Your tire pressure

I always wonder why the ratio between front and rear (35:33) is not proportional to the weight distribution (60:40) for cars in general. If it was proportional, the F/R pressures would be something like 35:23.

Can anyone hazard a guess? For bicycle tires you normally have the pressures proportional to your load. My only guess is that 1) they want to induce understeer by having the rear tire pressures higher proportionally, which is more safe for the general public, and 2) they are guessing that the rear may have an occasional load in the cargo area.

That's my guess anyways, and thats why I run the front pressure at 38:35 instead of 37:35 (not much diff. I admit).

 

Just a guess, but bicycle tires are relatively high pressure for the amount of weight they carry (i.e.: 75lbs on a tire at 60psi), so they may be in a more linear part of the curve.

Car tires are lower pressure and carrying a lot more weight (800lbs/35psi), so they may be in a more non-linear part of the curve.

Maybe...


BTW: where is the poll mentioned on the first page? Is it a sticky somewhere?

 

My Prius V is about 3 weeks old. Tires looked a little low, so I got out the tire guage. 20 - 22 lbs for all 4. No TPMS warning. Wondering if that was a dealer decision or just the way they were when shipped.

They are 17" Toyo Proxes and say max pressure of 51. Door label says 33.

Think I'll go up to 45 lbs or so and see how it goes. Maybe my 39 mpg fuel economy will improve?!

 

20/22 to 33 will be immediately noticeable. 20/22 to 45 may require you buy a bigger house to soak up all the fuel cost savings.

 

I think you are correct about manufacturers wanting to induce understeer, most drivers feel safer if the car understeers vice oversteers. But with the weight distribution of the Prius I think it would understeer pretty seriously anyway if the VSC would let it.

I have always used the same pressures front and rear with both my G2 and my G3, I believe a pound or two in a street car is not going to be very noticeable anyway. I am presently using 46 lbs (I have 51 psi tires) in all four, in my G2 I usually kept 42 lbs all around.

 

Thanks!

Haven't had to fill the tank yet. Still have 3 bars left. Might make it until Spring at this rate!

 

Definitely - I went to 42/40 on mine and am seeing about 3mph difference on the highway, slightly less around town.

 

Had my first oil change/tire rotation. Noticed my MPG was down a bit. So I checked my tires today and they had been lowered to 33 psi. So I put them back up to
44/42. (44 is max sidewall on Goodyear Assurance Fuel Max.)

We will see if it makes a difference.

 

I'm definitely sticking with the higher pressures - tasted 60mpg (displayed) on a 35-mile sample today. Temps were mid-40's.

(I just have to remember to let some air out when it warms up more than just temporarily.)

 

I put them up to 44/42 from stock and saw literally no increase in mileage. I think I may have unevenly inflated. Oops.

 

What was 'stock' psi?

What test protocol did you use?

 

If memory serves correctly, they were 34/32. Or whatever is recommended on the door label. The only test protocol I did was driving the same route in similar weather conditions on a new tank of gas. I reset trip A on every refill. There are a bunch of variables that I'm just catching onto with the 2010 that I never had to with my 2008. I think I'm just very heavy footed when in ECO mode, which I was using exclusively in the cold weather. I've learned from that mistake. I used ECO now during warmup then switch to normal once the engine begins shutting off when stopped.

Today, I drove my normal route at 34 degrees F in the morning and 40 degrees at night. 30 mile round trip, 52.5mpg on the display. This will lead to my next thread, but I have to wonder if it's my driving habits changing when in normal or something about ECO that I haven't bothered to figure out. Either way, this is without my grill blocked and it beats my 2008 by 4mpg with the 2008's grill blocked and tires at 42/40.

At 4500 miles driven from November through today, I'm at 51.5mpg. i can't complain about that. The display generally is pretty close to calculated. Some tanks the display actually is lower than the calculated.

