Gas Mileage Test: Tire Weight
12-13-2012, 10:27 AM
#1
Thread Starter
Join Date: 05-15-2010
Location: Nashville TN
Posts: 4
Gas Mileage Test: Tire Weight
Hello. This is only my 2nd post ever here on ChevyHHR.net, but I do lurk from time-to-time, mostly for maintenance related stuff.
Awhile back, I had posted up a gas mileage test I did on the stock airbox versus the K&N FIPK unit. Basic result: although the average goes to the stock unit, they are basically the same.
Shortly after posting that previous test, I had purchased new tires for my HHR. I went from the factory Firestone Affinity Tourings, to Bridgestone Turanza Serenitys.
Now, there are multiple differences within these tires that I am not fully accounting for. My main goal was to account for the difference in tire weight. Some of the differences include:
- different tread compound (I assume)
- old vs new tire. An old tire will theoretically have an inherent gas mileage advantage due to less weight (worn off tread), heat cycling making it harder over time, and less tread squirm (due to shorter tread blocks from wear). This was mitigated a little since the Firestone Affinity Tourings were not completely worn out. They were only at about 50% wear, I replaced them because I didn't like their wet performance.
- possible different tire construction
- tread weight.
Like I said, my focus was on the tire weight, as there is a significant difference. Tire rack has the Firestone Affinity Touring listed as 22lbs each, and the Bridgestone Turanza Serenity as 26lbs each. A 4lb difference in rotational mass for each corner of the car!!
The Firestone Affinity Touring data:
tire weight, when new: 22lbs
miles driven for this study: 6671
dates: 4/1/2010 - 12/2/2010
average MPG during this time: 31.8mpg
MPG stdev: 1.2mpg
The Bridgestone Turanza Serenity data:
tire weight, when new: 26lbs
miles driven for this study: 13397
dates: 12/2/2010 - 1/5/2012
average MPG during this time: 30.4mpg
MPG stdev: 1.3mpg
So, a 4lb heavier tire impacted my gas mileage by approximately 1.4MPG!! I could see this immediately from the first tank of gas.
There is also one compounding factor that I could not account for, which was a slight shift in my working hours that moved me away from peak-traffic rush-hour. My best estimate is that this improved my gas mileage by approximately 0.5MPG...which means that the tire change is really probably closer to a 2MPG impact!
With all of this being said, I am really happy with the Turanza Serenity purchase. The tire performs much better than the Affinity Touring in all conditions - period. Plus, this tire has a long treadwear warranty, so I expect to get my money back by not having to purchase tires as quickly.
Anyway, I hope this helps someone out there!
My next fuel mileage test is using Lucas Oil stabilizer. I hope to have that wrapped up within the next couple weeks. My goal is to not take so long to post it up here!
Troy
Awhile back, I had posted up a gas mileage test I did on the stock airbox versus the K&N FIPK unit. Basic result: although the average goes to the stock unit, they are basically the same.
Shortly after posting that previous test, I had purchased new tires for my HHR. I went from the factory Firestone Affinity Tourings, to Bridgestone Turanza Serenitys.
Now, there are multiple differences within these tires that I am not fully accounting for. My main goal was to account for the difference in tire weight. Some of the differences include:
- different tread compound (I assume)
- old vs new tire. An old tire will theoretically have an inherent gas mileage advantage due to less weight (worn off tread), heat cycling making it harder over time, and less tread squirm (due to shorter tread blocks from wear). This was mitigated a little since the Firestone Affinity Tourings were not completely worn out. They were only at about 50% wear, I replaced them because I didn't like their wet performance.
- possible different tire construction
- tread weight.
Like I said, my focus was on the tire weight, as there is a significant difference. Tire rack has the Firestone Affinity Touring listed as 22lbs each, and the Bridgestone Turanza Serenity as 26lbs each. A 4lb difference in rotational mass for each corner of the car!!
The Firestone Affinity Touring data:
tire weight, when new: 22lbs
miles driven for this study: 6671
dates: 4/1/2010 - 12/2/2010
average MPG during this time: 31.8mpg
MPG stdev: 1.2mpg
The Bridgestone Turanza Serenity data:
tire weight, when new: 26lbs
miles driven for this study: 13397
dates: 12/2/2010 - 1/5/2012
average MPG during this time: 30.4mpg
MPG stdev: 1.3mpg
So, a 4lb heavier tire impacted my gas mileage by approximately 1.4MPG!! I could see this immediately from the first tank of gas.
