I've been given the advice to put my tires PSI to above 42, to increase MPG. What's the worst that could happen to them? Doing so won't hurt the tires or increase the danger of driving, will it?
You will be OK as long as you don't go over the tire's rated pressure. The higher you go, the bumpier the ride will be. It's something to keep in mind. I keep mine and 42/40, and the handling/ride characteristics suit me just fine.
As the tire pressure goes higher, there is less flexing of the rubber parts and less waste heat generated and they run cooler. Not so much a problem with radial tires but the old cross belted tires could show center wear with higher pressure. Dept. of Transportation testing revealed higher pressure tires perform slightly better in braking tests. The load capacity of tires increases with tire pressure, which is one reason trucks have pressures of 90+ psi. The ride can be a little harder but softer shocks can help, somewhat. IMHO, high pressure and optimum wheel alignment is the way to go. Bob Wilson
I have the tires that came with my 2007 Touring#6. Once I accidentally inflated them to 120PSI and drove it about 5 miles home without any problems, or for that matter, without any noticable difference in handling.
The blowout scenario that Catgic describes is, as he implies, very unlikely. It almost certainly becomes more than a theoretical risk only at very high pressures -- i.e., substantially more than the tire (not the car) manufacturer's maximum sidewall cold pressure. Not suggesting it, but I've known people to run 15-20 PSI over the sidewall pressure with no problem. Tire manufacturers build in a substantial safety margin; they wouldn't state 44 PSI as a max if there was a chance of failure at 45. The risk of a blowout is much greater with underinflated tires. When I was in the tire business 25 years ago, most blowouts I saw were from underinflation. As Bob says, heat generation is higher, and if high enough, sidewalls weaken and eventually fail. The usual scenario was a road hazard that caused a slow leak, but I occasionally saw chronic underinflation from owner neglect get severe enough to cause a blowout.
I could see a debris-related blowout, maybe. But that is a risk no matter your tire pressure if you hit the right chunk of sharp metal. The other thing is that a blowout doesn't guarantee that you lose control of your car and careen across several lanes of traffic to a certain death. You aren't in serious danger until you react improperly to a blowout, e.g. slamming on the brakes and putting yourself into an instant spin when only one tire grabs. Just ease off the gas and carefully make your way to the hard shoulder, slowing down gradually.
Conventional wisdom indicates that: Tires that are inflated to the upper limits (i.e. 42 psi in our case) wear better, but offer less traction. Tires that are under-inflated (i.e. 35 psi in our case) offer better traction but wear faster. Tires that are over-inflated (i.e. 50 psi in our case) would have a poor wear pattern, and poor traction, so a lose-lose situation. It makes sense that senarios that produce less wear on the tires would also produce higher MPG for your Prius. Friction and heat means energy loss. Note that what I've said about better traction on slightly under-inflated tires doesn't necessarily go against what Bob Wilson stated about highly inflated tires braking better, as traction while tires are rolling isn't necessarily the same as breaking traction. Also note that I really don't have any hard data to back these claims up, it's just the conventional wisdom that has always been tossed around when I was hanging out with car guys. Someone correct me if they have data to support I'm wrong.
<div class='quotetop'>QUOTE(Sean Blumenthal @ Aug 22 2007, 12:06 AM) [snapback]500133[/snapback]</div> Nope, Nope, Nope. Tire traction at 42 vs. 35 psi is the same, tire manufacturers make sure traction is the same across the range of tire pressures. Waer better due to less flex of the tire casing/sidewalls. The only time underinflated tires offer better traction is when going through loose sand/gravel, they will wear faster because of the heat build-up from running weight on a under-inflated tire. Also leading cause of blow-outs. Wear pattern is not affected by pressure, modern radial tires hold even across the tread patch because of the orientation of the internal belts. Older bias-ply tires do balloon in the middle of the tread with higher pressures. Your braking traction is actually better at higher pressures, the government studies done to mandate tire pressure sensors found this. Wayne
<div class='quotetop'>QUOTE(FireEngineer @ Aug 21 2007, 10:22 PM) [snapback]500141[/snapback]</div> Thanks for the information, but I'll only believe you if you append an extra 'nope' first
<div class='quotetop'>QUOTE(Sprague @ Aug 18 2007, 09:56 AM) [snapback]498294[/snapback]</div> 120PSI? I doubt that.
<div class='quotetop'>QUOTE(Sprague @ Aug 18 2007, 08:56 AM) [snapback]498294[/snapback]</div> Woah. Glad you didn't unseat the bead and hurt yourself! Must have taken quite some time to get 'em up that high...weren't you kind of wondering why it was taking so long to add air? I'm really surprised that you didn't notice any difference in handling. I notice it when I air up from standard pressures to 42/40...we're talking THREE TIMES these pressures?!? I'd think it'd be pretty noticeable.
I've got about 250 miles on my Bridgestone Potenza RE92's @ 70psi. I've driven over 90,000 miles @60psi.
