Tire pressure does effect MPG - How much is too much ?

  #11  
Old 01-27-2005, 03:02 PM
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Default went from 39 to 43 MPG

I live in Chicago, and I was noticing very poor MPG since the weather turned cold. I hadn't touched my tires since my last oil change in November.

I added 8lbs to each tire, bringing them up to 33 lbs each (yes, they went down to 25 lbs from the cold weather!). My mileage is up to 43 MPG now! (Normally 51 MPG in warmer weather)

Stephen
 
  #12  
Old 01-28-2005, 09:43 AM
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Hi All:

___A great post by someone who goes by the nick Tempusvn over at Edmunds
Here are published numbers for Goodyear Tires with a Max Sidewall Inflation Pressure of 35 PSI for vehicles that 'recommend' a pressure below the maximum.

#############################

Dry Macadam Surface
(Stopping Distance in Feet)

2001 Dodge Grand Caravan Sport__20 psi__28 psi__35 psi
Full Depth Tread with ABS_________75.5____76.2____75.8
1/2 Depth Tread with ABS__________69.9____68.1____66.3
Full Depth Tread without ABS______98.3____95.9____91.6

1997 Ford Ranger
Full Depth Tread with ABS_________80.8____78.2____77.6
1/2 Depth Tread with ABS__________79.0____74.8____71.4
Full Depth Tread without ABS______97.8____96.5____94.1

#############################

0.02 Inch Wet Macadam Surface
(Stopping Distance in Feet)

2001 Dodge Grand Caravan Sport__20 psi__28 psi__35 psi
Full Depth Tread with ABS_________79.8____78.5____77.1
1/2 Depth Tread with ABS__________84.7____73.7____81.4
Full Depth Tread without ABS_____111.1___110.2___108.6

1997 Ford Ranger
Full Depth Tread with ABS_________83.8____81.5____79.8
1/2 Depth Tread with ABS__________91.5____89.4____84.6
Full Depth Tread without ABS_____131.9___126.0___118.4

#############################

0.05 Inch Wet Macadam Surface
(Stopping Distance in Feet)

2001 Dodge Grand Caravan Sport__20 psi__28 psi__35 psi
Full Depth Tread with ABS_________80.0____81.1____82.7
1/2 Depth Tread with ABS_________103.7____99.7____92.2
Full Depth Tread without ABS_____118.0___112.2___111.7

1997 Ford Ranger
Full Depth Tread with ABS_________89.7____86.0____81.5
1/2 Depth Tread with ABS_________125.7___118.5___104.5
Full Depth Tread without ABS_____142.9___134.8___125.7

#############################

Specialty snow tires on specific snow conditions are, obviously, a special case, but it has nothing to do with the general behaviour of the average passenger tire in most conditions. It also doesn't cover slush where again, the ability to bring maximum point pressure to bear is more important than a big footprint.

Manufacturers set the vehicle 'recommended' pressure for many reasons besides safety and performance. Remember the Bridgestone fiasco with Ford. Ford recommended a low pressure on the Exploder, because it decreased the chance of rollover (at least partially because you couldn't corner as fast with the sidewalls rolling over ). But, that caused the tires to blow out. Bridgestone took the heat, but it was Ford's fault. The tires were rated for higher inflation, and should have been run there.

Most instances now where the vehicle manufacturers recommend lower tire pressures are for comfort.

But, in the vast majority of real world situations you will get better performance and longer tire life by going closer to the sidewall rating. The possible exceptions being mud and some rare snow situations where you are looking more for a snowshoe than a tire. But, Slush, Ice, and Plowed snow all benefit greatly from higher pressure.

What's really bad is when people buy into this 'big footprint' myth and let air out of their tires in the winter

I'm not saying to always inflate tires to the sidewall max, but 99.9% of the time you'll do far better to inflate a bit over what's printed on the vehicle. I know many tire professionals who use the '5 Pounds Over' rule on their own cars. IE, if the vehicle manufacturer wants 28 pounds in the tires, they do 33. If the manufacturer wants 32, they do 37.

