock sensors which are pretty important in today's engines. So many owners complained that this was Dodge's response. Mine was pinging badly and since I had no idea what was happening, took it to the dealer who flashed it. The result was less power and mpg due to the change in timing. A simple Hypertech, Superchips or SCT tune overrides this flash. I have to run 89 on the 87 tune or else it pings still. Check your pcm for an additional sticker as well as the radiator support for one saying "authorized computer update" or some derivative thereof. (The poorly designed two-piece plenum with a gasket is a common failure which allows oil into the combustion chamber and one of the symptoms is ping. Do a search and you can read for a week on these two problems!)

Back on topic, I would highly suggest LT265/75/R16 on your truck for what your needs are. It is a good compromise, doesn't look too bad and won't break the bank (or the truck for that matter). It is a very common size and was standard on lots of trucks late in the 2nd gen run. Check your door sticker for the stock size, which is either 245 or 265/75. I ran a set of Cooper ST in this size and loved them.

 

Right on! Thank you!!!!!

 

good advice! also change to a 180* stat. preserve the truck. stock 195* is just too high

 

if you do an all terrain my truck had 265 went to a 285 bridgstone dullar A/T didnt even notice a change in gas mileage good light all around tire!

 

now my 315 pro comps very noticeable lol

 

I vote for the 265 75 16 size for a stock daily driver.

 

My first 2nd gen Dodge had 265 sized tires and it was quite zippy compared to my 2000 with its 285s. You could squeeze 16 mpg highway out of the 97 if you were very light footed.
Small, thinner and lighter is a good mileage idea for tires for city and light highway driving as long as they will handle your vehicles weight.

BTW...there is manufactuers rolling resistance rating for tires which helps determine the potential for optimum fuel economy. I know Michlen tires and a couple of others rank pretty high on the chart.
Mind you...these won't be agressively treaded tires, but for a daily driver in all types of weather this may be helpful.

 

Perfect!

That's exactly what I wanted to know!

I'm getting almost 13mpg now with my light foot and just need little bit more to keep the wifey happy!!

 

Save weight and leave her home lol.

 

Ha! I'll run that by her and see what she says.

I hope I can get an internet connection in the driveway as that's where I'll be sleeping.

 

i agree the 265 doesnt look bad. My first set of tires from the stock 245's was a set of bfg mud terrains of a newer jeep rubicon in the flavor of 255/75/17. This was an awesome size for stock. Although not much different than a 265. With my current tires over the 255's my rpm on the interstate has dropped 600 rpm at 65-70. While thats great and all i am not out of the power range and have to shift all the time. Stock the truck would get up and go in 5th. Oh well

 

I have 265/75/16 on my 96. I just finished a road trip getting 16 mpg if I drove 65 mph, and 15 if I ventured over 70 mph.
Over 50 mph, your fuel economy suffers no matter what you are driving.
The tire size is always a trade off. For argument sake, assume all these tires are the same width. To maximize economy, you would run a taller tire. This would work if you never stopped, and drove 50 mph all the time. As soon as you slow down to 30 to drive through a town, the taller tire looses it efficiency because it takes more power to accelerate. A smaller tire will accelerate with less power, and is good for city driving, but will never achieve the efficiency of a tall tire on the highway.

The tires that have been discussed may make as much as 1 mpg + or - difference in efficiency. The 265/70 or 265/75 are a nice compromise of power and efficiency.

 

I also agree with what has been said & with 265/75/16.. Had that size on a 95 2wd & a 98 Durango!

 

I appreciate the responses!

I know there is not going to be some magic answer that gets me 18mpg, just looking to maximize mpg's on something I need to replace anyway.

I'm consistanly looking at tires in parking lots and seeing how other trucks look.

Our brush/wildland fire rigs at the FD are F350's and run 245/75/16's! Might as well be bicylce tires. Looks dang silly, but that's what they came with. Those are more for snow and mild (and I mean mild) off-road. Too heavy to go anywhere!!

Thanks!

 

Late to the game here ...

I have a 99 5.2L QuadCab 4X4 with 3.55 rear.

Truck came with 265/75/16's which I changed to 17" rims (the ones from the OffRoad trucks) and 275/75/17 profile. Mileage dropped a couple MPG when I switched to the 17's (AFTER accounting for the difference in aspect ratio on the odometer) which I attribute to A) much heavier tire/wheel combo (hard to accelerate it) and b) wider tire (higher rolling resistance) and c) taller tire (lower coefficient of aerodynamic drag due to the entire truck sitting higher).
When the tires on the 17's wore out I decided to go back to my stock rims and put on 245/75/16's. Much lighter, lower rolling resistance and lower truck profile has gotten my mileage up by about 2-2.5MPG. I actually got 17.5 mpg on a trip I took this weekend, all highway driving. I'm happy with this setup as I don't wheel the thing and use the 4WD on ski trips only. Narrower tires are much better in the snow. I think my braking performance has improved a good bit as well with the lighter setup.

Side note: I think a lot of 4X4's that end up with trashed suspensions (besides wheeling them!) are due to the fact that people slap on these heavy rim/tire combinations (which is unsprung weight) which beat the crap out of suspension components. Even my 17" wheel setup that I used for a couple years was very mild compared to what most people throw on their trucks. Using the lighter rim/tire I'm still running all of my stock front end suspension with no problems whatsoever.