Incorrect Information re: Tire Pressure in Efficiency Mods

[VegasDude]

That last point I made was really speaking to well under-inflated tires, not those inflated according to spec. It's a practice often used by people drag racing with street tires. There's probably not much difference between over-inflated tires and normally inflated ones in this area.

[Clev]

The bottom line is that EM is responsible for what it puts on the site as fact and there is no proof that increasing tire pressure past the placard spec will increase traction. Just take it down already. I don't understand why EM would feel the need to say anything about wet traction anyway, many people here seem to feel it's a question better left to performance driving forums.

There's also no proof that increasing tire pressure beyond placard decreases traction to any significant degree. If you're worried about traction so much, you're going to be running soft tires with poor rolling resistance anyway.

My tires wear substantially at the edges at placard pressure. This is the case on at least six vehicles that I've owned over the last 10 years, from my '99 Metro to my '85 F250. Since airing up the tires on my three vehicles to sidewall pressure on two cars and a truck, the tires are wearing much more evenly. Higher tire pressures have contributed to over $1,600 in fuel savings over the past 2 years, and my tires are lasting longer because I'm not throwing them away with bald shoulders and tread left in the centers. The suspensions on both cars are both still fine after 100,000 miles, so I guess I'm not concerned that I might have to prematurely spend a whole $200 on replacement struts for my Honda.

[brucepick]

Please have a look at this article.
Driving Under Pressure (full article) - CleanMPG Forums

100 psi on Crown Vic tires on this Ford pickup:


In years past I ran my tires at max sidewall. They always wore down at the edges of the tread. I now run them at max sidewall + 6-8 lb, which means 50-52 psi. Very even tire wear after 54,000 miles on this set of tires.

Before buying my Civic I drove Volvo 240 wagons for over ten years, about 25,000-30,000 miles a year during the last few years of that period. Mostly highway miles of course but not exclusively by any means. I inflated my tires to 32 and 35 psi which was max sidewall for those tires in those days.

Every time a tire wore out - and they did wear out, driving that many miles - it was always the edges that wore. Plenty tread in the middle, shoulders always worn. But I'd run them at sidewall pressure, which was actually a few psi more than the vehicle placard spec! So what's up?? Worn at the edges supposedly means under-inflation, right?

Exactly. Bought new car (Civic), got it new tires. I've run these tires at about 50-52 psi. since about a week after purchase. Max sidewall is 44. And I'm happy with it. Now I'm not suggesting anyone do that. This set now has 54,000 miles on them. The center tread is only about .001 inch deeper than the edges. So I'd say I've beaten the edge wear issue.

And what's more, I think I can lay to rest the bunkum about over-inflation causing wear at the center of the tread. I'd think that after 54,000 miles at 50+ psi, on tires with a max sidewall rating of 44 psi, the center tread would be gone if there were any truth at all to that concept.

Oh yes, the long running debate about traction and handling etc. I take corners and curves fast enough to scare some of my passengers. The tires haven't let go of the pavement yet. Fortunately my current (very occasional) car pool buddy is a pilot so he's used to feeling some G-force in a turn.

[Xringer]

Hydroplaning info here: Tire Tech Information - Air Pressure vs. Wet Performance

Be sure to read that part under the last pic about the tests at 'Michelin's Laurens Proving Grounds'.


I like the HydroEdge (44 sidewall max) tires and normally try to keep them at 40 PSI, as a compromise between comfort and MPG+Performance.
Had them on my CRV and loved them. My wife has them on her Corolla and we maintain them at 40 PSI.

If they go down a few PSI over the winter, they will still be pretty safe.
But, if they were at 'factory' pressures and got low.?. Dangerous IMHO.

My compressor gets a lot of use on other people's cars. The guy across the street, my sister-in-law & etc.
When I can easily see their tires are low, it's not a surprise to see the meter reading 15 to 20 PSI.
That's just asking for poor handling and wear..

Speaking of wear, Hypermilers over at CleanMPG Driving Under Pressure (full article) - CleanMPG Forums sometimes use pressures above sidewall.
My guess is almost all of them are using well above factory placard pressures.
But, I don't hear them talking about excessive tire wear.. Some of them do report longer tire life.
Maybe, that long life could be due to hypermiler driving techniques. No jackrabbits or hard braking etc.

