Go Back   EcoModder Forum > EcoModding > Hypermiling / EcoDriver's Ed
Register Now
 Register Now
 

Reply  Post New Thread
 
Submit Tools LinkBack Thread Tools
Old 10-06-2014, 09:13 AM   #1 (permalink)
EcoModding Lurker
 
Join Date: Oct 2014
Location: England
Posts: 8
Thanks: 0
Thanked 1 Time in 1 Post
What is the optimum tyre pressure for fuel economy?

Hello everyone,

I used to own a car with 17 inch wheels and in the owners manuel it said that 38 PSI was the best pressure for economy.

I now own a car with 15 inch wheels and I have been over inflating all 4 tyres to 38 psi.

I 38 psi optimum for fuel economy? making the tyres have more rolling resistance with a higher psi?

What is the optimum for a 15 inch tyre?

I saw a myth busters episode and they said 30 psi was best.

Or does it depend on the wheel and tyre size?

Any help is much appreciated thank you

  Reply With Quote
Alt Today
Popular topics

Other popular topics in this forum...

   
Old 10-06-2014, 09:59 AM   #2 (permalink)
Batman Junior
 
MetroMPG's Avatar
 
Join Date: Nov 2007
Location: 1000 Islands, Ontario, Canada
Posts: 22,513

Blackfly - '98 Geo Metro
Team Metro
Last 3: 70.09 mpg (US)

MPGiata - '90 Mazda Miata
90 day: 52.71 mpg (US)

Even Fancier Metro - '14 Mitsubishi Mirage top spec
90 day: 70.75 mpg (US)

Appliance car - '14 Mitsubishi Mirage ES (base)
90 day: 60.16 mpg (US)
Thanks: 4,058
Thanked 6,957 Times in 3,602 Posts
30 is definitely not best for minimum rolling resistance... I think you might be mis-remembering that episode.

FYI:



Source: http://ecomodder.com/forum/showthrea...tml#post265379



Source: http://ecomodder.com/forum/showthrea...tire-2721.html
__________________
Project MPGiata! Mods for getting 50+ MPG from a 1990 Miata
Honda mods: Ecomodding my $800 Honda Fit 5-speed beater
Mitsu mods: 70 MPG in my ecomodded, dirt cheap, 3-cylinder Mirage.
Ecodriving test: Manual vs. automatic transmission MPG showdown



EcoModder
has launched a forum for the efficient new Mitsubishi Mirage
www.MetroMPG.com - fuel efficiency info for Geo Metro owners
www.ForkenSwift.com - electric car conversion on a beer budget
  Reply With Quote
The Following 5 Users Say Thank You to MetroMPG For This Useful Post:
bespurcell (11-23-2014), Daox (10-06-2014), dirtydave (10-07-2014), elhigh (10-17-2014), Frank Lee (10-15-2014)
Old 10-06-2014, 10:59 AM   #3 (permalink)
EcoModding Lurker
 
Join Date: Oct 2014
Location: England
Posts: 8
Thanks: 0
Thanked 1 Time in 1 Post
Thanks for replying!

So 55 psi would be optimum?

I know my spare wheel in my boot the space saver is about 60 psi.

I would be concerned about the tyres at that pressure. Could they blow out at speed? Would I have to check with the manufacturer?

How many people on here are rocking tyres over 50 psi? Any problems?

Thank you
  Reply With Quote
The Following User Says Thank You to mada88 For This Useful Post:
mcrews (10-06-2014)
Old 10-06-2014, 11:15 AM   #4 (permalink)
Administrator
 
Daox's Avatar
 
Join Date: Dec 2007
Location: Germantown, WI
Posts: 11,203

CM400E - '81 Honda CM400E
90 day: 51.49 mpg (US)

Daox's Grey Prius - '04 Toyota Prius
Team Toyota
90 day: 49.53 mpg (US)

Daox's Insight - '00 Honda Insight
90 day: 64.33 mpg (US)

Swarthy - '14 Mitsubishi Mirage DE
Mitsubishi
90 day: 56.69 mpg (US)

Daox's Volt - '13 Chevrolet Volt
Thanks: 2,501
Thanked 2,585 Times in 1,553 Posts
The test shows higher pressure is better period. How high you want to go is up to you. I typically just pump mine up to 50 psi and call it good enough. There is diminishing returns the higher you go.
__________________
Current project: A better alternator delete
  Reply With Quote
Old 10-06-2014, 11:56 AM   #5 (permalink)
Not bad for a machine
 
dirtydave's Avatar
 
Join Date: Mar 2014
Location: Baltimore
Posts: 1,024

Maechunbu - Retired - '00 Kia Sephia 1.8I4 16VDOHC
Last 3: 45.28 mpg (US)

