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Discussion Starter · #1 ·
So, based on various builds, it appears that gen4 siennas (assuming the same outer tire diameter) can accept 17", 18", and 19" rims (at least). So, assuming all other things being equal (so same tire brand/model), which rim size is the most fuel efficient?

If one changes the wheel size, but keeps the tire diameter the same, what really changes is the sidewall height. I was wondering about this because rivian offers three rim options and they say this regarding their EV range: "the 21 inch wheel combination is the most efficient, with the 20 inch and 22 inch wheels having a range reduction of 10-15% and 5-10% respectively."

So what is the optimal rim size or sidewall height for the sienna if the best fuel economy was one's highest priority?
 

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All stock options have similar outer diameters - smaller rims have taller sidewalls and vice-versa.

Also, all Sienna trims with stock tires and rims have same EPA mileage. I.e. tire and rims don't have measurable effects.
 

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Discussion Starter · #3 ·
All stock options have similar outer diameters - smaller rims have taller sidewalls and vice-versa.

Also, all Sienna trims with stock tires and rims have same EPA mileage. I.e. tire and rims don't have measurable effects.
Interesting.

But then why would a rim size change make such a big difference in efficiency on an EV (the rivian guidance above) ?
 

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Heavier wheels require more power to get up to speed, from what I've read (I'm not a physicist) this is more important with frequent starts/stops than highway travel due to rotational mass being less of a factor once in motion. They also alter ride and handling, stereotypically not for the better. I remember when Mazda made a big deal when removing one of 8 wheel spokes when copying British roadsters' Minilites for the OG Miata's 14" wheels. BTW Tesla also quotes different ranges between their standard and optional wheels, for the Model Y AWD LR it's 12 miles difference going from the 19" to 20" wheels.

Toyota does a bunch of things to keep average weights in the same ballpark - removing 2nd row ottomans when you opt for the spare tire, limit the number of 8 passenger Siennas by keeping them lower trims, and prevent them from having factory wheels larger than 17". I wouldn't be surprised if there's a cap on the number of US vans with the spare, it's standard in some other countries such as Mexico and China. There are likely small variations in fuel economy that when averaged across the entire FWD production that keeps EPA fuel economy estimates at 36mpg.

Consumer Reports has tested braking distances between hybrid and non-hybrid Toyotas/Lexuses, the former generally fitted with low rolling resistance tires and usually with measurably longer stopping distances. Don't know if the wheels tested were the same, on Toyota's configurator there are differences between some counterparts such as the Camry LE and LE Hybrid.
 

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Discussion Starter · #7 · (Edited)
Heavier wheels require more power to get up to speed, from what I've read (I'm not a physicist) this is more important with frequent starts/stops than highway travel due to rotational mass being less of a factor once in motion. They also alter ride and handling, stereotypically not for the better. I remember when Mazda made a big deal when removing one of 8 wheel spokes when copying British roadsters' Minilites for the OG Miata's 14" wheels. BTW Tesla also quotes different ranges between their standard and optional wheels, for the Model Y AWD LR it's 12 miles difference going from the 19" to 20" wheels.

Toyota does a bunch of things to keep average weights in the same ballpark - removing 2nd row ottomans when you opt for the spare tire, limit the number of 8 passenger Siennas by keeping them lower trims, and prevent them from having factory wheels larger than 17". I wouldn't be surprised if there's a cap on the number of US vans with the spare, it's standard in some other countries such as Mexico and China. There are likely small variations in fuel economy that when averaged across the entire FWD production that keeps EPA fuel economy estimates at 36mpg.

Consumer Reports has tested braking distances between hybrid and non-hybrid Toyotas/Lexuses, the former generally fitted with low rolling resistance tires and usually with measurably longer stopping distances. Don't know if the wheels tested were the same, on Toyota's configurator there are differences between some counterparts such as the Camry LE and LE Hybrid.
Some good thoughts, but I am more kinda interested in finding out if, on average (and all other things being equal), lower profile or higher profile tires have lower rolling resistance in just straight line highway driving. I have done some interweb searching on this topic, but all I find are a few bot authored sites that say one or the other but with no explanation and no evidence.

Specifically as it might apply to the gen4 Sienna, which appears to be able to run 17", 18", 19" rims, all with the same tire diameter (with different sidewall heights on the tires of course).
 

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So, based on various builds, it appears that gen4 siennas (assuming the same outer tire diameter) can accept 17", 18", and 19" rims (at least). So, assuming all other things being equal (so same tire brand/model), which rim size is the most fuel efficient?

If one changes the wheel size, but keeps the tire diameter the same, what really changes is the sidewall height. I was wondering about this because rivian offers three rim options and they say this regarding their EV range: "the 21 inch wheel combination is the most efficient, with the 20 inch and 22 inch wheels having a range reduction of 10-15% and 5-10% respectively."

So what is the optimal rim size or sidewall height for the sienna if the best fuel economy was one's highest priority?
Wheel size absolutely has an effect on fuel mileage. Larger diameter wheels are primarily for appearance. They have more mass farther away from the hub and take more energy to accelerate in addition to less compliant ride quality. I would not even consider the XSE trim due to wheel size. My preferred size is 17" for fuel mileage, ride quality, and cost of replacement.

Take a look at the 2023 Prius and see how significant a fuel mileage penalty due primarily to wheel size of different trims.
 

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Discussion Starter · #9 ·
Wheel size absolutely has an effect on fuel mileage. Larger diameter wheels are primarily for appearance. They have more mass farther away from the hub and take more energy to accelerate in addition to less compliant ride quality. I would not even consider the XSE trim due to wheel size. My preferred size is 17" for fuel mileage, ride quality, and cost of replacement.

