Tire Pressure/Prime

there's no way to determine without testing. we still don't know the best tyre pressure for mpg's on the gen 1, 2, 3 or 4.

 

that's the factory spec, not necessarily best mpg's. what is the prime factory spec?

 

no, the tpms is inside the tyre. but if the mech hasn't reset them to factory spec, you should adjust them at home if there is a pressure differential front to back. some people run the same pressure all around, with no reported detrimental effects, but we all have different driving styles.

 

On my current 2009 Touring (Gen-2) Prius, I confess that I overinflate by about ~5PSI. In combination with Bridgestone Ecopia Plus, that's enough to increase MPG by about 10MPG more than EPA, with little loss of traction (I tested both aspects carefully).

As another person replied, there are no simple answers; you really just have to test it. Always remember though, willy-nilly overinflation can be dangerous, so if you do choose to overinflate, then do so very cautiously! How much you can get away with depends upon many factors: the car, the tire type, the age of the tires, weather conditions...

 

There is no simple answer. The manufacturer suggested rating is a combination of safety, comfort, performance (steering and mpgs) and tire life (among others).

My Prime was delivered by the dealer with 44lbs in both front and back. While that would improve the mileage, the handling and ride comfort would have suffered. You'd think they would understand this as they took people for test drives.

I set mine to the factory spec. 36 front, 35 rear.

 

one pound differential now? interesting.

 

^ Yes. I can barely differentiate one point on my stick guage; the increments are two pound.

When you have a spec, it's not a crime to hold it at arms-length, consider your priorities, the why's-and-wherefores of the spec, and maybe "interpret" a bit. My interpretations:

1. A one or two pound difference, front to rear, is trivial. And it complicates tire rotations.

2. Higher pressures will you better mpg, but I suspect the increases are trivial, especially as you really start to raise them. I know too, the ride starts to get rough, and I suspect suspension components stress, maybe age quicker, with higher pressures. OTOH, the numbers the auto manufacturer come up are likely very conservative, a bit biased towards the comfort side.

Accordlingly, I pick a tire pressure just a few pounds higher than spec, and use the same for all four tires.

 

I had the Sonic's set to 44psi, the tire max, all around; the car spec had the the 2psi delta. Rode over a patch of smashed dirt at a gas station, and it didn't stick across the entire rear tread as it did in the front. The need for that pressure delta is going to vary on the model, and how high you take it.

The MPGs rise with the pressure; the first hot day of summer, my tires could be pushing 50psi if I hadn't adjusted them. The car will noticeably coast better.

Higher pressure does mean a rougher ride. I personally prefer that; go below 40psi on my car, and the ride starts feeling squishy to me. Dry traction shouldn't change as long as the tread edges are staying in contact with the road. Poor weather traction can get worse. I can't rule out car model, tire model, or being on an incline as other causes though. Best to just be more careful in poor weather no matter what.

Higher pressures will improve cornering and tread life sue to the stiffer sidewall.

 

Depends on what you mean by "overinflate". If you're comparing to the automobile manufacturer's recommendations, usually marked on the inside of the door sill, that should be fine. The proper inflation pressure is usually that which causes the tire to wear evenly, center to edge. Too much inflation and the center will wear faster than the edge. Too little and the edges will wear faster than the center.

If you are talking about the tire manufacturer's maximum inflation pressure, always stamped on the tire, then you should NEVER go past that.

 

Gen2 Prii set to manufacturer pressure limits wore the outside edges of the tread faster.

Modern belted radial tires help keep the tread flat as pressure increases.

 

That's why mine are at 44/42 - even wear patterns and better mileage.

 

Due to the negative camber in the rear I guess, ours always seem wear faster on the inner edge. Then outer edge, and least at centre.

 

Yeah, definitely never do that!

No, I was referring to Toyota's door-jam recommended pressure.

 

A great post, I suppose when it comes down to it, I do something similar, however I usually have the fronts a couple of pounds higher than the rears (most of the weight being at the front of the car)… …but as always, YMMV!

 

I finally checked the tire pressure yesterday (50 degrees F out) with a high quality gauge. The car had not been driven that day. As delivered from the dealer, 47 psi all around! I was surprised to discover that this wasn't adjusted as part of the pre-delivery set up.

I have to drive over speed bumps every day in the parking lot at work, and the Prime, at this pressure, takes them much more smoothly than my 2008 at 39/37. This is likely a result of the better rear suspension more than the tire pressure. I had noticed in the 2008 that when I increased the tire pressure as part of normal maintenance, the speed bumps seemed worse. My 2008 is low mileage (61K), so I don't think that enters into it too much.

I suppose I should let some air out. But I like the ride as it is, and haven't yet noticed any slippery traction in the rain we've had over the last couple of weeks.

 

Email the owner of the dealership, that might get you a few free car washes and a service credit. I would take them down some.

 

Yup, I decided I'm going to go to 40/39 when I head out later today.