Tire pressure?

[smacky]

Wow, I knew a thread about tire pressure wouldn't go well but I'm still surprised. Things have gone downhill since the hack.

[SeaYa]

Originally Posted by 1stToyota

If over-inflation wasn't ONLY about increased fuel economy, we'd be seeing actual real world test results with handling, braking, etc..., comparing the results of tires that have normal pressure with those with double pressure, not just fuel economy increases, or do the 60p.s.i.ers and the websites they go to consider *safe* being a tire that didn't blow out? I'd like to see some real test results of two cars being track test against each other. I'm betting the car with over-inflated will come in 2nd in every catagory except fuel economy.

Thank you! I tried something like this! Snowy parking lot (1-2 inches) and brought my pump. Did 30 psi and 45 psi two times each on a 20 mph turn in the middle of the lot. Here's what happened: 30psi, better traction, worse handling. I slid about 7 feet from my intended line of travel with the car pointed to the outside of the turn. At 45 psi, I had worse traction, but better handling. I slid nearly 12 feet from the intended line of travel, but the car was pointing nearly straight on the way I wanted to go. Did some reading and thinking and maybe this is why: The Yaris is a very light FF, and with an empty trunk, any increases in tire pressure will have a more dramatic effect on the rear tires, eg, smaller contact patch. Since there is already so little weight back there, the rear tires slip to an even greater degree than the front when at 45 psi, hence, the back sliding around more cuts down on the under steer, and you get the feel of better handling. Traction though, another story, I slid 5 extra feet off the 'road', which in straight line braking, could mean running into the hazard you were "looking ahead for and planning for, but still hit because I sacrificed my vehicles engineered performance for an extra 2 MPG"..and by the way, to all the 60psi people...I can't find your actual MPG savings on this post.

To the OP: I've done 35psi (42/44mpg) and 40psi (42/ 47mpg).

Seems to me like the hypermilers are trying to beat the EPA rating by as much as possible for bragging rights. Otherwise, why stop at 60? Why not do 100psi? If your answer is because the tire will burst, then you admit to already pushing the engineered limits of your tire. Otherwise, if traction isn't important to you, why not buy 3 extra spares and run them at 80psi? They're only rated for 60psi, but you don't seem to have a problem with doubling manufacturer recomendations. Let me know how that works out for you.

[otterhere]

Originally Posted by MadMax

By the way, what is the PSI level that kicks off the air pressure sensor light?

Hmmm; wonder why mine didn't go off? All four tires were at the same LOW level (26) when I finally checked them; with it increased to 38 -- didn't quite go to 40 -- I'm expecting better mileage the next time I check the MPGs...

[SilverGlow]

Originally Posted by YarisSedan

Here are some reputible, reliable sources of information that will tell you all you would ever want and need to know about tires and tire pressure to put this post to rest. If the quotes interest you click on the link to read the complete articles

http://www.betiresmart.ca/resources/...oc2=faqs#faq03
"Is over-inflation harmful?
Yes. One of the biggest tire maintenance-related myths is that over-inflation is not a problem. Often, even people who understand that under-inflation is a problem are unaware of the harmful effects of over-inflation.

An over-inflated tire rides on just the centre portion of the tread. The smaller contact area means reduced grip on the road leading to a harsh ride, handling issues (such as steering and stopping problems) and increased wear on tires and suspension components.

What should I do if my tires are over-inflated?
If you find that your tires are over-inflated, release air by pushing on the metal stem in the center of the valve, then re-measure the pressure. Never reduce pressure when tires are hot. Wait until they are cold, meaning that your vehicle has been stationary for at least 3 hours or has not been driven more than 2 km."

http://www.popularmechanics.com/blog...s/4199963.html

"Debunking a Mileage Myth: Can You Really "Pump Up" Your Fuel ..."

http://www.tirestamp.com/index.php?o...139&Itemid=177

"Question: Is my tread wear effected by overinflation?