There is also one compounding factor that I could not account for, which was a slight shift in my working hours that moved me away from peak-traffic rush-hour. My best estimate is that this improved my gas mileage by approximately 0.5MPG...which means that the tire change is really probably closer to a 2MPG impact!
With all of this being said, I am really happy with the Turanza Serenity purchase. The tire performs much better than the Affinity Touring in all conditions - period. Plus, this tire has a long treadwear warranty, so I expect to get my money back by not having to purchase tires as quickly.
Anyway, I hope this helps someone out there!
My next fuel mileage test is using Lucas Oil stabilizer. I hope to have that wrapped up within the next couple weeks. My goal is to not take so long to post it up here!
Troy
12-13-2012, 11:10 AM
#2
Platinum Member
Join Date: 05-09-2006
Location: "Upland" Mesa, Arizona
Posts: 6,804
Purely speculation and not very scientific. For example, you "tested" the tire during different weather seasons. You made no mention of tire pressures. You made no mention of gasoline brands, consistencies, or octanes. No mention of speeds.
I have the same tire and experienced about .5 MPG INCREASE (with approx. 15,000 miles on the tire).....also not very scientific.
JMO.
I have the same tire and experienced about .5 MPG INCREASE (with approx. 15,000 miles on the tire).....also not very scientific.
JMO.
12-13-2012, 11:25 AM
#3
Platinum Member
Join Date: 12-06-2009
Location: Alabama
Posts: 11,088
Gotta agree with Snoppy on this.
The first tire time frame didn't include all the winter months(winter blend gas) when mileage numbers are usually lower.
The second tire stats actually had more winter months because of the overlap of the time frame.( not my best explaination, but I think you folks understand
)
It's pretty much a "wash" as far as I can see.
The first tire time frame didn't include all the winter months(winter blend gas) when mileage numbers are usually lower.
The second tire stats actually had more winter months because of the overlap of the time frame.( not my best explaination, but I think you folks understand
)It's pretty much a "wash" as far as I can see.
12-13-2012, 12:00 PM
#4
Senior Member
Join Date: 09-11-2007
Location: Palm Bay, Florida
Posts: 1,378
I keep records in a spred sheet and this was one sub set of the spread sheet on mpg vs tires. A complete mix of seasons, long trips, short trips and various gasoline brands. At one std dev, the mpg overlap. I'm still trying to figure out why the Cooper Tires dropped the mpg average by 2-3 mpg.
One of these days I may break down mpg by gasoline brands.
The HHR has ~104,000 miles on the clock.
..fillups.....mpg................................s td dev
n=161.... 30.52... original tires....... 2.937203692
n=109.... 31.0.... Good years tires.. 2.859761562
n=35..... 28.2.... Cooper tires...... 2.126855393
One of these days I may break down mpg by gasoline brands.
The HHR has ~104,000 miles on the clock.
..fillups.....mpg................................s td dev
n=161.... 30.52... original tires....... 2.937203692
n=109.... 31.0.... Good years tires.. 2.859761562
n=35..... 28.2.... Cooper tires...... 2.126855393
12-13-2012, 12:50 PM
#5
Senior Member
Join Date: 01-13-2008
Location: Washington State, where it rains
Posts: 4,708
One more problem..actually two...1) the two tires are probably not the same diameter due to being diferent brands,, therefore the roll out distance will not be the same...2) A worn tire will not really be better as the tread is worn off and going back to #1 the tire is smaller and requires more turns to equal the same distance as a new like tire , negating any weight gains as most of your weight is in the sidewalls and belts. Any experiment like this will require both sets of tires to be near identical in diameter to have positive results. Though..tire weight will have an effect in the looooong run as 12lbs is really small in the milage game. Rain water will add weight as will dirt slush snow etc etc...so will daily use stuff that makes it way into and out of a vehicle...
12-18-2012, 01:39 PM
#6
Thread Starter
Join Date: 05-15-2010
Location: Nashville TN
Posts: 4
You guys don’t know me, or my dorky Engineer-ness, so I understand the skepticism. I’ll try to address some of your concerns about my data here.
