04-10-2018, 03:06 PM
|
#21 (permalink)
|
Master EcoWalker
Join Date: Dec 2012
Location: Nieuwegein, the Netherlands
Posts: 3,999
Thanks: 1,714
Thanked 2,247 Times in 1,455 Posts
|
Inertia The energy contained in a moving or rotating body is not linear but quadratic to speed.
It takes 0.5 Joule to speed up that kilogram to 1 meter per second, it takes 2 Joule for 2 m/s, 4.5 for 3 m/s, etc.
Inertia if you mean the contained energy in your formula is not mass * radius but just mass * (radius ^ 2) / 2.
And remember, only the speed matters, not the direction; whether it is straight, turning slowly in a big circle or fast in a tiny circle is indifferent. Only its speed matters.
__________________
2011 Honda Insight + HID, LEDs, tiny PV panel, extra brake pad return springs, neutral wheel alignment, 44/42 PSI (air), PHEV light (inop), tightened wheel nut.
lifetime FE over 0.2 Gmeter or 0.13 Mmile.
For confirmation go to people just like you.
For education go to people unlike yourself.
Last edited by RedDevil; 04-10-2018 at 06:43 PM..
|
|
|
Today
|
|
|
Other popular topics in this forum...
|
|
|
04-10-2018, 04:06 PM
|
#22 (permalink)
|
EcoModding Apprentice
Join Date: Oct 2010
Location: ireland
Posts: 102
Thanks: 8
Thanked 52 Times in 34 Posts
|
Quote:
Originally Posted by RedDevil
Inertia is not linear but quadratic to speed.
It takes 0.5 Joule to speed up that kilogram to 1 meter per second, it takes 2 Joule for 2 m/s, 4.5 for 3 m/s, etc.
Inertia, if you mean the contained energy, in your formula is not mass * radius but mass * (radius ^ 2) / 2.
And remember, only the speed matters, not the direction; whether it is straight, turning slowly in a big circle or fast in a tiny circle is indifferent. Only its speed matters.
|
You appear to be confusing the term "inertia" with "kinetic energy".
A mass M moving at a velocity V has a kinetic energy of 0.5 * M * V * V.
This however is not inertia.
Inertia is a measure of a body's resistance to changes in velocity.
It can be found from Newton's second law F = M * A and thus M = F / A
As there is no gravity in space, astronauts determine their mass (inertia) in a special device that applies a force and the rate of acceleration is measured. The rearranged Newtons 2nd equation is then used to calculate their mass (inertia).
|
|
|
The Following User Says Thank You to cr45 For This Useful Post:
|
|
04-10-2018, 05:36 PM
|
#23 (permalink)
|
Master EcoModder
Join Date: Aug 2012
Location: northwest of normal
Posts: 28,551
Thanks: 8,091
Thanked 8,880 Times in 7,328 Posts
|
Quote:
What are some of the best tire setups you have tried and also best mileage increaser. I know the biggest difference comes from driving habits. I am just curios to see what mods helped most too.
|
The received wisdom in the air-cooled VW world is to downsize the fronts. Keep the 165-15 in back for traction, and go to 135- or 145-15 in front. And put the nose on the ground.
Something closer to your front-wheel drive platform is the Rabbit pickups I've seen at the drag races. They run short, wide tires in front and tall, narrow tires in back. Maybe 14s and 16s?
Agree with CapriRacer at Permalink #7. Settle on the tire and then pick the wheel; and it's width (affects sidewall stiffness and turn-in).
__________________
.
.Without freedom of speech we wouldn't know who all the idiots are. -- anonymous poster
____________________
.
.Three conspiracy theorists walk into a bar --You can't say that is a coincidence.
|
|
|
04-10-2018, 06:39 PM
|
#24 (permalink)
|
Master EcoWalker
Join Date: Dec 2012
Location: Nieuwegein, the Netherlands
Posts: 3,999
Thanks: 1,714
Thanked 2,247 Times in 1,455 Posts
|
Quote:
Originally Posted by cr45
You appear to be confusing the term "inertia" with "kinetic energy".
A mass M moving at a velocity V has a kinetic energy of 0.5 * M * V * V.
This however is not inertia.
Inertia is a measure of a body's resistance to changes in velocity.
It can be found from Newton's second law F = M * A and thus M = F / A
As there is no gravity in space, astronauts determine their mass (inertia) in a special device that applies a force and the rate of acceleration is measured. The rearranged Newtons 2nd equation is then used to calculate their mass (inertia).
|
You are right. Inertia is mass (resistance to change speed), and rotational inertia is resistance to change rotational motion.
A bigger wheel has way bigger rotational inertia, but it covers a much larger distance than a smaller wheel rotating bat the same speed.
