Defender vs Energy Saver, or Math vs Intuition

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by jcgee88, Aug 6, 2014.

  1. jcgee88

    jcgee88 Member

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    Oh no, not another Defender vs Energy Saver thread?

    Yes, I admit I may be beating a dead horse.

    But, I would like to present what I think is a true business case, with
    real numbers, instead of relying on intuition. The objective function
    in this business case is lowest total life cycle cost. This analysis changed
    my mind as to which tire I am going to buy.

    My tire history is that I swapped OEM Goodyear Integrities at 37K miles
    for a set of Michelin Energy Savers. These have lasted 65K miles, and
    probably have enough tread life to go another 10K miles. I've been
    pleased with their handling, especially in wet weather, and how quiet they
    are. Nevertheless, I plan on replacing them within the next few months
    since they are nearing end of expected life.

    My original belief, also held by many other Prius owners, was that
    I would take a 2-3 mpg hit with Defenders, but that the Defenders'
    longer life (90K vs 65K for ES) would outweigh this relative deficiency.
    Consumer Reports also ranks Defender as their top all season tire, and
    their rating system gives Defender a 10% advantage over ES, based on
    10 different criteria. Thus, in spite of my positive experience with ES,
    Defender seems like a possibly better choice than ES.

    Being the analytical type, I researched by reading Priuschat threads on
    this topic, plus read the Consumer Reports tires test report and their Prius
    Owner reader reviews for both the Defender and ES. The most important
    data I was looking to extract was the mpg loss that Defender buyers
    experience due to the tire's lesser LRR. I'll warn you that this is the
    least rigorous part of my analysis, since tire reviewers who provided this data
    didn't typically give a full listing of their before and after environments. For
    the record, the lowest loss was 1 mpg, the highest 10 mpg, and the most
    typical was 5 mpg.

    For benchmark pricing, I used Sams and Costco (Consumer Reports
    also listed pricing that was on par with Sams and Costco).

    When I modeled the data and assumptions in an Excel spreadsheet,
    I came to a conclusion that surprised me. In virtually every case, ES
    costs less than Defender. The numbers were so compelling that I
    decided to go with Energy Saver even though I was at the time 90%
    sure I was going to buy Defenders.

    So, here's how I analyzed this...

    Part 1...Capital Cost...basically fixed cost

    While both tires cost roughly the same, $125/tire, the nominal
    big advantage for Defender is that it has a 90,000 mile warranty
    (=expected life) vs ES' 65K mile expected life. On a per mile basis,
    the Defender's capital cost is 38% less than that of ES. [Now, 38%
    is a sizeable advantage, and intuitively, you'd think this MUST
    make Defender cheaper in the long haul.]

    Thus, normalizing the cost of each tire over their expected life, you
    get, for Defender: $125 / 90K = .138 cents per mile; and for
    ES: $125 / 65K = .192 cents per mile. You then have to multiply
    by four to reflect that you have four tires.

    Note that normalizing the capital cost does ignore the fact that
    tires purchases follow a step function, i.e., we can theoretically
    compare normalized capital cost for any varying number of miles, but
    in real life you can't buy, say, 50,000 miles worth of tires.

    Part 2...Operational Cost due to mpg difference...varying cost by mile

    I sense from the various reviewers' posts that the average mpg loss
    for the Defender was 5 mpg, so that's what I started with. I also
    ran the numbers using a low of 2 mpg loss and a high of 10 mpg loss.
    My 2009 Prius Gen 2 gets 53 mpg, and that's what I used as a
    starting point. In other words, I modeled my Prius mileage as 53 mpg
    with Energy Savers and 48 mpg for Defender.

    I used $4 per gallon as the assumed price of gas over the expected
    life into the future of the tires. I also tried this using $3.50 per gallon
    as well.

