Recommended Tire Pressure

The tire pressure Toyota recommends will give the most comfortable ride.

The safest ride will be that pressure that yields the flattest Profile, that will often be 38f/36r or higher, but will be specific to your car, there is no general 'right' answer. It will improve mileage as well compared to maximum comfort.


The tire pressure that yields the best MPG will minimize the contact patch, resulting in unsafe handling, so I never recommend that. Never exceed the Maximum shown on the tire itself.

 

I went back to 35/33 because I was tired of the brittle ride. I don't notice any difference in mpg's - still getting 52-54 every tank.

 

I run mine at the recommended pressure on the B-pillar sticker. A few months after I got the car I tried 5 PSI higher, but it significantly increased the harshness of the ride--and interior rattles/squeaks--and what little MPG increase may have resulted just wasn't worth the pain (pun intended) for me, so I'm back to recommended PSI.

 

Take a look at the max pressure listed on the the tires installed and go there for the front and two pounds less on the rear. IIRC mine are set at 40/38....

 

If you think 38-42 "rides harsh" I guess I shouldnt say what I run...

 

with higher pressures, stiffer tires, you will put more stress on suspention components and may wear them out quicker. you may also need more alignments if you hit potholes with stiff tires.


my car is at 39 front/37 rear.

it's too stiff, the handling starts to get "squirrely", and emergency braking seems worse because the lack of contact

i'm lowering mine down to 36/34

 

The right tire pressure will likely depends on the driving environment.

If you are driving on good smooth roads then ride and handling from overinflating to 42/40 psi isn't too bad.

However, if you are driving on poor or rough roads then you might want to limit your overinflation to 38/36 psi.

Outside the box

I have experimented with tire pressure as high as 50/48 psi - My experience suggest that the Prius can deliver better fuel efficiency at higher tire pressures but it comes with some limitations: to get that better fuel efficiency, the Prius must be driven at a slower speed (<40 mph) and on a dry smooth road surface. When driven at speeds >55 mph OR driven on a wet or rough road - the Prius' fuel efficiency drops faster with the higher than maximum sidewall tire pressure settings (>44psi) than at tire pressures that are lower than the maximum sidewall tire pressure setting but lower than the recommended tire pressure settings(35/33psi). My limited superhighway tests suggest when the Prius goes over 55 mph it gets better fuel efficiency when the tire pressure is set to 42/40 psi than if it was set at 50/48 psi or 38/36 psi.

 

I tried all sorts of pressure levels, as well as, front back pressure ratios and ended back at recommended levels due to harsh ride. I could literally feel my teeth chatter while cruising 65mph on the interstate, even with minor pressure increases. Apparently, the suspension is "tuned" to the spec pressures.

 

Would you all agree for slick winter roads that a little lower (what Toyota recommends) be better for safety?

 

I won't agree:

(1) If tire pressure matters that much, then you need better tires;
(2) In my specific climate (not at all like Nebraska climate), winter means wet roads far far more often than icy roads, producing increased risk of hydroplaning. Various aviation industry sources show that lower tire pressures increase hydroplaning risk.

 

OK but we do have ice and wouldn't more tire touching the ground be good for traction?

 

The better the tread sits flat on the road, the better for safety. That it also has better MPG than Toyota's choice, is just a perk.

 

Technically, there should be no loss of a tire's road contact surface(or hydroplaning) as long as the tire pressure is under the tire's maximum sidewall pressure. The major difference between the recommended tire pressure and the maximum sidewall pressure is deformation of the tire when it hits a surface very hard irregular road surface. Less pressure will allow the tire to give a bit and deform - but IF a tire is hot (because its going very fast) AND deforms too much because of road irregularities THEN the tires are at risk of blowing out/falling apart. This is what happen to the Firestone tires on Ford Explorer a while back ago - several people died or were severely injured because Ford had recommended a lower tire pressure setting for a softer ride but this put the Firestone tires at risk of a blowout. Ford said it was Firestone's fault. Firestone said it was Ford's fault. When the tire pressure is higher than recommended tire pressure, the tire is less likely to give/deform (more rigid) and more likely to bounce/transmit the shock of the road surface irregularity (this puts more stress on the shock absorbers/springs the heavier the car). Normally, the weigh of the car keeps the tire in contact of the road unless the car is going very fast.

For slick winter roads, I'd recommend setting the tires between 35/33 to 38/35. I have not seen any evidence that lower the tire pressure any lower than what Toyota is recommending(35/33) will improve traction or safety. On my last super highway trip on I-70 (+800 miles/+12 hour trip in one direction) where my Prius was going up to 81 mph in the rain I had my tires set to 38 psi front and 35 psi in the rear in anticipation of going at hi speeds in bad weather. The bad weather did appear, but the Prius handled very well at at +80 mph even in busy traffic when driving downhill in the rain... The downside was that at 80 mph in the rain its almost impossible to hypermile and my 2010 Prius' mpg drop to about 44 mpg ...

 

The problem with this sketch is that it misrepresents both the design and actual behavior of modern tires. Looking at the cross-section of a real tire , you can see that the tread area is far thicker than the sidewalls. And the tread area is stiffened by circumferential steel belts. At a 'normal" inflation pressure, the sidewalls bulge near the contact patch. At higher or lower pressures they bulge a bit less or more, though the difference can be hard to see. IOW, higher pressures are taken up by reducing the bulge in the sidewall, not by deforming the contact patch as depicted here.

Lots of useful info in the Inflation Pressure section here:
Tire - Wikipedia, the free encyclopedia
"Modern tire designs allow for minimal tire contact surface deformity during high pressures, and as a result the traditional wear on the center of the tire due to reasonably high pressures is only known to very old or poorly designed tires."
"Many individuals have maintained their tire pressures at the maximum side wall printed value (inflated when cold) for the entire lifetime of the tire, with perfect wear until the end. This may be of negative economic value to the rubber and tire companies, as high tire pressures decrease wear, and minimize side wall blow outs."
"During the early stages of tire engineering, and with current basic tires, the tire contact patch is readily reduced by both over-and-under inflation. {With these tires] over-inflation may increase the wear on the center contact patch, and under-inflation will cause a concave tread, resulting in less center contact. Most modern tires will wear evenly at very high tire pressures, but will degrade prematurely due to low (or even standard) pressures. An increased tire pressure has many benefits, including decreased rolling resistance. It has been found, that an increased tire pressure almost exclusively results in shorter stopping distances, except in some circumstances that may be attributed to the low sample size."

I don't think there is "a pressure that will yield best mpg": as one increases pressure further and further above the sidewall rating, mpg will continue to improve but the improvements will get smaller and smaller as the pressure gets higher.

 

I can say by way of anecdote that my GY Integrity tires wore out on the edges, and the GY Viva Authority Fuel Max tires wore out in the center. You are correct that I can't prove that it was because I increased tire pressure. Or they may be 'basic tires'.

 

Congrat on the new ride. I tried many different PSI number, but...I went back to factory recommend 35 / 33 and it's the most comfortable ride and best mpg so far. I had 37 / 35 for a week...wife and kids complain it's too rough of a ride on the California highway 101 (my daily commute route), pot holes every where and rough / coarse uneven road surface, the factory is the best combination.