Topic: How paying more for bigger wheels can cost you more to roll on them.

[EV Dan]

And it's not only about the price of oversized tires or more likely damage to the rims due to potholes.

https://www.youtube.com/watch?v=NYvKxsYFqO8

(engineering explained)

[rrocket]

And it's not only about the price of oversized tires or more likely damage to the rims due to potholes.

https://www.youtube.com/watch?v=NYvKxsYFqO8

(engineering explained)

Somewhat a blanket statement.

You can get bigger/wider wheels that weigh LESS (or same) as the OEM stuff.

[EV Dan]

It's more about aerodynamics than weight. He explains it in the comments.

[rrocket]

It's more about aerodynamics than weight. He explains it in the comments.

That's only if you really upside on the width.

You can go up in wheel size while keeping a fairly similar width You usually got up 10mm in width or so.  Unless you're doing it for extreme performance traction..or just want the looks of big fat meats.  For example, the stock tires on the A5 are 245 width.  The upsize to the 19s is a 255 width.  Which the aerodynamics would be negligible...and offset by lighter wheel weights IMO.

[capriracer]

The problem with the video is that he exaggerates the affect of aero (100mm more:  Normal would be 10mm to 20mm increase), the rolling resistance effect (He uses coefficients of 3 times when the extreme range is about 60%, and like to like is a percent or 2.), then doesn't address the weight (moment of inertia).  He then takes data submitted for the Mulroney label (the one on a new car's window that says the MPG's) which is the combination of all 3, and declares that to be the definitive difference. 

What he leaves out is that the coast down values come in increments - which is one of the reasons why there is a difference in the models (15%, 8%, and 9%) for more or less the same 2" wheel diameter difference.

Do not get me wrong, I think his overall conclusion is correct, but he is doing a smoke and mirrors presentation and exaggerating the difference.

Here's my take on the tire portion of this:  http://barrystiretech.com/rrandfe.html

[draghon]

It's more about aerodynamics than weight. He explains it in the comments.

That's only if you really upside on the width.

You can go up in wheel size while keeping a fairly similar width You usually got up 10mm in width or so.  Unless you're doing it for extreme performance traction..or just want the looks of big fat meats.  For example, the stock tires on the A5 are 245 width.  The upsize to the 19s is a 255 width.  Which the aerodynamics would be negligible...and offset by lighter wheel weights IMO.

Agreed, I went up 1" in wheel width, +20mm in tire width with (I assume) higher rolling resistance summer tires and didn't see any appreciable difference in fuel economy from the stock setup. Big difference, is the wheels slightly while wider are at least 10 lbs lighter than stock as well.

[EV Dan]

The problem with the video is that he exaggerates the affect of aero (100mm more:  Normal would be 10mm to 20mm increase), the rolling resistance effect (He uses coefficients of 3 times when the extreme range is about 60%, and like to like is a percent or 2.), then doesn't address the weight (moment of inertia).  He then takes data submitted for the Mulroney label (the one on a new car's window that says the MPG's) which is the combination of all 3, and declares that to be the definitive difference. 

What he leaves out is that the coast down values come in increments - which is one of the reasons why there is a difference in the models (15%, 8%, and 9%) for more or less the same 2" wheel diameter difference.

Do not get me wrong, I think his overall conclusion is correct, but he is doing a smoke and mirrors presentation and exaggerating the difference.

Here's my take on the tire portion of this:  http://barrystiretech.com/rrandfe.html

I appreciate your input. Everybody is into breaking news style of reporting it seems. The reason I posted the link is in case of those Teslas and to the lesser extent hybrid cars the wheel size does make a noticeable difference on range and/or fuel consumption. And I think it's something important to keep in mind when choosing to buy a top car trim because it comes with flashier wheels. There seems to be a consensus among the average car buyers that standard size rims are "low rent" and thus should be "upgraded" while in reality the upsizing comes with a list of drawbacks, especially if the car is used as an A to B daily draiver.

[UnknownJinX]

And it's not only about the price of oversized tires or more likely damage to the rims due to potholes.

https://www.youtube.com/watch?v=NYvKxsYFqO8

(engineering explained)

Somewhat a blanket statement.

You can get bigger/wider wheels that weigh LESS (or same) as the OEM stuff.

For a rotational mass like a wheel, linear mass doesn't really count for much. Well, it does for unsprung mass, but weight distribution is equally important.

A bigger wheel and its tire will have more of its mass close to the outside of the whole assembly. This increase the moment of inertia. This is basically what mass is(resistance to a force), but in angular acceleration.

So even if a bigger wheel weighs the same as the smaller wheel, it will likely has a higher moment of inertia and thus, it will cost you more energy to accelerate with it and more energy to stop it.

[rrocket]

And it's not only about the price of oversized tires or more likely damage to the rims due to potholes.

https://www.youtube.com/watch?v=NYvKxsYFqO8

(engineering explained)

Somewhat a blanket statement.

You can get bigger/wider wheels that weigh LESS (or same) as the OEM stuff.

For a rotational mass like a wheel, linear mass doesn't really count for much. Well, it does for unsprung mass, but weight distribution is equally important.

