My Findings On Tire Choice and Its Effect On MPG

[Rand]

but you also have seasonal variation to account for and a small sampling of the energy saver. I'd say report back after a full year on them to have a decent mpg sample in all seasons and conditions.

Also you could be getting better mpg now that the car is well worn in vs brand new.

I know I get better mpg now than when new.

also I would have liked an exact rolling circumference of the 3 tires. its fairly easy to be a small % off.

for example the primacy rev per mile is 834
and the energy saver is 832
the yokohama is 829

 

[The Critic]

Originally Posted By: Rand
but you also have seasonal variation to account for and a small sampling of the energy saver. I'd say report back after a full year on them to have a decent mpg sample in all seasons and conditions.

Also you could be getting better mpg now that the car is well worn in vs brand new.

I know I get better mpg now than when new.

also I would have liked an exact rolling circumference of the 3 tires. its fairly easy to be a small % off.

for example the primacy rev per mile is 834
and the energy saver is 832
the yokohama is 829




I have yet to see any difference with vehicle break-in. The weather here in Monterey is extremely constant year round

 

[weebl]

Interesting observations, definitely. Don't know about how statistically significant the data you have is, but certainly suggests a trend.

Different performance criteria for different people and application out of a tire. Traction under the conditions I normally encounter are my primary consideration, and I understand that this may be at the expense of fuel economy.

 

[zanzabar]

Critic, send me your data and I will run some stats and see if it's significant. Or, you can just post the average, standard deviation, and # data points (tanks?).

 

[The Critic]

Originally Posted By: zanzabar
Critic, send me your data and I will run some stats and see if it's significant. Or, you can just post the average, standard deviation, and # data points (tanks?).


All of the data can be accessed from the link in my signature. Thanks.

 

[surfstar]

I'm still bothered by the 3 sets of tires required within one year and 30k miles.

 

[zanzabar]

Yes, the results are statistically significant.

 

[The Critic]

Thanks!

 

[SS1970chrysler]

Originally Posted By: surfstar
I'm still bothered by the 3 sets of tires required within one year and 30k miles.

That stuck out to me as well, though dates haven't been posted for the miles.

 

[The Critic]

Originally Posted By: SS1970chrysler
Originally Posted By: surfstar
I'm still bothered by the 3 sets of tires required within one year and 30k miles.

That stuck out to me as well, though dates haven't been posted for the miles.


I have had the car for 11 months.

The original tires were replaced due to poor wet performance after 14k miles. I received 50% trade-in credit on them due to a deal I worked out with the tire shop.

The Primacy MXV4 were replaced by the Energy Saver A/S since Michelin offered me a great deal. I wanted to try a different tire anyway and for the deal I was offered, I could not pass it up.

 

[IndyIan]

Originally Posted By: zanzabar



Yes, the results are statistically significant.

But what is the margin of error in producing the data? If the majority of his driving the same route at the same times of the day, he could still affect mileage +-25% just by driving differently.
To actually measure the rolling resistance, he should've measured the rolling resistance. A neutral coast down the same hill, from a stop to a stop, 5 times with each tire would get some more reliable data to compare the tires with.
I could believe that one tire could have 10% less rolling resistance but that doesn't translate into 10% better mileage.

 

[zanzabar]

Correlation does not equal causation!!! Certainly the behavior of The Critic's right foot would swamp all other factors in this analysis. But it sounds like he is maintaining a regular pattern here and the results do not seem to be sensitive to other factors that might come into play (seasonal temp + a/c use, frequency of fillups, # cold starts, etc). Adding a summer's worth of fillups on the new tires should help establish whether the mpg #s are due to the tires.

The one thing I found that might explain some of this is that the average # days between fillups on the Yokohama (1st set of tires) and the new michelins (3rd set) is about 3.4 days, whereas on the middle Michelins it's 4.75 days. Is there something about filling up more frequently that might give you better gas mileage? These things have a bladder system rather than a proper tank to minimize evaporation right? I dunno, I can't think of why that would make any difference except for the 3 or 4 extra cold starts per tank.

