Tire Pressures

I'm copying this from another thread as I feel it is just as important in this one. Plus I had to read a lot before posting it.

Higher psi tends to reduce rolling resistance and thus increase gliding ability and MPG. It also stiffens up the sidewall which allows me to corner a bit harder. Higher pressures also (within reason) reduce tire deformation which reduces heat buildup so you are less likely to experience tire failure.

Many people run very high pressures in their stock Integritys with great results and no abnormal wear. I've read of pressures up to 70psi and one bloke who runs 100+psi. We've had a lot of discussion on this subject and with the number of people running these high pressures and the fact that burst pressures are so high I feel safe enough to continue doing it. I never recommend it to anyone however. In the end I am pushing the pressure higher and higher till it seems I've reached a point of diminishing returns. I htink I'm near that point and I do not intend to go any higher. I may drop it back down a bit.

Here is a poll on tire pressure on CleanMPG.com

Awesome information contained in the article below.

Tires and Passanger Vehicle Fuel Economy (.pdf) data below is from pages 63-68 or so.​

"Only about 12 to 20 percent of the energy originating in the fuel tank is ultimately transmitted through the vehicle’s driveline as mechanical energy to turn the wheels. Rolling resistance consumes about one-third of this mechanical energy output. Rolling resistance, therefore, directly consumes a small portion (4 to 7 percent) of the total energy expended by the vehicle. However, reducing rolling resistance, and thus reducing mechanical energy demand, by a given amount will translate into a larger reduction in total fuel consumption because less fuel energy will need to be sent to the engine in the first place. The effect on total fuel consumption will depend on a number of factors, including the efficiency of the engine and driveline as well as the amount of energy used by accessories. As explained later in this chapter, for most passenger vehicles, a 10 percent reduction in rolling resistance will lead to a 1 to 2 percent increase in fuel economy and a proportional reduction in fuel consumption.
​

Tire Operating Variables and Hysteresis (pg 68)

Inflation pressure affects tire deformation. Tires with reduced inflation exhibit more sidewall bending and tread shearing. The relationship between rolling resistance and pressure is not linear, but it is consistent enough for rules of thumb to be applied. Schuring (1980) observes that
for conventional passenger tires, an increase in inflation pressure from 24 to 29 pounds per square inch (psi) will reduce rolling resistance by 10 percent. For a tire inflated to pressures between 24 and 36 psi, each drop of 1 psi leads to a 1.4 percent increase in its rolling resistance. The
response is even greater for pressure changes below 24 psi. Maintenance of tire pressure is therefore important in preventing excessive deformation and hysteresis, as well as in achieving intended wear, traction, handling,
and structural performance.The temperature of a tire is affected by ambient conditions, tire design and materials, running time, and speed. Higher ambient temperatures are
associated with reduced rolling resistance because the amount of energy dissipated when the rubber is subjected to repeated deformation declines moderately as temperature rises, which is a commonly observed behavior
of viscoelastic materials. Accordingly, the length of time a tire has been running since the last cool-off affects rolling resistance, which declines until the passenger tire has been rolling for about 30 minutes."​

Tire Design and Hysteresis (pg 67)

On a side note, I found this information regarding rolling resistance changes over the lifespan of a particular tire. ​

"Related to the effect of tread mass and volume on hysteresis is the effect of tread wear on rolling resistance. As tread depth (that is, the depth of grooves in the tread pattern) diminishes with wear, a tire loses about 15 percent of its mass—since the tread band typically accounts for about onequarter of a tire’s weight. The moderating effect of tread wear on rolling resistance has been examined and quantified to some extent. Martini (1983) compared the tire rolling resistance occurring when the tread was new (100 percent) with that occurring when the tire was buffed to various stages of wear (75, 50, 25, and 0 percent remaining tread). These experiments suggested that rolling resistance declined by 26 percent over the entire wear life. After reviewing many similar experimental studies conducted before 1980,
Schuring (1980, 683–684) concluded that rolling resistance declined by an average of about 20 percent over the tread life, dependent on design details.​

 

The Prius sways and corners a bit like an SUV. The wider tires in my experience made a difference with the SUV. And they seem to make a difference with other Prius owners here--at least with the Touring model--though there might be other factors. The drop in gas mileage with the Touring model might be attributed to the higher rolling resistance of wider tires. The handling would likely improve with a wider tire on the base model.

 

I've boosted mine up a tad recently and I think 50 front 48 rear is a very good sweet spot.

 

I agree. This is what I am running. Seems to work well.