fuel milage tanked with bigger tires

[TSimpler]

I upgraded to 285/75/R16 MTRs on my Dmax and the milage tanked. It went from 20 miles to the gallon down to 13-14. Is this normal and has it happpened to anyone else. I did add 8% to the milage to account for the bigger tires.

Would a computer reflash for the bigger tires help or will the dealer reflash just not help??

It still runs like a raped ape, but it is sucking up diesel like a oil junky.

Trent

[Idle_Chatter]

Tsimpler, my guess is that you've shifted your cruising (aka: most common) rpm down into an unecomomical range. Diesels have "sweet spot" rpm ranges that are really quite narrow and 500 rpm north or south can do exactly what you describe. I get 18.5 overall and high 19s keeping my rolling rpms in the 1500 to 1800 range. Once I get over 2000, mileage begins to really drop. I don't know what happens under 1500, because I never run there.

[NFLDMAX]

My mileage dropped a little, but no where near as far as yours. I lost about 1 mpg.

[schnier]

I have to chim in here and agree. My mileage dropped 1 to 1.5 miles per gallon also. Last year ran around 17.5mpg. switched to 265 tires and dropped to 16 and 16.5mpg. Added 4" Magnaflow and now it is only doing 15.5mpg stock. I had removed a programmer to update it to the new revision, so I can not blame it on aftermarket programs. Could winter blend fuel still be in the tanks? I do not know. I will have to test some more in May to see if it goes up a little. The only good thing is when my programmer comes back, I can calibrate the tires to the proper size and see if the clears up the mystery mileage problem. Probably not because my FOOT WILL BE TO THE FLOOR!!!!

[NFLDMAX]

I too, have removed my programmer for updates, but just recently finished my exhaust install. I haven't been able to run a full tank through yet to see what effects, if any, the exhaust did to my mileage.

[HD-Nate]

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I upgraded to 285/75/R16 MTRs on my Dmax and the milage tanked. It went from 20 miles to the gallon down to 13-14.
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:eek:

Wow, thats a heck of a drop. I went from the 245's to 285's. DIC indicated milage went down from avg 16-17 around town to 15-14 range. On the highway it stayed about the same 19-20. Remember you went to a wider tire also increasing rolling resistance.

[NWDmax]

13.5 in town only. 17.5 highway 65 to 70 mph.
Imho your tires didn't take your mileage that far down. Run another tank and let us know please. :D

[Minn-kota]

Also remember that going from 245's to 285's will change your speedometer and odometer readings. When you check the tripmeter next fill-up, you have to multiply that number by the percent of diameter difference of the old and new tires.

In other words, your tripmeter will show less miles than you actually drove and you have to compensate for that before doing the mpg calculation.


edit-
I just went back and re-read your message and see that you already figured in the difference. Disregard above. Many people forget that and then wonder why their mileage went down so much. As said above, the larger tire will produce more rolling resistance but that drop in mpg seems a little excessive for that.

I calculate a factor of 1.0775 that must be multiplied to your tripmeter. So you are correct.

[ 04-17-2003: Message edited by: Minn-kota ]</p>

[RWHP]

A friend of mine just bought an '03 2500 4x4, the next day he lifted it 6" and put on 35" tires. His milage is consistent 13 mpg on 3 tanks now.

[HoustonDMax]

I have tracked mileage since new, along with noting every change I made to the truck. Mileage around town stayed the same when I installed 285's. Went up very slightly on the highway.

No change when I added Juice either. I consider this good, as I drive a little harder since adding Juice.

[Stoner]

TSimpler, had a similar situation with an F250 I once owned.....went from 245/75/16 all season type tires to 265/75/16 B.F. Goodrich Mud Terrains. Mileage went from 15 to 11 - 12..... I'm thinking not only extra rolling resistance from the size upgrade....but those aggressive treads gotta be "paddling" a lot of air as well :eek:

[car of the week]

I have 295 BFG's and my milege is still at 15-15.5 but I run HOT Juice on level 2 and drive the truck hard...level 4 stoplight races and such. I can't complain, I drive a 7000lb truck like a sports car and it still gets 15 miles to the gallon.

