So 40 psi == bad idea? (Dealer says so.)

Why the somewhat snarky reply, Jim? I didn't argue for 34 psi and I'm not happy with anything. I said I won't have my Prius until sometime this week, so I'm only asking about center wear by inflating them too much. I've never had a reason to even check the recommended pressure against the tire's rated pressure with any car I've ever owned, so the idea of inflating above what's on the door sticker is new to me. Granted, this is the first time I've ever joined a car forum, so maybe I could have done better with previous cars if I had, but I've gotten over 90,000 miles on a set of tires on my van using what's on the door sticker. I'm just trying to make sure that if I add 4-6 lbs with the Prius I'm not going to wear my tires prematurely in the center. I realize the Prius is light-weight, but 75% of my driving is at highway speeds. Conversely, I don't want to underinflate them simply because Toyota recommends to do so for a softer ride. I'm more interested in tire life than softening the ride, or even tweaking the mpg to the max. And I fully understand the negatives of both underinflating or overinflating tires. I don't know anyone here yet, so pardon me if I don't take every comment at face value.

And I'll add that my tires will have nitrogen, but I don't care because he didn't charge extra for it. That doesn't mean he didn't get paid for it, but I made a deal I was happy with and nitrogen was part of it. Would I pay to have nitrogen put in? No, I wouldn't because even if it scientifically has some value, I don't think it has $40 worth of value. If it did, they'd use nitrogen everywhere and they'd use nitrogen when they have to add air.

And none of this answers the question I asked about what I should do with the rear pressure when I go on trips with it fully loaded? AFAIK, most all cars are front heavy these days and I've always used the same pressure in all 4 tires. Should I add 4 lbs all around keeping the front/rear difference or should I just use the same higher pressure in all 4 tires for overall wear given the higher ratio of fully loaded road trips?

I looking for information, not to be criticized for asking a question.

 

But Toyota's manual does say to run 2 pounds less in rears. This must be for a reason.
If you run 40-38 psi in your tires will be just fine on trip if 15 inch tires, if 17's and tire rated to 51 psi maybe then up them to 46-44.
Have a great trip and enjoy your new car!

 

^ The reason can't be that significant though. I'd suspect they're just thinking of the front weight bias. Lots of manufacturers of other similarly biased cars spec the same pressure all 'round.

Try this: set all four tires on the front tire spec'd psi. Take a drive around the block. Now bleed 2 lb's from the rear and repeat. I really doubt you'll detect any difference.

It doesn't hurt, it's a marginally good idea, but it makes for some farting around every time you rotate the tires.

And, I'd never run low profile 17's at higher pressures than the regular 15", regardless of the max pressure on either tires. The 17's are much less forgiving.

 

Mendel, that was going to be my next question/comment. I guess the bottom line is there's probably no way to prove running 40/38 or 40/40 will make any great difference. I can accept that 34 might be recommended for ride comfort, I guess I never considered that might be a reason for the pressures they put on the door sticker and never had a reason to question it before. I kind of always thought it was a compromise between comfort, braking and wear, but never thought about it that much. Since so many of you run higher pressures, including a friend I know (and trust), I guess I'll do the same. It's time to get the tires on my van rotated, so I'm going to talk it over with my tire guys to see what they say. Granted, they're in the business to sell tires, but I've purposely given then opportunities to take advantage of me (like I do with all shops) and they haven't, so I trust them more than most.

retired4999, I'm sure there's a 'technical' reason for the 2 lb difference, but I would think it has to do with the fact that most owners don't routinely carry much weight in the back. I'm just guessing though because I've never thought about this before. Unfortunately, this is probably one of the few places to even discuss it without a major bias, though some seem to think less of me for even asking a question. Anyway, if it's this big a deal though, you'd think someone might have gotten Toyota to explain it by now. I've read comments here about getting up to 70,000 miles on a set of tires, but I've also seen references to less than 24,000, with little or no info about which tires, pressures, etc. As a noob to the Pius, I've also read about the braking problems some have had and I don't want overinflated tires to cause a safety issue. Other than bicycle tires, I've never even looked at the max pressure rating on a car tires, so I'm just trying to understand.

 

I ran 39 and 37 for the three years I had my Prius, At higher pressures I could not stand the ride or the rattles. Toyota recommends a 2 pound difference in tire pressures front to rear so I always maintained that ratio.

 

Just a broken record on this: tires are relatively expendable, whereas the suspension and shocks not so much. For that reason, I push the pressures higher, but not too much. The firmer the tires, the more road deflections are going to transmit into the shocks and suspension.