    Part 3...Now let's crunch the numbers for three different expected tire
    lives. [note - approximately $1 of rounding error in calculations]

    Scenario 1: Total life cycle cost over 50,000 miles, gas $4/gallon:

    Defender = Capital cost [ (.138 cents per mile * 50,000) * 4 tires ] +
    Operational cost [ (50,000 miles / net mileage (53 mpg - 5 mpg loss) * $4/gal ]
    = $278 + $4167
    = $4667

    ES = Capital cost [ (.192 cents per mile * 50,000) * 4 tires ] +
    Operational cost [ (50,000 miles / net mileage (53 mpg - 0 mpg loss) * $4/gal ]
    = $385 + $3774
    = $4466

    ES life cycle savings = $4668 - $4467= $201

    --

    Scenario 2: Total life cycle cost over 65,000 miles, gas $4/gallon:

    Defender = Capital cost [ (.138 cents per mile * 65,000) * 4 tires ] +
    Operational cost [ (65,000 miles / net mileage (53 mpg - 5 mpg loss) * $4/gal ]
    = $361 + $5417
    = $5917

    ES = Capital cost [ (.192 cents per mile * 65,000) * 4 tires ] +
    Operational cost [ (65,000 miles / net mileage (53 mpg - 0 mpg loss) * $4/gal ]
    = $500 + $4906
    = $5406

    ES life cycle savings = $5917 - $5406 = $511

    Scenario 3: Total life cycle cost over 90,000 miles, gas $4/gallon:

    Defender = Capital cost [ (.138 cents per mile * 90,000) * 4 tires ] +
    Operational cost [ (90,000 miles / net mileage (53 mpg - 5 mpg loss) * $4/gal ]
    = $500 + $7500
    = $8000

    ES = Capital cost [ (.192 cents per mile * 90,000) * 4 tires ] +
    Operational cost [ (90,000 miles / net mileage (53 mpg - 0 mpg loss) * $4/gal ]
    = $692 + $6792
    = $7485

    ES life cycle savings = $8000 - $7485= $515

    --

    The first major finding of the analysis is that the cost of mpg loss over
    a large number of miles is by far the most significant factor. What this
    is saying is that a small percentage (mpg loss of 5 mpg or ~10%) times
    a big number (cost of gas over 50-90K miles) is more impactful than a
    big percentage (Defender's 38% price advantage) times a relatively small
    number (tire purchase price).

    The second finding is that the ES's lifecycle cost advantage holds true
    for virtually all reasonable scenarios, including Defender mileage loss
    of as little as 2 mpg and gas only $3.50. The only scenario I found
    where Defender has a lifecycle cost advantage is if its mileage loss
    is only 2 mpg and you only drive 50,000 miles on them, which doesn't
    seem like a reasonable, real life scenario. Even then, the advantage is
    only about $50.

    --

    I know this won't put "Defender vs Energy Savers" to rest. My hope
    is that actually quantifying the numbers, rather than relying on
    intuition about Defender costing less due to its longer expected life,
    is a useful tool for those who are still struggling with the decision.

    Disclaimers: my model doesn't attempt to factor in inflation, gas
    price variation due to external factors (like a Middle East war), net
    present value, etc.; I don't think doing so would change the results.
    And, there's more to judging a tire than just cost; indeed, other
    factors may be more important to you, say, traction in snow if you
    live in Minnesota.
     
    #1 jcgee88, Aug 6, 2014
    Last edited: Aug 6, 2014
  2. bisco

    bisco cookie crumbler

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    so you're buying new energy savers?
     
  3. nsfbr

    nsfbr Member

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    I find it very hard to imagine losing 5 mpg from a tire choice unless one of the choices was studded. Those Defenders must be horrible in terms of Crr. I'd look at the more likely 1-2 mpg scenario, especially assuming you pump up your tires.
     
  4. jcgee88

    jcgee88 Member

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    I currently pump up my ES to 42/40 psi.

    Whether you believe it or not, 5 mpg loss seems typical. Feel free to
    peruse the other posts in Prius Chat on this topic. Here's an example:

    And here's another from Consumer Reports:

    I purchased them because tires are advertised by Michelin as Low Rolling Resistance. ... Four new Defender XT tires were installed on well maintained 2011 Prius II, real fuel mpg went from avg of 55 / tank to 47 / tank. I expected a 2-3 mpg loss that happens when ever a new tire is installed but not 7-8 mpg lost. Miles driven were accurately measured using GPS and gallons were measured at the same gas station on the same pump that is calibrated yearly so the mpg loss is real. Prius display was reporting a solid 10 mpg less. Tire pressure cold was 39 psig front 36 psig rear, alignment was checked by Toyota and in spec, wheel bearing in normal condition.

    -- end quote --

    And, yes, I am going to buy ES...once Michelin re-instates their $70
    rebate again!
     
  5. MSA14

    MSA14 Junior Member

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    I thought the energy savers have been discontinued?
     
