Stock Steel Vs Stock Aluminum Wheels

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Lower Rolling Resistance or Lower Unsprung Weight??? I don't know.

What I do know is that I recorded a 21.2 mpg reading this morning. The highest since September of last year.

The change has definitely helped.

YMMV, Jim
 
Originally Posted By: AstroTurf
Which are better, and Why?

I have a set of each, Stock Steel and Stock Aluminum Wheels.

2005 Chevrolet Astro Van.
The steelies weigh 29 lbs, the aluminums weigh 19 lbs.
The steelies are 6.5" wide, the aluminums are 7" wide.
All other dimensions are the similar, the only exception might be offset/backspacing.

As I have said, Both are stock for this vehicle.

So which is better in your opinion?

Thanks, Jim


I am assuming the stock tires are 215/70R16. The wider rims allow for a wider tire.

You could get even better handling and mileage by going to a wider tire, such as 235/65R16, with the very close to the same outside diameter next time. Look for a light weight tire with low rolling resistance, if your main concern is mileage improvement.
 
Originally Posted By: mva
Originally Posted By: AstroTurf
Which are better, and Why?

I have a set of each, Stock Steel and Stock Aluminum Wheels.

2005 Chevrolet Astro Van.
The steelies weigh 29 lbs, the aluminums weigh 19 lbs.
The steelies are 6.5" wide, the aluminums are 7" wide.
All other dimensions are the similar, the only exception might be offset/backspacing.

As I have said, Both are stock for this vehicle.

So which is better in your opinion?

Thanks, Jim


I am assuming the stock tires are 215/70R16. The wider rims allow for a wider tire.

You could get even better handling and mileage by going to a wider tire, such as 235/65R16, with the very close to the same outside diameter next time. Look for a light weight tire with low rolling resistance, if your main concern is mileage improvement.


I am not sure I follow as to how a wider tire would improve my mpg.

Could you please explain?

Thanks, Jim
 
Originally Posted By: AstroTurf
I am not sure I follow as to how a wider tire would improve my mpg.

Could you please explain?

Thanks, Jim

It is counter intuitive but the wider tire should improve your mileage. The contact patch will be wider and more narrow therefore the wider tire will have less sidewall flex at the same load.

From Barry's tire tech:

http://www.barrystiretech.com/rrandfe2.html
 
Originally Posted By: CapriRacer
But the effect RR has on fuel economy depends on the driving condition for each individual driver. A driver who has to live in stop and go traffic is probably not going to see much, if any, improvement, where a driver with a long commute on an interstate is probably going to see a significant improvment.

So it comes down to this: Is YOUR situation such that the improvement in RR is going to be felt strongly enough to overcome the Traction / Treadwear compromise - and I don't know the answer to THAT!


For my mixed driving, there are probably so many other constantly changing variables, that I doubt I can observe any improvement that I can definitely aatribute to a LRR tire if there is an improvement in fuel economy.

I think I'm sticking with the criteria I've always used: traction first, followed by treadwear.
 
Originally Posted By: weebl
I think I'm sticking with the criteria I've always used: traction first, followed by treadwear.


Good Choices

Jim
 
Note that all of the car companies have been going to larger diameter and wider tire and rim sizes. You will not find many or any cars with 13" or 14" rims anymore. Partly for looks and handling but I think fuel economy is coming into play, as well.
 
I see a general trend of fuel economy increasing along with a general trend of increased tire sizes. There are many different factors but I don't think the larger rims and tires are hurting. I found this quote today:

"The trend toward bigger tires has been dramatic in recent years. According to Kelley Blue Book, the most popular factory wheel diameter for cars in 2000 was 15 inches. Today it's 17 inches, with 45 models coming standard with 19-inch wheels this year (up from zero models in 2000). Michelin says its most popular aftermarket tire last year was 20 millimeters wider than in 2001."

Back to fuel efficiency versus tire size. Where does the energy go as a tire rolls down the road?

I am thinking that flex of the tread and sidewalls to meet the flat road surface plays a large part in rolling resistance; along with the type of rubber and construction of a particular brand tire. The air pressure in the tire approximately defines the size of the contact patch. For example a tire at 30 psi with 900 lb load will have a contact patch of approximately 30 square inches. A narrow tire - say 6" wide will have a contact patch with the road approximately 6" wide by 5" long whereas a 10" wide tire would have a contact patch 10" wide by 3" long. Given the same psi, outside diameter and rim diameter, the narrow tire tread and sidewall will flex much more as it rolls.

