Fuel Consumption Whinge

[siringo]

I don't know if the tyres play that much of a part in it.

Do mud tyres have more rolling resistance than the almost street tyres the Navara's come out with stock? I'm having trouble saying yes. For example, you lock up your rear diff with a locker of some type then turn full lock and see which tyres give you more resistance to the turn, it'll be the street tyres. That tells me that mud tyres offer less rolling resistance (pls don't reply with 'but that's only on full lock blah blah blah), why? Because there is more rubber in contact with the road trying to resist the turn.

The tyres aren't any wider than the stock street tyres the thing came out with. Stock tyres were 255/65, muds are 285/75, yep, the number is bigger, but the mud tyres sidewall is MUCH stiffer, the only rubber on the road are the tread blocks, there is bugger all bulge, unlike the street tyre.

The mud tyres have individual blocks of tread that contact the road, the street tyres have an almost constant block of tread that contacts the road.

The 285 is taller, but it also lets the car sit on a set speed at lower revs. I'm no mechanic, but I'm pretty sure the lower revs would equate to less fuel being pumped into the motor.

The 285's are heavier, this could be where extra fuel is burnt in turning the things from a stop to a roll.

 

[qqc d22]

My expereince says yes im not gonna argue the point i could be wrong but from the use of both type of tyres on my last ute i have to say they do from what ive seen. both sets of tyres were bfg's and the same size with the muddies on it used more fuel. my thought would be that muddies being more individual blocks it creates more resistants. like trying to roll a tractor tyre with massive knobs compared to a bald tractor tyre, probably doesnt make a huge difference up top but on take off every one of thise lugs hit the road and would have to make it harder to start than a smooth surface. like i said i could be wrong its just a thought why but my fuel changed with muddies. different ute to nav to remember.. And i use to flog my old ute everywhere not baby it like i do with this one :shrug:

 

[nakedape]

That tells me that mud tyres offer less rolling resistance why?

Muddies offer more rolling resistance. Why? Because they are (in simple terms) less round than the streeties. Imagine a decagon or similarly multifaceted shape - every time it turns there is resistance from the sharp corners. Alright, that's not strictly true but it illustrates the point - all those large blocks generate an impact force that is transferred through the drive train and must be overcome. Ask yourself why muddies are noisy - friction/ resistance.

The mud tyres have individual blocks of tread that contact the road, the street tyres have an almost constant block of tread that contacts the road.

See above

The 285 is taller, but it also lets the car sit on a set speed at lower revs. I'm no mechanic, but I'm pretty sure the lower revs would equate to less fuel being pumped into the motor.

The taller tyre requires more energy to turn it than does a smaller tyre. Think in terms of a lever & the position of its fulcrum - if the fulcrum is closer to the load than the energy input then the force required to move the load is less than if the fulcrum was closer to the energy input. The fulcrum of the wheel is at the axle, its also where the energy is applied. So if you increase the distance from the axle to the outside of the wheel then you are increasing the load and thus the energy needed. Ergo more fuel.

The 285's are heavier, this could be where extra fuel is burnt in turning the things from a stop to a roll.

Correct, mostly. There is also a need for more energy to maintain the roll. If not, you'd be violating the second law of thermodynamics - and we'll be having none of that around here young man!

 

[johnbritto]

we realy need a energy in motion specialest its true if your tyres are taller biger overall diametre you require less engine revs to make the tyre move a certine speed ,but you do require more power torque to get those revs (more fuel ) its a catch 22 get i mini wheel and give it a push along a flat road then get a truck tyre and do the same thing withh one needs more energy to cover say 20 meters i have my answer and also the mini wheel is lighter to carry around

 

[siringo]

My expereince says yes im not gonna argue the point i could be wrong but from the use of both type of tyres on my last ute i have to say they do from what ive seen. both sets of tyres were bfg's and the same size with the muddies on it used more fuel. my thought would be that muddies being more individual blocks it creates more resistants. like trying to roll a tractor tyre with massive knobs compared to a bald tractor tyre, probably doesnt make a huge difference up top but on take off every one of thise lugs hit the road and would have to make it harder to start than a smooth surface. like i said i could be wrong its just a thought why but my fuel changed with muddies. different ute to nav to remember.. And i use to flog my old ute everywhere not baby it like i do with this one :shrug:

Yep, no. I wasn't having a go at anyone with my post, sorry if you thought I was having a go at you, I wasn't, apologies.

It's hard to argue with real world results. Thanks for your input.

 

[siringo]

The taller tyre requires more energy to turn it than does a smaller tyre. Think in terms of a lever & the position of its fulcrum - if the fulcrum is closer to the load than the energy input then the force required to move the load is less than if the fulcrum was closer to the energy input. The fulcrum of the wheel is at the axle, its also where the energy is applied. So if you increase the distance from the axle to the outside of the wheel then you are increasing the load and thus the energy needed. Ergo more fuel.

