do not know what pressures for 14in tires

Once you get into custom size tires the pressure is based on the load rating of the old tire vrs new.

 

Look for the sticker inside the drivers door jam.
Unless you have some really unusual tires, those pressures for 15s should be fine.

 

What you're saying is like this?:

If stock tires are 44 psi max pressure on the sidewall, and new ones are 51 psi, and the door jamb decal recommends 35 psi, with the new ones you'd use 35 x 51/44 psi, equals 41~ psi.

And if the new tires are also 44 psi max pressure on the sidewal, just follow the door jamb decal recommendation.

Hopefully all the stock tires are the same max pressure rating.

Just curious, are the 14" tires sized such that the outside diameter roughly matches stock tire size?

 

OD of that tire will be 23.1":



OD of the (stock) 175/65R15 is 24":




That's a fairly significant difference, maybe too much? You've lowered the car about 1/2", and the odo and gearing will be off by 24/23.1.

 

I could care less about the ODO But moving from a 88s tire down to a 81s tire means you need to up pressure from the 35psi on the door jam to 40-44PSI to keep the same wear metrics and reduce the risk of blowout.

 

Your cars body (door sills) are 1/2” closer to the ground along with you and everything else in the car.

ON a more important topic…
When you downsize tires you need to increase inflation pressures to make up for the lost load rating.

I would estimate 40+ PSI

 

Wth !?!?!?

The lug nuts need to be TIGHT regardless of what wheel you are using.
IF they won't tighten properly, you have the WRONG wheel.

THEN......have you ever told us WHY you have different sized wheels than what came on the car ???

I am beginning to think this whole thread really is just a TROLL.

 

??????? based on?

 

Over 1 million miles of driving mostly while towing a trailer(s) with an old truck / suburban. I’ve had to deal with innumerable sidewall blowouts over the years and found that higher pressures prevent blowouts when you have higher loads.

If you enjoy blowouts by all means do whatever you want.

Historically you would get load / pressure placards with the vehicle.

Tires with lower weight ratings need more pressure than OEM tires, otherwise it’s no different than running under inflated and overloaded.

 

Assuming, of course, that the tires are rated at a lower capacity.
For the OP: the sidewalls will have a minimum tire pressure rating for a specific load rating. Assuming that who ever replaced the original tires did so with ones rated for your car and you aren’t over loading your Prius, you should be fine using the pressures recommended on the door placard.
Having said that, you may find a recent YouTube video posted on The Car Care Nut’s channel about tires. It actually is titled something about noise issues but he gets into tire pressures and replacement tires.

 

The ops tires are 81s
OEM is supposed to be 88s

so yes they are a lower weight rating

 

I’ll take your word for it.

 

According to tirepressure.org those tires are rated at 1019 lbs (4076 lbs GVW) at 36 psi, and 849 lbs (3396 lbs GVW) at 29 psi. Given a curb weight (empty weight) of between 3000 and 3100 pounds and a carrying capacity of less than 900 pounds (based on other model years), a tire pressure of 35/33 is safe (assuming the poster is not overloading the Prius).
Running maximum tire pressures ignore wheel pressure ratings and can cause wheel failure, which is not something you want to stand around and watch.

 

Yes they are rated 25% lower than OEM

Historically (for longest life) you never want to load more than 65% of the carrying capacity of the tire, the OEM meet that criteria.

These tires don’t meet that criteria which means on a FWD biased car the front treads will fail rapidly if you don’t adjust pressures up.

Rim failures are a thing on vehicles like this, where you could run 200psi.
Me thinks you are worried about something that is virtually impossible (rim failure) in trade for something that runs to failure and occurs everyday (under inflation)


The tire manufacturers board describes under inflation as the most dangerous thing anyone can do but only mention “over inflation “ as possibly causing irregular wear or premature suspension damage.

One is a safety issue the other an inconvenience.

 

In 2019 I sold a travel trailer rated at 14,000 lbs GVWR that the 15 inch wheels were rated at a maximum pressure of 75 psig. The tires were of course rated at a much higher pressure. FWIW

 

Pretty much matched what I found.