Hey Guys, Thinking on up-sizing my Prius rims to 17". Should the target tire pressure be the same as with the stock 15" rims? I'm assuming yes, but I'm having a brain fart right now... Thanks,
The recommended tire pressures for the Prius that come with 17" tires (in 215/45R17) is a bit lower. Something like 35 vs 32? I've got the 17", run them at around 36~38 psi. In winter running 195/65R15 Michelin X-Ice, I set them much higher, around 46. And they still feel softer: the 17" give a harder ride, need to be a little lower, for your fillings.
Really? the pressure is lower? Can anyone that bought a 3rd gen Prius that had 17" stock rims confirm what the pressure is written on the door panel? Edit: I forgot I have the owners manual in pdf... Tire size P215/45R17 87V Front tire: 33 psi (230 kPa, 2.3 kgf/cm 2 or bar) Rear tire: 32 psi (220 kPa, 2.2 kgf/cm 2 or bar) Wheel size 17 × 7J Wheel nut torque 76 ft•lbf (103 N•m, 10.5 kgf•m) Tire size P195/65R15 89S Front tire: 35 psi (240 kPa, 2.4 kgf/cm 2 or bar) Rear tire: 33 psi (230 kPa, 2.3 kgf/cm 2 or bar) Wheel size 15 × 6J Wheel nut torque 76 ft•lbf (103 N•m, 10.5 kgf•m)
I have 17's on the car and run 34 psi front and 32 psi rear. The ride is jarring. I feel my brain wiggling in my skull when i go over bumps...kiddin. It's not that bad but I sure miss those comfortable days in my old civic w/13 inch rims.
Because the rims are larger the section hight gets smaller so the tires need higher pressure . Tire pressure is all about load on the tire, and a bit about speed and camber angle ( alighnment) The 17 inch rims have a 45% hight widht division and the 15 a 65%. Loadindex 17/87 V and 15 89S so can carry a higher load( the 15). Probably the 17 inch are XL/extraload/reinforced becaus low H/W tires mosty are. Those need a 41 psi pressure for the maximum load up to 160km/99m/h The 15 are probably standard load /P-tires wich need a pressure of 35 psi for their higher maximum load up to 99m/h. So the 17 inch need higher pressure then the 15 inch. Maximum technical car speed of your car is 180km/??m/h or lower, otherwise the S speedrated tires where not allowed on your car ( S speedrated is up to 180km/??m/h maximum speed of car. So give more car and tire details, and I will recalculate a save lowest pressure for the 17 inch tires. there is even more, the 45% H/W tires are allowed less percentage deflection of the free flexibel part of the sidewall. Tire makers calculate the maximum load using a formula in wich deflection is used in a by way. I have graphics that show a 45% to deflect about 25% when putting maximum load and needed pressure for that on it. A 80% H/W tire 20% and because they dont give tire damage in practice the 45 % H/W should also deflect only 20% , and I calculated it may only deflect 17% . taking this into acount , the 45% H/W tire should be substacte about 20% of the maximum load that belongs here to the loadindex 87 . This makes the needed save lowest pressure for the load on your tires need to be even higher. So I also dont agree that it can be lower, it should be even much higher.
^ I don't know, Toyota spec's lower pressure for the 17" than the 15". And that seems plausable in my experience, the lower profile have a harsher ride, at any pressure.
It's strongly size-dependent. For example, 205/50R17 may be XL (which provides harsher ride) whereas 215/45R17 isn't in some brands.
Here's the spec plate for my prius. Hope that helps. I know a lot of owners in this forum are running 40 psi or more. I would not go that high personally just because i have a bad back.
I set mine 33 psi both front and back, I also upgrade mine from 15" to 17". I've been playing with psi setting even since I upgrade the wheels/tires, I found that at 33 psi all around, the car feel less heavy and the rolling effect seems better, how I know...my CONS mpg is going up. Also the 17" tires noise less noticeable, more cushy ride and better braking distance. Be aware that the 17" wheels and tires WILL decrease the MPG by as much as 6 mpg. Good Luck.
