Tire Pressure

[Goddy]

I have a 2007 and just had my 5K service. The Dealer recommends 36 F and 32 R. I have talked to someone in Chicago while there this summer and they go upwards to 40 for ultimate mileage? Any thoughts on best air pressure?

Also. at the New Owner Appreciation Dinner, the Master Mechanic said when stock tires need to be replaced, place the widest tire that will fit on rim and you should se 2-3 mpg increase. Has anyone done this?

Thank you in advance.
Ride safe..
Goddy/San Diego

[firepa63]

I run mine 3 psi above the posted pressures on the driver's door jam.

[catgic]

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[Bob64]

<div class='quotetop'>QUOTE(catgic @ Sep 15 2007, 12:40 PM) [snapback]513029[/snapback]</div>

Run, do not walk to your nearest air pump.
[/b]

I purchased my very own electric air pump, so that I don't have to waste gas driving to some gas station.

[apriusfan]

<div class='quotetop'>QUOTE(Goddy @ Sep 15 2007, 09:15 AM) [snapback]513018[/snapback]</div>

...Also. at the New Owner Appreciation Dinner, the Master Mechanic said when stock tires need to be replaced, place the widest tire that will fit on rim and you should se 2-3 mpg increase. Has anyone done this?[/b]

I don't know if adding wider tires in isolation (e.g. not going to lighter wheels) will improve mileage. You are looking at the combined picture. Typically wider tires on stock wheels will result in an increase in rotational mass, which will in turn reduce your mileage (since the HSD has to do more work vs. the OEM tires). Conversely, if you were to reduce the rotational mass, then you should see an improvement in the mileage. For a point of reference, one PC member (my apologies, but memory escapes as to who it was) noted a 3-4 mpg hit by adding Michelin Pilot Exalto A/S tires in 205/60-15 to the stock wheels. I went the other route and swapped out the OEM wheels and tires on my 2007 Touring edition for 10 lb. forged wheels and Michelin Pilot Exalto A/S tires in 205/60-15 and noticed ~1 mpg improvement (which I would attribute to the lighter forged wheels).

I have since increased the tire pressure to 36 psi all around (from 34 psi) and have noticed another ~1 mpg improvement. I am wondering if I were to go to 38 psi, whether I would have problems with ride harshness (I have back problems, so for me, ride harshness is something to be avoided).

There is a causality to everything....

[jeffkprius01]

<div class='quotetop'>QUOTE(firepa63 @ Sep 15 2007, 12:28 PM) [snapback]513025[/snapback]</div>

I run mine 3 psi above the posted pressures on the driver's door jam.
[/b]

Isn't it true the more air you put in over the door posted recommendation, will also cause the tires to wear unevenly?

[brick]

<div class='quotetop'>QUOTE(Jeffk01 @ Sep 15 2007, 04:35 PM) [snapback]513108[/snapback]</div>

Isn't it true the more air you put in over the door posted recommendation, will also cause the tires to wear unevenly?
[/b]

Not even a little. The original reason that Prius drivers started inflating to higher pressures (42/40 is popular) is because the tires tend to wear very poorly at the recommended pressure. The edges round off due to excessive flex and the tires can be junk as early as 15-20k miles. Using higher pressures solves this problem for the most part. Modern steel belted radials maintain a nice flat tread so you won't see excessive center wear. Mine hardly show any wear after 12k mi of higher pressures since the day the car was delivered.

[Jeannie]

I had my 10,000 mile service at my Toyota dealer yesterday, and asked them to set the pressure at 42/40. I knew my tires were currently below that pressure, but hadn't bothered to adjust them on this tank of gas. The dealer actually DID set them at 42/40 this time. I've driven about 30 miles since then, typical driving for me (3 short trips of under 10 miles each and one of 12 miles), and the MFD MPG has gone up from 46.2 to 47.4, as my miles on this tank have gone up to 416 and my gas pips have fallen from 3 to 2. I think that's a pretty dramatic evidence that the higher tire pressure of 42/40 makes a HUGE difference.

[msirach]

<div class='quotetop'>QUOTE(Jeannie @ Sep 15 2007, 05:01 PM) [snapback]513122[/snapback]</div>

I had my 10,000 mile service at my Toyota dealer yesterday, and asked them to set the pressure at 42/40. I knew my tires were currently below that pressure, but hadn't bothered to adjust them on this tank of gas. The dealer actually DID set them at 42/40 this time. I've driven about 30 miles since then, typical driving for me (3 short trips of under 10 miles each and one of 12 miles), and the MFD MPG has gone up from 46.2 to 47.4, as my miles on this tank have gone up to 416 and my gas pips have fallen from 3 to 2. I think that's a pretty dramatic evidence that the higher tire pressure of 42/40 makes a HUGE difference.
[/b]

I pressed the pressure to 50psi the night in May we traded for a used 05. We have ran it all summer including a loaded down trip to Hybridfest and Mall of America.

[tochatihu]

Using anything lower than 35/33 psi Toyota spec. will almost certainly lead to excessive edge wear on the tires. Whether their number (diligently maintained) would do the same, remains to be demonstrated.

Using the maximum indicated sidewall pressure in your front tires, and a few psi less in the rears, will almost certainly slow down tread wear and increase mpg. The ride feel over bumpy roads will be worse. But I am still (still, still) waiting for the first post that demonstrates max sidewall inflation with radial tires causes excess center tread wear under Prius.

Please, all, choose your own numbers within that range. Long history of Prius posts suggests that most of the fuel economy gain will be found in the lower part. Tire longevity increase will probably be linear throughout the range.

Still hoping that someday we will test wet and dry road traction vs psi, with Prius, on some test course. My expectation is that the higher inflation pressures would do better. If someday that test gets done, surely it will be chronicled here.