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Old 08-29-2011, 04:01 AM   #1 (permalink)
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Aged tyres = LRR ??

G'day All.
I've had a jump in fuel economy in Zed over the last two tanks that has me wondering why.

My 3 tank average was 21.13mpg, then I put an old pair of tyres on the front of my car halfway through the next tank.
That tank returned 22.17mpg, a 4.9% increase and my best tank up to that point.
My latest tank (first full tank with these tyres) returned 23.18mpg, a further 4.6% increase, for a total of 9.7% from the old average.

These tyres still have lots of tread but the rubber is well cured (hard), could the rolling resistance have decreased as a result? Could it make that much difference?

Please understand, these tyres aren't unsafe. I can still push hard through a roundabout without under steering.

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Old 08-29-2011, 07:15 AM   #2 (permalink)
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I'm not a rubber chemist, but I would think that aging rubber would make the internal friction (hysteresis) higher and that is the largest contributor to rolling resistance. I would tend to think this would be a small change and certainly not as dramatic as you have posted. So I tend to think that the answer lies elsewhere.

One possibility is that given the wide range of values of rolling resistance within a given size, it is much more likely that the difference is caused by the inherent difference between the current set and the previous set.
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Old 08-29-2011, 12:46 PM   #3 (permalink)
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Seeing that you stated that these tires have a lot of tread on them, I would say the increase in mileage is probably due to the belts not being worn out. When they are newish they are stiff and keep rolling resistance down. I noticed this when I had to throw on my spare recently. ( sadly it was 25 years old and shed the cap two weeks later )
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Old 08-30-2011, 06:26 AM   #4 (permalink)
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Opps, wrong thread
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Old 09-03-2011, 07:42 AM   #5 (permalink)
Wanting more for less
 
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Join Date: Jan 2011
Location: New South Wales, Australia
Posts: 313

Metric - '94 Honda Magna 250
Motorcycle
90 day: 69.83 mpg (US)

RedCelica - '94 Toyota Celica ZR
90 day: 35.97 mpg (US)

i30 - '12 Hyundai i30 Elite
90 day: 39.84 mpg (US)

i30-22 - '12 Hyundai i30 Elite
90 day: 39.22 mpg (US)
Thanks: 23
Thanked 73 Times in 45 Posts
Thanks for the replies.
Either (or both?) of you comments could be right.
Now I find myself looking forward to these tyres wearing out, so I can try a set of four "real" LRR tyres.

I filled up today, for a result of 23.59mpg. Another small increase, maybe as I get used to the better coasting?

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