Tyre Pressure and Fuel Consumption

Submitted: Sunday, Feb 10, 2008 at 21:03
ThreadID: 54439 Views:6208 Replies:10 FollowUps:0
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I was reading thread 54414 and one of the replies pointed the thread to the following website :-

http://www.carbibles.com/tyre_bible.html

I went to this site which I found very interesting because I know very little about tyres. On page 2 there was a section about tyre pressures and fuel economy. One of the points was that the author inflated his tyre to 10% less than the maximum rated pressure for the tyre. The second was that by increasing his pressures e.g from 32/28 psi to 40 psi all round his fuel economy changed from 15.7 mpg (US) to 20,32 mpg (US). That is roughly a 1:1 ratio. Increase your pressures by about 25% and increase fuel economy by about the same.

Applied to my vehicle I would have to run my tyres at about 45 psi (that is exactly what the tyre place set them when I got new tyres. I dropped them to 34 psi because the ride was too rough) and my fuel economy would increase from 20 mpg to about 28 mpg.

In your collective experiences is this correct.

Note: I have spent about 3 hours searching this web for information on this without success.
My vehicle is a 2004 Hilux Cab chassis 3.0 l Td.
My tyres are Bridgstone DD 9R15LT 104N

Regards,
Bob
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Reply By: desert - Sunday, Feb 10, 2008 at 21:21

Sunday, Feb 10, 2008 at 21:21
Makes sense really. Inflate tyres to 60 psi and get fantastic, unbeleivable economy - if you can keep it on the road!
AnswerID: 286782

Reply By: Willem - Sunday, Feb 10, 2008 at 21:24

Sunday, Feb 10, 2008 at 21:24
We were airing up after coming off the sand at Beachport SA and an old fella came across for a chat asking what pressures we had been running. I said 15psi. Anyway he said that he ran his Hilux Van at 65psi on the bitumen so that he could save on fuel. Then I come across a bloke in Birdsville who ran his tyre pressures at 70psi on a Landrover. Might be a tad uncomfortable methinks.

Anyway. Yes, less rolling resistance but at what cost to the rest of the moving parts on your vehicle. You might save dollars on fuel consumption up front but you could lose out when having to replace broken parts. Probably much of a muchness.


Cheers
AnswerID: 286785

Reply By: Footloose - Sunday, Feb 10, 2008 at 21:25

Sunday, Feb 10, 2008 at 21:25
The correlation between tyre pressure, wear and consumption is well known.
Sadly the higher tyre pressures don't always provide a comfortable (or in some cases a safe) ride.
On one occasion I inadvertantly pumped my tyres up to over 45 psi. It handles like a loaded dog, all over the highway. Not good.
AnswerID: 286786

Reply By: Member - Oldplodder (QLD) - Sunday, Feb 10, 2008 at 22:12

Sunday, Feb 10, 2008 at 22:12
Yes,does work.
Read something similar about 20 years ago that for normal car tyres every 2 psi aboe 30psigives about 2% improvement.
Find it does, due to less rolling resistance. But there is a point , or to say, a pressure where it doesn't make that much difference, and you just wear the middle of the tyres and have a hard ride. :o)
AnswerID: 286803

Reply By: Jimbo (WA) - Sunday, Feb 10, 2008 at 22:51

Sunday, Feb 10, 2008 at 22:51
I normally run my BFG's at 46 psi around town and on the bitumen and don't get a rough ride, and my fuel economy is 11 ltrs per 100 km (25.68 mpg) .

I also get about 90 - 100,000 kms out of my tyres - and I stress that the ride is NOT rough.

This is on LT tyres and a vehicle that weighs substantially more than off the show room floor.
AnswerID: 286816

Reply By: T-Ribby - Monday, Feb 11, 2008 at 12:33

Monday, Feb 11, 2008 at 12:33
Hi Bob, interesting thread.
My philosolophy regarding tyre pressures is firstly safety, secondly wear. There are other ways of improving fuel economy. To me, overinflation and underinflation are both dangerous at highway speeds - saving a few dollars at the pump won't benefit you if you're dead because of tyre failure. I have to ask the question - is less or more of the rubber footprint adhering to the road (tarseal) safer, especially in the wet?
cheers
T.R.
AnswerID: 286862

Reply By: pathfinder - Monday, Feb 11, 2008 at 13:30

Monday, Feb 11, 2008 at 13:30
I think you can get away with quite high pressures on dry bitumen if you've got comfy suspension - not too firm coils and good shocks such as Bilsteins. However, there will obviously be a point at which the edges of the tyre will not be in firm contact with the ground resulting in uneven tyre wear (worn out tyre crowns) and therefore false economy.
AnswerID: 286871

Reply By: jeepthing - Monday, Feb 11, 2008 at 15:06

Monday, Feb 11, 2008 at 15:06
Cooper Tyres have a booklet called 4WD Drivers Guide there a very good section on Tyre Pressure, in particular the "4 PSI" Rule which applies to bitumen road use only which I follow and I believe works. Proper inflation is dependant on many factors such as what tyres you have, type of vehicle, amount of load, how the vehicle is driven and the condition of the road. As a starting point inflate the tyres to the recommended tyre pressure on your vehicles placard.
Drive several kilometres to ensure they are at operating temperature then check again. Coopers say they should be about 4psi above the cold pressure. If the pressure is more than 4psi above cold pressure you should add more air at cold pressure, this is because there is too much friction which builds up more heat than desirable.
Conversely,if they are less than 4psi the cold pressure is too high.
I believe this works and is a good rule of thumb to determine correct pressures when loaded and unloaded, otherwise it is nothing more than guess work.


AnswerID: 286885

Reply By: Leroy - Monday, Feb 11, 2008 at 15:38

Monday, Feb 11, 2008 at 15:38
I can save almost 1l/100km by running 45psi in a VT Commodore which means I'm getting clost to 9L/100km. But you have to watch the way your tyres wear also!

Leroy
AnswerID: 286889

Reply By: richor - Monday, Feb 11, 2008 at 18:27

Monday, Feb 11, 2008 at 18:27
To All,
I know that increasing your tyre pressures decreases your rolling resistance and hence better fuel economy but I must admit I was a bit astounded when I saw the fuel savings in the article and thought is was a bit much, but the rest of the information seemed reasonable accurate.

I normally set my tyre pressure to the 4 psi rule which generally seems to be close to the mark when it comes to looking after the tyres, getting a comfortable ride and getting a reasonable fuel economy. When I got my Hilux back from the tyre place I went for a drive down a typical bitumen country road and had trouble keeping it on the road at 100 km/h. When I checked they were all set to 45 psi. I am getting a canopy put on it a few weeks when they finish building it and it weighs about 200 Kg so I will have to redo the pressures.

Thanks for the replies. It is a great forum.

Bob
AnswerID: 286919

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