Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - View Single Post - Over intlated tires

slowmover · 12-14-2010, 08:06 AM

Where's the evidence that overinflation is beneficial? In forty years of reading about cars (and nearly that in owning them) I've yet to come across that benefit quantified.

Debunking a Mileage Myth: Can You Really "Pump Up" Your Fuel Economy? - Popular Mechanics

Is a typical response. It "may" be that some slight percentage pressure increase results in better handling/braking, but on new cars/trucks this is doubtful compared to the vehicles of the 60's and 70's. CAFE standards would seem to make a pressure increase an easy way for the automakers to achieve better numbers.

The problem is tire design & construction: tire tread and tire casing. Long life and higher fuel mileage offset by ride quality, traction, etc. These mean far more to fuel mileage -- by itself -- than ultimate pressure numbers.

In this linked .pdf from Cummins about big truck fuel economy, check the table of contents for the pages on tires. You'll see that to achieve even a 2% increse that the tires are over-inflated by 20% from optimum. The companies I drove for (or the trucks I leased) had company-mandated tire pressures ranging from 100 to 105 psi, sometimes 110, depending on truck, load, position and other. We were advised to never exceed this. And fuel economy was constantly stressed. (And it takes a good half-hour or longer to inflate 18-tires, I can tell you . . and you NEVER have a spare half hour as a truck driver . . . .

http://cumminsengines.com/assets/pdf...whitepaper.pdf

Let's say that the 32-psi tires on a car are really a bit better with some more air. We're willing to give up ride quality. But we'll have to go to 20% over, or 40-psi to achieve it. A 2% gain? On a 22 mpg car that's barely .5 mpg. And it assumes that the vehicle will operate in a steady state environment that the tires warm to operating temperature after 1.5-hours of driving in order to achieve it. A quite narrow, non-realistic "result" since for most driving that 2% won't be achieved.

Meanwhile we accept degraded performance as tire tread / casing design & construction mean more.

All I see is increased risk at a higher cost (tire damage, braking/handling problems, decreased service life) for a gain that isn't quantified.

Driver skill (or other factors) are more likely explanations of "increased mpg via overinflation" for all miles of driving.

Just buy the best tires, observe the placarded numbers and get a tire gauge that can be calibrated. And use it. And work on skills. Trip planning. The day on which we are sick, non-attentive and it's dark outside, rainy and lot's of traffic is the day it all matters. Just once is what it takes.

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12-14-2010, 08:06 AM	#23 (permalink)
slowmover Banned Join Date: Oct 2009 Location: Fort Worth, Texas Posts: 2,442 2004 CTD - '04 DODGE RAM 2500 SLT Team Cummins 90 day: 19.36 mpg (US) Thanks: 1,422 Thanked 737 Times in 557 Posts	Where's the evidence that overinflation is beneficial? In forty years of reading about cars (and nearly that in owning them) I've yet to come across that benefit quantified. Debunking a Mileage Myth: Can You Really "Pump Up" Your Fuel Economy? - Popular Mechanics Is a typical response. It "may" be that some slight percentage pressure increase results in better handling/braking, but on new cars/trucks this is doubtful compared to the vehicles of the 60's and 70's. CAFE standards would seem to make a pressure increase an easy way for the automakers to achieve better numbers. The problem is tire design & construction: tire tread and tire casing. Long life and higher fuel mileage offset by ride quality, traction, etc. These mean far more to fuel mileage -- by itself -- than ultimate pressure numbers. In this linked .pdf from Cummins about big truck fuel economy, check the table of contents for the pages on tires. You'll see that to achieve even a 2% increse that the tires are over-inflated by 20% from optimum. The companies I drove for (or the trucks I leased) had company-mandated tire pressures ranging from 100 to 105 psi, sometimes 110, depending on truck, load, position and other. We were advised to never exceed this. And fuel economy was constantly stressed. (And it takes a good half-hour or longer to inflate 18-tires, I can tell you . . and you NEVER have a spare half hour as a truck driver . . . . http://cumminsengines.com/assets/pdf...whitepaper.pdf Let's say that the 32-psi tires on a car are really a bit better with some more air. We're willing to give up ride quality. But we'll have to go to 20% over, or 40-psi to achieve it. A 2% gain? On a 22 mpg car that's barely .5 mpg. And it assumes that the vehicle will operate in a steady state environment that the tires warm to operating temperature after 1.5-hours of driving in order to achieve it. A quite narrow, non-realistic "result" since for most driving that 2% won't be achieved. Meanwhile we accept degraded performance as tire tread / casing design & construction mean more. All I see is increased risk at a higher cost (tire damage, braking/handling problems, decreased service life) for a gain that isn't quantified. Driver skill (or other factors) are more likely explanations of "increased mpg via overinflation" for all miles of driving. Just buy the best tires, observe the placarded numbers and get a tire gauge that can be calibrated. And use it. And work on skills. Trip planning. The day on which we are sick, non-attentive and it's dark outside, rainy and lot's of traffic is the day it all matters. Just once is what it takes. .