[zammit]

hey guys just wandering what sorta economy everyone is getting with 31+ tyres with either 1.3carb or 1.6efi..

cheers

[SuziBlu]

Bout 12/13 liters per hundred kays

[zammit]

are they highway miles? do you find your get heaaps less up the bush?

[SuziBlu]

Thats highway, out fanging, full noise, its more like 20 instead of 12, but that is an unfair comparison, you cannot take into account full noise feul milage.

[whincup]

zammit wrote:

are they highway miles? do you find your get heaaps less up the bush?

mines on 31's, carby 1.3, stock gears, and i seem to get better mileage in sand than i do on the highway...

[christover1]

speedo reading and thus the odometre will be out,
so you may be getting more k's to a litre than you think.
But the extra weight and tread width saps power, so I'd guess it use more fuel.

[smiffkid]

my jimny with the baleno 1.6 running 31 inch claws would get 10km per litre that was with a corrected speedo reading
changed to xterrains and got bit over a 11km to a litre
have since changed the gearing and am back to 10km but more responsive power wise
so pretty much the same as a bog stock jimny would get tho running alot bigger tread

[alien]

did a highway drive today - 100km used 11L of fuel... was doing 105-110km/hr most of the time, although i did plant my foot a few times up to 120ish... so i think it did well. These KM figures are off a GPS too.

[ando_zook94]

mines on 31's, carby 1.3, stock gears, and i seem to get better mileage in sand than i do on the highway...[/quote]



yeah im running same setup but only 30's and it really does seem better on sand

[alien]

yup - i get better economy 4wding than on the highway. I put it down to wind resistance.

[nato78]

If you're running 31's and standard speedo, multiply your odometer reading by 1.2, that will give you more accurate km figures

[SuziBlu]

alien wrote:

yup - i get better economy 4wding than on the highway. I put it down to wind resistance.

Crikey. I only sit on 90 or so in the toy, no need to go faster, use more fuel, for a few seconds arrival faster, if I want to go somewhere, I take another car.

When im out playing, she runs around at 3-7,000, mostly above 5k, peddle flat to the floor.

[alien]

haha yeh what can i say... lead foot.

i did do a long drive once down south and stuck to 80-85km/hr the whole way, got something like 480km to 30L (this was with 215/75 HT tyres and g13a engine with extractors and 1.5" pipe)... on the drive home i did the speed limit (100-110) and only go 350km to 30L (still pretty good though).

[Mike57]

There are a four factors which consume energy and fuel and these affect fuel consumption at different times.

WIND RESISTANCE
The energy required to keep the car moving is exponential with speed. That means that at 100 kph it is something like four times 50kph and not double. At highway speeds this is the dominant factor accounting for something like 70% I think of the energy to keep the car moving. Slowing down will significantly reduce fuel consumption in a car like a suzuki Jimny or the like which are not aerodynamically designed.

INERTIA
This is the energy required to start the car moving. In heavy stop start traffic it is not wind resistance which is the killer but the energy required to impart inertia to the vehicle. I forget what % this is but once you are moving it is no longer important.

ROLLING RESISTANCE
This is one that is affected by bigger tyres but more so the tread and width than the diameter. I have not seen any published figures for the rolling resistance of tyres but I am pretty sure mud terrains will be pretty bad. This one becomes important once you are moving and accounts for the energy to keep the car moving along with drive train losses and of course wind resistance.

DRIVE TRAIN LOSSES
This is the friction in the engine, gearbox, transfer case and all the rest of the drive train. This one is not so big but will increase when 4WD is selected. The energy is disippated as heat and this is why the gearbox and diffs etc get hot.

The lowest fuel consumption should occur when moving at a low and constant speed (and at engine revs which are close to the most efficient rev range). One of the reasons off road fuel consumption can be less in a car like a Sierra and a Jimny is that at highway speeds the wind resistance is a killer but that is not critical offroad at low speed. Constant stop/start driving offroad will take its toll though. You will probably find a better write up on the net with actual percentages if you search long enough.

My own experience is that by going up to 215/75 mud terrains on the Jimny I added about 1 litre per 100km to the fuel consumption on comparative highway testing (after taking the different radius into account), so the rolling resistance at speeds does have an affect.

Another affect of large diameter tyres might be that you are running the engine at a less efficient rev range (for the same speed) consuming more fuel. That part I am not so familiar with though so I can't explain how it works.

[alien]

if i remember correctly from when mine was on a dyno the loss through the tcase, gearbox and driveshafts was around 40% in my sierra... this lessens the more power you add.

[JrZook]

alien wrote:

if i remember correctly from when mine was on a dyno the loss through the tcase, gearbox and driveshafts was around 40% in my sierra... this lessens the more power you add.

