Hi!
Three questions.
Sidewall stiffness; how does it affect fuel economy?
Last November (over a year ago November) I replaced whatever my car came with, passenger tires with a wsw but I don't know the brand, with light truck tires.
My fuel economy got worse. For other reasons, like the fact that it was on the cusp of winter and winter gas and a colder, richer-running engine, I couldn't peg this entirely on the tires. But I felt it was so. I calculate fuel economy at every fresh tank of gas. Also, the tires had a greater width AND aspect ratio, so my apparent mileage (and therefore fuel economy) was going to be understated. However, the degree to which it is understated is around 5%.
It seemed that my fuel economy plummeted from 18-20 mpg averaged, to 15-16mpg. Again, this could have been due to winter...?
But then today, I had a discussion with an older guy at work, who said he had a customer with a prius who complained of greatly reduced fuel economy after an oil change. My dad has a prius, and I know he obsesses over "hypermiling"-- it becomes a hobby to anally track every last drop of gasoline for these folk, and god forbid they see a palpable drop!
Turned out, he got tires at the same time (elsewhere). That shop, mr tire, had talked him into more expensive tires with a better speed rating, and stiffer sidewalls. They accounted for a 9mpg averaged drop in fuel economy! Granted, we're talking 9mpg off a vehicle that started with 40-50mpg.
So I have my suspicions about my own light truck tires (versus my old passenger tires), and now this story.
Is there something to it; do stiffer sidewalls harm fuel economy?
I was trying to think about it, and could not come up with a good answer. After all, a stiffer tire should compress less, and therefore have a lower rolling resistance, right? And after all, it is known that low air pressure will dramatically raise rolling resistance as the tire sinks lower, and more rubber is constantly compressing and decompressing as it rolls-- and likewise that over filling a tire might aid fuel economy, at the cost of a risk of a blowout, and reduced traction, of course. So I'm not advising it. Wouldn't a stiffer tire do much the same thing as more air pressure, shrinking the contact patch with the road and lowering the amount of rubber that is being kneaded by the rolling wheel?
My other two questions are quicker.
I bought some uniroyal tiger paw tires for another car. There's a slight ripple in the side wall of one, perfectly radial. Definitely nut a bubble. Just a straight vertical line of a slight depression in the side. What causes that? Is it a problem? Is it a "slipped belt" that I've heard about?
Lastly, I was idly wondering... from an engineering standpoint, are perfectly radial spokes the ideal, or would any sort of curved, sweeping spoke, aside from being stylish, serve a function?
Three questions.
Sidewall stiffness; how does it affect fuel economy?
Last November (over a year ago November) I replaced whatever my car came with, passenger tires with a wsw but I don't know the brand, with light truck tires.
My fuel economy got worse. For other reasons, like the fact that it was on the cusp of winter and winter gas and a colder, richer-running engine, I couldn't peg this entirely on the tires. But I felt it was so. I calculate fuel economy at every fresh tank of gas. Also, the tires had a greater width AND aspect ratio, so my apparent mileage (and therefore fuel economy) was going to be understated. However, the degree to which it is understated is around 5%.
It seemed that my fuel economy plummeted from 18-20 mpg averaged, to 15-16mpg. Again, this could have been due to winter...?
But then today, I had a discussion with an older guy at work, who said he had a customer with a prius who complained of greatly reduced fuel economy after an oil change. My dad has a prius, and I know he obsesses over "hypermiling"-- it becomes a hobby to anally track every last drop of gasoline for these folk, and god forbid they see a palpable drop!
Turned out, he got tires at the same time (elsewhere). That shop, mr tire, had talked him into more expensive tires with a better speed rating, and stiffer sidewalls. They accounted for a 9mpg averaged drop in fuel economy! Granted, we're talking 9mpg off a vehicle that started with 40-50mpg.
So I have my suspicions about my own light truck tires (versus my old passenger tires), and now this story.
Is there something to it; do stiffer sidewalls harm fuel economy?
I was trying to think about it, and could not come up with a good answer. After all, a stiffer tire should compress less, and therefore have a lower rolling resistance, right? And after all, it is known that low air pressure will dramatically raise rolling resistance as the tire sinks lower, and more rubber is constantly compressing and decompressing as it rolls-- and likewise that over filling a tire might aid fuel economy, at the cost of a risk of a blowout, and reduced traction, of course. So I'm not advising it. Wouldn't a stiffer tire do much the same thing as more air pressure, shrinking the contact patch with the road and lowering the amount of rubber that is being kneaded by the rolling wheel?
My other two questions are quicker.
I bought some uniroyal tiger paw tires for another car. There's a slight ripple in the side wall of one, perfectly radial. Definitely nut a bubble. Just a straight vertical line of a slight depression in the side. What causes that? Is it a problem? Is it a "slipped belt" that I've heard about?
Lastly, I was idly wondering... from an engineering standpoint, are perfectly radial spokes the ideal, or would any sort of curved, sweeping spoke, aside from being stylish, serve a function?
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