  6. eblade

    eblade Junior Member

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    We just got a brand new set of Energy Savers to replace the mixed set of Nexen and Sumitomos that were on it when we bought it used. First 60 mile run shows an increase of 9mpg. I'm excited. That'll pay for the tires in practically no time, if it holds.
     
  7. Scallywag

    Scallywag Member

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    The only thing that your examination might be lacking is also something very difficult to quantify. I haven't driven with Energy Savers to compare, but the Defender is a really nice handling tire. Going from the non-LRR tires my Prius came with to the Defenders, I've not only noticed an increase in MPG (~5), but I've also noticed exceptionally superior handling. In the winter (and this last one was pretty bad), I rarely encountered any slipping or loss in traction, compared to the 2012-2013 winter where I was breaking free a lot more often. Also, there's a certain freeway interchange ramp nearby which I drive through frequently. The speed limit is 65 to 65 for the freeways, but the ramp has a posted sign for 50 mph. I like to try to keep speed through there as much as possible for mpg reasons, and I could previously only take the ramp at 60 in good dry conditions and the car felt like it was near its limits - I usually went through lower, around 55-57 in good conditions and even slower in wet. Now with the Defenders, the car feels stable going through over 65 - my record was 70 when I was specifically trying to test the curve, though I just take it at 65 for mpg now.

    Again, I'm not sure how to quantify this difference, and I haven't driven on Energy Savers to compare. But I think it's worth investigating, if you can think of a good way to look into it.
     
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  8. jcgee88

    jcgee88 Member

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    Consumer Reports' tire tests do include quantified results for six different
    types of handling. They use icons of filled/semi-filled red and black circles to
    represent the results, but in effect, it's a scale of from 1 to 5. On four of
    the six criteria, the two tires come out even. Defender edges ES on two
    criteria by one point. Interestingly, while they rate Defender as their top
    A/S tire, Continental ProContact EcoPlus is actually rated slightly better
    for handling than Defender (even in five categories, ahead by a point in
    one category). For the full results, please consult the latest Consumer
    Reports tire ratings article.

    Disclaimer: I have no affiliation with Consumer Reports magazine, I'm just
    a subscriber.
     
  9. vvillovv

    vvillovv Active Member

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    here's a bit of intuition to throw a monkey wrench into the math equation.

    what is the difference in handling on snow and ice for those of us that live in the great white north and don't run separate summer/winter sets?

    When I look at reviews I take a general consciences customer satisfaction
    How badly they suck or how much better they are then any other tire the reviewer has ever owned.

    Of course one has to read between the lines of each review for telling variables.
     
  10. priusgto

    priusgto Active Member

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    I would have been happy with just a 5MPG hit but mine was 7-10. I will say that I have never rode on a better handling tire than the Defender though, but living in the southwest, I don't need handling as much as I need MPG.
     
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  11. nsfbr

    nsfbr Member

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    7-10. Wow. And that is compared to the Energy saver I assume? How does it compare to the OEMs? I've been doing my best to gradually do better on tank average on the OEMs and after about 2/3 of my latest tank, doing my normal driving of commuting and smaller trips on the weekend, I'm tagging 55.0 according to the car. That will be about 53 in reality. I'm just wondering if the Energy saver would yield much better.
     
  12. bisco

    bisco cookie crumbler

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    not much, you just get a better handling, quieter, longer wearing, smoother tyre with similar mpg's.
     
  13. nsfbr

    nsfbr Member

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    Interesting. I'm the easiest person I know on tires. My 2nd generation took a total of 3 sets in its lifetime and the last set was in great shape when the car got totaled by someone too concerned about their cell phone to be bothered to stop at an intersection. I think the car's odo read about 164k at the time. It will be interesting to see what the best tires are in about 4 years when I need my first new set...
     
  14. CBarr31

    CBarr31 Active Member

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    Just to play devil's advocate I got 176,000+ miles out of my first set of Michelin Harmonies, precursor to Defender. And my current set of Harmonies are at about 135,000 miles with 4/32" still left.

    Happy driving,
    Chris
     
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  15. jcgee88

    jcgee88 Member

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    What kind of mileage do you get?
     
  16. CBarr31

    CBarr31 Active Member

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    My lifetime average is about 47.4 MPG and except for the first 70,000 on incrappities those are all Michelin Harmony miles. That is actually improving over the last 20,000 miles or so but that has to do with the switch to pure E0 gas and not the tires.

    Chris
     
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