Tire Pressure

I religiously carried the pressures recommended in the manual for the first 10,000 miles. The ride became stiffer when I jumped to 44 front and 42 rears thereafter, and MPG improved. I measure tire grooves at 5,000 mile intervals and, at 20,000 they are still deeper at the center groove than on either outer groove on the original Integras. I'll probably go back to the mfg. recommendations when the rainy season arrives positively in California, just to minimize the likelihood of hydroplaning.

 

Well milage varies! I run 42/40 the folks that did the marathon milage run last summer at 110 mpg, in August, in Pittsburg, used 60 and well worn tires. Again millage varies. As you increase the tire pressure the milage drops, but the ride gets worse and the handling diminishes. All of this is a compromise.

 

Against the advice of my tire guys, I keep the pressure at 38 and 36. They didn't want me to go over the stated tire pressure on the door frame. Still at 16,000 miles, the edges of my tires are approaching baldness. This is much too early. I'll be replacing them in the next month before we get into the rainy season here.

 

MYTH...Lowering tire pressure INCREASES possibility of hydroplaning. High pressures, over the recommended and/or max, result in less tread on the pavement (ballooning) causing loss of traction. Please do not think lowering pressure makes tires less liklely to hydroplane. I have the Michelin tire video to prove this.

 

I kept mine at 44/42 for a year. Two weeks ago, between fillups, I dropped them to 40/38 to see how it would affect the ride, and economy as reported by the MFD increased. I first suspected that the change in effective diameter was fooling the odometer, but it seems more likely that the outside temp went up a little, or my route or my driving habits changed a little.

 

At 36/34 the car rattles like crazy, at 42/40 it would probably break apart.

 

I have been using 42 lbs in all four. I tried 2 lbs less in the back and could tell no difference. I know what the owners manual and the door frame sticker say but I have been wondering why 2 lbs less in the back? Is there any good reason other than "Toyota says so".

 

I would like to know also. The dealer told me 35 in the front tires, but they always look low and squishy. Maybe a higher number would make the steering feel better.
What do you intend to put on for the winter?
Hope you get some responses from more experienced owners.

 

I believe in what is recommended by the manufacture personally. They made them they should know best.

Terry

 

The Auto manufacture always recommends lower pressures to allow for a softer ride. They don't care about longivity or handling. There is a tire pressure marked on the sidewall. It's 44 lbs, known as bead pressure. This is the safe pressure not to be exceeded when installing the tire on the rim. However, there is also some safety slack in this figure, and the tires not going to blow up at 45lbs. I always keep my tires at bead pressure and generally get >50,000 miles, OEM's or Michilins. Low pressure will definitely cause outside wear!

 

I'm not sure which would be most benificial against hydroplaneing?
The whole point of "tread" is to remove flat surfaces that can "lift" the car off the ground.
Imagine 10 inch tire width...... hydroplaning would be extremely easy to do!

Reduced tread at the center is definately not good, but having more tire on the road by reducing the tire pressure back down to normal may actually aggravate hydroplaning?

It just makes sense to me that a 3000 # vehicle on 4 motorcycle tires would hydroplane less than regular car tires?
*This is an exaggeration to state a point (for those legalist out there)

Traction on dry pavement is one issue, but hydroplaneing is a diffenrent issue.
Wider is better for traction on dry pavement.. look at the dragsters and racecars... but hydroplaneing is not better with wider tires "or more on the pavement".. its seems a matter of keeping in contact with the pavement "inspite" of the water underneath you... that requires narrower tires?

I'm not an expert by any means and this is simply a thought.. I'm not settled either way.... I expect should be up for discussion with others that may know more.

 

I'm glad you asked, windsprings. I am not in the "tire" business at all. I am a trainer of police drivers and have sat down with and spoken with "tire" experts. Plus I have my experience and training in crash reconstruction.

Hydroplaning occurs, simply, when the tire characteristics and speed,prevent it from pushing the water away fast enough and water builds up under the tread. Factors are:

depth of the water- you have no control over

tread depth- you have control over this by not letting tread get too low, but at the moment of driving, you have no control

speed- you ALWAYS have control over this.

I won't get into the issue of width because that is an exercise in rhetoric. Auot tires are what they are and putting wide-traks on y9our car isn't going to mean much if they have proper tread.

However, lower pressure means less "hydraulic" resistance so the water can push up the tread (it always starts in the center) easier.

As your tires wear, you have increased liklihood of hydroplaning at the same speed and water depth.

Always have your best tires in the rear as a rear slide is harder to control...I know, some people say the rear tires will track in the grooves of the front...and that's right, however, you will lose control when turning and then the rear tires do NOT stay in the grooves. It is for this reason I stopped rotating tires on my cars. I WANT the fronts to wear out first so I can replace two at a time and put them on the rear.

Oh, a drop of 5psi can change hydroplaning speed by 5 mph. I have video to show it.

So, it is far better to be over inflated than under inflated, particularly if you drive in an area that gets rain.

 

It depends on the tire too.

My Michelin Harmony P185/65 15 on my 2004 Prius have a bead pressure of 44 lbs. They claim to support 1,168 lbs at this pressure. As everybody knows, Toyota recommends 35F/33R.

I did try 44/44 and the ride became just too bone jarring for me. The slight improvement in fuel economy - maybe 2 MPG - wasn't worth hearing rattles. Of course, drive around on Winnipeg potholes and frost-heaved pavement and you'll know why.

My new Yokohama Ice Guard 10 winter tires are rated 35 psi maximum bead pressure. They claim to support 1,235 lbs at that pressure.

I have a gauge and after a year my Harmony tires run at 35/33 have uniform 10/32 depth.

 

Oh, and the reason for 2lbs more in the front is simply weight. The front tires caryy more weight. If you drove around with 150-250 lbs of sand in the rear hatch, I would recommend 35 F / 37 R (just an example)

 

I am with Jayman, 44/44 is a very harsh ride (hydroplaning will be lessened). Also, you are more likely to pick up road hazards. I run 40/38 and like it. It's a good balance for me.

I don't know where the term "bead pressure" comes from. It is not an official term. The sidewall pressure is the max pressure recommended and it the pressure you need to carry the listed weight.

When a tire blows, it is more likely the sidewall that will give, the bead has a ribbon of steel in it. (maybe I'm wrong here, I've never tried it)

The pressure on the car door jamb is the pressure the auto mfg has determined gives the optimal overall performance in ride/handling/mileage/etc. There are always trade-offs.

 

I took delivery of my Prius a week ago today. The temperature dropped pretty dramatically here over the last few days, and I've felt like the car was riding very sluggish. Relying on the ICE a lot more, plus VERY bad mpg ::edit very bad meaning about 5 - 10 mpg lower than I was getting earlier in the week::. At first I attributed it to the "winter slump" so well documented on the site, but I decided to check my tire pressures today. All 4 are reading 29 psi!!! Needless to say, first chance I get those suckers are gonna get pumped up, Ahnold-style

 

Yeah, that's something I should check on myself. Someone on the forum mentioned in another thread that they just happened to check their pressure and the back tyres were at 17 psi! Was that you Schmika? Anyways, as they said "Don't overlook the obvious" when it comes to crappy mpgs.