What is the correct tire pressure for Gen 4 195/65R15 91H

Discussion in 'Gen 4 Prius Technical Discussion' started by booke02, Jul 12, 2016.

  1. Hybridriver

    Hybridriver New Member

    Joined:
    Sep 12, 2017
    6
    5
    0
    Location:
    New Jersey
    Vehicle:
    2016 Prius
    Model:
    Three
    "What is the correct tire pressure for Gen 4 195/65R15 91H"

    To answer this question, it's necessary to ask first why Toyota recommends 32 psi front & rear when there is a full size spare 195/65R15 91H? My guess is in case of a flat tire, Toyota doesn't want the owner to mismatch the full-sized spare's tire pressure with the other tire at the front or rear, which would possibly be the case if the recommended tire pressures were 36 psi front & 35 psi rear. So, it recommends a uniform tire pressure on all four wheels.

    Now, the question is: why does Toyota indicate 36 psi front & 35 psi rear when there is no full-sized spare? This is a little bit more complicated. The tire pressure indicated on the inside of the driver's door assumes the weakest tire is installed on the car, which is a tire with a load rating of 89 and a speed rating of S. But the label on the driver's door doesn't indicate the load and speed rating of the tire, only its size. So, in order to avoid contradicting the information on the driver's door, Toyota recommends 36 psi front & 35 psi rear when there is no full-sized spare. In North America, the owners manual indicates there are two "types" of 15" tires: Type A which is rated at 89 S (and has a temporary spare), and Type B (with a full-sized spare) which is rated at 91 H (both types are the same size 195/65R15). For Type A tires, Toyota recommends 36 psi front & 35 psi rear. For Type B tires, it recommends 32 psi front & rear. So, it appears Toyota believes for the 91 H rated tires, the "optimal" tire pressure is 32 psi front & rear, although the 91 H rated tire can be safely operated at 36 psi front & 35 psi rear.
     
    RCO likes this.
  2. alanclarkeau

    alanclarkeau Senior Member

    Joined:
    Feb 24, 2016
    2,202
    2,543
    0
    Location:
    near Brisbane, Australia
    Vehicle:
    2016 Prius
    It could be that the different pattern ty res have different handling characteristics, and they're taking advantage of the differences? You can adjust the handling of a ty re by changing the tire pressures.

    Interesting - I was under the belief that no USA (or Australian) PRIUS was equipped with a full size spare wheel, only Middle East?
     
  3. Prodigyplace

    Prodigyplace Senior Member

    Joined:
    Nov 1, 2016
    4,059
    3,404
    0
    Location:
    Central Virginia
    Vehicle:
    2017 Prius
    Model:
    Two
    Toyota US only offers a space saver spare on some Gen 4 trims. Some countries have a full size spare since it is mentioned in the manual.
    IIRC the space saver spare tire requires a higher pressure contradicting your theory.
     
  4. Prodigyplace

    Prodigyplace Senior Member

    Joined:
    Nov 1, 2016
    4,059
    3,404
    0
    Location:
    Central Virginia
    Vehicle:
    2017 Prius
    Model:
    Two
    They apparently have not checked their spare tire.
     
    alanclarkeau likes this.
  5. Mendel Leisk

    Mendel Leisk Lapsed Cargo Cultist

    Joined:
    Oct 17, 2010
    21,285
    9,903
    80
    Location:
    Greater Vancouver, BC, Canada
    Vehicle:
    2010 Prius
    Model:
    Touring
    upload_2017-9-12_6-34-8.png

    I put all four tires on the same pressure. Mainly to avoid the need to adjust pressures when rotating the tires. That pressure varies, lower if it's our stock 17", higher with the 15" snows. Typically a few pounds higher than spec. A pound or two variation, the car doesn't complain.
     
    RCO and Prodigyplace like this.
  6. RCO

    RCO Senior Member

    Joined:
    Aug 31, 2016
    2,061
    2,465
    0
    Location:
    Cornwall
    Vehicle:
    2016 Prius
    Model:
    Three
    Nor were the British and, I suspect the Europeans either.
     
    #46 RCO, Sep 12, 2017
    Last edited: Sep 12, 2017
  7. Hybridriver

    Hybridriver New Member

    Joined:
    Sep 12, 2017
    6
    5
    0
    Location:
    New Jersey
    Vehicle:
    2016 Prius
    Model:
    Three
    To: Mendel Leisk: Lucky for you I didn't address the post to you.
     
    Mendel Leisk likes this.
  8. Hybridriver

    Hybridriver New Member

    Joined:
    Sep 12, 2017
    6
    5
    0
    Location:
    New Jersey
    Vehicle:
    2016 Prius
    Model:
    Three
    alanclarkeau,

    The movement away from full-sized spares is having consequences not easily seen by auto buyers or owners. When a full-sized spare is standard equipment, making the replacement of a flat tire as simple as possible is a natural goal of auto manufacturers. Having a uniform tire pressure on all four wheels clearly helps to simplify the process of replacing a flat tire. The owner doesn't have to be concerned, as in the case of different pressures for the front and rear wheels, with whether or not the full-sized spare's air pressure matches the pressure of the other tire at the front or rear.