Outstanding nakedape, that is the one and only explanation I have read, understand and now agree with, so thank you.

Correct, mostly. There is also a need for more energy to maintain the roll. If not, you'd be violating the second law of thermodynamics - and we'll be having none of that around here young man!

What do you have to do to violate the first law and is it more fun ..... the violate bit that is?

In seriousness, thanks mate, I'm all the more knowledgeable now.

 

[qqc d22]

I didnt think you were having a go at me mate its all good I just didnt want to come accross as what i say is definatly right and everyone else is wrong.
Nakeddrap excellent post pretty much put half of what i was trying to say into real terms that people can understand easier unlike my long winded half ass attempt lol, and i would have to agree with you that a taller tyre is definatly going to need force to move it even at a contlstant speed and especially when accelerating. lower revs will help with fuel economy a bit but not enough to over come the extra load from the taller tyre imo.

 

[nakedape]

What do you have to do to violate the first law and is it more fun ..... the violate bit that is?

Here you go - a link to all four laws of thermodynamics. Knock yourself out

http://en.wikipedia.org/wiki/Thermodynamics

 

[johnbritto]

i think i was right to i just didnt know how to spell fulcrum and thermodynamics been a good thread to look at though very educational and sume good opinions

 

[DieselSmart]

Lots of people complain about d40 auto navaras drinking petrol... there is a reason for this.. they have an o2 sensor in them.

so if you do the normal mods such as exhaust + snorkal you're going to free up the turbo which will see more oxygen go through the exhaust.... since the car has an o2 sensor in it, the o2 sensor will think the car is running really lean and tip petrol in to compensate.... so I would advise against putting a snorkal and exhaust on a d40... that being said it seems to be hit and miss on how many of these cars are affected by this.

There are a few other things you can do, one is check the earths on the sensors, make sure the rail-pressure sensor is okay as I've seen these fail and seen fuel consumption go up to 18-19L per hundred which you really don't want.

You can get devices which you wire into your o2 sensors to allow you to lean out your fuel mixture to increase economy.

As mentioned already mud tires will make a big difference to your power and fuel economy. if you just drive the car on the road put the streets back on it, will be much better to drive on the road

hope that information is useful!

Cheers,
Adam

 

[siringo]

Update.

At last fill, I:

- Used Shell (never use Shell)
- Added some Chemtech Diesel Power (http://www.chemtech.net.au/cr_fueladditives.html)
- Reset the ECM

Just about to hit 1/3 full and just about to clock up 500k's, never done that before.
Will drive until empty and report back later, but it looks like a considerable improvement.

 

[timmyd]

I have a RX nav in manual and got 686km the other day and when I filled up it only took 63L so I had heaps left even though it looked empty on the gauge. That was stop start driving, 2 highway trips one of which had a trailer with 2 bikes on it.

 

[kozzie2t]

i have an 09 stx,it was at 770km and still going but i filled up!6sp man...love it

 

[zebra]

I'm on my second navara first 07 2.5 stx manual getting 9kms to ltr standard then put accessories on canopy bars bigger tyres loose 2kms to the ltr second nav V6 deisel standard running about 10kms/ltr now with canopy/rack bigger tyres lift kit 7kms/ltr
I put it down to wind drag !

 

[KraftyPg]

Gaining 3lph by adding 100 odd kilos of fiberglass and bigger tyres, I'd be putting that down to magic.

 

[zebra]

no magic ! the extra drag from roof rack and the added surface area gained by being 3" taller with lift kit and bigger tyres plus the added effort needed to get the bigger tyres rolling means engine is working harder to get moving and stay moving ! Ask anyone with 35s on and they'll tell you how much power they sap from their engines

 

[KraftyPg]

Oh sorry I read it as going from 10lph to 7lph, not 10k/l to 7k/l

 

[Connaught]

apologies fellas, i did my math wrong and its not at 8.8l/100, its actually right now sittin at around 10.3l/100

and i forgot to mention the canopy, i am happy with the economy i just gotta stop driving so much

 

[siringo]

Well I went as far as I dared last night and got down to 5 litres left in the tank.

So out of 75 litres I did 633 k's which equates to 11.84 ltrs/100k.

All my driving is 100kmh, mild hills, no stop start.

It would be interesting to see what I got doing 60-80 k's everywhere. I read somewhere that there's a sweet spot up to about 90k/mh but after that is when you start really burning fuel. I'm guessing it has something to do with the density of the air and so on.

 

[morticus]

Haha i heard the faster you go with TD the more economical they become...