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mileage versus tire pressure

Discussion in 'Gen 2 Prius Main Forum' started by drew, Mar 20, 2004.

  1. drew

    drew New Member

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    ok i'm new to the group, but have used the search function (to no avail ) for about an hour trying to find others experience with, recommendations and some technical detail on a problem i have had and solved with my used 02 classic prius. it came from the dealer with new bridgestone tires set at 30-32 psi. our initial tank milage was 38 mpg here in nh in the winter. after complaining , the dealer checked out the whole car leaving the tire pressure at 32 psi. i said enough of this, raised it to 50 psi cold as allowed on the tires max pressure rating. my average mileage has gone up to 50 with no adverse effects in ride, handling etc. it also stays in stealth much easier and longer.

    since tires generally fail from overheating due to underinflation, and very seldomly due you see a tire worn out in the center(a symptomm of overinflation), i've not been in the least concerned at running at the max recom psi. has anyone had experience running significantly over that

    could anyone refer me to posts providing some detail on this .
     
  2. efusco

    efusco Moderator Emeritus
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    Drew,
    Welcome to the forum...there aren't many posts here about the 1st Generation Prius ('01-'03), but I know what you need baby!

    http://john1701a.com/

    Scroll to the bottom of the home page and click on "User Guide Classic". It should have lots of good info on ideal tire pressures and why you should do that...notice that there's a lot of other really great info in there too.

    Then, go back and just enjoy John's web site. It is probably the single best source of Prius info on the web--or anywhere else for that matter. It combines lots of specific technical data with lots of practical, real-world if annecdotal information that every Prius owner should know.

    Enjoy your car.
     
  3. bruceha_2000

    bruceha_2000 Senior Member

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    I think I would be a tad conservative trusting that your pressure guage is extremely accurate and that the tires, though spec'ed at 50 psi cold will REALLY be OK there. Could be the mfg sets the value low as compared to their "unsafe any higher" tests, 'just in case' but still :)
     
  4. drew

    drew New Member

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    thanks for the info lead to john's site which i have been to and it is helpful, but i couldn't find the link you mentioned on the this sites home page and i was hoping to find more technical info on the classic prius from owners or former owners on this site.

    if worse comes to worse i will do towing rolling resistance tests at various tire pressures.

    one of the reasons i'm making this plea for increased tire pressures is the response from bruceha which immediately cautions me about my gauge (yeah i'm sure they all have inaccuracies, as likely to be high as low (maybe ther's a consumers report on this), and we're not talking about being anywhere near the pressure required to explode a tire (whatever that is). i was particularly pleased to find the bridgestone tires rated for 50 psi which allows for considerable improvement while remaining within the tire supplier's specs.

    i'd like to find a source for real info (beyond the anecdotal although that is useful)on the reduction in rolling resistance, and hence increase in mileage with increased pressure . perhaps if we all tried it for the next tankful and reported back on a poll as i've submitted, we could do us all a favor.

    people seem to be interested in spending quite a bit of additional money for a car that gets no better mileage than a geo metro or a 1980 diesel rabbit , when it would just be easier to pump up the tires to get a marked free improvement in mileage (on any car, i might add). (they also seem to be willing to spend a lot on synthetic oil for supposedly the same reason)

    keep trying, i appreciate the feedback.
     
  5. efusco

    efusco Moderator Emeritus
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    Sorry to mislead you, the link I was talking about was at the bottom of John's Site, not here.

    If you want to abreviate your search for information a bit, cruise over to the Prius Yahoo Group at http://autos.groups.yahoo.com/group/toyota-prius/. That's loaded with Prius owners who can go through the whole gory history of tires on the 1st Gen. Prius. They have some pretty solid data on ideal tire pressures to use. But, you'll find all you need in John's User Guide too (at the bottom of HIS home page).
     
  6. Jonnycat26

    Jonnycat26 New Member

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    I'm likely to be flamed for this, but whatever...

    Folks, there's a reason the tires have recommended and maximum pressures. They recommend you stick with what they recommend. If the recommended pressure is 35, and max is 48, then you don't want to go straight to 48. 40, maybe. But inflating to max pressure is really not a wise move.

    When you drive, the air inside the tires gets warmer and the pressure goes up. As the tire ages, it starts to wear down. It's inevitable. If you're running at the maximum pressure and not the recommended pressure you're going to reduce the life of the tires, pure and simple.
     
  7. efusco

    efusco Moderator Emeritus
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  8. Wolfman

    Wolfman New Member

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    What you are stating here is already considered when stating the maximum safe pressure of the tire by the mfr. Tire pressure is measured "cold." If the tire is inflated to the maximum safe rating mentioned on the sidewall, it will still safely handle the "hot" tire pressure.
     
