Over-inflating tires

I'm running 44/42.

If overinflation causes excessive wear it will be in the middle of the tread. My tread wear at ~23K miles is even. On the other hand, I've read a number of reports of excessive wear on the edges -- the pattern typical of underinflation -- with pressures set "by the book." Having said that, I have to wonder how many of those folks check their tire pressures regularly. It wouldn't surprise me if some actually had a considerably lower pressure. Underinflation is one of the biggest causes of accelerated tire wear.

 

<div class='quotetop'>QUOTE(FishHawk @ Mar 26 2007, 07:02 AM) [snapback]412225[/snapback]</div>

Actually, it's exactly the opposite. We started experimenting with higher pressure as a solution to slow down the wear. And it did, rather dramatically. The fact that it also delivers higher MPG is a nice added perk.

And it isn't "over inflating" unless you exceed the tiremaker's maximum. For most, that's 44 PSI. So the common 42/40 is no big deal. I've been running 44/42 for years with even wear across the entire tire width.

 

<div class='quotetop'>QUOTE(JimboK @ Mar 26 2007, 08:29 AM) [snapback]412230[/snapback]</div>

Actually, it seemed to me that even when new, the tread groves on the edges of the OEM tires were about half as deep as those in the center of the tire. It seemed to be designed that way. Personally, I think that's where all the "excessive edge wear" reports came from. The edges wear out first because they weren't as deep to begin with. But when a Prius owner finally notices around 25K miles that the tread is getting thin on the edges, all they see is that the center grooves are significantly deeper than the edge grooves, without knowing that they were actually always significantly deeper.

 

<div class='quotetop'>QUOTE(Marlin @ Mar 26 2007, 05:49 AM) [snapback]412247[/snapback]</div>

It is common for tires to be manufactured as you say. The Prius OEM tires start with about 8 mm tread at the edges and 8.5 mm in the center. However, this small difference does not account for the edges wearing to bald with about 4 mm still remaining in the center tread. That is what most commonly occurs when Prius is set at the factory inflation spec. I believe that infrequent pressure checks can also contribute, because the tire effectively spends much of its time below that spec. Some types of suspension misalignment can also contribute.

For Prius drivers who find that following Toyota's inflation recommendation gives them even wear, good traction, mpg, and long tire life, I say change absolutely nothing. But I believe that you are in the minority, and all else that I read in the groups indicates that original and replacement Prius tires do much better using inflations that are closer to the max pressure listed on the tire sidewall.

My 2001 Prius is now using 3rd set of tires, of 3 different brands. I monitor tread wear extremely closely with a digital micrometer. In all cases, the key to even tread wear has been higher inflations.

It is also the case that the pressure gauge I use has been calibrated by access to 'real equipment'. Not all pressure gauges are accurate as sold, and it is not impossible that when your gauge says 35 it is actually 40 psi. Right where I want you to be...

 

<div class='quotetop'>QUOTE(tochatihu @ Mar 26 2007, 10:48 AM) [snapback]412263[/snapback]</div>

My recollection could be wrong, but I remember a significant difference between the tread depth of the center and edges of the tires when I checked my wife's tires when they had only a couple of hundred miles on them. It seemed visually noticable. But that was over a year ago, so my memory might be faulty.

 

I ran mine at 35/33 for the first year I had the Prius. The tires were replaced at 36k miles. One was flat, but the others were in need of replacement within the next 5k or so. I doubt the pressure had anything to do with the life of the tires.

 

When I took my car in for its first service, the sheet I got at the end said all the tires were 32 PSI. I begged to differ that was not the correct pressure. They checked the tires in front of me & all were 35 except the right front which was 36. I'm still running the 35/33 that is marked on the door of my 2007 Touring. They reset all of the tires to the "right" PSI while I watched. I'm not sure why 32 all around was marked on the tech's sheet, but I did tell them I would be sure to check each time from now on. And maybe they will, too.

I also checked the oil level the next day, and it was exactly at the full line. At least they got that part right!

 

This is food for thought for all you "over inflaters" out there in Priusland:

Lets see now, the Toyota engineers were smart enough to design a very complicated and efficient car. Remember, the main goal for them was to design a fuel efficient car, and that includes the tire pressures. But from what I read on this forum, they were totally stupid when, after running hundreds of hours of tests of tires at various pressures, they decided to "arbitrarily" recommend 35 and 33 psi for the Prius. Come on now, folks, there is a lot of wrongheaded thinking going around. Sure, you want the best gas mileage, but there are other things to consider that the Toyota engineers probably figured in. For example, the extra wear and detuning effects on the suspension components and the rest of the car. As a fellow engineer, I resent the second-quessing by many untrained people in this matter. If the tire pressures are so totally wrong, the rest of the car must also be quite poorly designed and therefore you should not have bought it.

 

eestlane:
"Remember, the main goal for them was to design a fuel efficient car ... "

===============================

My understanding is that the goal was to produce a low-emissions, "PZEV" car. The fact that it is fuel-efficient is icing on the cake. :hungry:

 

42/40 maybe, but beyond that, no.

But, hey, don't take all of this so personally. It isn't only engineers who make decisions about automotive product, as I'm sure you know.

Speaking of those "Godlike" engineers whom you seem so deferential to...I, for one, don't think that the traction control, and its willingness to basically bring power back to idle at the merest hint of tire spinning (my car is an '06), is something that the "engineers" got right, and there are other mechanical/electronic issues that also are less than fully thought out.

Do I love my car? Yes. But is it "perfect"? Absolutely not.

Stock, it was one of the poorest handling cars I've ever driven. Massive understeer, non-linear throttle response, and no traction to balance the chassis with. Sure, it's an econocar, but that's no excuse for plain wallow-y handling. My '73 Pinto (rear wheel drive, admittedly, with a four-speed) handles pretty well for what it is, even with the skinny 13" wheels.

The fact is, the tires on both the Touring and standard edition cars just aren't that good, especially the Integrities. I don't think ANYONE can say that engineers chose those tires (I sure hope not anyway)...that was strictly a marketing decision.

 

I would rather surmise that the goal was to meet both of the abovementioned objectives, to the extent that it was practical. By the way, I have nothing against people running their tires at whatever pressure, as long as they know what may result such as instability in crosswinds, extra rough ride that's hard on suspension components and passengers, increased risk of tire punctures, etc. I just think that maybe we shouldn't recommend higher pressures to all the "newbies" as the panacea to the nirvana of 1 or 2 more mpg, with no other side effects.