In the end what matters is how fast the thread moves - that's the same as the speed of the car, regardless of the size of the wheels.
__________________
2011 Honda Insight + HID, LEDs, tiny PV panel, extra brake pad return springs, neutral wheel alignment, 44/42 PSI (air), PHEV light (inop), tightened wheel nut.
lifetime FE over 0.2 Gmeter or 0.13 Mmile.
For confirmation go to people just like you.
For education go to people unlike yourself.
|
|
|
04-11-2018, 08:56 AM
|
#25 (permalink)
|
Master EcoModder
Join Date: Jun 2013
Location: Texas
Posts: 451
Thanks: 1,829
Thanked 127 Times in 106 Posts
|
Quote:
Originally Posted by RedDevil
You are right. [URL="https://en.wikipedia.org/wiki/Inertia"]...
In the end what matters is how fast the thread moves - that's the same as the speed of the car, regardless of the size of the wheels.
|
Well, my tires are in contact with the ground. When in contact with the ground the tread has zero forward motion. The car is still going 45 mph. The only thing on a wheel that is going the speed of the car is the axle. The top of the tire is going twice the speed of the car or 90 mph. Or is my thinkin' stinkin'...?
|
|
|
04-11-2018, 09:42 AM
|
#26 (permalink)
|
Master EcoModder
Join Date: May 2012
Location: Tampa, FL
Posts: 1,745
Thanks: 206
Thanked 420 Times in 302 Posts
|
Quote:
Originally Posted by Joggernot
Well, my tires are in contact with the ground. When in contact with the ground the tread has zero forward motion. The car is still going 45 mph. The only thing on a wheel that is going the speed of the car is the axle. The top of the tire is going twice the speed of the car or 90 mph. Or is my thinkin' stinkin'...?
|
I believe this is once again where a discussion spins off about linear and angular velocity.
__________________
|
|
|
04-11-2018, 10:22 AM
|
#27 (permalink)
|
Tire Geek
Join Date: May 2008
Location: Let's just say I'm in the US
Posts: 796
Thanks: 4
Thanked 393 Times in 240 Posts
|
I strongly suspect that the rotating mass of the tire causes an insignificant affect on fuel economy - that even a significantly wider tire barely changes the actual fuel consumption. I suspect this because the car manufacturers continue to go to wider and wider tires.
|
|
|
04-11-2018, 10:28 AM
|
#28 (permalink)
|
Master EcoModder
Join Date: Dec 2011
Location: New Zealand
Posts: 5,077
Thanks: 2,904
Thanked 2,560 Times in 1,586 Posts
|
Ahh, the march of progress.
Admittedly you get two more doors and it holds the brakes for you so you don't roll backward in neutral.
|
|
|
The Following User Says Thank You to Ecky For This Useful Post:
|
|
04-11-2018, 01:10 PM
|
#29 (permalink)
|
Master EcoWalker
Join Date: Dec 2012
Location: Nieuwegein, the Netherlands
Posts: 3,999
Thanks: 1,714
Thanked 2,247 Times in 1,455 Posts
|
Quote:
Originally Posted by Joggernot
Well, my tires are in contact with the ground. When in contact with the ground the tread has zero forward motion. The car is still going 45 mph. The only thing on a wheel that is going the speed of the car is the axle. The top of the tire is going twice the speed of the car or 90 mph. Or is my thinkin' stinkin'...?
|
On average every part of your wheels is moving forward at the same speed as the rest of your car. So the forward motion part of inertia is equal to fixed parts of the same mass.
Then it also takes energy to spin up the wheel; slightly less than the forward motion requires. The total inertia is the sum of both; slightly less than twice the mass of the wheel.
__________________
2011 Honda Insight + HID, LEDs, tiny PV panel, extra brake pad return springs, neutral wheel alignment, 44/42 PSI (air), PHEV light (inop), tightened wheel nut.
lifetime FE over 0.2 Gmeter or 0.13 Mmile.
For confirmation go to people just like you.
For education go to people unlike yourself.
|
|
|
04-11-2018, 01:53 PM
|
#30 (permalink)
|
Master EcoModder
Join Date: Aug 2012
Location: northwest of normal
Posts: 28,551
Thanks: 8,091
Thanked 8,880 Times in 7,328 Posts
|
Quote:
Originally Posted by Ecky
Ahh, the march of progress.
|
Similarly, over it's production run, the Beetle went from 25hp/40mpg to 50hp/28mpg.
__________________
.
.Without freedom of speech we wouldn't know who all the idiots are. -- anonymous poster
____________________
.
.Three conspiracy theorists walk into a bar --You can't say that is a coincidence.
|
|
|
|