  9. daniel

    daniel Cat Lovers Against the Bomb

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    I think I am speaking for a lot of folks when I say that I did not buy this car for the improved mileage. The mileage is a great talking point and gives me bragging rights. But it is only one of a great many selling points on this car. To compare it to a rattle-trap Geo Metro, or a dirty diesel Rabbit is a joke.
     
  10. SpartanPrius

    SpartanPrius New Member

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    That is true, except the car's suspension was not designed to be optimal to that pressure. When you play at the edge like this, you must be aware of the compromises. Tire manufacturers provide a maximum cold pressure value for the specific tire, and NOT that tire's application to the Prius model. Things that are potentially lost by doing this are: tire life; wet or snow traction; and, general handling characteristics. Any deviations made from Toyota's recommendation needs to take all of this into consideration. Afterall, they have spent considerable effort coming up with recommended values. Tire sidewall flex is key to how a car grips the road and rides smoothly.
     
  11. drew

    drew New Member

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    enough of the opinions, how about some experience. i really would like to see some data from other owners of classic prii

    again, i'm flabbergasted by the amazing improvement in mileage (and as a result emissions) by simply increasing the tire pressure to max.

    i reiterate mileage went from 35 to 50 when tires went from 32 to 50 psi. and no noticable effects in handling, ride, tire wear etc.

    a major selling point of the car is mileage. i can't believe people buy it for cupholders.

    from an environmental and financial point of view a used geo metro or diesel rabbit (burning biodiesel or grease of course ) are much better deals. you don't have to wait and you don't tie up 25 grand. :roll:
     
  12. SpartanPrius

    SpartanPrius New Member

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    Drew,

    Why not visit the local hardware store and see if they have some appropriately sized solid rubber tires.

    :lol:

    It is not opinion, it is fact. Sure, changes can be made, but it is reckless to do so without careful consideration of the tradeoffs.

    Skidpad, anyone?

    Paul
     
  13. efusco

    efusco Moderator Emeritus
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    Again, Drew, if you'll take the time to look around John's site he has journals and tons of information about the tire pressure. There are not many classic owners here, but having spent a lot of time on the old Prius Yahoo Group before getting my '04 I can tell you that there are thousands upon thousands of 1st gen. Prius owners who have had the same experience as you and found that higher pressures were MUCH better for tire wear, mileage, handling and it's basicly been universally accepted that the higher pressures are prefered. If you MUST get multiple voices to confirm what I'm telling you and what John has thoroughly documented at his site the you should go over to the Prius yahoo Group http://autos.groups.yahoo.com/group/toyota...yguid=102573742 and ask there, you'll get bombarded.
     
  14. Jonnycat26

    Jonnycat26 New Member

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    Keep in mind what else has been said in this thread about higher tire pressures... you are shortening the life of the tires. I remember seeing posts from classic owners who had to have tires replaced very early (under 20K miles even) and I wonder if these were the same people who were overinflating their tires.
     
  15. efusco

    efusco Moderator Emeritus
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    No, those are the people who EXTENDED the life of their tires. 'OVER-inflation' (i.e. higher than rated pressures for a given tire) can cause uneven wear, but under-inflation is the cause of excessive/premature wear. The original Prius tires were a very soft compound and at the manufacturer's rec. pressures people were having to replace tires as early as 12k miles, most by 20k. With the increased pressures alone they began seeing extended life times. With new tires altogether they started seeing normal life expectancy--and extended with increased pressures as well as improved mpg and handling.

    Please broach this topic at the Yahoo-Prius group if you have other questions, it's been covered again and again there and there is a ton of data. I've no first hand experience in this matter but have read innumerable threads over there on the topic.
     
  16. efusco

    efusco Moderator Emeritus
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    Drew, et al;
    I inquired as to this situation with Jerry Jorganson who I know to be a tire expert and Classic Prius owner who's discussed this issue several times in the past. He's had difficulty logging on here but he sent me his standard response and info so I'll post it here on his behalf until we can work out why he's having trouble getting on this board.

     
  17. drew

    drew New Member

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    thank you evan and particularly jerry for following up and confirming my suspicions that the recommended tire pressure is way to low. and for torpedoing many of the ill advised and thought out knee jerk reactions to someone noting the emperor (toyota and its dealers and the cupholder crowd) have no clothes on tire pressure. i'd venture to guess that the 04 prius owners could benefit in significant mileage improvements from a similar in depth look at the mnfr's recs and work towards higher pressure.

    i'm still running 45-55mpg with 48/50 psi in nh in winter on short and long trips. tire pressure does seem to make a significant difference.

    my question :p now is how do we get the word out? particularly to dealers and service people.

    i was unable to make the link to jerry's site work, i'm sure it would be helpful

    i would still like to see some real data, not opinions, for example other user's actual experience with different tire pressures versus milage, or rolling resistance tests at various pressures. thanks again for your persistance
     
  18. efusco

    efusco Moderator Emeritus
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    Well, Drew, the word has been out, for about 3-4 years (since 1991 anyway). Thus my previous references to the YG. It's just that Toyota has, for unknown reasons, decided not to make those recommendations though they're pretty universal in the 1st gen and now 2nd gen. communities.
     
