Tire pressure, Any guesses ?

Discussion in 'Gen 4 Prius Main Forum' started by Chris Wolfgram, Oct 30, 2019.

  1. Chris Wolfgram

    Joined:
    Oct 20, 2019
    159
    64
    0
    Location:
    Sacramento CA
    Vehicle:
    2019 Prius
    Model:
    LE
    So this morning (coldest morning since I got my new Prius LE 10 days ago) I hop in my car and I get a Tire Pressure light... Urggg... I'm thinking, not even two weeks in and I have to deal with a leaking tire already ? So I jump out to check them, and every single one of them was exactly 29 lb. So apparently, on the 85 degree afternoon I picked it up, they were all probably 33 or 34 lbs (still too low IMPO) but after dropping to the low 30's last might, so did the pressure in all my tires. I'm assuming the TPMS kicks on as soon as a tire drops below 30 lbs ?

    Anyway, I'm almost glad this happened.... and I feel a little dumb to have assumed that the dealership would have put a nice "high pressure" for the best mileage, and not to have checked them myself already.

    So, any guesses on how much of a MPG jump I am going to see, going from the minimum tire pressure of 29-33.... up to right at the max ? What are these 38 ? 40 ? So we are talking a pretty substantial 10 lb difference.... Hoping for 2 mpg ? Your guess ? '
     
  2. CooCooCaChoo

    CooCooCaChoo Active Member

    Joined:
    Jan 7, 2015
    498
    235
    0
    Location:
    Fresno, CA
    Vehicle:
    2017 Prius
    Model:
    Two
    Yeah, always check your tire pressure again AFTER the dealership touches it. One time I found that my front tires were 36 and my rears were 32. When they did the tire rotation, they didn't check the pressures afterward.

    But, on to the tire pressures. You should fill and then set them at the coldest part of the day after the car has been sitting for hours.
     
  3. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    83,817
    36,685
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    i set mine at 42f/40r, but admittedly don't maintain them regularly. the good thing is, when i do check them, they are way above the tpms set point.

    i think you might pick up an mpg or two
     
    alanclarkeau likes this.
  4. alanclarkeau

    alanclarkeau Senior Member

    Joined:
    Feb 24, 2016
    5,530
    6,147
    0
    Location:
    near Brisbane, Australia
    Vehicle:
    2016 Prius
    Model:
    N/A
    I put 38 all round - promising myself to drop them the next morning when they're cold.

    But I've been practising procrastinating - why do this week that which can be put off till the week after next.
     
    dig4dirt and bisco like this.
  5. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    83,817
    36,685
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    oh my, you've copied my playbook :oops:
     
    dig4dirt and alanclarkeau like this.
  6. sam spade 2

    sam spade 2 Senior Member

    Joined:
    Mar 31, 2018
    2,264
    1,020
    0
    Location:
    USA
    Vehicle:
    2017 Prius c
    Model:
    Four
    Might need to "reset" the TPMS too.
    Most people find that there is no significant increase in mileage from higher tire pressures.......unless you make them ridiculously high.
    The key words are "significant" and "ridiculous".

    Side note: Just rented a car last week in St. Louis.
    Immediately noticed that the ride was harsh and it was hard to hold a straight line at speed.
    Stopped at one of the rental locations to have the pressures checked.
    ALL were over 50 and two were over 70 !!!!!
     
    WilDavis likes this.
  7. Chris Wolfgram

    Joined:
    Oct 20, 2019
    159
    64
    0
    Location:
    Sacramento CA
    Vehicle:
    2019 Prius
    Model:
    LE
    Thanks guys, I guess we will see. I was quite surprised to see my tires were rated for up to 44 lbs ! So I put 42 in all of them..... Which from 29 lbs each, was a 13 lb increase ! Pretty substantial I'd say. Going to be surprised if I don't get at least 1 extra mpg.... 2 would be nice though :)
     
    krmcg likes this.
  8. alanclarkeau

    alanclarkeau Senior Member

    Joined:
    Feb 24, 2016
    5,530
    6,147
    0
    Location:
    near Brisbane, Australia
    Vehicle:
    2016 Prius
    Model:
    N/A
    Don't confuse the pressure that the tyre manufacturer prints on the sidewall of the tyre. That is just telling you what the maximum safe pressure the tyre is designed for - not what pressure you should run. Note that the tyre manufacturer prints the same pressure on the tyres, not knowing which vehicle it will be fitted to - nor whether it will be on the Front or Back axles.

    The pressure that TOYOTA prints on the tyre placard is the relevant one.

    My FOCUS - FORD specifies 33 PSI Fr/Rear - but the tyre sidewalls have 51 PSI MAXIMUM marked. That car would be terrible with 51 PSI - I usually ran about 35 which was the high-speed recommendation.

    In the case of my older MAZDA 929 wagon - 26 PSI front, 32 PSI back - but the tyres said 44 PSI maximum. I think MAZDA said to add 4 PSI for higher speeds, which is what I did - not 44.
     
  9. Chris Wolfgram

    Joined:
    Oct 20, 2019
    159
    64
    0
    Location:
    Sacramento CA
    Vehicle:
    2019 Prius
    Model:
    LE
    Well, as for how the car steers and corners, as well as how stiff the ride is, I'll be able to see that for myself.

    But as long as I don't go over the 44 max for the tire, I feel like the tire will be safe also. Of course you know they add a big safety margin to that 44 lbs too.

