Tire size vs. fuel mileage

[thirstyram]

Anyone have any personal experiance trying out different tire sizes and thier effect on fuel mileage? When I got my truck, it had 285/75's and I clocked my mileage at 24.5 combined city and hwy. Only checked it once before changing tires, (BAD tire pull)so it could have been a farce. Anyway I went to 265/75's and the mileage went waaaay down. I've got an Auto and I think it has 342 gears. Somewhere around there anyway. I'm thinking of trying some used 285's just to check it but I thought I'd check with you guys first. Any free advice on tire size?

 

[rebel_horseman]

Fill in your sig so we can know what kind of truck we're talking about. Running 285s I've gotta assume that you've got a 3/4 ton 4x4. If you got 24.5 combined with the high gears and auto then you've either miscalculated or you're looking at the overhead computer. With your combo I can see getting maybe 21 on the highway but definitely not combined.

Usually when you go up in tire size you get a mileage penalty. Going down you should pick up 1 or maybe 2 MPG. Course that depends on the type of tire it is too. If you step down in size but put on a set of mudders you may end up seeing a net loss in mileage.

 

[rebel_horseman]

Fill in your sig so we can know what kind of truck we're talking about. Running 285s I've gotta assume that you've got a 3/4 ton 4x4. If you got 24.5 combined with the high gears and auto then you've either miscalculated or you're looking at the overhead computer. With your combo I can see getting maybe 21 on the highway but definitely not combined.

Usually when you go up in tire size you get a mileage penalty. Going down you should pick up 1 or maybe 2 MPG. Course that depends on the type of tire it is too. If you step down in size but put on a set of mudders you may end up seeing a net loss in mileage.

 

[averagef250]

I think 255/85/16's are one of the best 3/4-1 ton tires for work and mileage.

Knowing how to drive your vehicle efficiently is the single biggest mileage adder.

 

[thirstyram]

Thanks for your input,Rebel Horseman and averagef250. The suggestion to use 255/85s really caught my eye. I did the math and if I,m correct,they're a little taller than 285/75s as well as being narrower. Am I right? Are you running them on any of your trucks? Thats a pretty unusual size though. Who makes them?

 

[Clydesdale]

yupper dead on with the numbers...

the 285/75 are not quite a 33/12.5, the 255/85 are truly a 33/9.50.... What I have on my 302 Bronco right now is the 33/9.5.. did immediately, so unsure if penalkized or not, but they corrected the speedometer, read horrendously fast with stock on there, and I pull 15... and it needs a tune.

My best mileage out of my last IDI was 20 at 60 on the speedo, 65 in real life, 315/75/16's, BFG Mud TA.. It even still had an exhaust leak right at the collector for the turbo...

I am a firm believer that increased rolling resistance on a gas truck is a big deal, and on a diesel, not the hugest deal,(point counter for sure, but not as much so as a gas engine due to the copious amounts of torque we produce) larger tires can turn into a Poor Man's OverDrive real quick, 4.10 gears stock, is stock, 4.10 stock become 3.73 with 315/75's-35"... 4.10 stock becomes 3.42ish with 37's..etc. etc. etc.

 

[thirstyram]

yeh my speedo still runs a little fasr with 265/75s so I bet its way fast with the stock 245s. Wierd huh?

 

[averagef250]

I am a firm believer that increased rolling resistance on a gas truck is a big deal, and on a diesel, not the hugest deal,(point counter for sure, but not as much so as a gas engine due to the copious amounts of torque we produce) larger tires can turn into a Poor Man's OverDrive real quick, 4.10 gears stock, is stock, 4.10 stock become 3.73 with 315/75's-35"... 4.10 stock becomes 3.42ish with 37's..etc. etc. etc.

That's exactly how I feel. My '71 is as aerodynamic as a barn and gets better mileage than a New V6 Toyota weighing twice as much and able to safely tow several times more. The truck sits on 35X12.50X16.5 BFG muds and has a real world running average of 25.2 MPG for 42,400 miles in the past 18 months.

An extreme example would be a fast-as-possible trailer delivery I did last summer to Boise Idaho. I towed 6000 pounds there from Portland, Oregon averaging over 65 MPH and averaged a tick over 21 MPG. I turned right around, being rather tired and constantly being passed by people going way too fast I put the pedal to the floor for the better part of 300 miles. Doing 90 MPH at 2850 RPM the truck actually got 22 MPG.

Yes, I've run 255/85R16 BFG Mud terrains on several vehicles and they work very well. BFG stopped making them, but they do now have an equivelent in a 17" wheel, though a forget the size. 255/85's are common used though. They are pretty much the "farm and ranch special" of tires. They are the 4x4 size most commonly used by the folks in the know, who understand that tall and skinny will best anything short of an R-1 tractor tire on a pickup.

Also, 255/85's seam to like being mounted on a skinny wheel. In my experience they have less than 9.5" of actual tread width and like around a 7.5" wheel width, perfect for most stock steel wheels.

 

[thirstyram]

Dustin, Are those mileage figures on your 5.9 Cummins? What is your Diff Ratio? I'd sure like to know more about your 3.9 CTD rig as well as your 4.5 project.

 

[thirstyram]

Hey rebel horseman, What does Sic Vis Pacem Para Bellum mean? Is that Latin??

 

[rebel_horseman]

'Tis Latin. It roughly translates: "To ensure peace, prepare for war."

 

[thirstyram]

well, Sic Vis Pacem,Para Bellum, makes sense to me!

 

[averagef250]

Dustin, Are those mileage figures on your 5.9 Cummins? What is your Diff Ratio? I'd sure like to know more about your 3.9 CTD rig as well as your 4.5 project.

When I wrote that I had a 71 F250 with a 3.9 4BT. The mileage figures were from that truck. I put the 71 together to see how I liked the 4BT in a fullsize pickup. I've had this 70 F250 for quite awhile, I'm attached to it and not willing to cut corners to make it as I feel it should be. I liked everything about the 3.9 except the non-boost off idle power so for the 70 I'm using a 4BT with a much longer stroke, more displacement and 16 valves instead of 8. It is the same bore/stroke as the 6.7 6BT. The 4.5 I have is a 2006 engine from a Clark forklift. It is rear geartrain which makes the engine much quieter and this engine is mechanical with a VE pump. I'm shooting for 300HP and 600 lb/ft with a single turbo, quiet and comfortable to drive. There are lots of variables still up in the air like how the VE pump will work and how to adapt power steering to this rather unique engine, but it'll get there eventually.

 

[thirstyram]

thanks for the info. sounds like you really know your way around these engine's

 

[pokesfan]

Tire sizes

Guys I have a 97 One ton dually with 4 10 rear end 2 wd. right now I am running 235 85 16. Anything better out there for me.