tire depth for state inspection?

Your last question makes no sense. The word "most" doesn't fit. The only thing that matters is the law in your state.

Time to do some reading:

8/32 is 1/4" which is fine, unless the tires are worn more in the center or on the sides. The legal requirements for most states is 2/32 (1/16").

Jeff

Actually, more important is when are the tires unsafe? They should be replaces around 4/32" according to Tire Rack. That's about right.

Thanks for the reply. I do notice that the side of tire seems worn more than the center, I do regularly balance and rotate my car's tires every 6000-7000 miles, does it indicate that alignment needed for my car?

Tires are functionally shot well before state limits.

True - but if you don't make unreasonable demands of the tires they are safe down to the "wear bars" (usually at 2/32) molded into the tires and indicated by arrows on the sidewall, and even a bit past.

An unreasonable demand would be freeway speed driving in pouring rain on 2/32 tires, since the tread grooves are needed to expel water at speed - otherwise it's not driving it's called Hydroplaning...

You can put off purchasing new tires for the summer, but before the first big storm of the year is when you need to take a serious look.

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Right!

Avoiding other cars might also be called unreasonable...

In most states, the minimum tread depth is 2/32" unless the wear bar is even with the tread on 2 adjacent treads. The tread depth on most new passenger car tires is somewhere from 10/32" to 12/32"

If the outsides are more worn than the inside and the tires are evenly worn (as opposed to a scalloped edge) then the tires were probably under-inflated. I recommend inflating the tires 5 or 6 PSI more than the pressure indicated by the automaker for longer tread life.

....and boy is that fun and interesting, like seeing a piano about to fall on your head. Happened to me once. Suddenly, there was no road noise.

Bottom line here is that it's false economy to try to squeeze the last couple of thousand miles out of tires that have only the memory of tread on them, or with funky sidewalls that you can't trust. They're the only things that keep your vehicle on the road, and it's worth your life to keep them with hefty tread, and not looking like racing slicks. If you've ever had a blowout at highway speed, you already know, and if you've never had one, you really don't want to know the sensation of one.

Are the inner and outer tread areas of all tires worn more than the center of the tires? If so, this would indicate the tires are under inflated. If it is just the outer or inner tread areas, it could be alignment, worn components, your driving style, or the sort of roads you drive on. You did not say how many miles are on your tires. If you have lots of miles on the tires (40k) and the uneven wear is just now apparent up, I'd forget about it for now. When you buy new tires, you could ask them to check the alignment. Some tire stores include an alignment check with the purchase of new tires. At some tire stores it is extra. If you are really worried about the alignment, take it to a front end shop just before you buy the new tires and have them do a 4 wheel alignment.

Ed

"Ray O" wrote in message news:nvudndxmwP2llNfanZ2dnUVZ snipped-for-privacy@comcast.com...

This is one time I'd have to disagree with Ray. I think inflating the tires 5 or 6 psi over the pressures recommended by the vehicle manufacturer is not always good idea. Certainly no tire manufacturer would agree with this recommendation (at least in writing). 2 to 3 psi over the recommended pressure is probably OK (as long as you don't exceed the maximum pressure listed on the tires sidewall), but unless you are doing something unusual I think 5 to 6 is too much. That much additional pressure can make some vehicles "squirrelly" to drive (they overreact to steering inputs, follow ridges in the roads, etc.). After I got new tires on one of my trucks, it drove like crap. You almost couldn't keep it in a straight line. When I got home, I found that the tire store had inflated the tires to the maximum pressure listed on the sidewalls, instead of the correct pressure. After dropping it back down to where it should have been, the truck drove like it should. On the other hand, I had a Saturn Vue. Originally the tires were to be inflated to 30 psi. After the vehicle failed a NHTSA test, GM sent out a letter and a sticker changing the recommendation to 35 psi. As instructed I upped the pressure to 35 psi. It definitely made the vehicle more nervous on the highway, but not horribly so. The ride wasn't affected to a noticeable degree. Unfortunately it caused the tires to wear out in the center. The gas mileage was not measurably different.

All tire manufacturers say things like this statement from Goodyear

"How much air should I put in my tires?

"Proper inflation is the single most important part of tire care. The inflation pressure on the side of the tire is the MAXIMUM operating pressure. It is not necessarily the right inflation for your vehicle. Always use the inflation recommended by the vehicle manufacturer. You can find it in your owner's manual, posted on the edge of the driver's door, on a door post or on the inside of the glovebox door. Always check inflation when tires are COLD: when the vehicle has been driven less than a mile or one hour or more after driving. Use a good quality tire gauge. Note: It's natural for radial tires to have a slight bulge in the sidewall at their proper inflation pressure. Check or adjust inflation every few weeks, before any long trip or if traveling with a heavy load. And don't forget to check the spare. Your Goodyear retailer can answer any questions you may have about tire inflation."

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However, just to confuse people, tire companies also say things like (from

): "For continuous high speed driving, tire pressures should be increased by 3 to 5 psi above the normal cold inflation recommended"

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Unfortunately that site doesn't define continuous high speed driving. Michelin does provide more detailed information. From

For high-speed driving, additional inflation pressure and possibly reduced tire loading and/or upsizing is required. In the absence of specific recommendations by the vehicle manufacturer, use the following guidelines based on those in the European Tyre and Rim Technical Organization Standards Manual.

For speeds over 160km/h (100 mph), load and inflation must be adjusted according to the table below.

