markrivers

Hi guys!

i got a little bit bored this 3 day weekend,
so i have decided to do what my " Prius" friends are doing with their cars. Hypermile.

Basically, they put a lot of air on their Low Rolling Resistance Tires for better mpgs.
most do 45, while i know some who puts 60psi.

Hmm.. so let's test that on a 2013 RX 350 running on regular unleaded 87 octane ( Costco gas) with OEM tires ( Dunlop Grandtek) and 19 inch rims.
every gauge was reset to ZERO
trip A
average mpg
average speed

here's my baseline: i do 85% highway and 15 % city driving.



and here's what happened after putting 38psi ( too scared to do 40)



and nearing the end of my commute



and at here's the final



Disclaimer: i don't recommend this practice at all.
Overinflating the tires can give you a lot of mpgs but it can be unsafe
Although, aside from a bumpier ride, i didn't feel any difference in the drive.

oohpapi44

iTrader: (1)

Could've just watched Mythbusters and come to same conclusion.

Not going to be unsafe and 'overinflate' is a misnomer. Tire is rated for 60psi so anything under won't be overinflating. Just exceeding what the manufacturer suggest for optimum ride comfort. You want to bounce around but get more mpg, then you've got plenty of room to play with. Go past what tire is rated for, then we are talking overinflating.

Props for experimenting though.

wase4711

if it ever warms up here,(7 degrees right now), and once I get the annoying dash rattle fixed,(only 250 miles, and until it warms up, no use asking the dealer to fix it), I plan on putting 40lbs in my tires, and see what I get. I put 45 in my 2008rh, and got 30mpg on a regular basis..I find it hard to believe you are getting those kinds of MPG's doing 60+mph...

corradoMR2

^^^ yeah, agree, hard to believe the 40 mpg. It's tough not to be skeptical since one can expect a 5-10% increase but not 35%.

By any chance, was your 27.5 mile a round trip on the same route? For instance, there could have been a slight downward grade as well as a backwind in the direction the tests were run favoring the the results, but if you went back on the same route, it would average out.

BTW, thanks for sharing and if anything, some of us will test this out over the next few days - I will.

fastnoypi

The max inflation on the sidewall is a safety max at cold tire pressure prior to bursting concerns that can be caused by bumps and road hazards once the tire air warms up.

Exceeding past the manufacturer's max load cold tire pressure recommendation will lead to a smaller contact patch with excessive wear in the center of your tire . It will affect handling characteristics and braking distance which is unsafe. You're compounding the risk of a blowout being in a heavy SUV.

Not worth the risk to the safety of yourself, passengers and others on the road, just to save on a few gallons of gas IMO.

TechNut

Is your car All Wheel Drive, or just Front Wheel? That will also impact mileage.

dctex99

I believe that my Michelins say do not exceed 44 PSI. On many cars that are brought over on ships from Japan they pump them to 60 PSI for the trip and then adjust them at the dealership; it is kind of a trade secret, but 30 days on a ship with normal air can cause flat spots in in our fine Steel belted radials. I have a friend who bought a Toyota and they forgot to adjust, and only when he complained of the hard ride did they adjust them. No blowouts; never hear of problems; tires can take a beating; think slaloming; when I did that, they check your wheel beariings, air your 32 PSI tires to 40 and require a helmet; did it a lot in my youth; and once after a run where I spun out I checked the air in that hot tire; 52PSI,,,,never saw blowouts....just a thought....

markrivers

2013 RX 350 FWD

Experiment was done here in SoCal. 4:30am ( no traffic!)
I-5 and then I-405 on a 57 F temp ( as you can see on the dash).
it's 85% highway and 15% city driving.
this is my route to work approx. 27 miles one way ( from my garage to the parking lot)
it WASN"T a round trip drive.

cruise control was ON at 70mph.
i change lanes every now and then, hence the 70+ mph on the picture.

the baseline was done on the same route BUT at 72F and 34psi a few weeks ago.

oohpapi44

iTrader: (1)

When I stated manufacturer, I should have specified car manufacturer (Lexus) recommends as best tire pressure for optimum ride comfort.

Believe you'd still have to exceed the tire manfacturer rating pretty far to see a significantly smaller contact patch. Todays tires stiffen the sidewalls (versus bubble out days of old). Agree the blowout risk increases significantly, but I think handling and braking wouldn't be affected too much with todays tires. Ride quality would be horrible though. Agree that none of it is worth it though. Especially in a city like NY with our huge potholes.

rayaans

My RXh is only doing 24 UK mpg at the moment

fastnoypi

I used to think the same thing till i was passenger in my co-workers IS300. He absolutely doesn't know anything about cars and maintained his tire pressures by the max psi indicated on his sidewalls. He would complain about tires and brag about how his car is a "sleeper" drift car because it was tail happy. I had to explain to him his tire pressures were so high it upset the handling and grip he had in the rear. I happened to be in the car when he had a blowout while on a lunch break. His tires were very much like the tire as pictured here on the right.

oohpapi44

iTrader: (1)

Not disagreeing with you. NY and NJ are different animals when it comes to tire pressure, compared to doing the same in CA or FL. It's asinine to max out tire pressure here and what happened (blow out) is exactly whats going to happen when hitting a pothole with a rock hard tire; or bent rim.

Would have been great to see the psi numbers associated with the picture you posted.

fastnoypi

My experience happened while i was living out in Scottsdale AZ, very flat and dry. I don't recall what make tires my co-worker had but i assume they were the OEM tire make and model that his IS300 came with.

I absolutely agree with you regarding maxing out tire pressure in the tri-state area. Too many potholes and road imperfections from the constant freezing and thawing here.
I've never been led astray to used the recommended inflation pressures found in the manual. I often get very good tire life and even wear patches unless i'm late to realize an alignment problem.

raylor4

David Letterman said the potholes in New York City are so big, you have to turn on your headlights half way in, and there's a Starbucks at the bottom.

oohpapi44

iTrader: (1)

LMAO, that's funny. Now if he wasn't only half joking:



lol that was a recent sinkhole as an extreme, but here are a couple of doozy potholes:







Supposedly every dot on this map represents a pothole that has been filled.



Ummm and that's just for one winter's month.