Freakenhye

Just cuz your not educated doesnt mean that its stupid.

Well, during the test, dropping the engine speed by 420 RPM (4th to 5th gear), or 16.8%, raised mpg by 8.9 mpg (47 to 55.9), or 18.9%. So switching to the 3.1% larger circumference wheel & tire would reduce RPM by the same percentage (3.1%). That would theoretically increase MPG by 3.1% / 16.8% * 8.9 mpg = 1.64 mpg (US) in top gear.


It would take me less RPM to run at 65mph with a 20 inch tires then you with 17's.

BlackGMC

iTrader: (31)

Actually it would take more gas to turn 20's(~90#s) than 17's (~60#s). Reason being the amount of rotational wieght, basically 20's are like pulling a small trailer. You are correct in that it will change your final drive ratio, but way off on your theory that 20's will yeild a higher MPG. And comparing a Cobalt to a truck is like comparing apples and donkeys....

Freakenhye

This is why 20's on the street is a bad idea. But there performance is best for the freeway. If you read my first post then you would know. And comparing a cobalt to a truck is not what i did, I compared rims sizes. Becuase its easier to accellerate a 17's but its harder to keep it at the same speed then it is 18's. You are right about rotational wieght, but to counter that i got 21 miles per gallon on the freeway out of my 4.8 Vortec on a stock engine and tires, with 500 pounds of load in the back, wieght isnt the problem that much becuase the car was rated at 21mpg. Its people. Just Becuase they see a difference in less mpg with taller tires and they contribute this to the tire and not the led foot they have, they arnt used to the decrease in acceleration from larger rims/tires, and push the gas pedal more to get the accelleration feel that they are used to.

BlackGMC

iTrader: (31)

I see what your saying, its a beautiful theory but speaking from experience I had 20's on my truck and switched to stock 16 and my MPG went up both city and highway it has to do with rotational weight....... I don't think I have ever heard of anyone getting better MPG with 20's compared to smaller wheels..... The only way your theory would work is if the 20's weighed less than the 16's.....

Freakenhye

And this is why gearing is important. To compensate for the tires, to get the car back into the torque sweet spot. Becuase a vehcile has its best MPG when the rpm is in that range at crusing speed which is 65.


All this mpg gallong talk is what i do all day. try to get the best mpg out of my trucks.


Best i got out of my 03 silverado was 600 miles on a full tank of gas(26Gal). 4.8 stock. rated at 19mpg, but with my driving i got a full 23mpg out of the truck.

BlackGMC

iTrader: (31)

It is still more weight and no way around that.
For Example:

Truck A:
29.5 tire, 3.42 gears, 0.7 overdrive @ 65 turns 1772 rpm
Truck B:
35.0 tire, 4.11 gears, 0.7 overdrive @ 65 turns 1795 rpm

So from what your saying is that the trucks will get the same MPG and will accelerate the same? If you say yes then please post up your City and State so I can send an email to NASA and notify them that the basic laws of Physics do not exist in your City/State.

BTW, the calculator for these numbers can be found at Richmond Gear....

Freakenhye

width of the tire matters. ill give you that but a rim/tire that is the same width but taller will result in better mpg on the freeway then a smaller rim/tire combo.


Ahh man i know what your saying wider and taller tires = less MPG. Thats a given.

weight of rim has something to do with it, yes i agree but given the same weight and same width a 20 inch rim/tire combo would be better for the freeway then a 17 inch rim/tire combo.

rivierakid55

iTrader: (1)

this post is an interesting read. i get about 10 miles to the gallon with 22's and 4.56's.

Torque_Wrench

iTrader: (13)

.....wHAT THE F*CK ARE YOU TALKING ABOUT?

BlackGMC

iTrader: (31)