Tyre size + mods vs fuel economy & range

[physh]

Hi all,

I have a 2002 Toyota Landcruiser FZJ105R GXL, with the A442F automatic.

First up, the mods:
- I had the Parnell VSI (Vapour Sequential Injection) LPG system installed, along with the twin belly tanks giving me 72L of usable LPG.
- I had a 2.5" free flow exhaust fitted (from Beaudesert exhausts in QLD)
- I changed the tyres to 305/70/R16 Mickey Thompson FC-II's, (from standard size of 275/70/R16).
- I lifted the vehicle 3" with OME springs, and had a snorkel, and dual battery fitted.
- A Unichip was installed and tuned to try to improve economy and power.

My speedo is now only 5% out (105km/hr actual speed at indicated 100km/hr), however my fuel economy has dumped in a big way.


Previously I was recording 16-17L/100 on petrol around town, and 15L/100 on the highway.



With new tyres and LPG fitted, I am getting a best of 21.5L/100 on petrol and 24.5L/100 on LPG around town.

I got the Unichip fitted and a dyno tune to try and recover some of the economy, but it has made no difference at all.


I am trying to chase better range for my vehicle, as the plan is to use it to travel the Canning Stock Route.
My best so far is 900KM range, which broke down as follows:
Main ULP 95L = ~ 420km
Sub ULP 50L = ~ 230km
Twin LPG 72L = ~ 250km

Not enough!


A few questions for the knowledgable:

1. If I go back to standard sized tyres, how much would my economy really improve?

2. Can I do the CSR on standard sized tyres (275/70/R16), given I have a 3" lift?

3. Is there any changes I can make to the automatic transmission to improve it's efficiency (power or economy)?

4. Would the exhaust make such a marked difference in fuel economy, given there was very little power gained?

5. Is my best option just to suck it up, and buy a Long Range tank from ARB etc giving me a total of 265L of ULP (1200km at best)?



Cheers
Nick
Canberra
2002 FZJ105R GXL Auto

[jessie928]

your economy problem does not stem so much from the tyres, it stems mostly from your 3" of lift.

ALSO, the unichip is only as good as the dynotune. maybe he did a BAD job with the maps, take it back and ask him its sucking to much juice.

Jes

[physh]

your economy problem does not stem so much from the tyres, it stems mostly from your 3" of lift.

ALSO, the unichip is only as good as the dynotune. maybe he did a BAD job with the maps, take it back and ask him its sucking to much juice.

Jes

Why would the lift make such a big difference in economy?
Would it come down to the extra weight of stiffer springs and shocks, or the bigger frontal area / more resistance from massive amounts of open space under the vehicle?
I dunno!


Yeah very good point about the tune - I'm going to take it back in to get it checked over and retuned just in case, the LPG is getting retuned at the same time too so hopefully that'll help too.

[rixrunner]

Why would the lift make such a big difference in economy?

Wind resistance.... It makes a big differance.

Ricky

[jessie928]

man it makes a HUGE difference.
even a set of rooofracks.....

i installed a 7" lift in my mates truck on day and it would not budge abover 100 on the freeway!

Jes

[TuffRR]

i installed a 7" lift in my mates truck on day and it would not budge abover 100 on the freeway!

In built safety feature. IMO something with a 7" lift should not be allowed out of a 60 zone.

[HotFourOk]

Our bricks on wheels offer enough resistance standard... then if you lift it a few inches higher, the amount of wind resistance is huge!
A 4x4 has a large frontal area it needs t punch through the air, and if you raise this by another 3".. it makes quite a difference.

I'd get the LPG setup looked at, something seems amiss.
You do have a lot of extra weight though, LPG setup, tanks, dual batteries, etc etc... it doesn't seem like much, but it all adds up.

[jessie928]

i installed a 7" lift in my mates truck on day and it would not budge abover 100 on the freeway!

In built safety feature. IMO something with a 7" lift should not be allowed out of a 60 zone.

my mats gq with a 7" has more stability and roll resistance than another mates discovery with a 3" lift

Jes