Ok, here's my situation....with gas prices getting outrageous I'm trying to squeeze every MPG out of my 2003 5.4L F150 with 78000K miles. I drive on average about 35,000 miles a year and every little bit will help. I love driving my truck too much to cram into a little hybrid....at least right now!

The good: I'm driving like I have my grandmother riding in the bed of the truck...no more than 55MPH on the highway which has helped.

The bad: 2 years ago I replaced my factory tires (P235/70r17) and rims with 18' factory alloy rims and P265 60r18 BF Goodrich AT tires. I believe these were factory off of an FX4. As would be expected I lost HP and MPG. ---not sure how much (I haven't always driven like my grandmother was in the back).

I'm in need of new tires so would it make sense to go back to a 17' rim given that now I would need to buy rims (and I really don't want the factory "work truck" rims that were on there before) or to buy a more fuel efficient 18' tire. How small of a tire can I put on the 18' rims? I assume the more narrow and harder the tire the better MPG.

Thanks for the help!!

 

Tires are not going to save you enough to make it even matter. Only larger, bulky tires like M/T's have a noticable effect on you mileage.

Your 18" tires are only a 1/2" OD larger than you stockers so your mileage difference would not even realy be noticable (maybe .1 MPG tops as they are slightly heavier than the stockers).

As far as losing HP from a tire swap, that has absolutely nothing to do with HP so there is no relation there at all.

I know you said that you don't really want to do it but if I was driving as much as you in a year, I would buy a Focus and the gas savings alone in a year would nearly pay for the car (assuming you are getting 14 MPG with your truck and driving 35k a year as you stated, that is almost $8,000 in gasoline per year at $3.15 per gallon for your truck - the Focus gas for 35k miles would cost about $3,200 for the year = savings of $4,800 per year).

 

It's the weight that is hurting you. I don't believe 235/70r17 was an OE size. If it was indeed a 17 inch wheel then it would have been a 265/75r17 or a 275/70r17. Either way they add up to be a 33x10.5. The 18" equivalent to that is a 265/70r18. You're already running less sidewall than that. Buying new wheels wouldn't help you financially since it would take forever for the cost of the wheels to balance out with the money saved at the pump. I would say if you're going to run the 18s, suck it up and replace the tires with a C or D rated tire and run the appropriate amount of air in them or go back to the 17 with the stock size tire. in a C or D rating. E rated tires generally weigh more and aren't going to be beneficial to your needs.

 

You would be surprised. I lost 2 mpg going from my stock 255/70r16s to my 265/75r16s. That was from a OE tire to MT MTZs in an E rating. It makes a difference. It's not only in larger tires.

 

could be due to the more aggresive tread and the added weight of tire... Keep in minding, adding 10 lbs to your tires is NOT the same as throwing a 10 lb barbell in the backseat. Rotating mass make a huge difference on a vehicles performance.

 

As stated above, bulky M/T tires which is what happened in your case.

 

Holding my cruise at 65mph and keeping 45 to 50psi air pressure in my 285x70x17 Toyo AT's, I can get a little over 18mpg. With my 315x70 BFG AT's I can still come close to 18mpg. Slowing down and running tires that have less rolling resistance are two great step's for increasing mpg's. I also have a bed cover, tuner and exhaust that help's too!

 

I know why my mileage dropped. It's definitely the weight. I was actually trying to get the point across that weight is a bigger factor than size, though very often size and weight go hand in hand. Though not always.

Actually you said larger, bulky tires like mud terrains. I took that as larger AND bulky not as larger OR bulky. I was just trying to give the OP a bit more of an understanding. Regardless, it's all cleared up now.

 

I'm not really sure if that was the original size of the tire. I copied this from the info on the driver's side door. The truck was a standard XL "work truck" with the 5.4 V8 Long bed.

I would like to replace the tires with either a Michelin or a Goodyear tire. I like the Goodyear Silent Armor but I can't see buying a tire these exspensive and then paying extra ever time I go to the pump. What is a good C or D rated tire? ...preferably a Michelin.

After driving almost a whole tank of gas out of the truck and not exceeding 55mph I think I may be able to break 18MPG!!! I've got my fingers crossed.

I'm going to change the fuel filter and air filter tomorrow. I changed the fuel filter about 30,000 miles ago. Should I expect an improvement? I've also though about popping the tailgate off to save on weight (I leave it down all the time). Maybe I'll go ahead and take the whole bed off while I'm at it.

Thanks for all the advice! This site Rocks....and probably saved me alot of money....I've decided to let someone else change the plugs and put the risk of screwing them up on them.

 

The weight of the tire and the increased rolling resistance is what kills your mileage.

Last I heard, Michelin made the tire with the least rolling resistance. The LTX M/S. Great tires. I had them on my 98 Explorer with the 5.0L and AWD, and consistently got 23 MPG highway driving 65. I rode on them for over 50k miles and only did a rotate and balance once.

They were a little on the pricey side at almost $650 for a set.

Changing the air and fuel filter can only help. As far as the tailgate, I get better mileage with it up.

 

What about these tires: Michelin® LTX® A/S Does anyone have any experience with these?

They claim to be top of the class in fuel effeciency. They come in P255/70R18 and P276/65R18. Will either of these work on my Rims?

Also, I'm not quite sure how to tell what class tire I'm looking at c,d,e etc.

 

Thanks for the response. I was posting the question while you were answering my question. Thanks

 

It should say load range C, D, or E somewhere in the specs. If it doesn't you can usually tell by the maximum psi rating on the tire. If it says Max 80 psi, it's an E. I believe 65 is the limit on a D and I've seen C ranges vary but they're lower than Ds. If your truck says it came with that size tire then I guess it did. It just seems awfully small and I didn't think they came that small.

 

I'm having a heck of a time finding tires that are rated C or D that will not through off the speed. I've found a great site that helps with this: www.1010tires.com/TireSizeCalculator.asp I like the LTX M/S but the only size that will work is P245/60R18 which are only rated for 45 PSI so I'm assuming these aren't rated C or D. I also like the Michelin® LTX® A/S but according to the site above they is too big of a difference between my original tires size.

Another question....Everything I've read on Michelin's website says to go buy the PSI that's listed on the truck door and not the psi listed on the tire. I'm currently doing that and my tires look under inflated. What do you guys recommend? It seems that adding a little more air would help MPG.

Update: after driving like my grandmother for a week I went from 14MPG to 18.1 (hand calc) MPG. If I can get to 20MPG I would be work happy driver

 

45 PSI is probably a C rated tire. Use whats on the trucks door as a guide more than anything. Tires are going to vary a bit based on how they're made. Some may run better with a bit more air and some with a bit less. If they look underinflated then put a bit more air in them but don't get carried away. Out of curiousity, what does the door sticker tell you to run them at?