Welcome to Just Commodores, a site specifically designed for all people who share the same passion as yourself.

New Posts Contact us

Just Commodores Forum Community

It takes just a moment to join our fantastic community

Register

Effects of wrongly inflated tyres

JSVSouth

New Member
Joined
Jun 27, 2011
Messages
12
Reaction score
2
Points
3
Location
Melbourne
Members Ride
VT Berlina / WH Statesman
Hi guys,

Recently I noticed my stock 3.8 auto had been absolutely guzzling the fuel. I checked the trip computer, and it was giving an average consumption of 21l/100km which is ridiculous, considering I never rev it over 3000rpm. After a couple days of grandpa driving, it went down to 19l/100km - still not good enough. Anyway today I checked my tyre pressures and they were all sitting on about 28psi except for the back left which for some reason was only 16psi, which is probably pretty dangerous. Anyhow, I topped them all up to about 33psi.

Is it possible for bad tyre pressure alone to get these sorts of fuel consumption figures? Or is something else at fault (O2 sensors, air filter)? The car's just been serviced by the way, so it's all a bit strange.

Cheers
 

Wombles

Cars cost too much.
Joined
Oct 28, 2009
Messages
2,091
Reaction score
30
Points
48
Location
Gippsland
Members Ride
'72 LJ Torana, '95 VS Acclaim and V8 wagon
I doubt a tyre pressure could cause that much.. Id reckon it would add a litre maybe 2 per 100.
How old is the O2 sensor? Did the fuel filter and air filter get changed?
How olds the plugs/leads?
 

VYMAD

SILVERFOX
Joined
Jun 6, 2008
Messages
1,908
Reaction score
13
Points
38
Age
48
Location
BUNDABERG Q
Members Ride
VY EXECUTIVE S2
What wombles said....
Why on earth don't you check your tyres
more often? I run 38 in mine and check
them with my own compressor each
fortnight or so.
 

SavVYute

Active Member
Joined
Nov 26, 2009
Messages
1,333
Reaction score
21
Points
38
Location
Townsville
Members Ride
VY S V6 Ute Series II 2004
At 38psi don't you get a really rough ride?
I pump mine to the recommended pressure on the tyre placard on the driver's door.
 

KTM mad

Donating Member
Joined
Mar 31, 2012
Messages
249
Reaction score
0
Points
0
Location
down south. West Oz
Members Ride
VT Wagon SII
i bought a 99 VT wagon about 6 months ago. i got it serviced when i bought it, then changed the fuel filter myself the day after. i was lucky to get 500km out of a tank. I just had it serviced again, and got a fuel system/carbon clean while it was there, which made it run so much better and now i can easily get 600km out of a tank. I put a 2.5 inch cat back system in between services too.

i can't see tyre pressures have a major impact on fuel econmy. maybe over the course of a year, it may make a couple of hundred dollars difference, but meh.....
 

Cheap6

New Member
Joined
Jun 19, 2005
Messages
2,498
Reaction score
74
Points
0
Members Ride
VP Exec
Rolling resistance is only a few percent of the energy used to move the car down the road. You can use more fuel by running them low but maybe a few % or so for 15psi below optimum. 38psi is fine, although, yes, noticeably harsher than 28psi but not teeth rattling.

On the tyre sidewall is an inflation limit which you shouldn't exceed - typically 44psi - but other than that consideration it costs nothing to experiment with a range of pressures.

16psi in one probably indicates a slow leak. If you look carefully around the tread you'll probably find a nail or similar in the tyre.

For fuel consumption to jump after a service is a bit sus (that's the way it reads). If they changed the fuel filter, maybe it's leaking, if they changed the spark plugs or checked/replaced the 'leads maybe one's cracked or a lead broken or not properly seated back on the 'plug.

O2 sensors (^) don't last forever so possibly... It won't be an air filter on a fuel injected car. That's a carry over from carburetor days where a restricted intake ahead of the carb could draw more fuel from it.
 

VYMAD

SILVERFOX
Joined
Jun 6, 2008
Messages
1,908
Reaction score
13
Points
38
Age
48
Location
BUNDABERG Q
Members Ride
VY EXECUTIVE S2
At 38psi don't you get a really rough ride?
I pump mine to the recommended pressure on the tyre placard on the driver's door.

No the ride is quite good. Tyre shops
recomend higher PSI for good brand
tyres.
Interestingly my missus had 'Blue
Streak' fitted to her Rio by Jax and
when I checked the pressure, they'd put
40 PSI all round, including the two old
Maxxis on the back, which weren't
replaced.....WTF?
 

SavVYute

Active Member
Joined
Nov 26, 2009
Messages
1,333
Reaction score
21
Points
38
Location
Townsville
Members Ride
VY S V6 Ute Series II 2004
Seems to me the pressures should be determined by what the car weighs and/or what load it is carrying.
All that info is spelled out on the tyre pressure placard inside the drivers door.
Stick to that and you can't go wrong.
 

wrx884

WA's ASR Rep
Joined
Mar 28, 2006
Messages
3,687
Reaction score
38
Points
48
Age
39
Location
Perth
Members Ride
VT Exec/ VT L67 Spac, 5L VP Calais, 77 TC Gemini
Seems to me the pressures should be determined by what the car weighs and/or what load it is carrying.
All that info is spelled out on the tyre pressure placard inside the drivers door.
Stick to that and you can't go wrong.

that is if u got stock tyres mayb, but as u said load does take into account but generally lower profile tyres run a slightly higher pressure so again depends on wats on the actual car.
 

JSVSouth

New Member
Joined
Jun 27, 2011
Messages
12
Reaction score
2
Points
3
Location
Melbourne
Members Ride
VT Berlina / WH Statesman
Cheers guys for the info.

After driving it today for about 20km in light traffic with hills the trip computer is reading 17.2l/100km. Obviously that's still too high, but it's continuing to fall which is good.

Mechanically it should all be in good shape, air filter and fuel filter etc is all up to date. If I don't see an improvement I'll have to book it in again and see what's going on. Hopefully I don't have to. I think that back tyre must have a slow leak, considering it was so low compared to all the others. I'll let you know how it goes.
 
Top