What tires can i fit?

[guesswho512]

i have not been able to hit 20+MPG since i change the rears from 33x12.5r16.5 to 245x75r16. and those were some heavy beasts! but it lowered 60mph rpm.

[Prowelder]

True... I just tend to think about majority of people live in the city and do a lot of start and stop driving in town... This is where it goes down hill... But yeah your right once the vehicle is rolling and can keep it rolling you will gain or keep the MPG's but getting caught in heavy traffic it can bite back...

I know exactly what you're saying and I'm not saying you're not right, this was just my thinking. I guess I know for sure once I put some new rubber on!!! For me, I run about 60 miles of highway to 10 miles of city. Of course that depends on where I go and what I'm doing. Sometimes there will only be 1-5 miles of city to that highway or more. Just depends but most of the time it is all highway.

[LiveOak]

My mileage actually increased with taller/wider tires. This is PROVIDED I keep my speed around 45 to 55 mph indicated on the speedo. Once my speed exceeds 45 mph, the fuel economy drops like a Simonized refridgerator. This is due in large part to wind resistance. In Aviation there are primarily 3 types of drag, parasitic, induced, and profile. Rather than get into a doctoral disertation on laminar flow dynamics which I am sure will bore and irritate AH64ID. I'll just post a the link below: http://en.wikipedia.org/wiki/Drag_(physics) In an over simplified attempt at quantifying drag physics for our trucks with respect to drag encountered at various speeds, the primary drags our trucks encount ar parasite and profile drag. The coefficient of drag for our trucks: http://en.wikipedia.org/wiki/Drag_coefficient http://en.wikipedia.org/wiki/Automobile_drag_coefficient I think would be pretty safe to say compete with a 4' x 8' sheet of plywood. http://en.wikipedia.org/wiki/Drag_equation Suffice it to say that as the velocity or speed doubles, the corresponding drag is mathematically SQUARED. This accounts for the HUGE drop in fuel economy. For the most part and there are some exceptions, the maximum efficient speed for most picups and SUV's is about 45 mph. Unfortunately most folks don't have the patience to drive this slow and additionally driving this slow on major highways can be a bit dangerous and risky. When you can drive on an isolated road with no traffic, try a very disciplined attempt to drive for a very long distance at 45 mph or a similar speed that will allow the most efficient rpm to do so. You will be amazed at the increase in fuel economy. I average between 21 to 24 mpg normally but when I get stuck in the insanity traffic on the interstate driving around 80 mph to the VA hospital, my fuel economy drops to around 11 to 13 mpg.

[AH64ID]

In Aviation there are primarily 3 types of drag, parasitic, induced, and profile. Rather than get into a doctoral disertation on laminar flow dynamics with I am sure will bore and irritate AH64ID. I'll just post a the link below:

Now thats funny :hyper: Along similar lines, it takes x hp to do 70 mph. It doesn't matter how many rpms your turning, it takes the same hp. With larger heavier tires the hp requirement goes up. So the only reason you can get better mileage is the parasitic drag from the drivetrain and accessories requires less hp at the new rpm than the tires take more of. On 12V trucks this is big, the static timing, the very simple injection setup and the older technology thruout the drivetrain will take more hp per rpm increase than VP44 trucks, and VP44 trucks take more than HPCR trucks. My dad has an 06 G56 (.79 OD) and he turns a lot more rpms than I do at 80, especially considering my 33" tires. At 80 he turns 2585 rpms, and I turn 2269 (my tires are 2.5lb heavier and turn 33 rev/mile less). We both run the same tuning, both have level kits, I have fender flares, but otherwise the trucks are very similar. I don't have a clear mpg advantage over him, sometime he will get better in a given condition and sometimes I will. Even when I ran a 285 AT, which was 6.5 lbs heavier and only 19 rev/mile fewer out mileage was near identical.