Author Topic: Tyre pressure V Fuel consumption.  (Read 5356 times)

Kenneve

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Tyre pressure V Fuel consumption.
« on: February 17, 2023, 05:03:32 PM »
With all the posts relating to Tyre Pressure and Fuel Consumption, I thought it might be an idea to combine the two.
Since I purchased my MK4 EX in April 21, I have always run my tyre pressures at around 31psi Front and 30psi Rear, I guess in the interest of slightly improved comfort
My best fuel consumption on my usual test run, from Solihull to Stratford-on-Avon via the A3400 (about 16 miles each way) has been around 84 Mpg going out and 65 Mpg on return. Its uphill coming back and the road is subject to 50 Mph speed limit with sections of 30 and 40 Mph.
So, following the post on Tyre pressures, decided to increase the pressures up to the recommended level ie 35psi Front 33psi Rear. and the attached picture shows the results achieved:-
As you can see there is a significant difference in fuel consumption, (93.2Mpg Going out & 70.3Mpg Return) even allowing for errors in the 'Fibometer' which in my view are only in the region of 2, or perhaps 3 Mpg and to me, unimportant. There is a very slight difference in comfort, on poor surfaced roads, but I can live with that.
I don't believe there was any significant difference in traffic conditions, or my style of driving.
I would be interested to see if others have found such differences.

« Last Edit: February 17, 2023, 07:12:55 PM by Kenneve »

Marco1979

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Re: Tyre pressure V Fuel consumption.
« Reply #1 on: February 17, 2023, 05:19:15 PM »
Interesting figures! I can totally agree with you: I use around 38 to 40 psi (roads are quite okay in The Netherlands) and it makes quite a difference.
When picking the car up after a service, I immediately notice worse economy and more braking when you lift off (higher rolling resistance). The dealer deflated the tires to normal pressure.

On each tire you can see a maximum pressure which is 60-ish. So there is enough safety left. Also I never noticed any additional wear in the middle of each tire, or at all. And I have been using these tire pressures for over 2 decades.

Jocko

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Re: Tyre pressure V Fuel consumption.
« Reply #2 on: February 17, 2023, 06:31:42 PM »
My Mk 1 Jazz pressures should have been 32/30 but I always ran with 35 front and rear. I got great mpg with no increased tyre wear.

Jazzik

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Re: Tyre pressure V Fuel consumption.
« Reply #3 on: February 17, 2023, 06:45:24 PM »
The Jazz has this nice label on the door jamb. I choose the pressure as recommended for 160 kph/100 mph.
Safe, and still fine in terms of comfort.
If nothing goes right, go left!

Kremmen

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Re: Tyre pressure V Fuel consumption.
« Reply #4 on: February 18, 2023, 04:09:49 AM »
First post - 31 front 30 rear ?

My EX door jamb says 35 front 33 rear so that's what I use
Let's be careful out there !

ColinB

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Re: Tyre pressure V Fuel consumption.
« Reply #5 on: February 18, 2023, 07:35:21 AM »
Several years ago I did a day’s course on a skid pan. As well as having a thoroughly greased area of smooth wet concrete, they increased the tyre pressures to reduce the area in contact. That’s an extreme example, but the principle is that if you increase the pressures above the recommended level you reduce the grip, and you may not find out about that until it’s too late. So if you run with pressures too low, you risk damaging the tyre and having a blowout, if you increase the pressures you reduce your contact with the road. Why not stop trying to second guess the engineers who designed the system and just do what they recommend?

Lord Voltermore

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Re: Tyre pressure V Fuel consumption.
« Reply #6 on: February 18, 2023, 10:29:38 AM »
I've long noticed that keeping pressures  at 35/33  psi (or even a bit higher)  improves mpg significantly, but its good to see it illustrated with actual figures. 

Like many jazz owners in the uk I can remember  when recommended tyre pressures were often in the 20's 
and cross ply tyres common. The new fangled radial ply tyres looked squishy and flat.  And maybe they were and would have benefitted from being 35 psi. 
Time for some of us to stop thinking we know better and run at current recommended pressures. 

Also  I find the accuracy of  tyre pressure gauges can vary a lot. Even good quality ones  and  those allegedly calibrated ones found on garage forecourts .
When I get a new gauge I always compare  it to the average reading of several others.  I had one that ,although apparently reasonable quality, read 2psi higher than average.  Had I been unaware of this I would have been running 33/31 psi thinking it was  35/33. Some gauges are even more inaccurate. 
  Trust a dog to guard your house  , but not your sandwich

Jocko

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Re: Tyre pressure V Fuel consumption.
« Reply #7 on: February 18, 2023, 11:30:08 AM »
The one I use is GS/TUV Approved and ANSI Grade B accuracy ( 2% accuracy).

peteo48

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Re: Tyre pressure V Fuel consumption.
« Reply #8 on: February 18, 2023, 12:11:46 PM »
Being risk averse I always stick to the manufacturer recommended pressures.

John Ratsey

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Re: Tyre pressure V Fuel consumption.
« Reply #9 on: February 18, 2023, 12:52:44 PM »
The pressures increase as the tyres warm up on a journey (more so in summer than winter). How much does this effect contribute to the better mpg in summer than in winter?
2022 HR-V Elegance, previously 2020 Jazz Crosstar

Kremmen

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Re: Tyre pressure V Fuel consumption.
« Reply #10 on: February 18, 2023, 12:55:44 PM »
I've often wondered exactly the same.

When I pump up in Summer is my running hot temp higher than Winter.
Let's be careful out there !

Pine

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Re: Tyre pressure V Fuel consumption.
« Reply #11 on: February 18, 2023, 01:26:13 PM »
The pressures increase as the tyres warm up on a journey (more so in summer than winter). How much does this effect contribute to the better mpg in summer than in winter?
The pressures do increase when motoring particularly on a motorway journey.  I had a BMW that showed the the pressures in the individual tyres.  After being parked in the sun on a summers day for a few hours the tyre pressures on the sunny side of the car would be 3 or 4 PSI higher than the shady side.

Kremmen

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Re: Tyre pressure V Fuel consumption.
« Reply #12 on: February 18, 2023, 01:34:58 PM »
I never pump mine up after any sun has been on them.

Let's be careful out there !

Jazzik

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Re: Tyre pressure V Fuel consumption.
« Reply #13 on: February 18, 2023, 02:16:48 PM »
Being risk averse I always stick to the manufacturer recommended pressures.

Yes, me to... only which one?
On my tire pressure sticker I see this:
~ 160 km/h/100 mph : 2.4 bar/35 psi - 2.3 bar/33 psi
160 km/h/100 mph ~ : 2.7 bar/39 psi - 2.6 bar/38 psi

If 39 - 38 is safe above 100 mph then who am I to think that pressure is not safe below 100 mph as well?
I even dare to add 1 or 2 psi extra!
I have been driving various cars for at least 10 years with tire pressures about 4 or 5 psi higher than recommended.
Handling and comfort still fine and the effect? See my (measured) fuel consumption... See also Kenneve's opening post.
« Last Edit: February 18, 2023, 02:46:15 PM by Jazzik »
If nothing goes right, go left!

Kremmen

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Re: Tyre pressure V Fuel consumption.
« Reply #14 on: February 18, 2023, 02:50:51 PM »
I could be wrong but I thought the higher pressures were for heavier loads ?

Must check the sticker ....... tomorrow
Let's be careful out there !

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