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post #1 of 3 (permalink) Old 06-02-2014, 05:43 PM Thread Starter
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Default Tires affecting MPG

Long time lurker, new member here with 2001 Prius 212,000 miles. On a road trip averaging 48 mpg I replaced my nail infested 175/65x14 tires with Firestone touring 185/65x14 and gas mileage dropped to 36 instantly. Now the local Firestone dealer is arguing that it is not the tires. Please, I have put 200,000 miles on this car and it now drives like I have 4 flat tires. Any advise on how to sound intelligent when navigating through this issue with the Firestone dealer? Thanks
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post #2 of 3 (permalink) Old 06-03-2014, 03:44 AM
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Make sure you have LLR (Low Rolling Resistance) tires. The 2001-2003s came with the LLR tires (if I remember correctly). Also make sure the new tires are inflated properly. There are a number of references to tire pressures in the archives (unless they have been deleted) as well as comments on LLR tires.
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post #3 of 3 (permalink) Old 06-03-2014, 02:54 PM
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Check sidewalls of your new tires. If Max Pressure is 44 psi (printed on sidewalls), inflate front tires to 44 psi, and rear tires to 40 or 42 psi. Otherwise, inflate front tires to maximum pressure printed on the sidewalls, with 2-4 psi less in rears.) Your mpg will probably return to normal.

Next time, suggest you check out Michelin Defender LRR tire:

Note: Classic Prius's came with 50 psi Bridgestones, which are no longer manufactured. Our original tires also did not wear long, as the tread rubber was very thin. I think they put special tires on the early models to increase the fuel economy, to emphasize the mpg advantage of early hybrid vehicles. I had a real problem with tire shops deflating the original tires to 24 psi (and ruining the mileage). Most, including Discount Tire and Costo, absolutely refused to inflate them to 50 psi, citing the safety hazard of over-inflation. Even when I pointed out the "max pressure" on the sidewalls and the owners manual, they refused to inflate to 50 psi.)

Now, with LRR tires, higher pressures are unnecessary; although I still run 44/42 in our 2002 Prius. In the spring and fall when the weather is nice for driving around with the windows down, I still get 51-53 mpg around town, and 44-48 at other times of the year.

Last edited by Phoenix; 06-03-2014 at 03:01 PM.
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