Tire Weight

rd618

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Agreed. The physics checks out.
The other poster’s comment about such poor fuel economy and performance seemed off to me, as I don’t understand how a modest change in size and weight impacted them so much.
I’d expect some loss of economy as the vehicle has to work slightly harder, But not more than 10-15% given the minimal tire size increase and moderate weight difference. granted it will take more effort to move a heavier larger tire but we’re talking 30-40 more lbs per tire (rolling) and 5% increase in circumference.
 

Deadman

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My neighbor took his F150 and put 10Ply tires on it and they immediately dropped him 2mpg because they were so heavy. Same exact size tires and not a mud tire.

Read up on Unsprung weight, it affects performance A LOT!
 

Fastcar

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i believe the taller your tire is the more you cut your gear ration down. Just a ****** example, if your stock tire are 30" and your gears are 3:73's and you jump to say 32" your actual gear ratio is around 3:33. This is by no way accurate but is what happens when you start going with taller tires.
 

LokiWolf

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My Statement was 100% accurate. It is not weight but unsprung weight. Size increase is a small part of the puzzle, weight and tread pattern are a bigger part of it. Weight being the most important part. Tire weight is the worst weight too, because it contributes to high moment polar inertia, because the added weight is closer to the edges of the rotating mass(Wheel/Tire Combo). Adding tire weight makes acceleration slower, stopping longer, and lowers fuel economy, because it take more energy to do everything.

Edit/Addition: We didn't even take the added wind resistance, both because of increased airflow under the vehicle if the tire is taller, but if the tire has increased surface area. That additional surface area and contact patch also increases rolling resistance. All of these add to the decreased MPG.
 

LokiWolf

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This seems wrong at first glance, it seems like the tire is rolling and should not need a lot to keep that happening. Until you consider that when the car is running at 60 MPH, the outside tread of the tire is going from zero when it is in contact with the road to 120 MPH at the top of the tire, to zero again when it reaches the bottom again. Hundreds of times per minute. That is a lot of mass to accelerate and slow that often.
Like Laz said, not quite how it works. "Object in motion tends to stay in motion", it is the changing of the direction of that motion that takse the most energy.
 

rd618

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i think it’s straight forward, more weight, bigger, lower performance and economy.
The question should be, how much of an impact is made on average for the increased weight and tire size?
The math is do-able, but I’m not a mechanical engineer or physics expert.
20lbs increase in unsprung weight will impact performance, how much is “expected” impact all else equal?
like I said above 15-20% performance and economy hit is expected for a 20-30% increase in weight is what I’ve seen. It’s not directly linear relationship. But that’s not “scientific”.
 

LokiWolf

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i think it’s straight forward, more weight, bigger, lower performance and economy.
The question should be, how much of an impact is made on average for the increased weight and tire size?
The math is do-able, but I’m not a mechanical engineer or physics expert.
20lbs increase in unsprung weight will impact performance, how much is “expected” impact all else equal?
like I said above 15-20% performance and economy hit is expected for a 20-30% increase in weight is what I’ve seen. It’s not directly linear relationship. But that’s not “scientific”.
Correct, it makes a bigger impact than most expect. It is definitely not linear. In addition driving surface, and style will make a difference also.
 

JohnSC

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Has anyone moved from 22" factory tires to 18" wheels and LT tires for towing safety? What should I expect to see in ride and fuel economy effects with that change?
 

rd618

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Was eating at me so here’s part of the math to get the physics portion. https://www.maplesoft.com/content/E...4/MapleDocument_30/Rotation MI and Torque.pdf

Long story short, your wheel can weigh a lot. But the more it weighs the slower you have to accelerate to achieve the desired speed. If you try to accelerate at the same rate as before, you require more power to spin the larger size of mass. The actual dimensions of the wheel we are discussing are small, they will have a negligible impact.
As Loki and others point out also, tire compound, friction, and rolling resistance will more significantly impact the “maintenance” of the desired RPM.
Bigger and heavier = more power to move and keep moving. The amount of power is actually up to the user. Time to achieve speed and maintain it will determine the power and efficiency needed.
 

JasonH

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Has anyone moved from 22" factory tires to 18" wheels and LT tires for towing safety? What should I expect to see in ride and fuel economy effects with that change?

I put LT tires on my 20s. It rides a bit harder and lost ~1 mpg, but the peace of mind and improved stability while towing was worth it. Try finding a shop that will let you swap back if you don't like the LT tires.
 
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