Fuel mileage going from stock wheels/tires to larger tires

[1997XLTRollover]

Hard to compare two different trucks from different years... even of the same model. There are just too many variables. I'm pretty sure I never got 19 on my sport from the factory.... but the SOHC6 4WD is a completely different beast than your AWD V8 so to some extent my mileage means nothing .

To get back to the point... I doubt a 1-2" change in diameter and/or tread pattern could be responsible for a 40% drop in gas mileage. I'd guess (before running off to read your link and others...) 10-20% max. There are certainly multiple factors involved in the difference.

My 96:

5.0 AWD 5k miles on brand new engine
Brush Guard
Hitch
Roof Rack
3.73 gears
1.5-2" lift
32" AT tires
Fuel mileage 10 mixed 13 highway

My 99:

5.0 AWD 160k miles on original not maintianed engine
Brush Guard
Hitch
Roof Rack
3.73 gears
4-5" lift
30" highway tires
Fuel mileage 17 mixed 19 highway



Now my 96 has headers and the 99 had stock 99 manifolds.
The 96 has a metal engine fan and the 99 was plastic
the 96 of course has GT40 heads and the 99 GT40P heads but my 96 also had the heads shaved and is a 306 so I would think that would make up for the head difference. It does have 25% stiffer than stock valve springs but I can't see that changing much either.


According to that article an AT tires can drop fuel mileage as much as 15%.

 

[MAS Tequila]

2000 Mountie 5.0 3.73 AWD

Stock wheels and 235/70/15 tires, 16ish town and 21 highway

18" wheels with 265/70/18 Cooper AT tires, 11 town and 14 highway

Last October while towing my bike to Daytona the truck kept downshifting unless I kept the speed below 70 mph, it would not hold overdrive.

After the 4406 swap

15 mpg town and 19ish highway

It will hold overdrive @ 85 mph with the bike and trailer now

I'm going to try a set of Michelin M+S next time.

I'm sick and tired of the tire noise from the AT tires.

And one pair have cupped so bad that they sound like a bearing has gone bad.

I hope this helps.

MT

 

[1997XLTRollover]

2000 Mountie 5.0 3.73 AWD

Stock wheels and 235/70/15 tires, 16ish town and 21 highway

18" wheels with 265/70/18 Cooper AT tires, 11 town and 14 highway

Last October while towing my bike to Daytona the truck kept downshifting unless I kept the speed below 70 mph, it would not hold overdrive.

After the 4406 swap

15 mpg town and 19ish highway

It will hold overdrive @ 85 mph with the bike and trailer now

I'm going to try a set of Michelin M+S next time.

I'm sick and tired of the tire noise from the AT tires.

And one pair have cupped so bad that they sound like a bearing has gone bad.

I hope this helps.

MT

That absolutely helps. Thanks for taking the time to post.

 

[turboranger91]

On my old black 93 4x4 w/3.73 gears, 5.5" lift, and 33" m/t's, I was still getting about 16mpg. On my last 93 4x4 w/3.73 gears, all stock running 32" m/t's, I was getting about 17-18mpg. Current completely stock 94 4x4 w/ 3.73 gears, im getting around 20mpg.

 

[1997XLTRollover]

On my old black 93 4x4 w/3.73 gears, 5.5" lift, and 33" m/t's, I was still getting about 16mpg. On my last 93 4x4 w/3.73 gears, all stock running 32" m/t's, I was getting about 17-18mpg. Current completely stock 94 4x4 w/ 3.73 gears, im getting around 20mpg.

Hmmm. V8 probably sucks a lot more fuel when worked harder. Could be why you're doing ok.

 

[SWIGIN]

My 96:

5.0 AWD 5k miles on brand new engine
Brush Guard
Hitch
Roof Rack
3.73 gears
1.5-2" lift
32" AT tires
Fuel mileage 10 mixed 13 highway

My 99:

5.0 AWD 160k miles on original not maintianed engine
Brush Guard
Hitch
Roof Rack
3.73 gears
4-5" lift
30" highway tires
Fuel mileage 17 mixed 19 highway



Now my 96 has headers and the 99 had stock 99 manifolds.
The 96 has a metal engine fan and the 99 was plastic
the 96 of course has GT40 heads and the 99 GT40P heads but my 96 also had the heads shaved and is a 306 so I would think that would make up for the head difference. It does have 25% stiffer than stock valve springs but I can't see that changing much either.


According to that article an AT tires can drop fuel mileage as much as 15%.

Without reading your other thread, I see you didn't say if your new motor has low tension piston rings. From the factory ( and I don't know how many EX guys know this) Ford used low tension rings in the 5.0 H.O motors.