 

[CMMeadAM]

The 3rd generation Prius does NOT have a bladder gas tank.
Nevertheless, his findings of such a large increase in MPG's over the prior tires in such a short period of time is highly
questionable.

 

[F8L]

Why should the results be suspect?

It is common knowledge that tire choice can significantly affect mpg. At least this is the case for those with vehicles getting over 40mpg where the numbers tend to be larger.

In the Prius community we have watched many owners switch their OE LRR tires for a cheap or high performance non-LRR tire only to lose quite a bit of fuel economy that persists even after the tires are broke in. In most cases, owners will replace the OE tire with another LRR tire and they observe a small drop in mpg until the tires are broke in. Mpg tends to come back up and may surpass the OE tire but the numbers are small so it it is hard to really say anything significant. In the case of the Energy Saver A/S, many owners observe and instant gain in mpg over their older worn tires. We all know this shouldn't be the case unless the new tire is significantly better in terms of fuel efficiency. The "Round and Black Becomes Lean and Green" showed the same results.

When TheCritic went from a more performance oriented non-LRR tire to the best LRR tire we know of I expected his mpg to jump significantly.

 

[Gene K]

Tread depth has a pronounced effect on fuel mileage.

The Michelins will get better as they wear.

 

[F8L]

Indeed. Tread depth does play a part and the Energy Saver A/S has only 9.5/32 when brand new. Design can play a big part too. Especially if designed to reduce tread deformation like many new tires are with their adaptive wear designs. Interestingly, my AVID Ascends do quite well despite a 12/32 tread depth. I wouldn't pit them against the Energy Saver A/S in a max fuel economy match up though.

 

[The Critic]

Originally Posted By: zanzabar
Correlation does not equal causation!!! Certainly the behavior of The Critic's right foot would swamp all other factors in this analysis. But it sounds like he is maintaining a regular pattern here and the results do not seem to be sensitive to other factors that might come into play (seasonal temp + a/c use, frequency of fillups, # cold starts, etc). Adding a summer's worth of fillups on the new tires should help establish whether the mpg #s are due to the tires.

The one thing I found that might explain some of this is that the average # days between fillups on the Yokohama (1st set of tires) and the new michelins (3rd set) is about 3.4 days, whereas on the middle Michelins it's 4.75 days. Is there something about filling up more frequently that might give you better gas mileage? These things have a bladder system rather than a proper tank to minimize evaporation right? I dunno, I can't think of why that would make any difference except for the 3 or 4 extra cold starts per tank.


No bladder on the Gen III. The weather here is fairly constant throughout the year so I doubt summer will make a difference at all. As far as the frequency of fill-ups, I am not sure why that is different, but my trips and commute have not changed one bit.

CM, it has been well-established both on tire rack and priuschat that the Energy Saver A/S deliver at least a 5% improvement in fuel economy compared to the OE tires. Since my previous set of tires delivered worse fuel economy than the OE tires, a double digit gain with new tires alone should not be a surprise.

 

[F8L]

I would only be careful with consideration to fuel formulation. I'm not sure what they put in the gas in your area.

 

[friendly_jacek]

Originally Posted By: JosephHarmon
I do believe the trade off between safety & MPG is in only pennys per 10,000 miles. I like my Michilens Sennergys.


Not sure what you mean but LRR tires can save a lot of money. I run a calculation for my "gas guzzler" (RAV4) and LRR tires almost pay for themself during their entire life.

 

[friendly_jacek]

Originally Posted By: PandaBear
The OE LRR tires with very low UTQG seems to be very safe, around 140 is what I've seen in many case. You probably won't want to replace it with the same tire as they are very expensive in aftermarket and they don't last very long.

Those OE LRR with high UTQG tends to be horrible in traction, especially wet traction, that makes the car feel unsafe. I've thrown away a few of them before they are worn.



That used to be true when LRR tires were Goodyear Integrity. Modern LRR tires with their silica based thread give similar performance to non-LRR tires. The only drawback is slightly higher price (due to advanced materials).

I will never go back to non-LRR tires. 2 of my cars have Ecopia tires and they are very comfortable with decent traction.