Regards,

Ryan

[TSimpler]

Just did two more tanks after the first three at 13 or so and was able to get 17mpgd each 17.2,17.3,and 17.2(mpg Diesel) but the three first were in the wind.

I am still unhappy with the new milage.

Any thoughts would be helpful.

Wish I had gotten the Goodyear Workhorse instead

They (MTR's) wollow a bit.

Trent

[The boss]

Ive been juiced almost 2 months now and Ive had the 285s 1 month. My milage hasnt fluctuated hardly any from the mid 19s (highway) before or after the new tires. Im getting 17 or so in town. Oh, and this last tank I set the Juice to "0" to see if my milage was being impaired. The result was I made it 460 miles before a fill up. With the fudge factor of 1.0775 on the trip milage came to 18.7. I am staying juiced and feeling good about it.

[SoMnDMAX]

1544 mile road trip Thursday-Friday from Minnesota to Detroit, MI yeilded 18.8 average fuel mileage. Temps in the low 40's for 75% of the trip. All interstate driving, running 75 MPH, and racing unsuspecting folk out of toll booths.

Average speed- including fuel stops, 1 hour breakfast stop, and 1.5 hours of stop and go in Chicago rush hour traffic- 57.18 MPH (27 hour trip).

Low- 18.4
High- 19.1

Juice on "timing only" setting- "R" setting. Level 4 HOT setting used for racing and passing (when necessary).

This is with 285's on the truck- 50 PSI in the rear, 58 PSI in the front. Fuel mileage is greatly affected by tire pressure. With my truck, I've found these pressures to give the best balance between mileage and even tire wear.

[ 04-20-2003: Message edited by: SoMnDMAX ]</p>

[afp]

You guys now have me second guessing where I want tires larger than the 265s I have now. The only reason I want them is for looks and a little more ground clearance. However, a 1/2" more ground clearacne is worth 2 mpg to me.

Do you guys think regearing the truck--so it'a like 265s with 3.73s--would bring the mileage back? At least most of it?

That does make for an expensive job. Wheels, tires, gears................

Blaine

[DMAXDiva]

When I swapped the 245's for 285's last year my mileage only dropped a couple of mpg's, but when I went with the 6 inch lift and 37's it really took a nose-dive! I knew the mods would effectively change the gear ratio and by doing so would affect fuel mileage; and these 37's have a whole LOTTA rolling mass...so, needless to say, my mileage went from 19-20 all the way down to around 12... :rolleyes: ...oh well, I'm still happy with the decision to lift and re-shoe!

:cool:

DMD

[TexasMax]

Been there done that with my other trucks

Keep in mind that not only do you lose mileage when you put larger tires on (rolling resistance) but when you lift a truck you also start exposing more of the underside to the airflow (wind resistance).

But they sure look good lifted. :cool:

[ski]

Diva,

Ever thought about regearing with 4.10s to restore the original gear ratio. An ex-coworker did this and was very pleased with the results. BTW, he also added a locker in the front and was nuetral about that mod, said if he was to do it again he would skip it. The 4.10s may be something to consider, would even restore the original grunt (past any current chips, etc). I have to think your current ratio is close to a 3.42-3.50 after adding the meats !

[Gbenzx01]

Trent,

I recently changed 1500 sierra 5.3 from 245 to 285 grip tires & saw the same results you had.
I asked my friend (I trust) at the dealer to repro the tire size & he said he couldn't do this with this 99 truck. But went on to say that after the computer gets used to them mileage will go back up some. I thought, have they ruined this guy too but sure enough after the 4th tank of gas it was back up to within 1.5mpg of what it always did or 17.5mpg. And over 20k mi it's still right there every time!
Also he said it takes power to keep on reshapeing the tires so keep pressure up as much as possible.
He says these computers relate power setting to speed & taller tires with lower speed & same or greater power setting (throttle) makes the sensor keep demanding more fuel thinking the driver still wants to speed up. And of course he dosen't.
You just wouldn't think a 300hp engine would be that sensitive as the little 5.3.