Slasher - '96 Chevy Corsica 2.2L 3speedauto
Duct Tape Aero Crew
Team Chevy
90 day: 34.76 mpg (US)
Thanks: 279
Thanked 242 Times in 179 Posts
I have mine set to 5 over sidewall max in the summer and 10 over that in the winter.
One of the best mods you can do.
__________________




  Reply With Quote
Old 10-06-2014, 12:26 PM   #6 (permalink)
Master EcoModder
 
mcrews's Avatar
 
Join Date: Oct 2009
Location: Texas
Posts: 3,523

The Q Sold - '02 Infiniti Q45 Sport
90 day: 23.08 mpg (US)

blackie - '14 nissan altima sv
Thanks: 2,203
Thanked 663 Times in 478 Posts
Quote:
Originally Posted by mada88 View Post
Thanks for replying!

So 55 psi would be optimum?

I know my spare wheel in my boot the space saver is about 60 psi.

I would be concerned about the tyres at that pressure. Could they blow out at speed? Would I have to check with the manufacturer?

How many people on here are rocking tyres over 50 psi? Any problems?

Thank you
Maybe spend some time using the search button.....but use 'tire'

probably over 100 threads on increasing tire psi for better mileage.
it would save having all those w/ high psi having to answer here to relive your concerns.
__________________
MetroMPG: "Get the MPG gauge - it turns driving into a fuel & money saving game."

ECO MODS PERFORMED:
First: ScangaugeII
http://ecomodder.com/forum/showthrea...eii-23306.html

Second: Grille Block
http://ecomodder.com/forum/showthrea...e-10912-2.html

Third: Full underbelly pan
http://ecomodder.com/forum/showthrea...q45-11402.html

Fourth: rear skirts and 30.4mpg on trip!
http://ecomodder.com/forum/showthrea...tml#post247938
  Reply With Quote
Old 10-06-2014, 07:03 PM   #7 (permalink)
Master EcoModder
 
101Volts's Avatar
 
Join Date: Dec 2012
Location: Pennsylvania
Posts: 506

Woody - '90 Mercury Grand Marquis Wagon LS
Last 3: 19.57 mpg (US)

Brick - '99 Chevrolet K2500 Suburban LS
Last 3: 12.94 mpg (US)

M. C. - '01 Chevrolet Impala Base
90 day: 17.09 mpg (US)

R. J. - '05 Ford Explorer 4wd
90 day: 16 mpg (US)
Thanks: 934
Thanked 34 Times in 28 Posts
Quote:
Originally Posted by dirtydave View Post
I have mine set to 5 over sidewall max in the summer and 10 over that in the winter.
One of the best mods you can do.
Are you sure you didn't swap the numbers around by mistake? I thought normally a person would put the pressure lower in the winter than in the summer, for traction.
__________________



  Reply With Quote
Old 10-06-2014, 08:52 PM   #8 (permalink)
5 pin sensor
 
Join Date: Sep 2014
Location: Dallas
Posts: 350

Zippy - '96 Honda Civic Hx
Team Honda
90 day: 40.77 mpg (US)

Boring - '11 Ford Fusion Sel
90 day: 21.88 mpg (US)
Thanks: 38
Thanked 73 Times in 56 Posts
Quote:
Originally Posted by 101Volts View Post
Are you sure you didn't swap the numbers around by mistake? I thought normally a person would put the pressure lower in the winter than in the summer, for traction.
Nope. Google search winter rally tires.