This has another benefit. It makes sure you don't run under-inflated, because it's ALWAYS far safer to be a few pounds over than a few pounds under.
___Good Luck

___Wayne R. Gerdes
___Hunt Club Farms Landscaping Ltd.
___[email protected]
 
  #13  
Old 02-07-2005, 08:17 AM
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Default Update from RoyalF on tire pressure

AT last writing, I had increased tire pressure from 30 psi (as it came from dealer) to 35 psi. The tank trip meter settled in around 49 mpg but over time (and traffic) ended at just below 45 mpg. Measuring at fillup I got right at 45 so the trip meter and fillup calculation were on the money, getting just over 500 miles for the tank full. It got pretty cold for the next tank which ended at 42.0 mpg on the trip meter but only 39 mpg when calculated (and I really did not top off to excess). With the fillup yesterday ( high temps in the 60's - sweet -) I increased the psi to 39, with trip meter mpg around 49 but still too early to tell. Will report back in a week or so. Enjoying the feedback and insight (no pun intended).
 
  #14  
Old 02-19-2005, 12:17 PM
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Another thing to keep in mind with regards to tire pressures and inflation pressure is road conditions. If you hit a pothole with your tires inflated to 32psi, they will flex plenty and deform with probably a bit of a pressure spike from hitting the pothole and suddenly compressing the tire far above what it would normally be. If you had the tires at 55psi, the spike in pressure would be far higher; possibly well above 100psi or so. I know I've had friends who blew out tires from hitting potholes and it blew it from pressure alone - no wheel damage.
 
  #15  
Old 02-19-2005, 12:28 PM
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Hi AZCivic:

___I know of at least 2 guys at work that have lost tires when hitting pot holes (Blowout) but I have never heard of a hypermiler with MAX sidewall or above losing them when hitting potholes. Even when running the RE92s at 60 #s for the Attempt last year I did hit potholes and other such debris. No blowouts have been recorded.

___Those of us that do press up our tires to these levels do apparently suffer from a higher percentage of debris stuck in the tires however. I know at least 3 that have lost a tire due to this. I lost an RE92 late last year from a screw just above the tread at the sidewall. I believe Hot_Georgia_2004 lost a B381 with a screw or similar. Rick Reese lost an RE92 to a screw or similar late last year as well.

___Good Luck

___Wayne R. Gerdes
___Hunt Club Farms Landscaping Ltd.
___[email protected]
 
  #16  
Old 03-31-2005, 03:35 PM
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I'm running my stock tires at 42 PSI and my MPG for this tank is currently 49.9 MPG in the past 212 miles. My most recent trip today was about 65 miles and I got 57.5 MPG... I'm using all the tricks I've read here, such as accellerating a bit fast then getting off the gas... Oh, and driving behind semi trucks to help reduce wind resistance. Hot_Georgia_2004 has an EXCELLENT article on this site for driving tips.

Just my $0.02.
 
  #17  
Old 04-04-2005, 10:08 AM
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Default Re: Tire pressure does effect MPG - How much is too much ?

I haven't read all the reponsed, but I pumped my up to 36 based on some guy on hybridcars.com's recommendation. It was scary to drive and hard to handle. I dropped it down to around 32 and has been much more stable.
 
  #18  
Old 04-04-2005, 08:07 PM
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Default Re: Tire pressure does effect MPG - How much is too much ?

You may want to check your alignment or something. 36psi would barely even be noticeable. I'm especially concerned that someone who has experience with a Porsche 911's handling could ever characterize a stock Civic's handling as scary and hard to handle. Definitely get that alignment checked!
 
  #19  
Old 04-04-2005, 08:33 PM
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Default Re: Tire pressure does effect MPG - How much is too much ?

I'll admit that at 42PSI my HCH does get a little bit wibbly-wobbly when I hit an awkard area of the pavement. (e.g. Kirby Rd. when it crosses over the 267 Dulles Toll road bridge in Northern Virginia), albeit this is VERY seldom, and it still handles 1000 times better than my 2003 VW Beetle at the same spot. Really the most notable difference is I can feel every bump in the pavement (which I inform all my passengers I have the tires at 42PSI so they dont think all HCHs drive that bumpy). Get that alignment checked.
 
  #20  
Old 04-05-2005, 05:38 PM
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Default Re: Tire pressure does effect MPG - How much is too much ?

Originally Posted by AZCivic
You may want to check your alignment or something. 36psi would barely even be noticeable. I'm especially concerned that someone who has experience with a Porsche 911's handling could ever characterize a stock Civic's handling as scary and hard to handle. Definitely get that alignment checked!

It was perhaps an exaggeration. The Honda has super light power steering for such a small car. Add some extra PSI to the tires and it gets a little weird at 70 or so.

911 has no power steering and at 22 years old is rock solid at similar speeds....on the track...well... One of our other cars is a 3 series, which has less power steering input than the HCH, so the HCH seems like overkill when compared to those two. Next to our Cherokee, the Honda is the same.
 

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