Tire pressure

Yes

 

And of course you will notice the increase of gas mpg though the riding is a bit harsh and more road noise.

 

Always check tires cold, heat build-up is already considered in the design, as well as many other parameters. I keep mine at 50 lbs for longevity. Some, keep thier tires at 75 lbs, that is probably extreme.

 

As andy wrote check tires when "cold", which means "not driven more than 1 mile in the past hour". The outside temperature does not matter. The rated value on the sidewall allows for any heating that happens while driving.

 

and oddly, under inflated tires heat up more than properly inflated tires, so after a 100 miles the under inflated tires may have more pressure than normal.

 

Our new to us Gen II had 42 PSI both ends when we got it and after one tank of gas the average was 47.1
I lowered it to 36F -34R .... and right now the average is 47.1 but it is plenty more quiet.

Cheap tires with a 44 "Max" reading on sidewall.

 

Your driving habits or route improved, or the outdoor temperature increased after you changed the pressure. Higher tire pressures increase fuel economy by making the tires stiffer, the same reason that it makes the ride harsher (as you noticed).

 

Higher pressure also improves handling.

 

Higher pressure reduces the size of the contact patch, which degrades handling and increases stopping distances.

 

Higher pressure reduces the size of the contact patch, thus reducing the amount of tire in contact with the road and decreasing drag because of it.

 

Yes, no, and yes.

 

Contact patch is not really affected until very high pressures are used. Most of the decrease in rolling resistance is due to a reduction in tire deformation. HandlIng will improve, up to a point, with higher pressure. All of this really depends on the tire and the pressures we are talking about.

 

With the stock Goodyear Integrity tires on a Gen 2, I was getting classic under inflation wear patterns at 35f/33r. Increasing my tire pressure to 42f/40r yielded even wear patterns. A tire that is wearing evenly has better handling, shorter stopping distances, but may have worse ride. Once you get center wear via over inflation, then yes, you are getting better mileage through reduced handling.

For the Gen2, the only Prius I have owned, the stock tire pressure is not the best handling or shortest stopping distance. By advising folks to increase their tire pressure only to even out tread wear, (and more importantly, never to exceed the max pressure on the tire itself) I do not feel I am putting any human at risk to save a gallon of gas.

 

FWIW I have ran 6 different brands/models of tire on my GenII and now GenIII and I have never ran less than 42psi for any great number of miles except the original Integrity tires. None of my tires showed signed of overinflation but the Integritys did show start to show signs of underinflation so I bumped up the pressure. I eventually ran them as high as 60psi and still they wore evenly.

http://priuschat.com/forums/gen-ii-...24-integritys-over-35k-miles-50-psi-pics.html

The one drawback I have found with higher tire pressure besides increased ride harshness is an increase in twitchiness on the highway. They car just steers, well, twitchy.

 

I'll have to check my pressures when I get home as my car is wandery on the highway. It appears to follow every little groove in the road or is very sensitive steering

Mike


iPhone

 

I still recall reading about some of the PC folks running 50lbs ... and being disturbed by it. Now? Now, some of the folks are disturbed at ME running 50lbs. MAN! The hydroedge tires just go & go & go & go ... I don't know if it's the nature of their rubber chemestry, or the 50lbs tire pressure, or a combo of both. It's no wonder their warranty goes to 90k miles. Even at 100K plus, you're hard pressed to notice any wear.

 

I had the same problem on my Gen III with the OEM Yoko Avids. After switching to the Michelin's it totally went away.

 

I have not found that to be true at all. Increased pressure, within reason, will improve tracking because it stiffens the sidewall. For the same reason turn-in and cornering are improved. The slight decrease in the size of the contact patch is more than overcome by the increased ability of the tread to remain in contact with the road. If you experience "twitchy" behavior I suspect it may be due to a suspension problem.

I am probably more sensitive to poor tracking than most because of the suspension problems with my Gen2 Prius. My present Gen3 Prius has never exhibited any such problems, it is as good in that respect as any car I have owned. I have had three sets of tires and experimented with pressures ranging from recommended to 50 psi cold and there have been no signs of twitchy behavior or tramlining.