Tyre pressue vs fuel economy

Submitted: Tuesday, May 13, 2008 at 21:20
ThreadID: 57584 Views:2217 Replies:11 FollowUps:1
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Does low tyre pressure say 2-3 psi have much of an effect on fuel consumption ??? Whats everyones thoughts on this Why I ask the question is because with the cost of fuel these days every bit helps, and if you are like me I dont check the tyre pressures very often. Maybe I should
Greenant
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Reply By: Angler - Tuesday, May 13, 2008 at 21:29

Tuesday, May 13, 2008 at 21:29
I believe upping the pressure does help.

Every little bit helps said the monkey as he P'd in the river.

Taking off my roof rack improved my economy by about 2 litres per 100.

Pooley
AnswerID: 303672

Reply By: Member - Royce- Tuesday, May 13, 2008 at 21:49

Tuesday, May 13, 2008 at 21:49
Good reminder. I'll check my pressures tomorrow morning before we head off to the big smoke.
AnswerID: 303679

Reply By: Member - Duncs - Tuesday, May 13, 2008 at 22:11

Tuesday, May 13, 2008 at 22:11
Higher tyre pressures definately help with fuel consumption, but don't get carried away.

I made the mistake of thinking high pressures were good, especially on the bitumen. On the last trip up the coast I was running about 45psi and it was great. I shot up the expressway to Newcastle and could see the difference on the fuel gauge.

North of Hexham the traffic was crawling and we decided to go up Buckets Way. With a little bit of rain about and the patched and quite rough road surface I found the car was bouncing and skipping all over the road. It was quite scary so I stopped and pressured down. 40psi on the warm tyres felt a lot better.

When I did a cold tyre pressure check they were at 36psi and have remained there ever since.

I am using a little more fuel but what price safety?

Duncs
AnswerID: 303683

Reply By: Member - Michael O (NSW) - Wednesday, May 14, 2008 at 07:32

Wednesday, May 14, 2008 at 07:32
Speaking of pressures, I note the recommended tyre pressures in my Patrol are 29 front and 36 rear.

I know that 3 litre is a "lightweight" engine but that seems a little odd to me, especially when the car is empty...
Monday I have Friday on my mind...
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AnswerID: 303704

Reply By: Member - Oldplodder (QLD) - Wednesday, May 14, 2008 at 08:15

Wednesday, May 14, 2008 at 08:15
I was told with a car that for every 3 psi above 30psi, up to about 40psi, it gives a 2% improvement in less rolling resistance created by the flexing of the side walls. Most tyres, unless LT, have a maximum pressure of 40 psi.
With the experimentation I have done over the years, it seems about right.
AnswerID: 303711

Reply By: DesF - Wednesday, May 14, 2008 at 16:04

Wednesday, May 14, 2008 at 16:04
Hi, Just a point , I ride a mountain bike about town and when the tyres are pumped up hard ( not the best ride ) , it is amazing the difference in rolling ease .
You tend not to notice the slight reduction in pressure , same in the 4x4 , but it definately affects the freedom of rolling and the steering as well.
Cheers Des.
AnswerID: 303763

Reply By: mattie - Wednesday, May 14, 2008 at 20:07

Wednesday, May 14, 2008 at 20:07
Hi Greenant
We have a Nissan wagon and i just run 35psi front and back regardless of ct and weight, maybe i could let the front down a little probably down to 30, we have 10 ply rated tyres and if you had them at 45 it would not be comfortable.
I have never checked the difference in fuel consumption between pressures i find this interesting as i set them to a practical or comfortable pressure.

Mattie
AnswerID: 303805

Reply By: Member - graeme W (WA) - Wednesday, May 14, 2008 at 21:09

Wednesday, May 14, 2008 at 21:09
Hi Guys.

Just an observation but looks as though most run higher pressures in the rear than the front. Put my hilux loaded up as for a trip the other week over a weigh bridge and the front was 100 kilos heavier than the rear.

Cheers Graeme
AnswerID: 303822

Follow Up By: Steve - Wednesday, May 14, 2008 at 21:53

Wednesday, May 14, 2008 at 21:53
I've noticed that. Far heavier upfront - when unloaded at the back. I remember the Coopers guy on 4wd Monthly dvd saying the vehicle manufacturers do those recommended pressures because so many people are unlikely to air-up in the back when you put a load on so what they do is the lesser of the two evils.
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FollowupID: 569949

Reply By: Andrew - Thursday, May 15, 2008 at 14:47

Thursday, May 15, 2008 at 14:47
Hi All

from what I have been told by the tyre experts (manufacturers) once the pressure is correct for the weight being carried and the speed you are traveling then you will only gain about 2 percent in reduced rolling rsistance.

This may be because making the tyre stand up more makes the gearing higher (fractionally) so the engine is pushing harder.

Of course if this puts you into a better part of your torque band you could be gaining bith ways.

Of course driving steadily and anticipating so you don't need to brake and accelerate as much can make up to 10% difference, at least thats what I notice when the wife (she of the lead foot) gets behind the wheel.

regards

A
AnswerID: 303929

Reply By: Dunedigger - Thursday, May 15, 2008 at 18:09

Thursday, May 15, 2008 at 18:09
One further issue, The higher the tyre pressures, the harder it is in your suspension, Shocks springs & bushes. I now go for a slightly lower pressure and look to see a slight 'bag' in the tyres, but still over 30 psi

Dunedigger
AnswerID: 303969

Reply By: Muddy doe (SA) - Thursday, May 15, 2008 at 19:41

Thursday, May 15, 2008 at 19:41
It is all about finding that perfect balance for your particular set-up. After trying a few different pressures you will find a point where they tyres are not so soft that the vehicle squirms around and not so hard that it rides like a pogo stick.

As Duncs pointed out above - the higher the pressure the less rubber you have on the road.

Like walking on the ball of your foot a rounder harder tyre with high pressure has less of a footprint than a softer lower pressure tyre that has a greater flat spot at the bottom. This leads to extra rolling resistance as the softer tyre has to flex more every time it rotates. The flexing takes more energy to push along increasing fuel consumption as well as creating heat in the tyre which causes the rubber to wear more and shortens tyre life.

I run my tyres on the Prado at 40psi which seems to give a good ride (firm without squirming) while keeping heat buildup to a minimum. At this pressre there still seems to be a good flat section of rubber in contact with the road.

To go for better fuel economy then definately go a bit harder to reduce that rolling resistance to a minimum but just don't go so high as to make the ride too bouncy which may indicate that there is not enough of a contact patch on the road to be safe. Too high a pressure is also evident when the centre of the tread starts to wear out before the edges.

Have fun.
Muddy

AnswerID: 303986

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