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.:thumbup:

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.

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 :( )

Opps, wrong thread

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. :D

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