What happens to old tires...

[CapriRacer]

Originally Posted by Clev

Wouldn't LT tires have less sidewall flex on a lighter truck, giving increased mileage at the expense of ride quality?

The improvement in rolling resistance in a tire comes from the tread compound. Sidewall plays almost no role in what can be changed to affect RR.

But even when LT type tires start coming in LRR varieties, the fact that LT tires have high unit loading (high loads compared to the amount of space they occupy), P metric tires will always have better RR.

Based on the most recent study, larger tires have better RR. I know this sounds counter intuitive but that is what it says. I discuss this here:

http://www.barrystiretech.com/rrandfe2.html

[comptiger5000]

Larger tires are less disturbed by small imperfections in the road, which makes sense for lower real-world rolling resistance. That, and taller effective gearing, combined with off-road use are why I upgraded my Jeep from the stock 225/70R16 tires to 245/70R16.

It had no noticeable effect around town (not a lot of extra weight, and taller effective gearing), and a fraction of an mpg gain on the highway at 60mph. The instant mpg on the overhead display reads the same as before most of the time (better RR, but worse aero), but when climbing steeper hills, it typically stays about 1mpg higher than it used to due to the taller effective gearing.

The effects will, however, vary from vehicle to vehicle. In my case, I think the primary reason I saw gains was due to the Jeep needing taller gearing on the highway (with current 3.73 axle gears and larger tires, it turns 1750 at 60mph and climbs any hill without downshifting).

[d0sitmatr]

if you have ever faced a blowout or tire separation at highway spds, you might reconsider over inflation

[Frank Lee]

I have many times. It goes: flap flap flap flap flap... what's that sound?... FLAP FLAP FLAP... Oh yeah, blowout. Then I gently pull over and change it. No drama. At worst, cold fingers when it happens in winter.

[PaleMelanesian]

I've done it. No biggie. It was due to old tires, again. That was back in the day when I was running "normal" pressure (lower than placard due to neglect ).

[Wonderboy]

if you have ever faced a blowout or tire separation at highway spds, you might reconsider over inflation

Oh you mean YOUR highway speeds. If you're actually going the speed limit or slightly less it's just like Frankly says: "flap flap flap flap.....oh... I've got a flat." This just happened to me recently and coincidentally I was listening to Car Talk on NPR when it happened . I wouldn't advocate people to do things that make them feel unsafe, but I would advocate for people to gain perspective on what is and isn't safe - put your idea of safeness to the test every once and a while.

I just got both my cars inspected and I was running some junkyard tires on one of them - unacceptable to the inspector. So I just throw a couple of other, better looking junkyard tires on and it passed. I personally love recovering perfectly good stuff from being wastefully destroyed and embrace the recycle, reduce, reuse ethic. I'm glad I've got the personal patience enough to calmly change a tire when it blows out. There's something very cool calm and collected about most of the things I've learned here and practiced on the road - a zen feeling I never ever got before.

[euromodder]

Did any of these blow-outs happen in a fairly tight curve ?
Friend of mine had it happen : poof flap screech flap screech flap crash.

It was a worst case scenario though : outside front wheel blowing out

[jamesqf]

Originally Posted by d0sitmatr

if you have ever faced a blowout or tire separation at highway spds, you might reconsider over inflation

What's over-inflation got to do with it? Under-inflation would be far more likely to cause blowouts. (Due to increased flexing and heat buildup.) But out here in the real world, every one of the few blowouts I've had has been caused by road debris puncturing the tire.

[endurance]

I agree that the risk produced by a blowout or other sudden deflation is a lot higher in an SUV or truck than it is in a low profile Honda Civic or other passenger car. I'm sure everyone remembers the fiasco Firestone went through because their product was used on a defective vehicle (a blown tire should not present a life threatening emergency and if it does, there's a design flaw with the vehicle, not the tire, but Ford's spin doctors got there first). In any case, you might want to look at the NTSB data on rollover rates for your vehicle just for reassurance. If there's a problem, I wouldn't run anything but the best Michelins your money will buy. If there's not a problem, it's because the vehicle was designed to handle problems like flat tires.

BTW, as a sidenote, before the Ford Explorer fiasco, Ford was up against the wall with the Bronco II, which had an even worse rollover record. At the time, the Bronco II was flipping at a rate of 22/100,000 while the Suzuki Samurai was catching all the heat with a rate of 6/100,000. Why? Ford quietly settled hundreds of law suits when the family bread winners were killed and the other spouse needed the settlement to make the mortgage payment. But since the Suzukis were $6,000 cars marketed toward teenagers, mom and dad were still working and they were pissed; thus more cases went to court. Only when the tire failures happened was Ford vulnerable because it was clear they were selling a defective product (the tires, of course).

[d0sitmatr]

Originally Posted by Wonderboy

Oh you mean YOUR highway speeds.

my highway speeds are most likely the same as yours, 70mph ?
you also might change your tune if you happened to have a 3 yr old (your only child) in the vehicle with you when it happens...
but hey, maybe not.