Can wider tires affect MPG? 20mpg@80mph
#16
Originally Posted by csdstudio
^^ Correct. I'm just comparing lighter wheels to heavier wheels. Once in motion and at a fixed velocity there would be no more drag with heavier wheels than lighter ones. Heavier wheels only affect change of velocity, resulting in slower acceleration and slower deceleration. Are we talking the same?
#17
Originally Posted by csdstudio
But weight is only 5lbs each wheel, no more than a couple 12 packs on the trunk. I understand acceleration is hindered with added wheel weight, but once cruising, weight is just added car weight just like adding passengers. My mileage is the same with just me, or with 4 passengers. And overall diameter is the same as stock 18's.
-Sean
#18
Originally Posted by redlude97
THis is an incorrect assumption, the friction is a function of the weight and width of the tires. Added width to the tires means more perisitic friction loss due to contact with the road surface. This can result in lower mileage.
From a friction standpoint a 225 tire increased to 245 is ~9% increase in friction? As far is friction is concerned, added weight is hardly noticeable because each tire already has 900+ lbs between it and the ground. But, what has more friction, aerodynamic resistance, or tire resistance? Because let's say if the ratio between air and tire resitance is 1:1, then total resitance has increased only ~4%. Uh, this is crazy.
Originally Posted by Nismo G
5 pounds to the each wheel is a HUGE ammount of weight to the car. Its rotational and unsprung weight. That 20 pounds is probably equal to 60 pounds of extra weight inside the car. You car is probably .3 seconds slower than it was before as well, if not more.-Sean
Last edited by csdstudio; 11-05-2007 at 07:30 PM.
#19
Originally Posted by csdstudio
Not ranting at all, but I know I've heard that a million times. Are there any studies or data to show that the difference is that great? Has someone done back to back time trials? Are there any formulas to calculate differences between different weight/diameter wheels? I just don't feel any difference compared to stock. And I DID notice a big difference in acceleration from my old 05 Coupe (~14.2 car) to my new car (~13.9 car) so at least I know my butt dyno isn't numb.
Anyways, if i remember unsprung weight has a 1 to 8 factor. 1 pound of unsprung weight is equal to 8 pounds of sprung weight. I have not yet taken my car to the track to test this theory, but maybe this thursday i will. Then again weather conditions come into play as well so it is hard to tell. With my OEM 17" rims my best run was a 13.8 i have lost about 3 to 4 pounds per wheel when i put my 19" rims on and thats factoring the tires as well. So if i do the math thats equal to about 96 pounds of regular weight i lost. Which would be something around .2 seconds off the 1/4 mile.
-Sean
#20
Originally Posted by Nismo G
What jeff said is correct. 5 pounds to the each wheel is a HUGE ammount of weight to the car. Its rotational and unsprung weight. That 20 pounds is probably equal to 60 pounds of extra weight inside the car. You car is probably .3 seconds slower than it was before as well, if not more.
-Sean
-Sean
All I know is that heavier wheels and tires hurt fuel economy, acceleration, etc. more than just adding that weight to the trunk.
But 4mpg seems too much.
#21
#22
I could get WAY involved with this, but according to my calculations, with the rated PSI on the tire, you should lose about 4.6-4.7% mpg. This is due to the "sag" of the tire at the point of contact. Where the car weighs down, there is a larger contact point and the tire sags under the weight., this is why a rolling ball stops (eventually) even if air resistance in negligible.
Dont make me get into it.
Kevin
Dont make me get into it.
Kevin
#23
Originally Posted by ABQ_G35
Maybe this sounds dumb, but when you change the size of your wheels/tires, it affects the speedometer and odometer, so perhaps that is the difference?
#24
#26
Red Card Crew
iTrader: (24)
Or just put your stock wheels/tires back on and compare.
Originally Posted by csdstudio
I see, so if we're not talking acceleration, just rolling resistance:
From a friction standpoint a 225 tire increased to 245 is ~9% increase in friction? As far is friction is concerned, added weight is hardly noticeable because each tire already has 900+ lbs between it and the ground. But, what has more friction, aerodynamic resistance, or tire resistance? Because let's say if the ratio between air and tire resitance is 1:1, then total resitance has increased only ~4%. Uh, this is crazy.
Not ranting at all, but I know I've heard that a million times. Are there any studies or data to show that the difference is that great? Has someone done back to back time trials? Are there any formulas to calculate differences between different weight/diameter wheels? I just don't feel any difference compared to stock. And I DID notice a big difference in acceleration from my old 05 Coupe (~14.2 car) to my new car (~13.9 car) so at least I know my butt dyno isn't numb.
From a friction standpoint a 225 tire increased to 245 is ~9% increase in friction? As far is friction is concerned, added weight is hardly noticeable because each tire already has 900+ lbs between it and the ground. But, what has more friction, aerodynamic resistance, or tire resistance? Because let's say if the ratio between air and tire resitance is 1:1, then total resitance has increased only ~4%. Uh, this is crazy.
Not ranting at all, but I know I've heard that a million times. Are there any studies or data to show that the difference is that great? Has someone done back to back time trials? Are there any formulas to calculate differences between different weight/diameter wheels? I just don't feel any difference compared to stock. And I DID notice a big difference in acceleration from my old 05 Coupe (~14.2 car) to my new car (~13.9 car) so at least I know my butt dyno isn't numb.
#27
Originally Posted by 06g35meister
I could get WAY involved with this, but according to my calculations, with the rated PSI on the tire, you should lose about 4.6-4.7% mpg. This is due to the "sag" of the tire at the point of contact. Where the car weighs down, there is a larger contact point and the tire sags under the weight., this is why a rolling ball stops (eventually) even if air resistance in negligible.
Dont make me get into it.
Kevin
Dont make me get into it.
Kevin
Tires are same diameter as stock.
I'd put my stock wheels back on to compare, but I'm trying to sell them.
"But 4mpg seems too much." Agreed, that's why I'm trying to figure this out.
#28
Originally Posted by redlude97
THis is an incorrect assumption, the friction is a function of the weight and width of the tires. Added width to the tires means more perisitic friction loss due to contact with the road surface. This can result in lower mileage.
The tread and compound material determine rolling resistance, not tire width. Big wide slicks have almost no rolling resistance, but narrower snows still have a lot. Mileage with slicks is better than with snows, regardless of width.
my 2 pennies ;-)
#29
Something else to try: Calculate the fuel economy yourself. Fill up tank, drive on highway, measure distance, fill up again, divide the two numbers.
Heat, humidity, wind, speed, etc. can also affect fuel economy.
But, I still can't see how you'd be getting as low as 20mpg. I'm assuming you're resetting your average fuel economy when you're on the highway, right?
Heat, humidity, wind, speed, etc. can also affect fuel economy.
But, I still can't see how you'd be getting as low as 20mpg. I'm assuming you're resetting your average fuel economy when you're on the highway, right?
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