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Discussion Starter · #1 ·
So I was getting 18-19mpg's with my 305's, but towing and city mileage were horrible. Went back to the stock wheels and 265's that came with the truck when I bought it and got about 21 highway/16 city/14 towing...then came time for new tires and I needed to max out my mpg's so I went with stock 245's. I put on some Grabber HTS's and now run 2000rpm at 65mph and have dropped to 17mpg highway :WTF Don't know what the towing economy is yet. Is this normal? I thought the 245's got u the best results?? What rpms/mpg's are u guys seeing with 245/265's ???
 

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man, i looked at this yesterday. i will try to remember, but i think it was somewhere around 1600-1800rpms at 65-70mph... best guess for now. Im on 265s
 

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smaller tires will bring up rpms over larger tires at the same speed. but the downside is taller tires weigh more.

if you want better mpg you will need to keep the rpms down. also are you sure the spedo is correct? that has a big effect on mileage.
 

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Discussion Starter · #4 ·
No speedo is about 5-6mph off right now, but I'm tracking mileage on GPS unit and hand calculating economy. Hard to keep rpms any lower....I can't drive 55 :rockin
 

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i got the same problem at 65mph im at 2000rpm getting 16mpg highway, im lookin at getting 285 75 16 and hoping ill see a differnence
 

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With the 245's on my truck I run a lil over 2000 at 70 i think...I know I get between 19-21 on the highway though and around 16-17 around town.
 

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Discussion Starter · #7 ·
70mph gives me about 2200rpm which is a tad high for a comfortable cruise. Sounds to me like the 265's are the perfect compromise unless towing heavy where the extra rpm's would be beneficial.

The Suncoast 6spd upgrade drops the rpms by 325 putting it in that sweet 1800-1900 range, however $$$. ....wish I had an LBZ !! :drink
 

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i got the same problem at 65mph im at 2000rpm getting 16mpg highway, im lookin at getting 285 75 16 and hoping ill see a differnence

I went from 265s to 285 and fuel mileage dropped. 265s with the speedo on 70 (really probably 72-73 mph) I was getting 18-19 on the interstate. 285s with the speedo at 68 (probably 71-72 mph) getting 16-17 on the interstate. I didn't notice a big difference in RPM going to the 285s. I would say its only running 50 RPM lower at 70 mph with the 285s than when I was running 265s. Based on my VIN ( I think) my truck is running 3.73 gearing. Not sure why my RPMs aren't around 1800 when in the 65 mph range. If I set my truck at 73 on the speedo I am running about 2300 RPM?? Seems high to me, but oh well. Looking at throwing on an intake and getting EFI Live this summer to help out. Right now is a crap shoot to figure out real economy running winter blend. Need to get my fuel filter changed too, so hopefully that boosts it a little.

racer
 

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do you have winter fuel were you are at? headwinds,road conditions, all play a part. how long have you been running this set up? enough time to confrim your avg has dropped off that far.

I have been around approximently 20-30 trucks who have increased tire sizes and all dropped mileage.
 

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I have 243's stock rims, LB7, 70mph is alittle over 2000rpms and the instant milage is around 21-24 highway, on 6gun setting 5 an banks cold air. before I had the banks it was around 20-21,22 instant, but on a 240 mi round trip ( before banks ) i was running 20.5 avg.mpg, my brother has 285's an dropped 2-3 mpg, with his lly
 

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Kinda weird....when my truck was bone stock with 245's.....I was averaging 17.5 city and 21-22MPG highway....and that was hand calculated. Right now I run 305/70-17's and get 15-16 city and 19 Hwy.
 

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Discussion Starter · #13 ·
Who knows, maybe the Grabbers have grabbed my fuel economy lol...in all fairness they do seem like a really nice tire. I'm thinking I'm gonna take advantage of that 30 day exchange and go back to 265's...look better, run better, might as well !! :drink
 

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i dunno, size does drop rpm alittle but i cant believe it would make all that much difference , tread compound and tread design IMO is the big factor here, ive owned my dmax for a year now and mpg's vary quite a bit. when i got my truck it had 4 new bridgestone v-steel radials E load 245 75 16 and i ran them at 80psi, overall average was around 19-20 if i didnt haul anything and kept my foot out of it. these tires are a hard compound with a highway rib type tread = very little rolling resistance. i do know than when i put my snows on which are 265 75 16 C load (off my old halfton.. i know they are alittle weak) run em at 50psi and my milage is down to 14.5-15 hand calc. rpms run prety close to the 245's, truck definetly has alot of rolling resistance that i can feel, especially towing. can wait for spring to get my summer tires on and get my mpgs up
 

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With 265's im getting 14.3mpg just driving around and my truck is BONE STOCK. I kinda wish i stuck with the 245's. I see peeps sayin they are getting this many mpg's, but you have to look down and read list of add on's lol. How many people on here have a completely stock truck? I find it hard to drop all that cash of mods just to gain a few mpg's. Im happy witht the power of my truck.
 

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Trickydave,

80 psi, wow. I know it says that is max pressure on the tire, but that rattles the fillings out of my teeth with every bump I hit. No joke though, it did rattle my right side blinker bulb out of the socket with 70-80psi. Makes the steering column shake real bad too.
 

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I still have the stockers, and have gotten as high as 24 mpg on the highway. Towing mileage around 14 mpg (7500 lb) boat or Toy Hauler. I only drive the truck maybe 12,000 miles a year....putting a set of 305's or 315's later this year...I expect fuel mileage to drop when I put on the H2's, but with the miles I drive it isn't a deal breaker...
 

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Discussion Starter · #19 ·
FYI - just burnt through my 4th tankful since getting the new 245's. Results so far consistently at 17.1-17.4mpg running on flat freeway 65-70mph (2000-2200rpm). Truck runs great so I have to assume it's the tire size and/or construction :mad:
 

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Does it calculate the mileage on the dash? Is the PCM reflashed for the different tire sizes? If not changing tire sizes and using that reading is meaningless... Might not vary much at all on your speedo, but from 245's to 285's even though the RPM difference the revolutions they turn to make 1 mile will be exactly the same....even if it takes you 1.1 miles..or more. So your mpg reading is NOT accurate.

So if it says your getting 20mpg and had 245's stock. And with 285's it says your getting 17mpg.... Your covering more ground with the 285's. .....probably getting the same mpg, just the reading is false. .... thats if you never corrected your speedo. :)
 
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