Answer: Overinflation is almost as bad as underinflation. Overinflation is any pressure that exceeds the pressure needed to carry the load by 10% or more. Just as with underinflation, overinflation changes the footprint too. The contact patch actually becomes shorter and narrower. This results in the shoulders of the tire scuffing along while only the center of the tire makes full contact with the road which leads to irregular wear patterns and lost tread mileage. Center rib wear, flaking, chunking, erratic depression wear are commonly observed conditions in addition to overall rapid tread wear. A tire that is overinflated by 20% will lose 10% of its tread mileage. In addition, traction is negatively impacted since the contact patch is much smaller than is optimal. The ride is harsher since the sidewall is much stiffer and handling is different since the footprint has changed. Vehicle suspension and steering system components are also affected by the harsher ride and handling due to over inflation. Overinflated tires are also prone to cuts and snags, impact breaks, and sidewall and crown penetrations affect a vehicle’s handling. "

Those links you reference are mostly bool sheet.

And in fact, I have my tires all pumped up at 45 PSI, and:

(1) My milage is about 12% higher.

(2) My tires are wearing EVENLY across the thread. Center of tire shows EXACTLY THE SAME as the shoulders of all tires.

(3) My tires are about 80% worn, and after 52,000 miles. At that rate I should get at least 65,000 before I the wear indicators show.

(4) The degration in handling and grip is INSIGNIFICANT.

So you see, you can't always believe everything you read on those "expert" sites.

[1stToyota]

Originally Posted by SilverGlow

Those links you reference are mostly bool sheet.

And in fact, I have my tires all pumped up at 45 PSI, and:

(1) My milage is about 12% higher.

(2) My tires are wearing EVENLY across the thread. Center of tire shows EXACTLY THE SAME as the shoulders of all tires.

(3) My tires are about 80% worn, and after 52,000 miles. At that rate I should get at least 65,000 before I the wear indicators show.

(4) The degration in handling and grip is INSIGNIFICANT.

So you see, you can't always believe everything you read on those "expert" sites.

12% higher? That seems like a pretty good number for you...I think that's about what the Lucas f.i. cleaner did for you.

And if your tires are 80% worn, grip and handling are already WAY down from what it was when your tires had 50+% tread left on them. Most tire *experts* believe in the Washington's head rule now instead of the old Lincoln's head rule. Stopping distance for the latter can be up to twice the distance.

[1stToyota]

Originally Posted by SeaYa

Thank you! I tried something like this! Snowy parking lot (1-2 inches) and brought my pump. Did 30 psi and 45 psi two times each on a 20 mph turn in the middle of the lot. Here's what happened: 30psi, better traction, worse handling. I slid about 7 feet from my intended line of travel with the car pointed to the outside of the turn. At 45 psi, I had worse traction, but better handling. I slid nearly 12 feet from the intended line of travel, but the car was pointing nearly straight on the way I wanted to go. Did some reading and thinking and maybe this is why: The Yaris is a very light FR, and with an empty trunk, any increases in tire pressure will have a more dramatic effect on the rear tires, eg, smaller contact patch. Since there is already so little weight back there, the rear tires slip to an even greater degree than the front when at 45 psi, hence, the back sliding around more cuts down on the under steer, and you get the feel of better handling. Traction though, another story, I slid 5 extra feet off the 'road', which in straight line braking, could mean running into the hazard you were "looking ahead for and planning for, but still hit because I sacrificed my vehicles engineered performance for an extra 2 MPG"..and by the way, to all the 60psi people...I can't find your actual MPG savings on this post.

To the OP: I've done 35psi (42/44mpg) and 40psi (42/ 47mpg).

Seems to me like the hypermilers are trying to beat the EPA rating by as much as possible for bragging rights. Otherwise, why stop at 60? Why not do 100psi? If your answer is because the tire will burst, then you admit to already pushing the engineered limits of your tire. Otherwise, if traction isn't important to you, why not buy 3 extra spares and run them at 80psi? They're only rated for 60psi, but you don't seem to have a problem with doubling manufacturer recomendations. Let me know how that works out for you.

Good rule of thumb for them is to just throw their gauges away and air the tires up until they resemble motorcycle tires...bet their cars will corner better with a little bit of body-english.

[dg4rez]

Originally Posted by b_hickman11

I wonder if they could make tires out of used condoms.....

some people dont like riding on rims.