With all of that said, I just realized I have no way of telling how much of an improvement I've gained from the higher tire pressure. Why am I even posting this? :smash:

 

YMMV, but I would be surprised if 44/42 didn't beat the pants off of 34/32 whether city or highway. Anything one is comfortable with above placard will help measurably and it is (essentially) free for the picking.

 

NOT all Prius III have a MAX SIDEWALL PRESSURE of 44! Mine is 50 and I have all my wheels at 45.

 

Agreed,

The 2013 Model 3 Prius we now have has the Max Sidewall Pressure on the tires at 51 PSI. The placard on the car shows one (1) pound more difference in the front rather than two because of the 17" rubber that came on the car. I run 51 F, and 50 R. My MPG has drastically improved since I implemented the increase in pressure along with a mix of other things such as climate control usage limitation along with hyper miling at every chance I can. Even when I am on a road that has a speed limit of 45 or 50 MPH, I choose to feather the pedal as much as possible. Even though the ICE is using fuel at those speeds, the RPM's are very low as the ICE is basically idling with out a heavy load. Over long distances I have recorded MPG readouts of 60 to 75 on the five minute and one minute displays. What I do is get the Prius about two to three miles per hour faster than my target speed, then ease off the go pedal until the HSI reads just above the middle line where the ICE normally kicks in. I find that the instantaneous read out will hover around 70 to 85 depending on conditions, time of day, and climate control as well as the outside ambient temperature along with the ICE being is S4 mode. When I see the speed drop back to the target, I increase pressure on the go pedal just enough to get about three MPH faster and then repeat the process. I normally drive in "Regular" mode. I find "ECO" mode effects the A/C too much and requires more travel of the accelerator (go) pedal to achieve the same results. I rarely use the "Power" mode. Also I rarely use "EV Mode". I can easily EV if I choose to do so without having to invoke "EV" mode. Of course the above figures are for the current season which is Summer. Here in Houston, we normally a short Spring and a little longer Fall. Winter usually kicks in somewhere around November, and usually by March or April, it is warm again. This year has been a lot cooler than the last few years, as the area has been experiencing a drought for quite some time now.

The Gen III Prius is better at gliding and more economical than the Gen II in many aspects. However that does not mean that you can't get just as good MPG with a Gen II. Our Gen II gave us an overall average of 51.5 MPG when you look at the data from the 36 months of operation. The first year was not the greatest as I was still learning about how to drive the Prius for maximum economy. After that, the numbers kept improving as I slowly changed my driving habits as well as changing things on the Prius itself such as running Mobil 1 Synthetic Oil and mounting a set of the Michelin Energy Saver A/S tires. I was running 42 F, 40 R on the Gen II with the Michelin's. I did have trouble finding a set of them, but in the end it was worth the effort of locating and purchasing them.

Ron (dorunron)

 

I run 38/36 psi. More inflation pressure causes the ride quality to suffer. I wonder if I can go lower in the back because the front tires are more pooched out at the bottom from the weight of the car.

 

I have the OEM tires that came on my 2010 Toyota Auris HSD, Michelin Primacy HP, 215/45/17 and they are currently inflated at 42/40 when cold. I had them inflated a few psi more but the handling on curvy roads was dangerous!

 

My pressure was 28/30 when i checked it, and I just upped it to 41/39. I dont notice much of a difference yet except when in ev mode. I put it is ev mode everytime I hit a stoplight to accelerate from 0 to 25 mph and it seems like in the same places it takes 2 lights to drop a bar on the battery level instead of one light. Other than that I havent noticed much, but Ill see its true effects once I fill up later this week.

 

For maximum economy learn how to Pulse and Glide. Using EV the way you are can be at times non productive since the power being used is derived from regeneration and from the ICE. The power conversion is not 100% efficient also. Just saying...

You are lucky to live in McKinney. It is a nice part of Texas. Only bad thing is the weather up there. Can get kind of windy and the winter's can be a little rough at time. But McKinney is a very nice place to live IMO. Great places to eat too down in Plano.

Best of luck to you,
Ron (dorunron)