Concern #1: Different weather seasons for the comparison.
I reported the Firestone data starting in April due to that being when I changed to the K&N FIPK, just to keep that ruled out. I do see a large difference summer/winter versus spring/fall, so a valid concern.
Really though, no difference in the results:
Posted results above for the Firestones: 31.8mpg
Results when including 1 total year (Dec 2009-Dec 2010): 31.7mpg
Results when including almost 2 years of data (March 2009-Dec 2010): 32.0mpg
So, nothing changing the conclusion there.
Concern #2: Misc of tire pressure, gasoline brand, octane, speeds.
Tire Pressure: I set my tire pressure to 40psi (there is usually a +/-1psi in there). Checked about every other month (these tires hold air REALLY well, almost never needing adjustment).
Gasoline brand and octane: whatever Kroger or Mapco provide, @ 87 octane. According to my data, 60%ish are Kroger, 30%ish are Mapco, and the rest are miscellaneous. I have noticed a difference with ethanol vs no-ethanol, but it is getting really hard to find any non-ethanol anymore.
Speeds / driving habits: I took out any abnormal data. I consider this data all from the same basic driving mix of highway and side-roads. Looking at the stdev backs that up also.
Concern #3: Tire diameter due to being different brands
That is certainly easy enough to de-bunk.
1)Bridgestone and Firestone are the same tire company. Link: http://www.bridgestone-firestone.com/about_bg_index.asp
2)According to tire rack, both tires have exactly the same OD: 25.3”, and 823 and 824 revolutions per mile respectively. I would say that is the same.
Concern #4: “A worn tire will not really be better as the tread is worn off and going back to #1 the tire is smaller and requires more turns to equal the same distance as the new tire”
This is something I have always wondered about, but never run the numbers on myself.
New tread depth: 12/32”
Completely worn out tread depth: 2/32”
Difference: 0.31”; OD difference: 0.625”
New OD for these tires: 25.3”
Completely worn out OD = 25.3-0.625 = 24.7”
New Revolutions / mile (from tire rack) = 824
Completely worn out revolutions / mile = 843
2.3% increase in revolutions per mile
New Tire weight = 26 lbs
New Tread weight (37% of tire mass) = 9.6lbs
Completely worn out tread weight = 4.8lbs (note the tread weight above includes sub-tread with the component, so you will not get a full removal of tread weight).
Worn tire weight = 21.2lbs
19% decrease in tire weight
2% increase in revolutions per mile over the life of a tire = unnoticeable.
19% decrease in tire weight over the life of a tire = noticeable
The increase in fuel efficiency of a tire as it wears is also compounded by a reduction in tread squirm as it rotates through the contact patch.
Overall, the same exact tire worn will always give better gas mileage than that tire when new. Much testing regarding rolling resistance have shown this. (Hence Snoopy’s comment about seeing an increase in gas mileage after 15K miles??)
Note: The impact of changes in tire weight over the life of the tire was reduced some during this trial. When I took the Firestones off of the car, they still had 50-75% of life remaining. They probably were not at their original 22lbs anymore…perhaps closer to 21lbs or so.
Random Inaccurate Comment: “Most of your weight is in the sidewalls and belts”
Tire weight breakdown (not the specific tire size or construction we are talking about here, but close enough):
Tread = 37%
Both sidewalls + both belts = 27%
Body plies = 17%
All other = 18%
Overall conclusion: A lighter weight tire will allow for better gas mileage results. During my trial I attempted to see if I could put a # to this. Is it 100% accurate? Probably not. Is it pretty danged close? Yes.
Concern #1: Different weather seasons for the comparison.
I reported the Firestone data starting in April due to that being when I changed to the K&N FIPK, just to keep that ruled out. I do see a large difference summer/winter versus spring/fall, so a valid concern.
Really though, no difference in the results:
Posted results above for the Firestones: 31.8mpg
Results when including 1 total year (Dec 2009-Dec 2010): 31.7mpg
Results when including almost 2 years of data (March 2009-Dec 2010): 32.0mpg
So, nothing changing the conclusion there.
Concern #2: Misc of tire pressure, gasoline brand, octane, speeds.
