It's just about time to upgrade my dinky looking 265/75/16's on my 04 6.0 fx4 cc. I think bigger looks better on these trucks, but how big can you go (without lifting) before economy and performance begin to suffer? I have read posts where some people say they actually gotten better MPG from bigger tires. Is this possible? Others say they have lost a couple of MPG. Is everyone working the different tire diameter into their calculations? So what is your tire size and how does it perform? Oh and it might be good to state what gear you have too, mine is 3.73.

 

I would suggest 33's. I have 35's but have a 4.5" hanger/shackle set up. I can get up to 19mpg going 65mph. Usually around 14 to 17 though. I like the nitto terra grapplers or the toyo at's.

 

The nittos are very expensive.

 

Power and economy immediately suffer. Larger diameter tires raise the gear ratio making you loose power. Any larger is usually wider with more rolling resistance which lowers milage..

If you are chipped all this may not matter, especially the larger diameter. Best milage is usually made with the skinniest tires possible normally an 85 series with about 60 to 70 pounds of air pressure...Good Luck

 

your stock size is just over 31 1/2 tall Lt285/75r16 is just over 32 3/4 tall this is the most common upgrade size. You could also fit a Lt305/70r16 which is also about 32 3/4 tall. Most are only 8ply tires but hold almost the same weight because of the bigger size and more air volume. In theroy it would take more power in stop and go to get going so you might get lower mpg, but at highway speeds your rpm will drop so you should get better mpg. The 285 is 3/4 wider than stock and the 305 is 2 inches wider. If you want to go tall and narrow go with Lt255/75r16 it is 33 inches tall and a 1/2 inch narrower than stock. Stock width is just about 10 1/2 wide. hope this helps

 

your stock size is just over 31 1/2 tall Lt285/75r16 is just over 32 3/4 tall this is the most common upgrade size. You could also fit a Lt305/70r16 which is also about 32 3/4 tall. Most are only 8ply tires but hold almost the same weight because of the bigger size and more air volume. In theroy it would take more power in stop and go to get going so you might get lower mpg, but at highway speeds your rpm will drop so you should get better mpg. The 285 is 3/4 wider than stock and the 305 is 2 inches wider. If you want to go tall and narrow go with Lt255/85r16 it is 33 inches tall and a 1/2 inch narrower than stock. Stock width is just about 10 1/2 wide. hope this helps

 

How many here are running bigger tires without changing speedo settings and what effect (if any) do you feel like it has?

elee, I've been wondering the same thing. My 05 came to me with 245's, and that's the size listed on the door jamb sticker, but at 65 mph on my speedo, radars show me to be doing 61 mph. I want to go to a bigger tire, but I don't want to lose any noticeable performance, and I'd really rather not go back to the dealer to reset the computer for bigger tires, just because everything seems to be working great as it is. I'd love to go to 305's, but I can't really afford new wheels right now (I have the factory steel wheel 17 x 7 or 7.5? ) so I'm leaning hard toward 285's. A couple of local tire stores refuse to even price me 285's though, saying it'll throw the computer off too much (I don't think they believe my current speedo discrepancy), and though I really don't think it'll hurt anything, I have to admit they've got me a little bit concerned about it. I tow up to 12K pretty regularly, and I don't want to risk losing performance.


No offense Mike, but I've been pricing tires here, and I can get Nitto's noticeably cheaper than Goodrich, Goodyear, Bridgestone, Firestone, Michelin, or Cooper. Maxxis and Hankook are the only other tires available locally in the same price range. I can get LT285/70R x 17 E Terra Grapplers (rated at 3750# @ 80 psi) for $180 a piece, mounted and balanced, compared to $200+ for the "big" name brands...

 

I run 35's w/ stock 373 gears and speedo error increases w/ MPH. I also have a GPS that I use for MPH readings. At 65-70 MPH on speedo I am actually going 8 MPH faster according to GPS which has a very high rate of accuracy. Rule of thumb (mine) is I assume I am running 10 MPH over speedo's reading at highway speed so I don't get too close a look from the gentlemen in blue.

 

Thanks Excursionator. I can live with the speedo discrepancy once I figure out what it is. Do you feel like it's made a big difference in shift points or the abs system? Or do your performance mods compensate for that?

 

ramblincowboy,
I have the same speedo discrepancy as you. When it reads 65, my GPS and the roadside radars tell me I'm going 61. I have a flashpaq tuner that allows you to adjust tire size, but I don't know if that affects the speedo or just the shifting. Besides I'm not currently using it (tuner) and I don't think you can use the tire size option with the stock tune. I think that superlift sells a gizmo for setting the speedometer, but I don't know anything about it or how much it costs.

 

actually the nittos are quite cheap, the toyo's are very expensive.

i run the 35" nittos but i have 6" lift. and with 3.73's i get around 10-15mpg depending on conditions

 

How about the stock 20s with the nittos?

 

i run 35 inch procomp xtreme terrain, i get about 14-15 on highway now and my speedo is right on...at least thats what this radar thing says when i pass it everyday haha

 

Is it (the radar) flashing wildly when you pass? I always feel like those things are yelling SLOW DOWN!

 

You didn't say wether you are going to get new wheels, if so you have tons of options, if not , as fgibby states the Lt305 70 16 or Lt285 75 16 woul be your best bet. I run Lt 285 75 16's BFG all-terrains on my stock 16"KR rims. I like a wide tire with a lot of sidewall too. The speedo is off about 2 mph at 70, and everything stays inside the fenders.