Also running 35 psi on a 150 degree asphalt raises tire pressure from heat expanding the oxygen. When winter hits in Texas without touching the tires I lose about 10psi from the abient temp. The tire also does not get up to the same heat from friction of the road, that is to say the rolling resistance generates heat as well as getting heated from contacting the 150 degree pavement. That 35 psi in the morning can turn into 50psi really quickly on a long drive. However 35psi on a 35 degree pavement with a 35 ambient temp really won't affect the tire pressure so you would need to add more air pressure to get that same pressure youre running on long drives in the summer

Running nitrogen in the tires would cure both problems and tire pressure would remain constant through the temperature changes as it is not as heat sensitive as oxygen molecules

So yes I'm sure he's correct as I am forced to check pressure as Texas really only has summer and two months of winter every year lol
__________________
Current: 1997 civic lx
Past: 1998hx/1996hx/1997lx/1997hx Cali/1997hx
OG lean burn member

My civic thread

Last edited by Chrysler kid; 10-06-2014 at 09:09 PM..
  Reply With Quote
Old 10-06-2014, 08:52 PM   #9 (permalink)
EcoModding Apprentice
 
adam728's Avatar
 
Join Date: May 2008
Location: Michigan
Posts: 161

Mazda3 - '08 Mazda 3 S
90 day: 29.65 mpg (US)

DR650SE - '13 Suzuki DR650SE
90 day: 46.16 mpg (US)

Wife's - '12 GMC Terrain SLE-2
Thanks: 2
Thanked 22 Times in 18 Posts
Quote:
Originally Posted by 101Volts View Post
Are you sure you didn't swap the numbers around by mistake? I thought normally a person would put the pressure lower in the winter than in the summer, for traction.
Depending on the type of snow/ice cover on the road a higher psi and smaller footprint could give better traction due to higher ground contact pressure. Same resaon a skinnier tire works better than a wide one in snow (unless you are talking bottomless snow offroad, where those awesome polar exploration trucks use gargantuan tires for flotation.
__________________
  Reply With Quote
Old 10-07-2014, 07:24 AM   #10 (permalink)
Tire Geek
 
CapriRacer's Avatar
 
Join Date: May 2008
Location: Let's just say I'm in the US
Posts: 794
Thanks: 4
Thanked 388 Times in 237 Posts
Quote:
Originally Posted by mada88 View Post
Hello everyone,

I used to own a car with 17 inch wheels and in the owners manuel it said that 38 PSI was the best pressure for economy.

I now own a car with 15 inch wheels and I have been over inflating all 4 tyres to 38 psi.

I 38 psi optimum for fuel economy? making the tyres have more rolling resistance with a higher psi?

What is the optimum for a 15 inch tyre?

I saw a myth busters episode and they said 30 psi was best.

Or does it depend on the wheel and tyre size?

Any help is much appreciated thank you
First, in the US, every car has a vehicle tire placard which lists the original tire size and the specified pressure for that size. I believe other countries use a placard as well - may be even the same one. Since 2008 the placard is supposed to be on the driver's doorframe, but prior to 2008 it could also be found in the glove box, on the fuel filler door or in the trunk (boot).

Second, "optimum" means there is a peak value - and for RR, increased pressure always results in better RR - up until the tire explodes. However, beyond a certain point, the increases in pressure don't result in much improvement in RR.

Third, the maximum pressure listed on the sidewall of a tire is exactly that - a maximum. It is NOT a recommendation. It also is relatively arbitrary - which I explain here:

Barry's Tire Tech - Load Tables

About 1/3 of the way down, I talk about "The notes on page 1-34", which deal will the maximum pressure. Others may disagree, but I think the maximum pressure is not something that tire manufacturers do a lot of thinking about as the load table is what is important and the load tabl;e defines the relationship between pressure and load.

Fourth, while RR improves with inflation pressure, other properties don't. The most obvious is traction which likely peaks, then goes down. This is the result of the shrinking contact patch. The problem here is that this is not well documented. There aren't charts for the literally thousands of different tires out there showing where that peak is. What we have is anecdotes.

Also, tire wear is somewhat tied to inflation pressure, with increasing inflation pressure causing more wear in the center of the tread. Again, this is not well documented - in fact hardly documented at all. All we seem to have is those ubiquitous anecdotes.

Other properties that seem to be adversely affected by increased inflation pressure are groove wander (aka tramlining), puncture resistant, impact resistant, and durability - again, anecdotal.

And lastly, I am NOT a fan of using a lot of inflation pressure, mainly because of the compromise in traction. So I don't recommend using more than 5 psi over the placard pressure. Other people have different opinions.

__________________
CapriRacer

Visit my website: www.BarrysTireTech.com
New Content every month!
  Reply With Quote
The Following 2 Users Say Thank You to CapriRacer For This Useful Post:
bespurcell (11-23-2014), MetroMPG (10-07-2014)
Reply  Post New Thread


Thread Tools




Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
Content Relevant URLs by vBSEO 3.5.2
All content copyright EcoModder.com