[mrv]

Please forward more details: Tire size, inflation pressure, etc.

175/65R14
tried different inflation
42/40 seems to improve a little

as far as putting the original tires on they just don't last long enough. i drive about 4 thousand miles a month. that's new tires every 3 to 4 months maybe 5.

ok, so 4000 miles a month, lasting maybe 5 months, means only 20,000 miles out of your Goodyears? What Goodyears are you using with that 14" diameter wheel, and what was the treadwear rating? 2004+ Prius has a 15" wheel in the US (unless you get the SE region 17" upgrade), and internationally the 2004+ Prius has 16" wheels. The Classic Prius has 14" wheels.

US 2001-2003 OEM Prius tire:
Bridgestone Potenza RE92 XL (Extra Load)
P175/65 R14
84S
Treadwear 160
Temperature A
Traction A
50psi max. cold pressure

with the low treadwear rating on the Potenzas of 160, 20,000 miles was about the average that most people reported, although Bridgestone warrantees them for 40,000 miles. (There are some exceptions to the 20,000 mile average - for example, my mother is at ~38,000 miles on the original tires, while I've heard of 1 or 2 people needing new tires at 5,000 miles...) Alignment is very sensitive, and if you're getting a fast wear you should have the alignment checked soon... And be sure to check both the load rating of the replacement tires (to see if it can carry the Prius) and watch the max cold pressure (many tires only go up to 35psi, so going up to 42/40 is overinflating them!)...

 

[mrv]

20k miles life on these tires is too low, you should get at least twice, if not three times out of them!

Also, don't panic yet on the mileage, tires need to be worn in, and mileage should improve after about 500 to 1000 miles!

As I said, if he was talking about the OEM Bridgestone Potenza RE92 XL tires for the Classic, 20,000 miles is about average. The original poster hasn't stated what Goodyears he was trying (but at 175/65 R14 it's obvioius it's a Classic Prius.)