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Old 01-03-2013, 09:13 PM   #21 (permalink)
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I'd like to know how I missed this thread! I am curious about the same thing.
Quote:
Originally Posted by oil pan 4 View Post
You said it your self, you're only changing speed by 5-10mph most of the time. The faster you are going the less that 5-10mph change will matter.
The more the RPMs your wheel or drive train changes the more this mod will be worth. The RPM change in the rotating mass is the only accelerating that matters here.
I think the key phrase is CHANGE in speed. F=ma, so this wheel weight will have the most affect during accel/decel, I think.
Quote:
Originally Posted by ProDarwin View Post
Jesus, how heavy is the stock wheel/tire combo on the EvoX? Also, one thing to consider is that most lightweight aftermarket combos are going to be wider than stock. 9-10" wheels wont help your aero much.

That said, yes, anytime the velocity of the car is changing, rotational inertia is working against you. You will never recover all of it by coasting so lowering the amount of inertia stored in the wheel/tire/brake combo would be beneficial.

I'd like to see someone do an ABA test with the same tires/wheel specs but somehow make one combo much heavier... weld a 10lb weight to each wheel or something.
You should see the specs on my wheels. 42# each, and 43# tires. I made a thread about wanting to get some Centerline forged replacements, but I did the math for payback, assuming a 1mpg gain and it'd take me 168,000 miles to recoup. Dodge RAM 1500 wheel/tire size/weight debate But there is another thread from a Prius owner that shows some FE gains... Prius 15's are better than aftermarket 17's! (Wrong wheels/tires can wreck your MPG)

[edit] I learned my truck's alloy wheels are 37# each. Chrome plated ones are 38# each. The steel spare is 42#.

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Last edited by ECONORAM; 01-19-2013 at 01:11 PM.. Reason: wheel weight update
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Old 01-03-2013, 09:22 PM   #22 (permalink)
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Quote:
Originally Posted by ECONORAM View Post
I'd like to know how I missed this thread! I am curious about the same thing.

I think the key phrase is CHANGE in speed. F=ma, so this wheel weight will have the most affect during accel/decel, I think.


You should see the specs on my wheels. 42# each, and 43# tires. I made a thread about wanting to get some Centerline forged replacements, but I did the math for payback, assuming a 1mpg gain and it'd take me 168,000 miles to recoup. Dodge RAM 1500 wheel/tire size/weight debate But there is another thread from a Prius owner that shows some FE gains... Prius 15's are better than aftermarket 17's! (Wrong wheels/tires can wreck your MPG)
The main reason for the gain associated with the Prius in that thread is due to tire design changes and less to do with weight. 15" tires are just better for FE than 17" tires. We have many members who have tried to use lightweight wheels and the FE change was negligible. in stop and go driving, lightweight is still better.

Acceleration and braking should be much better.
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Old 01-03-2013, 09:37 PM   #23 (permalink)
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The ratio of sprung to unsprung weight determines the amount of spring rate and stiffness of the shock absorbers that are necessary to arrest the inertia of the components of the wheels and suspension that are "fired" at the vehicle by bumps and potholes. If you reduce the mass of the unsprung weight by 50 % then it takes a lot less spring force and shock dampening to stop that mass from bottoming out the suspensions travel. Drive a pickup with a solid rear axle down a washboard road, the do the same in a Mercedes to understand the difference.

In the example of the Prius getting better mileage with the proper low rolling resistance tires, most of the difference was the tires as well as the rim width and agressive tire design. My brothers Prius increased it average MPG by close to 5 by going from cheap 15inch tires to Ecopia 422s with no change in rims.

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Old 01-03-2013, 11:40 PM   #24 (permalink)
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Went from 235/75/15 to 205/76/15. Lost 15 lbs a tire. Could of gained about 2mpg per tank if I would have turned a blind eye to the loss of tire circumference. No significant change in FE but it was at a season change. At least I now have tires that grip in rain.
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Old 01-04-2013, 01:35 AM   #25 (permalink)
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Shame on you guys...

Quote:
Originally Posted by Ladogaboy View Post
So velocity might not be the right word to describe what I am talking about. So what force, specifically, is causing my car to require more energy to climb an incline than it does to maintain the same speed on level ground? For example, my car gets ~ 19 mpg cruising up a ~ 4% grade at 65 mph but gets ~ 28 mpg cruising at 65 mph on level ground. What's causing my car to burn that extra 30% energy?
for hijacking the OP's thread and not answering his questions.

The specific force you are looking for, is the force of gravity that is causing you to burn the extra fuel. Why? because you are not only pushing the car through the air at 65 mph, same as on the flat lands, BUT IN ADDITION TO THAT, you are also lifting it vertically up the hill against the force of gravity that wants to pull you back down the hill.

Your vertical speed is not at the same speed as your horizontal rate, but you are moving up away from the center of the earth, and you are fighting gravity with a force equal to the entire weight of your vehicle. To climb a 5% incline at a constant speed requires twice as much power at 65 mph as just moving on flat land. How do you make more power--you burn more fuel. Hope this helps, i can supply the maths if you desire a numerical explanation.
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Old 01-07-2013, 11:43 PM   #26 (permalink)
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ECONORAM - '07 Dodge RAM 1500 QC SLT flex-fuel
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Found these threads elsewhere on the Internet pertaining to wheel weight vs mpg:
Wheel Tech - Road Wheel Weights Can Affect Your Vehicle's Show...and Go
Light Wheels Vs Heavy Wheels - Wheel Tech - Comparison - Car Craft
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Old 01-08-2013, 12:21 AM   #27 (permalink)
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Quote:
Originally Posted by ECONORAM View Post
Check this out too, right here on EM: Tall tire test (taller gearing advantage offset by wider, heavier wheels/tires?)
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See my MODDING THREAD for ongoing projects. Black and Green's garage entry has more details. I plan to DIY rebuild this car over decades as parts die--replacing or modding small and major parts until it becomes a different car of roughly the same shape. My fuel economy goal is 60+ mpg while averaging posted speed limits.
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Old 01-08-2013, 06:13 PM   #28 (permalink)
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Quote:
Originally Posted by kennybobby Southern Squidbillie
Your vertical speed is not at the same speed as your horizontal rate, but you are moving up away from the center of the earth, and you are fighting gravity with a force equal to the entire weight of your vehicle. To climb a 5% incline at a constant speed requires twice as much power at 65 mph as just moving on flat land. How do you make more power--you burn more fuel. Hope this helps, i can supply the maths if you desire a numerical explanation.
Bingo. It's why when you collide two locomotives head-on, they go up; away from the center of the Earth.

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