For the OP's situation the effect will be very small and it will be somewhat offset by increased aerodynamic drag and weight of the wider tire. We are splitting hairs but that is how progress in fuel economy is made.
 
Originally Posted By: mva
......Back to fuel efficiency versus tire size. Where does the energy go as a tire rolls down the road?....

It leaves in the form of heat.

Quote:
.......I am thinking that flex of the tread and sidewalls to meet the flat road surface plays a large part in rolling resistance.....

Most RR is caused by the tread area. The sidewall plays little role in RR.

Quote:
..... along with the type of rubber and construction of a particular brand tire.......

Yes, the type of rubber plays a HUGE role, but the construction, not so much, as there is very little difference (mass-wise) between various constructions of tires.

Quote:
.....The air pressure in the tire approximately defines the size of the contact patch. For example a tire at 30 psi with 900 lb load will have a contact patch of approximately 30 square inches.......

I am hoping you realize this is not true and I hope you are just using this as an approximation to try to illustrate a point.

Quote:
....A narrow tire - say 6" wide will have a contact patch with the road approximately 6" wide by 5" long whereas a 10" wide tire would have a contact patch 10" wide by 3" long. Given the same psi, outside diameter and rim diameter, the narrow tire tread and sidewall will flex much more as it rolls......

Nope. I was wrong.

First, the inflation pressure may change the size of the footprint within a given tire, but different sizes have different characteristics - so the size of the footprint can NOT be determined without actually measuring it.

And, - NO! - the narrower tire will flex exactly the same if you control the things that are important.

Let me state it this way: If I take 2 identical tires of different size, but the same load carrying capacity, then under the same load, both tires deflect the same percentage. That's just the way tires work.

And I think the reason the wider tires produce lower RR is because percentage-wise, the amount of tread involved gets less as you go wider.

Quote:
.....For the OP's situation the effect will be very small and it will be somewhat offset by increased aerodynamic drag and weight of the wider tire. We are splitting hairs but that is how progress in fuel economy is made.

I agree the amount is small - and I agree that progress in fuel economy comes from comparing notes. We just need to be sure we are getting the technical details correct.
 
Originally Posted By: CapriRacer

And I think the reason the wider tires produce lower RR is because percentage-wise, the amount of tread involved gets less as you go wider.


I predict you will re-think your RRC (Rolling Resistance Coefficient) argument. I don't see how you can figure that having less resistance per payload weight unit would translate to a similar resistance per payload weight unit when used in a lower payload application.

If wider tires on a given vehicle produced lower rolling resistance, solar-powered racers would use wide tires. Bicycle racers (assuming their stilted rules permitted it) would use wide tires. Balloon tires on bikes would give easier pedaling than lightweight tires.
 
Originally Posted By: Carbon
......I predict you will re-think your RRC (Rolling Resistance Coefficient) argument. I don't see how you can figure that having less resistance per payload weight unit would translate to a similar resistance per payload weight unit when used in a lower payload application.....


Here is what I am basing this on:

http://www.barrystiretech.com/rrandfe2.html

The bicycle tire argument you presented doesn't take into account the inflation pressure and the weight of the tires - neither of which are of significant for passenger car tires.

I'm guessing the solar powered car argument is the same as the bicycle argument in that these vehicles tend to use bicycle type tires.

I don't think these 2 arguments apply to passenger car tires.
 
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Bicycle tires only see symmetrical loads, and car tires must also deal with torques at right angles to the axle. Other than that, I see bicycle tires as a low load tire. If mileage contesters choose a tire that looks like a bicycle tire, I don't see that that makes the choice to not choose wider tire for economy not relevant.

I thought it would seem to be fairly simple to look at pictures of the winners of economy contests, and look for those with wider-than-stock tires. It is hard to find pictures of the winner's car, and when I do the tires are hard to see. They are in shadows, or they are behind fairings.

I did find in the 2011 Shell Eco-marathon Official Rules Chapter I http://www-static.shell.com/static/ecomarathon/downloads/2011/global/SEM_Rules_2011_Final.pdf a rule that says "Article 58: Tyres; All tyre types are allowed as long as they are fitted on the type and size of rims recommended by their manufacturers. The tyre / rim assembly must have a minimum width of 80mm, measured from sidewall to sidewall." I note there is no maximum. So if going to a 235 mm tire would give better fuel economy if wider tires give better mileage, right? I wish I could have found better instances.

But at the same time, I did not find any instances of a hypermiler or a winning economy contest winner going to wider tires to save fuel.