    BTW, my truck tires have a max tire pressure of 68 lbs ! I've run them at 60 lbs for a long time. They handle and wear great
    I bet the stock tires on my truck had a max of like 42 lbs.... Just checked and the door sticker suggests 35 lbs... Ha ! I bet 35 lbs is lower than the minimum rating for my aftermarket tires.
     
  10. kithmo

    kithmo Couch Potato

    Joined:
    Apr 25, 2010
    2,143
    2,399
    45
    Location:
    South Yorkshire, UK
    Vehicle:
    2016 Prius
    TPMS light comes on when there's around a 20% drop in pressure from whatever you set the TPMS at. Whilst cold, I pump my tyres up to around 25% higher than recommended, set the TPMS, then drop them to about 2 psi above the recommended. This means the TPMS will warn me when the pressures drops by about 2 psi. I like an early warning rather than waiting for a 20% loss.
     
    Mambo Dave likes this.
  11. Mambo Dave

    Mambo Dave Member

    Joined:
    Jul 5, 2019
    135
    71
    0
    Location:
    33312
    Vehicle:
    2019 Prius
    Model:
    L Eco
    Do our gen 4's have a TPMS readout at all on the data screen? My 2015 truck would tell me the pressure in each tire (a base-model feature), but I haven't found that yet on my 2019 Prius.
     
    Salamander_King likes this.
  12. Salamander_King

    Salamander_King Senior Member

    Joined:
    Nov 8, 2015
    4,671
    3,539
    0
    Location:
    New England
    Vehicle:
    2017 Prius Prime
    Model:
    Prime Premium
    Nop. Never did, and probably never will.
     
  13. Mambo Dave

    Mambo Dave Member

    Joined:
    Jul 5, 2019
    135
    71
    0
    Location:
    33312
    Vehicle:
    2019 Prius
    Model:
    L Eco
    :confused:

    That's pretty archaic of them, but then my 2019 radio is based on 2013 tech.

    I'd bet that Gen 5's will get it.
     
  14. Salamander_King

    Salamander_King Senior Member

    Joined:
    Nov 8, 2015
    4,671
    3,539
    0
    Location:
    New England
    Vehicle:
    2017 Prius Prime
    Model:
    Prime Premium
    I hope so. All TPMS sensors (internal ones) are sending pressure and temperature data, and ECU is receiving them. It is just a matter of displaying it on the screen. But somehow, Toyota do not want to do that on PRIUS. I have no idea why. You can capture the data and display it by using TechStream or other OBD apps including ScanGauge II.
     
    Mambo Dave and Fester like this.
  15. Mambo Dave

    Mambo Dave Member

    Joined:
    Jul 5, 2019
    135
    71
    0
    Location:
    33312
    Vehicle:
    2019 Prius
    Model:
    L Eco
    I agree that folks should not confuse max pressure for max load info with what they should run (unless they are running five people + gear in their Prius most days).

    Likewise, especially true for pickup trucks and station wagons that aren't treated like work-vehicles (my father's station wagons, for example, were work cars - they were loaded to the max at in the rear and rear-seats with brochures, equipment, and sales products), the running tire pressure for the rear should often be lower than the front tires. The front tires carry the weight of the driver, the engine, much of the transmission (or, again, nearly all of it), plus the additional loads of braking (75% to 95% of braking traction and braking come from the front two tires) and cornering. In a commuter vehicle, like my Prius or my Ram 1500, the front tires were the ones that should have had - and did have - the higher pressures (compared to the rears). If I knew I was going to load my truck down, I'd pressure-up the rears. Now, on the work-trucks I've used, we ran max pressure on the rears all the time, as - day in and day out - each was loaded with equipment and trailers.
     
    alanclarkeau likes this.
  16. alanclarkeau

    alanclarkeau Senior Member

    Joined:
    Feb 24, 2016
    5,530
    6,147
    0
    Location:
    near Brisbane, Australia
    Vehicle:
    2016 Prius
    Model:
    N/A
    The other thing that tyre pressures do is change the handling (by changing the grip) - to balance out understeer or oversteer. My 1977 Renault 12 wagon, front engine, FWD ran 23 Fr, 27 Rear (or 24/29 if laden) - it understeered, but was safe.

    I rotated the tyres front to back and drove to the Service Station to adjust the pressures - and on the way the car oversteered quite noticeably - at higher speeds would have been verging on dangerous (or like a rally car!!).
     
    Mambo Dave and kithmo like this.
  17. blane

    blane Carmudgeon

    Joined:
    Apr 10, 2012
    62
    33
    0
    Location:
    NJ Suburb of NYC
    Vehicle:
    2019 Prius
    Model:
    XLE
    deleted
     
  18. Chris Wolfgram

    Joined:
    Oct 20, 2019
    159
    64
    0
    Location:
    Sacramento CA
    Vehicle:
    2019 Prius
    Model:
    LE
    Update; Alright, so I lowered my tire pressure a little, from 44, to 40.But still, since I've been running them at 40..... vs. 29... I've managed to improve my average by a full 2 mpg ! This sounds pretty big to me. Maybe on wet roads this Winter, I might consider dropping down to 36 lbs, but for now, they seem to handle great.
     
    #19 Chris Wolfgram, Nov 8, 2019
    Last edited: Nov 8, 2019
Loading...