Take a look at the 2023 Prius and see how significant a fuel mileage penalty due primarily to wheel size of different trims.
I will look at that. Does the toyota USA website have that info?

So, all other things being equal, is it safe to say that lower profile tires have worse rolling resistance over higher profile (but otherwise identical) tires? If yes, any thoughts about why Rivian, with available 20", 21", and 22" rims on their R1T, but yet Rivian says that the 20" rims have worse range compared to the 21" rims? That is puzzling.
 

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I will look at that. Does the toyota USA website have that info?

So, all other things being equal, is it safe to say that lower profile tires have worse rolling resistance over higher profile (but otherwise identical) tires? If yes, any thoughts about why Rivian, with available 20", 21", and 22" rims on their R1T, but yet Rivian says that the 20" rims have worse range compared to the 21" rims? That is puzzling.
Yes. The mileage penalty is 4-5 mpg.

Not likely rolling resistance but weight and where the weight is.

The Rivian numbers are puzzling for sure.
 

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Rim diameters specifically don't affect mpg. However total rim/tire mass will.

To optimize MPG you need the lightest wheel mass possible, with the smallest contact patch and a harder rubber compound.

Your example of the rivian 20"/21"/22“ leaves out a key detail:

The 20" is an all terrain tire which in itself is heavy. The mass of the rim/tire is 88 lbm
The 21" is considered a road tire. The mass of the rim/tire is 79 lbm
The 22" is their sport tire which has a lower tread wear (softer rubber, more grip). The mass of the rim/tire is 83 lbm

The 21" is the lightest of the options, so it makes sense that it has the longer range.
 

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Discussion Starter · #13 ·
Rim diameters specifically don't affect mpg. However total rim/tire mass will.

To optimize MPG you need the lightest wheel mass possible, with the smallest contact patch and a harder rubber compound.

Your example of the rivian 20"/21"/22“ leaves out a key detail:

The 20" is an all terrain tire which in itself is heavy. The mass of the rim/tire is 88 lbm
The 21" is considered a road tire. The mass of the rim/tire is 79 lbm
The 22" is their sport tire which has a lower tread wear (softer rubber, more grip). The mass of the rim/tire is 83 lbm

The 21" is the lightest of the options, so it makes sense that it has the longer range.
Ah, that makes sense for the Rivian. I thought that they were all similar (but I did not look at the exact tire specs, so thanks for catching that).

So, I am curious, if one is looking at rolling resistance only at a constant speed on the highway, does sidewall height affect rolling resistance/efficiency (if overall tire diameter is held constant) and, if yes, in what direction? And, if you know the answer, are there places on the interwebs where this is published and/or explained? Thanks.
 

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But rims that are only, say, 20% heavier than some smaller ones, that would affect mpg on a multi-thousand pound van at a constant speed on the highway? Really?
There is plenty of articles on this very subject. Again, it is not just the weight but where it is. A larger wheel has more mass further from the center. Your vehicle does not travel at constant speed and neither does mine.

Here is one article I found in .02 seconds.

Wheel diameter effect on performance
 

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Discussion Starter · #15 ·
There is plenty of articles on this very subject. Again, it is not just the weight but where it is. A larger wheel has more mass further from the center. Your vehicle does not travel at constant speed and neither does mine.

Here is one article I found in .02 seconds.

Wheel diameter effect on performance
Thanks for the reply and for the interesting article, but that article that was on overall wheel diameter. No doubt, putting huge wheels on a given car does not improve performance or efficiency.

But I am more wondering on tire sidewall height when overall tire/wheel diameter is kept constant. More specifically on sidewall height's effect on rolling resistance at a constant highway speed.

I tried to search that specific question on the web, but I didn't have much luck ...
 

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Ah, that makes sense for the Rivian. I thought that they were all similar (but I did not look at the exact tire specs, so thanks for catching that).

So, I am curious, if one is looking at rolling resistance only at a constant speed on the highway, does sidewall height affect rolling resistance/efficiency (if overall tire diameter is held constant) and, if yes, in what direction? And, if you know the answer, are there places on the interwebs where this is published and/or explained? Thanks.
Sidewall height may affect rolling resistance. What does affect rolling resistance is the stiffness of the sidewall. A softer sidewall will increase the resistance. If the stiffness is equal between different sidewall heights then there will be no difference.

But practically smaller sidewall tires do have stiffer sidewalls and therefore will have technically less rolling resistance.

There isnt a test that compares it.
 

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Thanks for the reply and for the interesting article, but that article that was on overall wheel diameter. No doubt, putting huge wheels on a given car does not improve performance or efficiency.

But I am more wondering on tire sidewall height when overall tire/wheel diameter is kept constant. More specifically on sidewall height's effect on rolling resistance at a constant highway speed.

I tried to search that specific question on the web, but I didn't have much luck ...
Pointless discussion
 

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Discussion Starter · #18 ·
Sidewall height may affect rolling resistance. What does affect rolling resistance is the stiffness of the sidewall. A softer sidewall will increase the resistance. If the stiffness is equal between different sidewall heights then there will be no difference.

But practically smaller sidewall tires do have stiffer sidewalls and therefore will have technically less rolling resistance.

There isnt a test that compares it.
Sure, that makes logical sense, that a shorter sidewall would be stiffer, and so would have less rolling resistance than a taller sidewall, all other things being equal.

But, oddly, there is some info online that seems to conflict with this (who knows if it is correct). And it seems to say that a smaller diameter rim with a relatively taller tire sidewall has lower rolling resistance than one with a shorter sidewall? (if tire diameter is held constant)

It is weird, there hundreds of millions of cars on the roads, but yet there is no clear answer to this l thought fairly basic question?
 
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