One side benny is less brake dust on your alloy wheels!!


This baby came from the dealer at 40 PSI. Same Low-rolling resistance tires they give you on the Escape Hybrid..
I keep them at 40 (sidewall 44 max) and the ride is good for an SUV.

[trikkonceptz]

Adding my experience to the story,

When I began hypermiling with my Vibe I was careful to make one change at a time and watch the changes to see if it was worth the modification. I can absolutely attest to the MPG increase once I raised the tire pressure from placard to 50 psi cold. Now with my increase I used the nitrogen product in order to keep the pressure stable as the tire temp increased.

I did notice a harsdher ride, but I also witnessed improved traction when cornering, (No squealing tires) and improved wet weather traction, (no hydroplaning). In line with that I saw a nice 3mpg bump in mileage.

Now I also believe that in order to save money manufacturers use the tire as an additional dampner in their suspension design to make cars roll smoother.

I say this because I also have a vehicle that has a very low profile tire. 225/30/20. These tires have to run at higher PSI because sidewall flexing results in breaking of the bead and destroying a rim. In addition I spent some serious coin and bought an adjustable coil over suspension for this vehicle and had it professionally tuned for proper height and dampening.

WOW !! this vehicle rides likes a serious luxury car with nothing felt as far as bumps. In fact if I do not remind myself that i am 2 inches off the ground I will rip my bumper off the car accidentally. That proved to me that a properly engineered suspension can do its job properly despite the tire and independent of it.

Its just too many companies count on soft squooshy tires to act as a suspension instead of the suspension doing the work.

Also and I saw no mention of this in this post. There is no money in replacing tires every 80K miles or more. Dealers make more money off of parts and service than the sale of the car. Ergo, a tire that wears faster means more trips to the dealer for new tires and other related services.

I would also like to add that I have no data on better braking for the simple reason that our driving habits tend to teach us to brake very little and respond to changing road enviroments much sooner than later. I also have the added benefit of owning a vehicle that has ABS and traction control which negates the need to skid all together.

[autoteach]

Not trying to argue either way, arguing for science. Found this. Like the idea of the chalk...
Proper Tire Inflation

edit: I know I said I wouldn't reply, and I just didn't see a reason to withhold this information.

[pgmomni]

Originally Posted by autoteach

Not trying to argue either way, arguing for science. Found this. Like the idea of the chalk...
Proper Tire Inflation

edit: I know I said I wouldn't reply, and I just didn't see a reason to withhold this information.

I keep my Yokohama Avid Touring tires inflated 44 front, 40 back.
Over 44 and ride starts to get too harsh.

At 44 front, 40 rear the front and rear both have the same small amount of sidewall bulge.

I gotta try the chalk test. I expect it could reveal wheel alignment issues too.

Pete

[trikkonceptz]

So it sounds like we can resolve some of the mystery by chalking our tires and seeing if we are wearing unevenly ... I hope to try this tonight or tomorrow with my daughters sidewalk chalk ..lol

[markweatherill]

I think it's received wisdom that over-inflated tyres bulge in the centre of the tread and wear unevenly, from the olden days of cross-ply tyres.

'Overinflation' of a radial tyre will reduce sidewall flex and that is where rolling resistance is reduced. Not due to a smaller contact patch (which may exist due to the circumference of the tyre sitting a little less 'flat' on the road, possibly)

[user removed]

Inflaton pressure is equal on the inside of the tread area and the sidewalls of the tire.

Since there are two sidewalls for each tread area the increased pressure should not really affect the tread wear. That has been my observation over 50,000 miles on my VX and Insight.

When I put the new OEM tires on the Insight I monitored how long it took the nibs to wear off the tread area, and I do not drive around corners slowly.

It was 1000 miles before the nibs were worn off the center of the tread, and I was averaging close to 70 MPG in the Insight, and it was a automatic (CVT).

I will probably never run manufacturers recommended pressures in any car I own again.

I'll bet the Michelins on my VX will last 100,000 miles at 44 PSI and the 10% increase in mileage will easily pay for the $225 total the tires cost me, and I can still go close to 60 MPH on an average Interstate cloverleaf.

My 59 Corvette would do 70 , manual steering and 4 wheel manual brakes.

regards
Mech