[obermd]

Tom McCahill of Mechanics Illustrated was always recommending 50 psi for tire pressure back in the 50's. Does have some negative effects, like major wear in the center of the threads, hard on your back with any kind of bump, and really rough on your suspension, especially control arms and ball joints, and far poorer traction in the snow.

I always went with the sticker values, best all around, but tend to go 10% more with the Cruze because of this crazy TPMS. Tire pressure should be check when tires are cold, but in this kind of weather with a garage temperature of 30+*F, and outdoor temps like -30*F, at 30 psi can drop to like 26 psi.

And the more you fool around with these way overpriced tire valves, the quicker you will wear them out.

In the 50s all passenger car tires were bias-ply. Bias-ply tires bulge when you over inflate them which is why you get uneven wear from over inflation. Modern radial tires don't bulge. Different technology.

The correct tire pressure is no lower than the door placard and no higher than the max PSI embossed in the sidewall. Find a pressure that meets your personal desire for ride comfort (read - no road feel) and handling. There is a huge amount of safety margin in a tire, even at max sidewall PSI.

With radial tires the front tires will wear faster at the shoulders and the rear tires faster in the middle of the tread. This is the nature of vehicle suspensions. To counter this tendency you must rotate your tires. GM recommends every 7,500. I recommend every 5,000 based on personal experience. If you see any other type of uneven wear get an alignment. Also get an alignment immediately after purchasing new tires.

 

[obermd]

sidewall max psi isn't the whole story, you have to consider load as well... I wouldn't run a tire @ max indicated PSI.... we run ours around 35psi cold

Your choice and I understand the hesitation to running at max sidewall. I ran my Fieros, Transport, and Montana at the next 5 PSI above the door placard and run my wife's Solara at the next 5 above the door placard. My ECO MT is the first car I've been comfortable driving at max sidewall.

However, consider that the single biggest factor in the rate of tread wear is the degradation of the rubber compound. The biggest contributor to the rubber compound degradation is heat and the largest heat source in a tire is the sidewall flex. Higher pressures reduce sidewall flex, which reduces both rolling resistance and internal heat buildup. As for load, heavier vehicles require higher tire pressures simply to reduce the sidewall flex. The penultimate example of a manufacturer recommending too low of a pressure was the Ford Explorer with their tire blowouts leading to rollovers. When Firestone got involved they looked at the tire, looked at the weight of the vehicle with four adults (700-800 lbs total passenger/cargo weight) and came back with the public statement that at the door placard pressure the tire was simply not safe as it was under inflated. Over inflation based on load was a problem with bias-ply tires; it's not an issue with radials. Bias-ply bulged when over inflated relative to the load; radials don't.

Some of us running our ECO LRR tires close to or at max PSI have tracked our tread wear and have discovered that not only is the tread wear even at max sidewall PSI but it doesn't appear to wear as fast. As I posted in the TPMS thread yesterday I discovered last summer that in the 90+ temperatures it didn't matter if I ran at 45 PSI or 50 PSI based on the TPMS. The TPMS would max out at 52-53 PSI in either case. Even driving across Kansas last summer at 80 MPH in 113 degree weather my TPMS still didn't show higher than 55 PSI. I started the tires at 50 PSI cold the day before in New Hampshire.

 

[obermd]

Wonder if my photographic memory is over exposed at times. Bias tires as I recall weren't introduce unit the late mid 60's, 50's used narrow thread Rayon tires. And were very expensive, a set of four ran around 200 bucks. Ha, when shopping around for old cars in the 50 buck range, just looked at the tires, if they were like new, didn't care what the rest of the car looked like.

Tire pressures? 15 psi for rear farm tractor tires, 30-35 psi for practically all car tires, 60 psi for boat trailer tires, 65 psi all around for motorhome tires, bicycle, the old light weight design, 105 psi.

Could ask the question about putting 45 psi in very low profile tire as to what happens to the alloy wheel rim when hitting a pot hole.

You may be correct on the change to bias ply. The technology used before bias ply also bulged. Radial tire construction was a major change in technology and eliminated over pressure vs. loading bulges. As for what happens with 50 PSI hitting a pothole at speed - I did it at about 30 MPH last summer on I-70 in a down pour that made a cow pissing on a flat rock look like a slow drip (you could only see the taillights of the car in front of you if you were tailgating). No damage to the tire, rim, or alignment. As hard as I hit I really expected to have damage.

 

[obermd]

I know of one exception to this - the rear tires on several GM models will see severe wear on the inner shoulder under the stock alignment. The most prominent models for this were some recent W-platform (Impala, Grand Prix, etc.) vehicles. They set the rear camber so severely (3 degrees if I remember correctly) on these vehicles that you can see it when you're driving behind an unmodified vehicle. I had a set of Firestones on my Grand Prix that were pretty much junk after being left on the rear of the vehicle for 15,000 miles (after 23,000 total miles on a 55,000 mile tire) because the inner shoulder was so badly cupped (front tires easily had another 35,000 left in them). Ever since, I have my tire guy install a camber bolt kit when installing my first set of tires to bring them back within a degree of vertical.

From what I have seen of our Cruze (at least my Diesel), it looks like GM used a similar rear camber setup. If anyone has had their Cruze on an alignment rig and seen the rear camber numbers, I would like to see what they are stock (maybe I'll start another thread for that), but to me it looks like they're at least 2 degrees, and maybe more. I guess I don't mind, because it will help me burn through these OEM Goodyears faster so I can put a better tire on next fall, but when I do it looks like a camber bolt kit is in my future again.

I've seen cars like this and I don't think the Cruze has this issue. If it did it would have been reported by now.