1HZ economy & larger tyres....

Submitted: Friday, Feb 29, 2008 at 22:44
ThreadID: 55063 Views:4837 Replies:4 FollowUps:0
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Howdy Folks, hows things?

I own a trusty 80 series 1HZ diesel. pretty happy with it.

My tyres needing changing & so, as I had some larger 33 inch tyres lying around, I threw them on. While I haven't kept accurate figures, I'd swear that my economy is notably worse. I sorta hoped that with a larger circumference that I may get better economy?

Or, as the tyres are DICK CEPEK FCII (33x12.5r15) which are 1/2 way between all terrains & muds & the last tyres were all terrains 31 inch, does the extra drag & softer rubber have a notable effect on economy the other way?

While we are chatting re: 1HZ economy, any other recommendations? I have extractors, Unifilter (foam filter), 2 inch exhaust & new oil & fuel filters....

Cheers in advance...


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Reply By: Andrew from Vivid Adventures - Friday, Feb 29, 2008 at 22:50

Friday, Feb 29, 2008 at 22:50
Have you allowed for the impact of the under-reading of the odometer due to the larger tyres?
AnswerID: 290139

Reply By: apriti00 - Friday, Feb 29, 2008 at 23:08

Friday, Feb 29, 2008 at 23:08
Not sure how much notable worst is in real figures, the larger tyre will take extra effort to move and hence a probable increase in consumption, one thing you must allow for is the extra distance travelled as the tyre footprint or circumference is bigger when you do your calculations. I would suggest that you check your actual speed with a gps or some other means with reasonable precision as you will find the 33's will about 4 to 5 % out if you started of with oe size tyres. For example the speedo will show 100k and the gps will tell you you might be doing as mentioned about 104 or 105kph. Keep this in mind also when driving as you could end up over the speed limit even if you speedo says your within the limit.Re other recomendations keep in mind that consumption is greatly affected by wieight and driving styles, drive economically and keep the weight down.
AnswerID: 290142

Reply By: Member - Doug T (FNQ) - Friday, Feb 29, 2008 at 23:53

Friday, Feb 29, 2008 at 23:53
Of course the economy will be worse, Bigger tyres = higher gearing = harder work , smaller tyres = lower gearing = easier work, I noticed the differnce when I went to 265/75/R16's from 31/10R/15's years ago , the benefit of standard size is 200rpm less at 100Kph and 1kph speedo error over 6kph error with 15s, the only benefit I would suggest is that with 15" would be easier for towing.

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AnswerID: 290149

Reply By: Member - Shane D (QLD) - Sunday, Mar 02, 2008 at 02:04

Sunday, Mar 02, 2008 at 02:04
Hi Rowen,
When I first bought my 100series (same 1HZ motor) I took it on 300 k drive, you know, just for the fun of it, once i got it home I re-filled it, and it got 12.4l/100k.
Now with the leccy winch, second battery, low lying roofrack, cb/uhf/hf radios and antenna's, slightly bigger but much more agressive 235/85 -16's (7.50 16 equipt) have affected the economy up to around the 14l/100k.
Loaded up for my 6 week trip with a few things including second spare up on the roof rack and grossing close to 3.5 tons got close to 15l/100 over 11000klm, including crossing the Simpson Desert.
I'd say one of the single biggest contribution to my fuel economy lowering was becuase of tyre choice, They are only marginally bigger in diameter (close to 32 inch) but have aggresive lugs that can drag thru the air.
I'd say my tyres would account for 1-1.5l/100k and others who have the luxury of afforting 2 sets of tyres would agree with this theory.

AnswerID: 290329

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