Tyres vs Fuel Consumption

Submitted: Thursday, Nov 27, 2003 at 20:12
ThreadID: 8802 Views:1495 Replies:4 FollowUps:1
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I have a 2003 3ltr Turbo Diesel Hi lux ute. I have done 50000km on the original Road Grippers with split rims. 3 tanks of fuel ago I put some 15x7 inch rims and 9.5R15 Desert Duellers in a 604V pattern. I noticed an immediate difference. The car now holds the road so much better. Slightly more road noise. Cornering speed increased, but....

The car dust doesnt seem to be as "snappy" now. It seems to accelerate a little slower and fuel consumption seems to have risen . I haven't done any exact calculations but I always reset the speedo when I fill up and 50km per tank appear to have disappeared. I am told the diameter is approx 9mm larger with the Desert Duellers but surely that will not attribute to approx 10 % difference in KM travelled.
80 % of my driving is at 80 to 110km/hr.(in the country)

What could it be?
Extra mass of the new wheels and tyres?
More rolling resistance?
Me driving faster due to more grip hence greater cornering speeds and on the gas quicker?

I don't really care about the fuel consumption as it is a Company car and I don't pay for fuel but I am interested if any one else has had this experience.
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Reply By: friar - Thursday, Nov 27, 2003 at 20:35

Thursday, Nov 27, 2003 at 20:35
Hi Brett
I have just had the same experiance, changed to a larger diameter tyre
but no wider than the original tyres I went 20m diameter larger ,i did
this to lower my revs at cruising speed only to find it made the hilux
a little less responsive of the mark & on the hills, to fix the problem
i have just fitted a snorkel & mandrel exaust which with the few klms
i have done since appears to given me the power back that i lost
AnswerID: 38718

Reply By: Russell [Pajero] - Thursday, Nov 27, 2003 at 20:53

Thursday, Nov 27, 2003 at 20:53
Have you checked your speedo accuracy, its all a matter of mathematics, increase the diameter of the tyres and change the ratio the speedo is measuring.

Under ADR speedos can be out by as much as 15%, increase or decreases the tyre sizes and watch that change.

Do a speed/distance check at road checks (like outside Ballaraat)

Imagine the variation and surprise that I found.

Coaster bus out by 10%, 1997 Lance out by 15%, Nissan Pajero out by 3%.

It all can make quite a difference.



This should light some fires
AnswerID: 38719

Reply By: Goodsy - Thursday, Nov 27, 2003 at 23:21

Thursday, Nov 27, 2003 at 23:21
G'day Brett
Also own a hilux TD. Run 245/90R15 centipedes for playing. These are about 2.5 inches bigger than standard. The lux is a slug with them on and fuel econmony is up around 2 litres per 100k's. Bigger tyres cost but they are worth it. :)
AnswerID: 38747

Follow Up By: Member - Ross - Friday, Nov 28, 2003 at 07:22

Friday, Nov 28, 2003 at 07:22

About 50mm increase in dia. equates to increase of 160mm in circumference .. i.e. the distance travelled with each wheel revolution, which of course is not shown on your odometer readout.

Figure out how many times your wheels revolve to travel 100km and you'll be surprised how much further you've actually travelled than your odometer says.Rosco
FollowupID: 82630

Reply By: howesy - Friday, Nov 28, 2003 at 18:12

Friday, Nov 28, 2003 at 18:12
The more tyre you put on the road the more resistance. thats number one.
Number two , You have changed the rolling diam. of the tyre. Just how much this has put your speedo out is to be seen but rest assured it will be out and you may be going faster than you think. I suggest you borrow (if you aint got one) a GPS and while your driving at 80 and 100kph check it against the GPS as this will measure your speed by communicating with several satellites. It's a very accurate way to check.
Number three, what are your tyre pressures. Big tyres with low pressures create extreme drag and limit vehicle response. Forget what the tyre says I run 40psi on the highway in all brands and I get exceptional wear ( 110000 to 150000km) Only the tyres go hard as they get old and limit grip in the wet.
Others may disagree but that is my bible and everyone has an opinion, there is never a right or wrong.
AnswerID: 38831

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