EcoModder Forum Tires. Skinny/wide? Tall/low pro?

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 04-10-2018, 02:06 PM #21 (permalink) Duck duck duck     Join Date: Dec 2012 Location: Nieuwegein, the Netherlands Posts: 2,317 Red Devil - '11 Honda Insight Elegance Team Honda 90 day: 54.95 mpg (US) It - '09 Hyundai I10 Active Cool Team Hyundai 90 day: 29.32 mpg (US) Thanks: 846 Thanked 933 Times in 601 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, UG, partial LGB, extra brake pad return springs, neutral wheel alignment, 44/42 PSI (air), PHEV light (inop), tightened wheel nut. lifetime FE over 0.12 Gm or 0.08 MM. Last edited by RedDevil; 04-10-2018 at 05:43 PM..
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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).

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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).
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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.
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 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'...?

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 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.
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 04-11-2018, 09:22 AM #27 (permalink) Tire Geek     Join Date: May 2008 Location: Let's just say I'm in the US Posts: 672 Thanks: 0 Thanked 257 Times in 166 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. __________________ CapriRacer Visit my website: www.BarrysTireTech.com
 04-11-2018, 09:28 AM #28 (permalink) Master EcoModder     Join Date: Dec 2011 Location: Vermont Posts: 2,355 Gaptooth - '00 Honda Insight Team HondaGen-1 Insights 90 day: 58.91 mpg (US) Such Fit - '07 Honda Fit Sport 90 day: 41.27 mpg (US) Thanks: 775 Thanked 889 Times in 562 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. __________________ 2000 Insight TLC & Build Thread HCH1 Ecomodding
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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.
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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.

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