Joy, Gben

[James S]

Hey Guys and Gals,

Let's clear this whole thing up right now. When you increase tire size you affect your gear ratio, acceleration, increase roling resistance, impact: shift points, tripmeter, fuel milage, which we all know, correct??? However, one thing that some people don't take into account is the kind of tires they are buying in terms of the tread ON the tires. The tread also plays a factor in all the things listed above, given as another poster stated, how much air the tread "paddles". The more aggressive and larger the tread, the more air it "paddles", or pushes around, thus causing the air resistance. We can get in to physics formulae if you want, but I think that will be rather boring for alot of you. If you look at some of the milage reports, for those with completely stock trucks, they have the best milage, for the ones with 265 tires of either all season or all terrain, there milage is impacted minimally, [more so with the all terrain because of the slightly more aggressive tread, but minimally], but for those with 285 tires the wider tire gives that much more roling resistance, the shifting can not be calibrated, therefor everything gets screwed up, resulting in a decrease in milage. This is furthered if you go from all season, to all terrain, then the worst if you go to maximum traction tires, like Trent has done. His gearing, shifting is all screwed up and cannot be calibrated, the aggressive tread is "paddling" huge amounts of air, thus causing significant air resistance, RPM's are affected by the improper shift points, and the roling resistance from the wider tire. Trent, my advice to you, take them off, go to an all terrain tire of 265, get your shift points calibrated, and gearing corrected by your dealer, and enjoy the truck. They are nice tires, I agree with you, but the headaches they are causing you, are not worth it for you, in my oppinion. You also might want to look at your other mods, and see if any of them are causing any mor resistance. If so, yank them off. They look nice, but again, get the best milage out of your truck.
I also have to give those who have lifted their trucks a warning. I am sure you all are aware of this, however as a poster on this forum, I feel I need to help you try and avoid some vary serious consequences. From what I UNDERSTAND, lifted trucks, are not legal road vehicles. If you are ever involved in an accident, you will have no insurance coverage, given you have strengthened your truck, and increased the size of your truck from it's original size, if you know what I mean. You also could be opening yourselves up to SIGNIFICANT law suits, if there are injuries to the occupants of the other vehicle. By this I mean, if your bumper hits the driver's window instead of the lower section of the door, this could result in serious head injuries for the driver, compared to potentially no injuries at all, or a relatively minor one, [GIVEN THE CIRCUMSTANCES] like a broken ankle or leg. Also, for those of you who have large steel bumpers or any other accessories that will inflict more damage or injury, than factory parts of the vehicle, the same applies to you. I CANNOT guarantee this, but I was told this by a FAIRLY confident source. I just thought I would let you all know. Accessorize the truck, enjoy them, but most of all, be safe.

James

[conradv]

So since 255's are skinnier, tall tires, will the mpg be similar to the stock 245's with a not too aggressive tread? I'm looking into replacing my stock firestones with 'em.

[James S]

Hey There,

If your milage is impacted, it should be impacted, vary MINIMALLY. What kind of milage are you getting right now, in town and on the highway? What speed do you travel at on the highway? What do you get for milage at sixty miles an hour on the highway?

James

[afp]

Many states do have laws on how much lift is acceptable. 4" is a number I have heard bantered about in such discussions. The best bet is to check your state and local laws to see for sure.

I think in any such lawsuit, the lifted truck driver would have to be the one at fault, then they'd only be liable up to their liability limit. From that point, the "ambulance chaser" would probably go after the bumper manufacturer and the state--asssuming such mods are legal.

Blaine

[WillowCreekStable]

Yup, the shotgun approach to litigation. Find the deepest pockets. Been there, done that, couldn't afford the T-shirt after. :rolleyes: :rolleyes:

[TSimpler]

Got the truck back from the stealer after they reprogramed the tranny and such. They told be it was within a half an inch of being the correct tire size, only time will tell.

They also replaced a leaky brake hydro booster, replaced and retorqued the rear leaf spring spacers, reflashed the confuser with the updates,and tried to charge me for "shop supplies"... they were not able to get me to eat those costs.

The reflash cost me 75 bucks and I will let you guys know if it helps

Trent

[Kennedy]

TSimpler,

What did the dealer reprogram? I haven't read the entire thread, but $75 for .5hrs TOPS??? More like 10 minutes to build the truck in, access proper tables etc.

The only tire tables available (to the best of my knowledge) to reprogram on the Dmax are for the ABS system, and do not affect speedo/engine/trans data tables...