Discussion in 'Fuel Economy' started by lamebums, May 11, 2008.
35psi on the S2000, 44psi on the Accord, both sidewall max @44psi.
I got my car serviced with Honda and find it hard to find a pump, but last weekend I finally put air in. I was shocked to find the pressure of one tire in the low 20s, another in the high 20s. I decided to pump them up. They are now in the 50-60 range. My last trip to Tuesday dance lessons with low tire pressure clocked in at 63.4 mpg for 20.3 miles. This was higher than the 60 mpg average I expect to get. After the tires were pumped I got an astounding (for me) 65.8 mpg. This is the highest I remember it being for this trip. Plus there was the factor of rain during the trip out that cost a bit of mpg. 25-35psi increased to 50-60psi looks like it increase milege by almost 5 mpg ( I have bumped the 2.4 difference a bit to account for the expected average, rain, and a full gas tank making the car heavier.)
Mine are now up to 56 PSI.
I'm rolling around at 40psi and I'm kind of nervous about going up to the max of 44. The ride is rough enough over the crappy roads here with my lowered suspension as it is now. I work at a dealership so we have the fancy gauges and it's easy for me to just pull in and adjust it, I suppose. I guess I'm shocked to see so many so far over the max pressure with no problems.
running 55 pounds in my saturn on pretty much worn out tires with around 40k with no ill effects so far but I haven't done it for months and months so will have to see how they make it.
Of course, you all read the article that a CleanMPG member found: http://www.officer.com/article/article.jsp?siteSection=19&id=27281
nice find - love the quote
'In 1999 the San Jose Police Department realized a significant cost savings by increasing the pressure in the training fleet to 50 psi. They soon followed up by increasing the pressure in the patrol fleet to 44 psi. For liability reasons, most agencies are reluctant to exceed the maximum pressure listed on the tire for actual patrol vehicles, but they reap the cost saving when going to 50 psi on training vehicles.'
I use 44, which is max load rating on my Goodyear Viva 2's. Could not find the Sumitoyos in my 13 size. 44 pounds shakes the daylights out of me in my lightweight Echo. I'd like to run them a bit lower.
I'm wondering if anyone has done any actual data gathering of the change in MPG versus tire inflation pressure. With the SGII it would not seem a difficult experiment. Guess I'll do some experimenting when I get a chance.
I ran my tires at 50 PSI normally. When the shop flattened them out to 32, I dropped from ~52 MPG to 45 on a commute.
I had to compensate by pressing them up to 52 PSI.
Although my poll answer doesn't change, after seeing diamondlarry run his at 80+ PSI I pressed mine up to 54 all around. I'm afraid to go any higher because of the potholes.
I run mine at 35 PSI - - anything higher than that makes my teeth rattle & vibrates the car too much & gives a real rough ride.
I have stiff suspension, and the car has a ton of understeer so I run 35 front, and 40 rear.
I keep mine at 55psi, but I have found drastic wearing on the front end, with only 17k.
50psi on tires rated at 44psi. No uneven wear after 70,000km with probably another 50,000km left in them. Grips great, glides great, i might go more....
50 psi on Mich MXV5s. Actually better ride than priot OEM Dunlops at 45psi, although less gliding distance.
I think the Dunlops might have been bicycle tires...
I keep it at 44 psi which is the max pressure on my Mazda B2300. With the engine off it's still pretty easy to steer tight turns at low speed. Though I'm not sure if that's how it was at recommended pressure. But it's definitely a lot harder in the Acura, even at 44 psi.
I keep the motorcycle at 21/25, mfg recommended for higher loads. I don't want to overinflate tires on a motorcycle because of possible safety reasons.
I rent cars fairly often and usually pump them up to max pressure too.
It's good to hear people aren't getting uneven wear from overinflating.
50psi since joining this site. My vehicle specified 26R/24F (door label pressure) - REALLY nice ride, but showed underinflation wear within first month after I bought it new, so up to 35 they went at that time. Rides somewhat rough, but hey, it's a 4x4! First two sets of (40,000 mile) tires averaged 91,000 without touching a wear bar, and the first set had to be replaced due to sidewall cracking (due to age/uv exposure) after 4.5 years, not wear. And that was at 35psi. My second set succumbed to alignment wear following a bad pothole encounter and not getting the alignment checked for several weeks after. $Lesson$ learned here.
