Over intlated tires - how much do you do?

[redpoint5]

How much over the sidewall rating do you run in PSI? As a general rule, what % over sidewall do you consider to be safe?

I tend to wear out the edges of my tires first since I don't brake before entering turns, so perhaps over-inflating by a decent amount would help to even the wear out.

Right now I think I'm running 5lbs over the manufacturers recommended pressure, but I might go for more and monitor my resulting MPG.

[euromodder]

Originally Posted by redpoint5

How much over the sidewall rating do you run in PSI? As a general rule, what % over sidewall do you consider to be safe?

I run 45 psi, near but below the sidewall limit (51psi).

I tend to wear out the edges of my tires first since I don't brake before entering turns, so perhaps over-inflating by a decent amount would help to even the wear out.

Same here, and the higher inflation seems to help to spread the wear more evenly.

[endurance]

I go with the sidewall limit (51 front, 44 rear), but fill first thing in the morning, before I've even rolled the car out of the garage. Once they're warmed up, it's not unusual to see them at 55/48 or even a little higher. If we get a really heavy snow, I'll drop them down into the 35-40 pound range until the roads are clear, then pump them back up. It helps to have your own compressor at home. I actually have two, one I bought for air stapling to put in trim that I picked up for cheap at Harbor Freight and one that's a combo jumpstarter, compressor, inverter. Both work great for the work I make them do (pretty light duty stuff, never any prolonged jobs).

[Piwoslaw]

I've read in a few places that it's good to start at MAX-10% (46psi for 51 max sidewall), and increase when you feel good with it. I've inched up to my MAX=51psi and try to keep it there. My summer tires may be starting to wear down in the middle, but I'm not 100% sure yet. Supposedly that's normal in many front heavy diesels, plus I can't wait for an excuse to buy new summer tires (upgrade to LRR).

[UFO]

NEVER over-inflate your tires. Run them to the sidewall rating, but do not inflate them above it.

[redpoint5]

I probably won't be exceeding the sidewall rating, but I would have no reservations about doing so for several reasons. Oregon has relatively cool temperatures, I don't ever exceed 75mph, and the ratings are conservative figures.

In HS I would over-inflate the bicycle tires on the electric vehicle I made by 10% to give lower rolling resistance. We would distance race against other cars in a closed circuit.

Of course, I'm not an expert and will not be liable for anyone who chooses to over-inflate their tires.

[endurance]

I know Mythbusters has lousy control in their fuel economy tests, but they did a test with various PSI and while above sidewall rating did yield slightly high mpg. The real margin for improvement was getting above the typical American driving around on unchecked tires at 20psi. If you want good tire wear, good handling and good mileage, your best results are somewhere between the driver's door plackard and the sidewall max. The closer I get to sidewall max, the more it feels like someone greased my tires. They don't break loose, but it feels a little sketchy. I drive less aggressively during the winter anyway, so there's no harm, IMHO, in running them high when the roads are dry and dropping them down when the roads are icy. If I lived where we had continuous winter, I'd just suffer with lower mpg, but I don't, so I won't. Our typical storm comes in, drops 6" on Sunday, it's melted off the roads by Tuesday.

[slowmover]

Use a certified scale, here, to determine truck weight. Dodge guidelines are pretty well right on the money in regards the Michelin Load & Pressure Table. Best LT tire life, best braking, best handling are a result of matching pressure to load. Screwing around with what works is a lousy idea.

On a cars P-radials I may start with 75% of sidewall max to see how it is; and then adjust FF/RR according to factory-recommended pressure bias. Generally I wind up within only a few pounds the door sticker numbers and default to them (when tire size is non-stock).

Overly stiff tires simply damage the vehicle long-term as the tire does have a function of shock absorbtion and side-to-side roll resistance. Any so-called mpg gain doesn't offset shorter component life and reduced performance. Safety trumps all.

On my truck I'm on track to get 250,000 miles out of the first two sets of tires via this method -- plus easy driving -- on MICHELIN LTX A/S.

[redpoint5]

Originally Posted by slowmover

On a cars P-radials I may start with 75% of sidewall max to see how it is; and then adjust FF/RR according to factory-recommended pressure bias. Generally I wind up within only a few pounds the door sticker numbers and default to them (when tire size is non-stock).

Overly stiff tires simply damage the vehicle long-term as the tire does have a function of shock absorbtion and side-to-side roll resistance. Any so-called mpg gain doesn't offset shorter component life and reduced performance. Safety trumps all.

You bring up many good points. I do keep the front and rear pressure differential the same for safety and handling reasons. This is funny because I acknowledge that over-inflating tires will cause longer braking distances, increased rollover tendency and create a stiffer ride, and yet I still do it.

Everything in life is a trade-off that must be carefully weighed. Running higher pressure does have some notable advantages besides fuel economy. As I have stated, my tires do not wear evenly because I corner hard. Over-inflating helps to even this out. Also, a higher pressure tire is less prone to damage from a pinch-flat (hitting a curb for example).

So, the gamble is whether you will save money by having higher MPGs and better tire wear, or loose money by wearing out suspension components or having an accident.

[Big Dave]

I run 25% over on my truck, but these are Firestones.

It gets better than the MPG I got with the tires pressured up to the sidewall number (80 psi) but I suspect anything over 90 psi is a waste. At 100 psi, I don't notice any "crowning" of the tires - the tread is dead-flat across.

I'm talking "E" rated (ten-ply) tires.