To those of you with 2nd gen auto rigs that have 285/75/16s...did you change your gear ratio? If not, did you notice a drop in power or rise fuel economy when switching to taller tires?
I certainly noticed a drop of about 1mpg with the install of the tires. As for power, a little less acceleration on the road, but nothing so bad where I regretted getting the tires.To those of you with 2nd gen auto rigs that have 285/75/16s...did you change your gear ratio? If not, did you notice a drop in power or rise fuel economy when switching to taller tires?
Why would you experience a drop in MPG? In theory, because more ground is covered in a single rotation, your fuel economy should go up (additional weight of tires not withstanding)I certainly noticed a drop of about 1mpg with the install of the tires. As for power, a little less acceleration on the road, but nothing so bad where I regretted getting the tires.
Another thing to take into account, is that if you get larger tires and calculate your gas mileage by the odometer mileage divided by the gallons input, you will seem like you're getting way less than you actually are. Because if you don't get your ECU recalibrated, your tires are actually spinning slower at the same speed due to the larger circumferance, therefore tricking the ECU. I found that I am off ~6% with mileage and speed. So at 70 on my speedometer, I'm really going ~74. And for every 1000 miles (actual), you only register 940. So make sure you take that into account if you calculate your gas MPG dropping.
I only thought about that when I got stopped for speeding, even though I had my cruise set at 74, I got popped for 79 in a 65 after I got my tires. I then set my cruise to 60MPH then timed how long a mile took to get my error in my speedometer, and I found it to be off by roughly 6% or 56seconds/per mile at a 60MPH gauge reading.
And one more thing, it also messes with the ABS computer sometimes when braking while making a turn. It thinks that the wheel is slipping due to the larger difference of wheel speed per degree of steering angle. I might be wrong about this last point, but it makes sense to me. I've felt the ABS kick in more than a couple of times when it shouldn't have.
Rotating mass is a MPG killer, and my tires weigh about 60/tire. I believe my stocks were about 40/tire about a 33% increase . The weight will depend on a lot of things, but the more ply's they have = more weight = less MPG.Why would you experience a drop in MPG? In theory, because more ground is covered in a single rotation, your fuel economy should go up (additional weight of tires not withstanding)
MPG's will decrease by roughly 2 to 3 MPG w/ the 285's due in part to weight of the tires.. I haven't noticed any difference in power, your speedo will also be off roughly 3 to 4mph at 65I'm just saying that if you don't regear your diff, the math says your mpgs should increase and power decrease. Of course, that's in a vacuum.
Nope, that was the first thing I did to her, was buy her new shoes. So even with a stock ride height, only thing I had to do was a melt mod....and I know this has been asked time and time again, but I need to be 100% sure. Nothing more than a melt mod is necessary to clear 285/75/16s on stock S rims with a 2" daystar lift (front spacer/rear shackle) Also, I have the stock spring packs and shocks on there. Is that going to be a problem?
Correct.. No it won't be a problem...and I know this has been asked time and time again, but I need to be 100% sure. Nothing more than a melt mod is necessary to clear 285/75/16s on stock S rims with a 2" daystar lift (front spacer/rear shackle) Also, I have the stock spring packs and shocks on there. Is that going to be a problem?
Yup,At highway speeds, once your speed is stabalized... the tires are also allowing the engine operate at a lower RPM (taller tire, numerically higher gearing), also with the extra rotational mass, and the momentum it has... its a small trade off. Either way... some notice a difference , some dont at all.There are 3 weights that you need to contend with and consider in a car design and they are:
#1. Sprung weight
#2. Unsprung weight
#3. Rotational mass
They all have an effect on overall handling and performance. However unsprung weight will have more of an effect than sprung weight. Rotational mass will have a bigger effect on the acceleration or your car and its overall quickness. Hence is why some cars opt for reduced mass flywheels and lighter driveshafts and axles.
To get more weight moving, you need more power, plain and simple. That power comes in the form of gasoline
However......driving at a constant speed, if you have 30lbs on each wheel or 300lbs, your gas mileage should be the same, because the mass is moving. However city driving (which I do about %30 of) accelerating that mass takes a lot more energy with more weight.
Take look here, I found this online http://www.physicsforums.com/showthread.php?t=488123
Aerodynamics get very complicated very fast when you start getting into the turbulence area. They may have gotten around it by now, but I remember when the best super computers could only handle the aerodynamics of the space shuttle without the external fuel tank and booster rockets. Add those parts and nothing could calculate the aerodynamics. Just putting random underbody shields in place could make things better, or worse, or do nothing. It would take a little (expensive) time in a wind tunnel to know.Im curious as to running full skids under the truck would cut down on wind drag under the truck as your creating a flat surface ? Hence the reason some race cars and new vehicles have plastic plates covering the whole underside .
Sorry to jump off topic.