S-Speed Rated Sizes: Maximum Speed (mph) 100 106 112 Inflation Increase (psi) 0.0 1.0 2.0 Load Capacity (% of max.) 100 100 100

T-Speed Rated Sizes: Maximum Speed (mph) 100 106 112 118 Inflation Increase (psi) 0.0 1.0 2.0 3.0 Load Capacity (% of max.) 100 100 100 100

H-Speed Rated Sizes: Maximum Speed (mph) 100 106 112 118 124 130 Inflation Increase (psi) 0.0 1.0 2.0 3.0 4.0 5.0 Load Capacity (% of max.) 100 100 100 100 100 100

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So unless you are driving over 100, you don't need to worry about increasing the pressure above the vehicle manufacturer's recommended pressure.

My recommendation is to stick with the vehicle manufacturer's recommendation as long as you are still using the original size and type of tire. If you fell like you need a stiffer ride, then upping the pressure by 2 to 3 psi is not going to hurt anything (going higher is almost always better than going lower). Upping the pressure by more than 5 psi is probably not a great idea unless you are doing something unusual. It will affect the ride and handling of the car. Too high a pressure may also cause the tires to wear out in the center. Too high a pressure will increase the vulnerability of the tire to damage from stones and road defects. If you change to a difference size or type of tire, then all bets are off. If it is an optional size offered on the vehicle, then you probably can use the vehicle manufacturer's recommended inflation pressure for that size. If it is not an optional size, then you will probably have to get help from the tire installer, and/or experiment to get the pressure right.

One final thing to think about - Why would vehicle manufacturer's deliberately recommend too low a pressure? If the pressure is too low, fuel economy will suffer, and this will impact the CAFE numbers. If the pressure is too low or too high, safety may be compromised. Vehicle manufacturers arrive at a pressure recommendation based on lots of factors (safety, fuel economy, tire loading, normal handling, emergency handling, tire wear, ride comfort, tire cost, etc.). Individuals may have different ideas about the ideal compromise. However, I believe it is unwise for the typical motorist to stray too far from the vehicle manufacturer's recommendation. "Experts" and "Professionals" may have the knowledge and experience to make other choices.

Ed

My advice comes from years of experience and experimentation. Adding 2 or 3 PSI will not make much of a difference in handling or ride quality, but it probably won't make much of a difference in tread life either. I've found that adding 5 or 6 PSI will even out tread wear, and since tires lose air over time, it takes longer for a tire to become under-inflated, which is usually more dangerous than over-inflated. Higher tire pressure will reduce tread squirm, which scrubs off rubber and the higher pressure reduces sidewall flex, which generates heat, which makes a tire wear more quickly. The only tradeoff I've found is a slightly harsher ride, but Toyotas tend to be pretty softly sprung so the harsher ride doesn't bother me. I think the Toyota engineers have a bias towards a soft cushy ride, so they seem to use lower tire pressures than necessary. Toyotas also tend to have quite a bit of positive caster so the car has more of a tendency to track in a straight line, so I have not noticed any noticeable adverse effect on handling by increasing tire pressure and have not experienced the short tire life on the original factory tires that many people complain about.

I'll admit that I have not experimented with other car brands, so my advice may not be good for them.

Before inspection, swap tires with a friend with better tires and swap back after inspection. problem solved =)

Right. It's not always a good idea, but it's also not always a bad idea. The car maker's recommended pressure is based on...what? The tires the vehicle came with? Maybe? What about the next set of tires, which may be vastly different than what the vehicle came with? The sticker on the door can't take those into account.

The only way to know what works best is to experiment. The AAA has claimed for years that almost 60% of cars have underinflated tires, so it's safe to say that 60% of drivers don't experiment with tire pressure. Hell...they never even touch their tires, hoping instead that their mechanic will check them once or twice a year when the car's in for other service.

Tires of the same type, size and load rating have the same pressure requirements. Michelin, Goodyear, Firestone, Cooper, etc., all use the same load vs inflation tables for a given size and type of tire (it is a tire manufacturer's standard). As long as you don't change either the size, type, or load rating of the tires, the pressures listed on the vehicle placard are correct.

Hmmm..this seems to be an illogical conclusion. I suspect that AAA is claiming that 60% of vehicles have tires not inflated to the proper inflation pressure as specified by the vehicle manufacturer. I don't think AAA or any tire manufacturer is going to suggest that vehicle owners experiment with tire pressures. If, instead of saying "experiment with" tire pressure, you had said "check" tire pressure, then I would agree with you. Heavy truck tire suppliers do often discusses methods of determining the correct tire pressure, but then you are dealing with tire loads that can vary drastically even for the same truck. The typical passenger car tires are not subjected to a vast range of loads. And in all the cases I am aware of, the vehicle manufacturer's recommended pressures are will above that required by the tire manufacturers for the maximum load the vehicle is designed for.

Well this is true, but it doesn't imply they need to experiment with tire pressures. Most people (even ones who think they know better) aren't able to conduct meaningful experiments to determine the correct tire pressure. Mostly they end up going with what "feels" right without really knowing the long term effects on emergency handling, tire life, or tire durability. For the vast majority of car owners, the best pressure is the one recommended by the vehicle manufacturer. I don't see anything wrong with increasing the pressure slightly if you want a stiffer ride or more responsive steering, but I don't think you should get carried away. You should not exceed the maximum inflation pressure listed on the tire and never go lower than the pressure recommended by the vehicle manufacturer (assuming you have the OE size and type of tire).

Ed