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Old 07-10-2021, 09:26 AM   #1 (permalink)
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Tire width and economy

I bought an e series ambulance a while back. It ce with 225/75 r16, and I have the ability to pick up a set of less than half worn 215/85 r16 for free. Load rating on both is identical, and the pattern is street

https://www.tirerack.com/tires/tires...um=185R6R500HD

I want to rock these solely due to how new they are (2019) is tire width something that can help measurably?

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Old 07-10-2021, 10:18 AM   #2 (permalink)
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The 215's need a higher pressure to not look buldgey flat and cup the center tread. Therefore, less rolling resistance at that higher pressure. Or at least on my 7.3 f250.
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Old 07-10-2021, 04:06 PM   #3 (permalink)
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All high economy cars (even economy "supercars") come with narrow tires. Those that take it farther use narrow, larger diameter tires (see BMW i3). I can't tell you the math behind it, but this is pretty much universal across all OEMs.
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Old 07-10-2021, 04:39 PM   #4 (permalink)
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Quote:
Originally Posted by hansj3 View Post
I bought an e series ambulance a while back. It ce with 225/75 r16, and I have the ability to pick up a set of less than half worn 215/85 r16 for free. Load rating on both is identical, and the pattern is street

https://www.tirerack.com/tires/tires...um=185R6R500HD

I want to rock these solely due to how new they are (2019) is tire width something that can help measurably?
Yes. It can help. I would not expect a big, or even measureable maybe, change from a 10mm diff in width. Be aware that a change in diameter will change displayed RPMs, speed, and measured distances.
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Old 07-10-2021, 05:34 PM   #5 (permalink)
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I can't tell you the math behind it, but this is pretty much universal across all OEMs.
It has to do with the shape of the contact patch. A longer, narrow patch of equal area results in less air resistance.
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Old 07-10-2021, 08:14 PM   #6 (permalink)
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Narrower and slightly taller, maybe those tires could lead to a small improvement to fuel economy. But if you're not in a hurry to change tires, it may not be so easy to justify the expense.
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Old 07-12-2021, 07:42 AM   #7 (permalink)
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First, there is a HUGE!! range in rolling resistance between make and models of tires within a given tire size. So large that changing tire sizes is small potatoes. In this case, the change would be less than 2% (in RR)

Now the LT215/85R16 is slightly larger in diameter, and that may result in slightly better fuel economy, but again, small.

I don't think you'll be able to measure a difference - and what difference you might be able to measure might be the difference in the amount of tread rubber. Worn tires get better fuel economy than new ones.
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Old 07-12-2021, 10:14 AM   #8 (permalink)
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I have anecdotal evidence from when I went from 195- 15 tire to a 215- 17 tire on my Jetta TDi. Sorry but can't recall the aspect ratios. The tires were very close to the same diameter, the larger tire and wheels being an option on higher trim models.

It absolutly had a negative effect on MPG. roughly 2 mpg. The larger tire has more weight and also more rolling resistance. Car did handle and look much better.

I would think there would be a measurable positive effect going to a smaller tire.
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Old 07-13-2021, 07:59 PM   #9 (permalink)
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Quote:
Originally Posted by CapriRacer View Post
First, there is a HUGE!! range in rolling resistance between make and models of tires within a given tire size.
Now that's a point most people forget, even though finding LRR tires for a truck is not easy to any extent.
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Old 07-15-2021, 11:20 PM   #10 (permalink)
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Quote:
Originally Posted by cRiPpLe_rOoStEr View Post
Narrower and slightly taller, maybe those tires could lead to a small improvement to fuel economy. But if you're not in a hurry to change tires, it may not be so easy to justify the expense.
Thankfully I have access to a shop, so costs are just time.

Even .25mpg increase would net me almost 14 miles per tank.

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