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

"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.

 

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 tyre pressures.

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

 

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.

 

They apparently have not checked their spare tire.

 

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.

 

Nor were the British and, I suspect the Europeans either.

 

To: Mendel Leisk: Lucky for you I didn't address the post to you.

 

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.

 

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.

 

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.

 

BUT - the answer to the question we asked:
"Do you have a FULL SIZED SPARE? If so, how did you organise it?"

 

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.

 

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.

 

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.

 

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.

 

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.

 

Must be an age thing, I remember when all cars had a full size spare! Of course they were cross ply tyres back then, radials hadn't been invented.

 

bbald123 said, "And I don't believe I have ever owned a car with a full-sized spare."

I would think someone would KNOW something like that.

 

Fascinating, aren't you.

 

I reviewed the 2016 Prius brochure again to see if there is any mention of the availability of a full-size spare and there is none.

What I find troubling is the pressure indicated on the driver's door misleads people into believing there is only one recommended pressure when in fact the pressure recommended is dependent on the load and speed rating of the tire.