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Discussion Starter #1
I've read posts saying that owners have replaced the OEM 15 inchers with 17 inch wheels and upgraded the tires. However, when I checked with the my dealer (I have a 2004 Prius) I was stringly cautioned to leave alone the OEM configuration. He used the phrase "low rolling resistance" in the context of better fuel economy. Also, since increasing the tire pressure from the stock 35 to 44, my milage has increased from 39MPG to 52. But the dealer also felt that pressure to be dangerously high. I'd like to hear from a tire/wheel maven about this. Thanks......


"retreat hell, I'm just attacking from a different direction!"
 

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Re: What is the definitive answer re 'larger than oem' wheel

Richard Cook said:
I've read posts saying that owners have replaced the OEM 15 inchers with 17 inch wheels and upgraded the tires. However, when I checked with the my dealer (I have a 2004 Prius) I was stringly cautioned to leave alone the OEM configuration. He used the phrase "low rolling resistance" in the context of better fuel economy. Also, since increasing the tire pressure from the stock 35 to 44, my milage has increased from 39MPG to 52. But the dealer also felt that pressure to be dangerously high. I'd like to hear from a tire/wheel maven about this. Thanks......


"retreat hell, I'm just attacking from a different direction!"
Assuming that you have a US 2004 Prius with the usual OEM tires (Goodyear Integrity Standard Load P185/65 R15 86S),
then running the tires at 52psi is dangerously high, as the max. cold pressure stated on the sidewall is 44psi.

Even the 2001-2003 Prius OEM tire (Bridgestone Potenza RE92 XL) only had a max. cold pressure of 50psi.

Most tires on the market seem to have a max. cold pressure of 35psi, so do check your tire's sidewall first!
 

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Discussion Starter #3
The 52 Refers to MPG, not PSI.

Thanks for your response Michelle - I was a little unclear in my original post as the 52 refers to the MPG increase I obtained <partailly> from increasing the tire pressure, front and rear, to 44PSI. The other "tricks" I pulled to get the mileage increase were cutting freeway speed to 100 KPH, getting the most out of the vehicle's momentum, and maximizing the brake pedal time when coming to a stop. In fact, the other night I ran the 'slow and go' freeway gauntlet from Newbury Park to Tarzana, a distance of about 20 miles, and got an astonishing 68 MPG! tHAT'S BECAUSE THE AVERAGE SPEED WAS ABOUT 20-25 mph AND i WAS ABLE to get the car to use only the electric motor for most of the trip. By the time I arrived at my destination I was down to the last 4 bars (still blue) on the battery usage indicator.

'Roses wilt; the PRIUS rules!'

Rick Cook
 

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I have been involved with tires and wheels to an extent at work for many years. The Prius specific issues are:

- changing any tire to a tire with an improved contact patch (better traction) is fine, however you will increase rolling resistance. This also may be worth it.

- changing the rolling radius, either by tire change alone or wheel and tire change is bad. This adversely affects ABS, TRAC, VSC, and the NAV system.

- changing to 16" or 17" wheels and tires is fine as long as you consider my previous two comments. As long as the increased diameter is offset by a lower tire profile and you will accept the increased rolling resistance, all is well if the rolling radius is within 2% of the original tires and wheels.

- The 44psi tire pressure may also be fine as reported by others. The key is to monitor your tire wear characteristics. If the tire is overinflated, by this I mean the pressure is less than or equal to the max sidewall rating when cold (undriven overnight) but greater than the OEM tire placard, the center tread area will wear faster than the outer tread area. If the tire is underinflated, the outer tread area will wear faster than the center tread area. Adjust the pressures until you get uniform wear across the tread.

The OEM pressure recommendation is a compromise of tire life, ride and handling, with emphasis on ride and handling. Many find the higher pressures offer a better ride with less sidewall deflection while improving fuel economy. Dealers are instructed, for liability reasons, to strongly encourage adherence to the tire placard. However, as I said, you may find higher pressures are more to your liking. DO NOT use lower pressures as you risk high tire temperatures and failure.

Personally, I find the 44 front/40 rear psi levels to improve ride and handling, and I do not see abnormal tire wear. However, my mileage is low and I will keep monitoring. I have done this on other vehicles for over 17 years with great success. It has also improved tire life.
 

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44psi on the 2004 Prius with US OEM tires should be fine, if measured when cold/undriven.

However, I would suggest that the rear tires be about 2psi lower than the fronts, to improve handling.


Unfortunately, with my route to work in the morning, I'm forced to make a number of "panic stops" when someone in front of me decides to suddenly throw on their brakes and pull into the Dunkin' Donuts without signaling. All too common an occurance, and I pass 1-2 Dunkin Donuts depending on my morning route.
When I had my tires on my 2001 at 40psi all around, I found my car would "fishtail" (back kept going while front stopped) when in the panic stop situation. Changed to 40psi front, 38psi rear, and the whole car would stop at the same time under a similar panic stop.

(My hours have since been changed, so now instead of the Dunkin Donuts in the morning, I have to brake for the Wendy's at lunchtime...)
 
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