Can't wait to see what I get now. My guess is that the tire life will be limited by sidewall life instead of wear, so I will be taking extra care to apply some type of good UV protectant for tires at more regular intervals to get the most life out of my tires. If anyone can recommend a good one, please let me know!
I bought struts/shocks with a Lifetime Warranty from Autozone several years ago, and every year I walk into the store and get a new set free, no questions asked. Sort of keeps the ride issues minimized.
I found you can usually get a shop to inflate to max sidewall for an alignment, but no higher due to liability. Some shops are stuck in the mentality of inflating to door label pressure. If they align at "normal" values then you raise the psi afterwards, it may affect the values to the point of causing some wear or steering issues on some car/tire combinations, since "overinflation" can notably increase the sidewall height.
Madcows2010, What does the wear look like? Is it an even section in the very center of the tread or at the edges? Is it "scalloped" or smooth? Can you post a picture? I would rely on objective reports of wear trends by those who have similar cars/tires to yours at higher psi values, and consider having the alignment checked. Realign if necessary, as the cost of premature tire replacement greatly outweighs the cost of an alignment (not to mention the gas savings with proper alignment!).
I have a real concern about this article, but first I’m going to make this statement:
If you have an SUV, don’t hyper-inflate your tires.
To get there, let me start by addressing that web page.
Here’s one statement made: “The proper tire pressure for the Police Crown Victoria is 44 psi. If you look on the sidewall of the tire, you will see that it lists 44 psi max pressure. Regardless of what vehicle you have, use the maximum pressure listed on the sidewall.”
Sgt. Storton goes on to explain why the pressure ought to be different than the civilian version – fundamentally load and speed.
As a check I looked up the pressure specs for the civilian version and the police version of Crown Victorias! Just as I suspected, Ford does specify a difference: 32 vs 35 psi (as listed in Tire Guides, a publication that lists the original tire size and the specified inflation pressure as delineated on the vehicle placard.)
I have a friend who has 2 ex-cop Crown Victorias. He buys them at government auctions. They have lots of miles, but in general are in pretty decent shape. All the “cop” stuff has been taken out, but there are holes that testify to it’s previous usage. (not to mention the way those funky hazard lights blink)
At my request, we went out to his car and looked at the vehicle placard – 35 psi, just like the book said.
OK, second point: Sgt Storton cites Bobby Ore Motorsports driving a Ford Ranger on 2 wheels and the pressure in the tires is 100 psi. The reason the pressure is that high is to make the tire as stiff as it can be, so they can do the trick. At ordinary pressures, the tire’s bead would be pulled off the rim, not to mention trying to support the whole vehicle on 2 sidewalls.
Also the high pressure makes the vehicle easier to tip up. Remember the Ford / Firestone situation and the discussion over the inflation pressure specified by Ford? The 26 psi Ford specified on those Explorers was to reduce the chance that the vehicle would tip over. (There a video of some Ford test engineers doing rollover test and making that verbal comment, but I can’t seem to find it on Youtube)
In the meantime, there has been a lot of testing to determine what things affect a vehicle’s propensity to tip over. Here’s what I remember from a seminar I attended about what makes the vehicle more “tippy” (How’s that for a technical term?): Higher center of gravity, narrower track, shorter wheelbase, higher inflation pressure, stiffer springs / shocks / sway bars.
The bottom line is that standing a vehicle on 2 wheels is a trick and what they do to make the trick work has no bearing on what is applicable on the street. The same is true for racing.
When I was racing on street tires, we used to shave them and run them at about 40 psi. This really helped the initial turn-in response and made the vehicle a little more predictable. But tires used in racing – and trick driving – have short lives. They don’t have to last 50,000 miles.
I want to emphasize that point one more time: If you have an SUV, don’t hyper-inflate your tires.
I'm running 41 psi front & 38 psi rear on my Fit. Am I the only one that adjusts for weight distribution tire loading? I believe the Fit has 62% weight bias to the front.
PS: TireRack claims that tire damage from potholes etc. can be worse with very overinflated tires. I suspect that potholes are even worse with very underinflated tires, but it seems logical that 50+ psi could be bad also.
If I'm not mistaken, the 100psi doesn't have anything to do with how they initiated the trick. They drive the vehicle over a set of ramps with only one side of the car going over the ramps. This is what gets the car up on two wheels. Getting the car up on two wheels in this way with the ramps could also be achieved with the lower stock pressures. Anyway, if you drive correctly for the purpose of achieving max FE, you are not going to come anywhere close tipping a car over even it that could be done by higher pressures.
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