 

Tires are also a lot more expensive than gas if you're blowing through a set of four sooner than later. Not to mention tires are a bit energy hungry to produce. And yes, the struts and so forth are even more expensive. I've never had a Toyota product (yet) where I've had to replace the struts before 90,000 miles. They last a long time, and they are expensive to replace.

 

This is one of those personal experience, belief, protocol "voodoo" topics in which everyone has a opinion and you can never really reach a full consensus.

I experimented with some higher than recommended PSI's when I first got my Prius, now I'm pretty much running at recommended or 2 psi above- at most.

I honestly did not notice that much, if any benefit, from running 3 or more PSI above recommended. If there is any gas mileage benefit my guess is it is offset by the "Potential" for wear, and wear on the suspension because the tires are now absorbing less. So in my experience, higher inflation did not translate into a great enough MPG benefit and it did translate into a much harsher ride.

I'd rather protect my suspension and my butt...and just ride at the recommended PSI.

 

DoubleDAZ, you have read an unintended emotion in my response. I run the same tp front & back regardless of how loaded the car is. A heavy load should ride on higher tp.

Lower pressure leads to higher temperature. A comment about the Ford/Firestone situation (the official tp was very low) from Tire pressure with heavy loads: "You are right about more friction, but this also means higher temperature. This was one reason for the fiasco on Explorer tires. Folks were loading all their vacation gear in the back of the vehicle, but not adjusting tire pressures up to accomodate the extra load. Overloaded tires and a tire pressure already four PSI too low led to high heat and then tread separation."

 

Sorry, Jim, but when someone says "be my guest" it's not usually meant kindly. Anyway, given the last couple of responses I'm not sure what to do. I guess I'll start with checking the pressure when it arrives and go from there. I generally don't expect much out of original tires and so far no one seems to be able to point to anything definitive about tread life either way. I get all the dynamics, but I have to admit I never added air to my tires for trips in the van even though it was often really loaded. I always managed to exceed the guaranteed mileage, so I figured I was doing things right.

 

40/38 here, no problems at all. Several 1,000 mile trips included.

 

Nonsense.... as was said max pressure is COLD number

My Toyota dealer had NO problem re-setting front 42 back 40 every time rotation was done writer put it on the order and it was done. Of course the first time I checked with my own tirepressure gauge VERY visible way ... since then no problem...

Same thing when Mavis fixed the tire they put it on the order and that was it.

 

Going by the industry standard, when I worked for Goodyear, a load range "c" tire inflates from 33psi up to 44psi. Your fine and dandy at 40. There is a phenomenon that happens when you go above a load range in a radial built tire. The center of the tire stretches no more (unlike the bias ply tires of old) and the sidewalks actually start to bulge out. It starts to almost look like an under inflated tire. This can lead to serious hydro-planing. The edges of the tread push down and begin to lift the center creating a nice channel for the water. What you end up with is 4 concave water skis.

 

i went out and bought a digital tire gauge "Accutire MS-4350B Setpoint Tire Gauge" i saw it on Amazon for $11. TireRack sells the same item for more and when i spoke to the tech they said that gauge was a descent tire gauge. I got to agree and I am very happy with the gauge. I fill the tires at Costco for free using Nitrogen. The tires take quite a bit of time to heat up and from testing the tires and run pressures, i have estimated at 2psi above the cold pressure.

So i set all the tires for 42psi. I spoke to the tire tech at Bridgestone Technical Support (level 2) and he didn't see that as being an issue. I believe running the tires at 40+ psi has increased the mileage by around 8 miles per gallon? Rather it is much easier to keep rolling given the circumstances and do SWM - P&G - SHM and coasting in Neutral downhill (as necessary). Very happy running the tires at 42psi.

I also was able to find a extremely small wire that pierced my tire with the gauge. i noticed after 2 weeks i would loose 6 psi on one tire. After the second go around i brought the tire into Costco. they ended up inflating the tire to 60psi before they noticed the leak.

 

My winter 15s I run 44 / 42 , my summer tires 15s I run 42 / 40
Both sets wearing normal , and I'm enjoying better MPG than at lower inflation

 

Newbies, beware of penny wise, pound foolish. Don't assume that a cheap or free gauge is accurate. Check it against other gauges.

Two of the airpumps (one electric, one hand powered) I have came with built-in gauges that misread by more than 25%.

 

'Penny wise, pound foolish' also applies to assuming without verification that a 'free' gauge is accurate. If it is not, the few dollars saved on the gauge could easily cost hundreds of dollars in wasted fuel and tire life.