Tire Pressure: I set my tire pressure to 40psi (there is usually a +/-1psi in there). Checked about every other month (these tires hold air REALLY well, almost never needing adjustment).
Gasoline brand and octane: whatever Kroger or Mapco provide, @ 87 octane. According to my data, 60%ish are Kroger, 30%ish are Mapco, and the rest are miscellaneous. I have noticed a difference with ethanol vs no-ethanol, but it is getting really hard to find any non-ethanol anymore.
Speeds / driving habits: I took out any abnormal data. I consider this data all from the same basic driving mix of highway and side-roads. Looking at the stdev backs that up also.
Concern #3: Tire diameter due to being different brands
That is certainly easy enough to de-bunk.
1)Bridgestone and Firestone are the same tire company. Link: http://www.bridgestone-firestone.com/about_bg_index.asp
2)According to tire rack, both tires have exactly the same OD: 25.3”, and 823 and 824 revolutions per mile respectively. I would say that is the same.
Concern #4: “A worn tire will not really be better as the tread is worn off and going back to #1 the tire is smaller and requires more turns to equal the same distance as the new tire”
This is something I have always wondered about, but never run the numbers on myself.
New tread depth: 12/32”
Completely worn out tread depth: 2/32”
Difference: 0.31”; OD difference: 0.625”
New OD for these tires: 25.3”
Completely worn out OD = 25.3-0.625 = 24.7”
New Revolutions / mile (from tire rack) = 824
Completely worn out revolutions / mile = 843
2.3% increase in revolutions per mile
New Tire weight = 26 lbs
New Tread weight (37% of tire mass) = 9.6lbs
Completely worn out tread weight = 4.8lbs (note the tread weight above includes sub-tread with the component, so you will not get a full removal of tread weight).
Worn tire weight = 21.2lbs
19% decrease in tire weight
2% increase in revolutions per mile over the life of a tire = unnoticeable.
19% decrease in tire weight over the life of a tire = noticeable
The increase in fuel efficiency of a tire as it wears is also compounded by a reduction in tread squirm as it rotates through the contact patch.
Overall, the same exact tire worn will always give better gas mileage than that tire when new. Much testing regarding rolling resistance have shown this. (Hence Snoopy’s comment about seeing an increase in gas mileage after 15K miles??)
Note: The impact of changes in tire weight over the life of the tire was reduced some during this trial. When I took the Firestones off of the car, they still had 50-75% of life remaining. They probably were not at their original 22lbs anymore…perhaps closer to 21lbs or so.
Random Inaccurate Comment: “Most of your weight is in the sidewalls and belts”
Tire weight breakdown (not the specific tire size or construction we are talking about here, but close enough):
Tread = 37%
Both sidewalls + both belts = 27%
Body plies = 17%
All other = 18%
Overall conclusion: A lighter weight tire will allow for better gas mileage results. During my trial I attempted to see if I could put a # to this. Is it 100% accurate? Probably not. Is it pretty danged close? Yes.
12-18-2012, 01:55 PM
#7
Senior Member
Join Date: 07-17-2006
Location: Dallas, GA
Posts: 6,050
I think your actually "thinking" too deep into this. There is a differance in "science" and real world. I definately increased the unsprung weight changing from a 215/55R16 on a cast aluminum wheel to a 245/40R18 on a forged aluminum wheel (even had a 225/40R18 and a 225/45R18 at times). My mileage has not changed, and this is factoring in the overall diameter difference. I can get a 1-2 mpg change (-/+) with each tank. I've even hit my best highway mileage using the larger diameter tire (calculated).
And most passenger car tires come new with a 10/32 tread depth.
And most passenger car tires come new with a 10/32 tread depth.
12-18-2012, 11:26 PM
#10
Platinum Member
Join Date: 01-09-2007
Location: SE USA
Posts: 15,856
"I've even hit my best highway mileage using the larger diameter tire (calculated)."
I have larger tire diams too. & Hi-way mpg is also improved.
The taller tires actually lower the final drive axle ratio (slightly) aka lower rpms @ speed..
not ta mention my new tires are lighter than the stock flintstones..
I have larger tire diams too. & Hi-way mpg is also improved.
The taller tires actually lower the final drive axle ratio (slightly) aka lower rpms @ speed..
not ta mention my new tires are lighter than the stock flintstones..