  19. FredWB

    FredWB New Member

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    OK, here's the preliminary results of my first weekend of pressure VS mpg testing. Please don't call the reaction to over pressure knee jerk. My comments were based on logic, researched data, and of course personal experience. There are other "experts" in the group that might disagree that's all. As a Mechanical Engineer I don't, and never will, "knee jerk". But instead I research the data and try to evaluate it in the most objective way I can. Then I try some real world experiments to valid or disprove what my research might suggest. I have nothing to gain by saying extra pressure is the wrong or right thing to do.

    My qualifications are about 5 years working in a very reputable tire store back east. Radials were introduced while I was there and of course the state of the art has changed and improved since then. I also have a BSME that I received in 1980. I do not consider myself a "tire expert". An expert would be one that has worked in the industry, designed tires, is familar with the very non-linear and difficult to analyse behavior of tires, in my opinion. I've performed lots of FEA (finite element analysis) on rubbers and elasomers and believe me when I say that it's pretty complicated stuff even with the right tools. As stiff as a tread section on a tire can be, since it's not perfectly rigid, eventually at some internal pressure and vehicle load it will begin to deform into a somewhat curved shape due to the boundary conditions, pressure, and contact pressures. The debate is at what pressure will that begin to happen.

    However many here might have long term experience with their cars and tires and I'm not minimizing that, I'm just saying while knowledgeable as they are, unless they have participated in the actual R&D effort designing radial tires I would not consider them experts...just knowledgable. If they have that expert experience, that's good too. I would love to have a tire design engineer step forward and add to this discussion.

    So on to the data. I posted data yesterday that had a big mistake. That was the data for the 35/33 pressure run. As I found out last night I had not lowered the pressure so that was the 42/40 data. I posted that in the other tread on tire pressure. Those of you familar with Wayne's program know there are lots of factors that can affect gas mileage. The things not on his list like traffic, lights, hills can really affect a test like this. I've tried to normalize all the factors that I could, but the ambient temperture for the low pressure test was somewhat higher on average (5 deg). That was offset somewhat by the increased traffic today. I have not checked the computer data for the low pressure run with a fillup because it too warm here now and so will fillup tomorrow morning. But my 1st set of test data shows a 3% improvement in gas mileage with 42/40 VS 35/33. I did 3 round trip runs to work, 11 mi each way, 18 lights each way, 2 mi of freeway and lots of hills. I plan to repeat this next week, switching the days I do the low and high pressure test. Here's what I've learned so far:

    42/40, temp range 55-63F, no appreciable wind
    71 out, 41.1 back, 56.2 RT
    78.8 out, 40.6 back, 59.7 RT
    77.8 out, 37 back, 57.4 RT
    Computer overall: 57.8
    Actual: 53.8 (the trips to and from the gas station acted to lower the actual somewhat along with the "computer optimism".

    35/33 temp range 59-70F, no appreciable wind
    67.1 out, 42.1 back, 54.6 RT (caught 2 major lights, lost momentum)
    77.5 out, 35.3 back, 56.4 RT
    75.2 out, 41.4 back, 58.3 RT
    Computer overall: 56.1
    Actual: TBD tomorrow morning.

    Qualified experts state that consistant gas mileage data is very very difficult to produce. There are too many variables to control that have a significant influence when looking for a couple of percent change. And when someone suddenly has say a 10 mpg improvement under an uncontrolled commute, I really question the vailidity of the immediate conclusion that it was the pressure in the tire that did all of it. It needs to be repeated over and over again and other variables carefully controlled. So I offer this data as preliminary. Since these runs take about 2 hours each day, I think I'm only going to repeat once next week. It's just too nice here now to spend weekends in my Prius doing a science experiment, as fun as it might be.
     
  20. FredWB

    FredWB New Member

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    Oh I just realized that I could easily (well with some time) do a similar test to evaluate Mobil 1. I plan to go to that at 5K and I'm about 3700 now. So if I get to the point where thing looks reasonably repeatable I might do that. Luckily the temperatures are usually pretty moderate here so I might be able to minimize temperature effects. Although today did get warm fast and by 9 AM it was 70.