It was your web page I was referring to when I wrote "RRC (Rolling Resistance Coefficient)".
 
I think the biggest problem with wider tire is increased weight and rotational mass that cause more energy in acceleration, which is independent of rolling resistance.
 
Carbon,

Allow me to approach this problem from a different angle:

First, the discussion concerning tire width and RRC is applicable to passenger car tires used in normal service – and in particular, inflated to normal pressures. We could apply the principle to other tires if we desire, but we have to be careful to make sure we are doing apples to apples types of omparisons. For example, if we start comparing bicycle tires, we need to make sure that the inflation pressures are the same – and
from personal experience, those skinny tires on those racing bikes are inflated to 100 psi! – while those wider street and mountain bike sizes are much lower (60 psi!).

If we start talking about economy contests where there is a large amount of “wiggle room”, then that’s a different ballgame. For example, if I were competing in these contests, I would inflate the tires to rock hard – and for practical purposes, the differences in RR due to width, tread compound,
etc. would disappear!

But that’s not what we are discussing. So I am having trouble
understanding what it is about the data that is not convincing.
 
Originally Posted By: CapriRacer
Originally Posted By: Carbon
......I predict you will re-think your RRC (Rolling Resistance Coefficient) argument. I don't see how you can figure that having less resistance per payload weight unit would translate to a similar resistance per payload weight unit when used in a lower payload application.....


Here is what I am basing this on:

http://www.barrystiretech.com/rrandfe2.html

The bicycle tire argument you presented doesn't take into account the inflation pressure and the weight of the tires - neither of which are of significant for passenger car tires.

I'm guessing the solar powered car argument is the same as the bicycle argument in that these vehicles tend to use bicycle type tires.

I don't think these 2 arguments apply to passenger car tires.


I think the article is made on the assumption to roll the tyre on the lab but not on the real world. On road, the wider the tyre, the more drag caused by uneven surface and this at the end will make the fuel economy worsen. Granted same type of rubber, construction, typically wider tyre will worsen the fuel economy and put more stress to the suspension and steering components(if installed in front).
 
Originally Posted By: CapriRacer
But that’s not what we are discussing. So I am having trouble
understanding what it is about the data that is not convincing.


Between page 30 and 31, there is an implication that for a given tire, RollingResistance = K*Load , where K is a constant for that tire. That leads to the conclusion that for fuel economy and tire width for the same vehicle and load, "Larger is better!" That is the part I doubt.

If (RollingResistance = K*Load) were true, wouldn't I expect to improve mileage significantly by replacing a P tire of a given size with an LT tire?
 
Originally Posted By: Carbon
..........wouldn't I expect to improve mileage significantly by replacing a P tire of a given size with an LT tire?


If P tires were built like LT tires, yes - but they are not.

Among the things that are different with LT tires is that the materials have good resistance to compression set. Compression set is where rubber will flow a bit under load and take on a different unloaded shape. This is important in high loading situations - like LT, truck, and mining tires - where there is a large amount of load compared to the physical dimensions. Low compression set rubbers are also are not good for RR.

Hence, changing from a P type tire to an LT type tire of the same dimensions - even utilizing the increased inflation pressure - is likely not a good move from a RR point of view. I wish I had data to back that up, so this is just an educated guess on my part.
 
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Originally Posted By: CapriRacer
Originally Posted By: Carbon
..........wouldn't I expect to improve mileage significantly by replacing a P tire of a given size with an LT tire?


If P tires were built like LT tires, yes - but they are not.

Among the things that are different with LT tires is that the materials have good resistance to compression set. Compression set is where rubber will flow a bit under load and take on a different unloaded shape. This is important in high loading situations - like LT, truck, and mining tires - where there is a large amount of load compared to the physical dimensions. Low compression set rubbers are also are not good for RR.

Hence, changing from a P type tire to an LT type tire of the same dimensions - even utilizing the increased inflation pressure - is likely not a good move from a RR point of view. I wish I had data to back that up, so this is just an educated guess on my part.


My point with the LT and P example was to argue against (RollingResistance = K*Load) and its implications.
 
Originally Posted By: Carbon
My point with the LT and P example was to argue against (RollingResistance = K*Load) and its implications.


Perhaps it would help if I told you that if you rearrange the equation (and change the symbols to conform with the way this is normally expressed:

RRC = RRF / Load

That is:

Rolling Resistance Coefficient = Rolling Resistance Force diivided by the Load on the tire

- and that is a definition!

So I am totally not following you.
 
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