Errr WTF captain sssiera??

[sideways]

JrZook wrote:

alien wrote:

if i remember correctly from when mine was on a dyno the loss through the tcase, gearbox and driveshafts was around 40% in my sierra... this lessens the more power you add.

Errr WTF captain sssiera??

The more power you have, the lower the resistance percentage.

[Mike57]

That makes sense because the drive train losses are probably almost constant increasing only a small amount when more power is applied.

[christover1]

Mike57 wrote:

That makes sense because the drive train losses are probably almost constant increasing only a small amount when more power is applied.

But then resistance decreases to zero after drive line breaks

[SuziBlu]

JrZook wrote:

alien wrote:

if i remember correctly from when mine was on a dyno the loss through the tcase, gearbox and driveshafts was around 40% in my sierra... this lessens the more power you add.

Errr WTF captain sssiera??

Just say for argument sake, that you have a 100kw motor, and the drive train loss is 40%, ok, cool, there is a 40kw power loss, so you have 60kw to the wheels.

Now, up the anty some, and get a 200kw motor, it still takes the same loss thru the drive train, 40kw, not 40%, you cannot talk precentages, the drive train only needs the same power, regardless of the engine size, there is a very big difference, you now have 160kw to the wheels.

Up the power of your engine by 100%, and gain, a 266% power increase to the wheels

[JrZook]

SuziBlu wrote:

JrZook wrote:

alien wrote:

if i remember correctly from when mine was on a dyno the loss through the tcase, gearbox and driveshafts was around 40% in my sierra... this lessens the more power you add.

Errr WTF captain sssiera??

Just say for argument sake, that you have a 100kw motor, and the drive train loss is 40%, ok, cool, there is a 40kw power loss, so you have 60kw to the wheels.

Now, up the anty some, and get a 200kw motor, it still takes the same loss thru the drive train, 40kw, not 40%, you cannot talk precentages, the drive train only needs the same power, regardless of the engine size, there is a very big difference, you now have 160kw to the wheels.

Up the power of your engine by 100%, and gain, a 266% power increase to the wheels

All good, I was just picking on his funky wording for the explanation

[SuziBlu]

JrZook wrote:

SuziBlu wrote:

JrZook wrote:

alien wrote:

if i remember correctly from when mine was on a dyno the loss through the tcase, gearbox and driveshafts was around 40% in my sierra... this lessens the more power you add.

Errr WTF captain sssiera??

Just say for argument sake, that you have a 100kw motor, and the drive train loss is 40%, ok, cool, there is a 40kw power loss, so you have 60kw to the wheels.

Now, up the anty some, and get a 200kw motor, it still takes the same loss thru the drive train, 40kw, not 40%, you cannot talk precentages, the drive train only needs the same power, regardless of the engine size, there is a very big difference, you now have 160kw to the wheels.

Up the power of your engine by 100%, and gain, a 266% power increase to the wheels

All good, I was just picking on his funky wording for the explanation

Doh

[christover1]

extra heat generated by higher power can increase resistance, due to expansion and oil losing viscosity

[JrZook]

SuziBlu wrote:

JrZook wrote:

SuziBlu wrote:

JrZook wrote:

alien wrote:

if i remember correctly from when mine was on a dyno the loss through the tcase, gearbox and driveshafts was around 40% in my sierra... this lessens the more power you add.

Errr WTF captain sssiera??

Just say for argument sake, that you have a 100kw motor, and the drive train loss is 40%, ok, cool, there is a 40kw power loss, so you have 60kw to the wheels.

Now, up the anty some, and get a 200kw motor, it still takes the same loss thru the drive train, 40kw, not 40%, you cannot talk precentages, the drive train only needs the same power, regardless of the engine size, there is a very big difference, you now have 160kw to the wheels.

Up the power of your engine by 100%, and gain, a 266% power increase to the wheels

All good, I was just picking on his funky wording for the explanation

Doh

But I'll give it to ya, that's one of your best technical descriptions I have ever read. Easy to read and makes sense, just cept the last bit as 100->200kw at the engine will not = 60 -> (200*266% = 532kw ATW)

[SuziBlu]

Talk power at the wheels, not engine power.

60kw*266% = 159.6kw

[alien]

nerds.

[SuziBlu]

lol I live mathematics every day of my life, love it.

Well, till I hit the piss or get into my toy.

[alien]

alright... no googling and no graphics calculator...

x * (e ^(0.5x)) = 0.5

whats the value of x? =)

[SuziBlu]

Exponential functions off the top of my head, at midnight, lol yea goodo.

[alien]

do it in the morning then =P