Why does larger wheels/tires on a car cause significantly reduced mpg, and more stress on the transmission and suspension?
I get that they may weigh more, but a larger diameter means that you go farther in one rotation, so shouldn’t you be able to go farther with the same amount of work from the engine?
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It doesn’t necessarily increase or decrease mpg, it can do either, depending on if the gear ratio is closer to the ideal for whatever speed/load you’re at. It will increase load on the transmission because the bigger diameter needs more torque from the driveshaft to get the same force to the road.
If your car has a MPG meter, it will read lower MPG even if real MPG increases, because it doesn’t know you put bigger wheels on.
The more tire you have touching the road, the more friction you’ll have to overcome to get the same speed with a smaller tire. Better traction overall means more work to move. I’m sure there’s a physics formula somewhere that explains it better but that’s my understanding
There are a couple of things happening:
1. Unless the speedometer has been re-calibrated to reflect the different diameter of the wheel, it will be off and show lower MPG/ higher speed if the wheel is smaller (more tire rotations per mile) and higher MPG/ lower speed if the wheel is larger (fewer rotations per mile).
2. Weight. Large tires are heavy, and usually the large aftermarket rims are stupidly heavy. It’s easy to create a large wheel. It’s much harder (and much more expensive) to create a *lightweight* large wheel. Wheels and tires are what is called “unsprung weight”, which directly affects how quickly the car can change directions and how hard the parts have to work to do so. A 3lb reduction in unsprung weight at each corner can increase MPG by 5%
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