Tire break in and rolling resistance?

[CapriRacer]

Originally Posted By: FZ1
60% of what? It's not 60% of mpg,is it?......

No, it's 60% of the RR.

It's been estimated that 16% of a vehicle's fuel consumption is caused by tires. If you choose a tire that is 25% better for RR (certainly a reasonable number based on that 60% figure), then that is a 4% improvment. That's bigger than the 2% difference caused by the size change I illustrated.

Originally Posted By: FZ1
.......Look,if Diameter increases,it's implicit that tire mass and,therefore,RR would also increase........

I know it's not in the CEC presentation, but if you'll look at the the chart on page 31, you notice that small tires have larger RRC's (Rolling Resistance Coefficient) than larger tires. Here's the link again so you don't have to go back and look for it:

http://www.energy.ca.gov/transportation/...e%20Testing.pdf

BTW, be careful about confusing when to use RRF (Rolling Resistance Force) and RRC. You use RRC if you want to compare tires tested under different load conditions - and in many cases - and certainly when different tire sizes are compared - the test load is different, where in use on the same vehicle, the load is the same.

I go into a more detailed explanation of this presentation here:

http://www.barrystiretech.com/rrandfe2.html

Bottomline: Larger diameter tires are more efficient than smaller diameter tires, even though they weigh more. I know that seems counter-intuitive, but that was the point of Smithers' test.

Originally Posted By: FZ1
..... Again,my point is than "new tire breakin",per se,is not even measureable tank to tank. Lot's of reasons a new set of tires will get different,apparent,or actual,mpg from the tires taken off,but "new tire break in" isn't one of them.

And we agree on that point.

 

[FZ1]

Very interesting links,Racer. Thank you. Look at the RR chart. the RR % only changes apprx 20% between the 13" tires and the 16" tires. Most of us are going to be running the same size tire that we took off,so I can't get a reduction of 25% in RR,even if I drop from 16" to 13" tires,which I'm not gonna do. So the RR reduction in tires of the same size spec will be much smaller than your 25%. It is said that a 10% decrease in RR results in a range of 1/2 to 2% increase in mpg,so you can see,that for most of us,using the same spec tire,the RR difference is going to be so small as to be un noticeable on a tank to tank basis. I do think it would be interesting to see the RR numbers on tires of the same size and category from the different mfgs., say Michelin and Goodyear,etc. Any body got one of those charts available?

 

[CapriRacer]

Originally Posted By: FZ1
Very interesting links,Racer. Thank you. Look at the RR chart. the RR % only changes apprx 20% between the 13" tires and the 16" tires. Most of us are going to be running the same size tire that we took off,so I can't get a reduction of 25% in RR,even if I drop from 16" to 13" tires,which I'm not gonna do. So the RR reduction in tires of the same size spec will be much smaller than your 25%. It is said that a 10% decrease in RR results in a range of 1/2 to 2% increase in mpg,so you can see,that for most of us,using the same spec tire,the RR difference is going to be so small as to be un noticeable on a tank to tank basis. I do think it would be interesting to see the RR numbers on tires of the same size and category from the different mfgs., say Michelin and Goodyear,etc. Any body got one of those charts available?


::::mutters to no one in particular...."Why do I bother?"::::


http://www.energy.ca.gov/transportation/...e%20Testing.pdf

See pages 11 and 12.

That's where I got the 60% value!

 

[SubLGT]

Originally Posted By: CapriRacer
...............Here's the link again so you don't have to go back and look for it:

http://www.energy.ca.gov/transportation/...e%20Testing.pdf

................


Thanks for that link.
I am struck by one of their conclusions:

"Linear correlation studies of rolling resistances with the basic
parameters of tire weight, overall diameter, tread depth, and
UTQG treadwear rating did not generate correlations that
could be considered to represent useful tools to the consumer
for predicting rolling resistance qualities of tires."

 

[FZ1]

Sorry,I looked at the coefficient graph. My point is that RR isn't a huge factor in mpg. Even using your maximum 60% departure in RR,the mpg difference range would be only 3% to 12% of mpg. You could blow that difference on a few extra trips, waiting in line,at the drive thru.

 

[weebl]

Originally Posted By: CapriRacer

::::mutters to no one in particular...."Why do I bother?"::::


Some of us appreciate the insight you bring. And then there are self proclaimed experts who figure they know more than someone who's spent their life working in a certain field. Such is the nature of the internet... or my sister-in-law.

 

[mva]

Originally Posted By: weebl

Some of us appreciate the insight you bring. And then there are self proclaimed experts who figure they know more than someone who's spent their life working in a certain field. Such is the nature of the internet... or my sister-in-law.

+1 Capri - thanks for the interesting links.

I think i actually learned something new from this thread.

 

[mshu7]

To the OP, you might want to compare the weight specifications of your old tires and your new/current tires.

A few years ago I noticed a big decrease in MPG's (and power, I might add) in a Grand Am GT that I owned and after doing much research I realized that the tires I put on were considerably heavier than the ones I replaced.

IMO, tire weight makes can make a very noticeable difference.