    The inclusion of a full-sized spare then creates another criteria in the selection of a tire to be standard equipment on a vehicle, ie, will the tire be able to support uniform pressures on all four wheels while delivering the vehicle's expected performance. With the abandonment of full-sized spares, auto manufacturers have one less criteria to worry about in selecting a tire as standard equipment on a vehicle. In the case of the Prius, this is leading to the selection of a less capable tire to be standard equipment (at least in some markets) resulting in different pressures for the front and rear wheels, and higher pressures for both the front and rear wheels (compared to the tire used as a full-sized spare). This is, in turn, compromising ride quality and possibly traction.
     
  9. alanclarkeau

    alanclarkeau Senior Member

    Joined:
    Feb 24, 2016
    2,202
    2,543
    0
    Location:
    near Brisbane, Australia
    Vehicle:
    2016 Prius
    Do you have a FULL SIZED SPARE? If so, how did you organise it?

    The OP is in Israel which is one of the few places where it is available.
     
    Prodigyplace likes this.
  10. Hybridriver

    Hybridriver New Member

    Joined:
    Sep 12, 2017
    6
    5
    0
    Location:
    New Jersey
    Vehicle:
    2016 Prius
    Model:
    Three
    alanclarkeau,

    The car came with 89 S rated tires which I eventually replaced with 91 H rated tires by another brand. The 89 S rated tires at 36 psi front & 35 psi rear made the Prius feel insubstantial. With the 91 H rated tires at 32 psi front & rear, I am getting 2% to 3% improved fuel economy, better traction and a better ride.
     
    Merkey and RCO like this.
  11. alanclarkeau

    alanclarkeau Senior Member

    Joined:
    Feb 24, 2016
    2,202
    2,543
    0
    Location:
    near Brisbane, Australia
    Vehicle:
    2016 Prius
    BUT - the answer to the question we asked:
    "Do you have a FULL SIZED SPARE? If so, how did you organise it?"
     
    RCO and Prodigyplace like this.
  12. Hybridriver

    Hybridriver New Member

    Joined:
    Sep 12, 2017
    6
    5
    0
    Location:
    New Jersey
    Vehicle:
    2016 Prius
    Model:
    Three
    alanclarkeau,

    Your question suggests Toyota offers a full-sized spare as either standard equipment or as an option to the Prius sold in the US. I wish you could point me to the source of your information.

    My personal preference is to have a full-sized spare as standard equipment on a new vehicle, or, lacking that, to have the option to equip the new vehicle with a full-sized spare.

    In the case of the Prius, I narrowed my choices to either the Three Model or the Four Model. The advantage of the Four Model is it has heated seats which are not available on the other models, either as standard equipment or as an option(!). The disadvantage is it has no spare, period. In the end I opted for the Three Model because it has a spare, although only a temporary one.
     
  13. Mendel Leisk

    Mendel Leisk Lapsed Cargo Cultist

    Joined:
    Oct 17, 2010
    21,285
    9,903
    80
    Location:
    Greater Vancouver, BC, Canada
    Vehicle:
    2010 Prius
    Model:
    Touring
    The Owner's Manual shows a full size spare option.

    FWIW I'm happy with a temp spare, have used them several times over the years with various cars.
     
    Merkey likes this.
  14. Prodigyplace

    Prodigyplace Senior Member

    Joined:
    Nov 1, 2016
    4,059
    3,404
    0
    Location:
    Central Virginia
    Vehicle:
    2017 Prius
    Model:
    Two
    In the post Alan responded to, you indicated your strong preference for a full-sized spare tire and chose a 2016 Prius.

    Many people here have added spare tires to Gen 4 Prius.
    Alan was merely asking whether you had upgraded to a full-sized spare tire. It would fit the car since there is at least one market where it is offered. I do not know if the foam would need to be altered.
     
    RCO and alanclarkeau like this.
  15. Hybridriver

    Hybridriver New Member

    Joined:
    Sep 12, 2017
    6
    5
    0
    Location:
    New Jersey
    Vehicle:
    2016 Prius
    Model:
    Three
    Prodigyplace,

    You appear to be missing the point. The point is not what my personal preference is. The point is the abandonment of full-sized spares is leading some auto manufacturers -- I suspect not just Toyota -- to equip their vehicles with less capable tires as standard equipment. This may affect the quality of the vehicle's ride as well as its traction.
     
    RCO likes this.
  16. bbald123

    bbald123 Thermodynamics Law Enforcement

    Joined:
    Nov 13, 2007
    320
    169
    0
    Location:
    Harrisburg, PA
    Vehicle:
    2016 Prius
    Model:
    Four
    How do you draw a line from removal of full-sized spare to equipping inferior OEM tires?

    Tire quality on new cars when I first started buying cars was much better than it is now. And I don't believe I have ever owned a car with a full-sized spare.
     
    alanclarkeau, Mendel Leisk and RCO like this.
  17. RCO

    RCO Senior Member

    Joined:
    Aug 31, 2016
    2,061
    2,465
    0
    Location:
    Cornwall
    Vehicle:
    2016 Prius
    Model:
    Three
    Must be an age thing, I remember when all cars had a full size spare! Of course they were cross ply tires back then, radials hadn't been invented.