Tire Pressures

There are drivers that inflate to the max 40 psi for increased mpg. I don't know how much it helps, but I haven't heard any of them come across any issues due to it being over what the factory recommends.

 

Your max pressure is likely 44psi. The 40psi you are referring to is the make pressure for setting the bead when mounting the tire on the wheel.

Going up to 44/42psi is likely good for approx. 1mpg or more depending on how much you hypermile or coast/glide. The higher pressures definitely help but you hit a point of diminishing returns where rolling distance doesn't increase as much per PSI and the ride comfort deteriorates rapidly. So in a nutshell anything above sidewall max pressure is not worth it to most people. Dedicated hypermilers usually go well above sidewall max but they drive much slower and more carefully than the average driver.

 

I was thinking about raising the pressure on mine, but if it's only around 1mpg gain, it's not worth the hassle for me.

 

Unless you are a serious hypermiler I doubt it's worth more than a couple mpg going from 35/33 to 44/42. I could be wrong,however.

 

I have tons of potholes and uneven roads on my commute. Would it be better to slightly over inflate my tires (up to 40?) to keep them from getting sidewall bubbles? The other car has had two tires replaced because of that already.

 

I'm not sure. I would think that staying near 35/33 would probably be the safest option. 37/35 shouldn't be too bad but high pressure and potholes don't mix too well. Neither does low pressure and potholes so it is imperative that you check your tires often.

When it is time for a replacement tire I would highly recommend you buy a tire with a rating of 91H instead of the S and T ratings that are common to Prius tires. The 91H rated tire will provide a more stout internal structure and will be less likely to fail. TireRack.com provides the tire's load index (the number) and the speed rating (the letter) in the tire specs listing when you do a search on their website.

 

I have logged 1500 miles on my Gen 3 Prius 2, and averaged 55 mpg on every tank, strictly used in my 70 mile per day highway commute. same speeds (65 mph) highway, 4 miles on and off interstate, same speed, no traffic.

My stock tires (Yokohama S33D Avid) have been inflated to 37.5 psi, from the dealer new. Monday, I inflated all tires to 42 psi, and every day since my daily and tank average is 50mpg - no other change in commute, weather has been consistent.

The change was immediate and very real.

Going back to 37.5 next week for confirmation.

Just a surprised FYI.

 

There is a reason for different pressures front to rear, and that is the weight distribution of the vehicle. There is more weight on the front wheels; therefore, you need more pressure to support it. Aside from that, if you over inflate the rear tires, the rear end may hop when encountering bumps in a curve.

 

Yes, I did run the same pressure in all tires for the trial, due to what I found in the tires already. I will run diff pressure in the future.

The car came with 37.5 all around, new. I wanted to conduct a comparison by equally increasing psi to 42 all around for a clearer understanding of the psi mpg relationship - within the stated psi range.

I understand there should be a differential, and the posted tire pressure, on the drivers side door jamb, states 35 front 33 rear.

I will return to the 37.5 for a week, and then recommended pressure for a week.

 

You should get merely a 0.3 increase to your mpg by increasing by 2 psi. According to U.S Dept of Energy, for every 1 psi increase in all 4 tires, you increase fuel economy by 0.3%. So 2 psi increase for you would translate to a .6% mpg increase. .006 x 50 = 0.3. Your increase will probably be less that 0.3 mpgs because the dept of energy figures are for underinflated tires. Since your tires are not underinflated, you get a smaller benefit when you increase your tire pressure.

 

Here is a nice list of things you can do to increase mpg.

100+ Hypermiling / ecodriving tips & tactics for better mpg - EcoModder.com