If you used old school ''tight'' rings your motor will have much more rolling resistance when spinning it over by hand then it would with low tension rings.

I have often wondered what rings guys use when they rebuild 5.0 roller motors but most never give it a thought because they didn't know.

Just a thought.

 

[1997XLTRollover]

Without reading your other thread, I see you didn't say if your new motor has low tension piston rings. From the factory ( and I don't know how many EX guys know this) Ford used low tension rings in the 5.0 H.O motors.

If you used old school ''tight'' rings your motor will have much more rolling resistance when spinning it over by hand then it would with low tension rings.

I have often wondered what rings guys use when they rebuild 5.0 roller motors but most never give it a thought because they didn't know.

Just a thought.

I would fall under the category of didn't know lol. I just bought an eBay rebuild kit.

I'm starting to think 15% loss for at tires, 2 mpg loss due to worse gearing which brings it down something like 4 mpg from stock. I really need to just find a set of stock size tires with a highway tread to borrow for a week.

 

[SWIGIN]

Well then right there is a few mpg I'd guess.

With the normal rings I mean.

 

[1997XLTRollover]

Well then right there is a few mpg I'd guess.

With the normal rings I mean.

Just by running a standard ring would cause that huge of a drop? I can't believe there is that much more friction, the rings would overheat I would think.

Here's the kit I used.

http://vi.raptor.ebaydesc.com/ws/eB...0309&category=33620&pm=1&ds=0&t=1460075175574

 

[SWIGIN]

Why do you think Ford went to low tension? They have to do whatever they can to meet the government regulations.

Your milage sounds right to me for an old school (normal ringed) 302.

 

[SWIGIN]

Why do t you think Ford went to low tension? They have to do whatever they can to meet the government regulations.

Your milage sounds right to me for an old school (normal ringed) 302.

 

[1997XLTRollover]

Why do t you think Ford went to low tension? They have to do whatever they can to meet the government regulations.

Your milage sounds right to me for an old school (normal ringed) 302.

Well hell, I learned something else today haha as usual the hard way. Thanks for the input I never even know about ring tension.

 

[SWIGIN]

Aint no thang.

Just to be clear, I don't think your low MPG is too be blamed all on the rings. It is a perfect storm combo you have going there IMO.

 

[1997XLTRollover]

Aint no thang.

Just to be clear, I don't think your low MPG is too be blamed all on the rings. It is a perfect storm combo you have going there IMO.

Agreed. I may do 4.10s and run synthetic engine oil soon. Got about 5k miles on the new engine now.

 

[1997XLTRollover]

I could have worn valve guides or a screwed up head gasket too because I get about a 1 mm hg flutter on my vacuum gauge. I wouldn't be surprised because my machinist was a complete idiot and I could see him not even checking them.

 

[SWIGIN]

If you haven't done a 4406 yet you might want to.

I tested my 98 before and after and I went from 15.5 mpg to 17.2 average.

That's 80% back roads/town driving and 20% highway.

 

[1997XLTRollover]

If you haven't done a 4406 yet you might want to.

I tested my 98 before and after and I went from 15.5 mpg to 17.2 average.

That's 80% back roads/town driving and 20% highway.

I may start gathering parts as soon as snow is no longer in the forcast. This weather won't quit.

 

[Josh C.]

I just wanted to chime in also. I'm running 33x12.5 BFG AT with the 5.0, 3.73 and 4406swap, roof rack, tow hitch front and back, and my front fenders are pretty cut up making for nice parachutes. Most of my driving is a mix of city and highway and I'm averaging 10-11mpg including the speedo conversion. I did a trip from Mammoth Lakes back to Santa Ana and got 14mpg, full gear and family, I thought I hit the lottery. I also think about buying a set of more street friendly tires for runs to the grocery store.
Also, when I did my 4406 swap my mpg didnt change at all.

 

[1997XLTRollover]

I just wanted to chime in also. I'm running 33x12.5 BFG AT with the 5.0, 3.73 and 4406swap, roof rack, tow hitch front and back, and my front fenders are pretty cut up making for nice parachutes. Most of my driving is a mix of city and highway and I'm averaging 10-11mpg including the speedo conversion. I did a trip from Mammoth Lakes back to Santa Ana and got 14mpg, full gear and family, I thought I hit the lottery. I also think about buying a set of more street friendly tires for runs to the grocery store.
Also, when I did my 4406 swap my mpg didnt change at all.

Interesting. I guess these 5.0 trucks don't take well to larger tires. As much as it sucks it makes me feel better that there probably isn't something drastically wrong with my rig.

 

[rabbit91]

When I went from 30 to 32 inch tires my mileage barely went down. At the time 5.0L not much lift, awd, I squeezed 375miles out of a tank on the highway