A bigger wheel and its tire will have more of its mass close to the outside of the whole assembly. This increase the moment of inertia. This is basically what mass is(resistance to a force), but in angular acceleration.

So even if a bigger wheel weighs the same as the smaller wheel, it will likely has a higher moment of inertia and thus, it will cost you more energy to accelerate with it and more energy to stop it.

Would love to see the actual calculation.

In the one example I recall, 245/40/18 vs. 255/35/19 TOTAL wheel/tire weight was 3lbs. a corner less on the 19".  Rolling diameter about the same.

Sadly, I don't recall TOTAL wheel/tire weight.

[UnknownJinX]

And it's not only about the price of oversized tires or more likely damage to the rims due to potholes.

https://www.youtube.com/watch?v=NYvKxsYFqO8

(engineering explained)

Somewhat a blanket statement.

You can get bigger/wider wheels that weigh LESS (or same) as the OEM stuff.

For a rotational mass like a wheel, linear mass doesn't really count for much. Well, it does for unsprung mass, but weight distribution is equally important.

A bigger wheel and its tire will have more of its mass close to the outside of the whole assembly. This increase the moment of inertia. This is basically what mass is(resistance to a force), but in angular acceleration.

So even if a bigger wheel weighs the same as the smaller wheel, it will likely has a higher moment of inertia and thus, it will cost you more energy to accelerate with it and more energy to stop it.

Would love to see the actual calculation.

In the one example I recall, 245/40/18 vs. 255/35/19 TOTAL wheel/tire weight was 3lbs. a corner less on the 19".  Rolling diameter about the same.

Sadly, I don't recall TOTAL wheel/tire weight.

Well I would be more curious to see the weight distribution rather than just the (linear) mass. The function of moment of inertia is proportional to the square of distance of the mass from the axis of rotation, so distance(weight distribution) has more impact on moment of inertia. I don't know how you can get the weight distribution of a wheel, but weighing the tires by themself could be a start(it is the farther from the centre of a wheel).

It's like a flywheel. Some flywheels have a greater mass but with how the mass is distributed, it may actually end up being more responsive, which is what really matters for anyone modding a flywheel.

Jason also mentioned that his math can be a bit rough, specifically the last one which is a bit of a back-of-envelope calculations. Either way, I have 20” rim with 285+ width tires on my Camaro SS 1LE so I should shut up, LOL.

Speaking of the Camaro SS 1LE, I log the fuel economy of it in Fuelly and I noticed that the in-car display is always about 10% less than the actual fuel consumption. I wonder if the fuel economy calculations are based on the standard SS tires that are thinner and likely less sticky. Just thinking out loud here.

[rrocket]

And it's not only about the price of oversized tires or more likely damage to the rims due to potholes.

https://www.youtube.com/watch?v=NYvKxsYFqO8

(engineering explained)

Somewhat a blanket statement.

You can get bigger/wider wheels that weigh LESS (or same) as the OEM stuff.

For a rotational mass like a wheel, linear mass doesn't really count for much. Well, it does for unsprung mass, but weight distribution is equally important.

A bigger wheel and its tire will have more of its mass close to the outside of the whole assembly. This increase the moment of inertia. This is basically what mass is(resistance to a force), but in angular acceleration.

So even if a bigger wheel weighs the same as the smaller wheel, it will likely has a higher moment of inertia and thus, it will cost you more energy to accelerate with it and more energy to stop it.

Would love to see the actual calculation.

In the one example I recall, 245/40/18 vs. 255/35/19 TOTAL wheel/tire weight was 3lbs. a corner less on the 19".  Rolling diameter about the same.

Sadly, I don't recall TOTAL wheel/tire weight.

Well I would be more curious to see the weight distribution rather than just the (linear) mass. The function of moment of inertia is proportional to the square of distance of the mass from the axis of rotation, so distance(weight distribution) has more impact on moment of inertia. I don't know how you can get the weight distribution of a wheel, but weighing the tires by themself could be a start(it is the farther from the centre of a wheel).

It's like a flywheel. Some flywheels have a greater mass but with how the mass is distributed, it may actually end up being more responsive, which is what really matters for anyone modding a flywheel.

Jason also mentioned that his math can be a bit rough, specifically the last one which is a bit of a back-of-envelope calculations. Either way, I have 20” rim with 285+ width tires on my Camaro SS 1LE so I should shut up, LOL.

Speaking of the Camaro SS 1LE, I log the fuel economy of it in Fuelly and I noticed that the in-car display is always about 10% less than the actual fuel consumption. I wonder if the fuel economy calculations are based on the standard SS tires that are thinner and likely less sticky. Just thinking out loud here.

Yep..lots of gray.

[HeliDriver]

Car and Driver did an interesting test ten years ago with a VW Golf on a range of wheel/tire combos from 15" to 19".

https://www.caranddriver.com/features/a15130598/upsized-wheels-tires/

[capriracer]

Car and Driver did an interesting test ten years ago with a VW Golf on a range of wheel/tire combos from 15" to 19".

https://www.caranddriver.com/features/a15130598/upsized-wheels-tires/

This is an interesting test, but one of the things they didn't comment on was the fact that there was a different tread compound on the W speed rated tires and that would have negatively affected the rolling resistance.  So some of that 10% loss was due to that.