Discussion on tire efficiency

[Ernie Rogers]

Originally Posted by Blue Bomber Man

. . . I think I disagree with the stiffness argument.

Train wheels are made of steel and thus are exceptionally stiff. They use these tires specifically for this reason, since the majority of a train's losses are due to rolling resistance. This stiffness decreases that internal resistance that you speak of.

Hello, Blue Bomber. You made a good argument. Let's study the question.

Work = force x distance. What we don't want is to put work into the wheel material. For the train wheel, force is a given number, the weight of the train and all its cargo. So, you gain by making the distance as small as you can, and steel wheels don't deflect much at all. (A smart guy willl point out that the rails often deflect a lot, but they spring back and return most of that strain energy.)

Okay, now for the car tire. In this case, it's the distance (related to the contact patch) that is fixed, based on the air pressure in the tire. So, now you want to make the force to flex the rubber as small as possible, and that means to choose material that flexes very easily.

In both cases, materials with low internal friction are the best to use.

Ernie Rogers

[Ernie Rogers]

Originally Posted by CapriRacer

. . . I think tread rubber with good hysteretic properties tend to be soft (I am going to check on this, but I am under the impression that good wearing tread rubber tends to be "hard".)

I definitely agree with this statement, although I allow that there may be exceptions. (Example: tombstones are routinely cut by sandblasting. rubber is placed over the hard stone where they don't want to cut. The hard stone is cut, but the soft rubber isn't.)

I have a high regard for CapriRacer's knowedge and engineering skill. We can just admit we disagree on a few points now and then. But, notice that this question of how rubber properties and contact patch affect Crr is mostly academic. We should just judge tires by the Crr and forget much of the rest.

My advice to Harry is to use 205/60R16. That was the middle choice for size increase, as I recall. This is expected to give good benefits with much less risk. So, Harry, ask around and make your best guess. I would buy from a local dealer, and I would ask, "do these tires have a customer-satisfaction guarantee?" Most tire companies will let you return tires within 30 days for a full refund. (You may get stuck on the local service, like balancing.)

I would carefully check mileage before changing, and after. And, you can bet I would return tires that don't improve mileage. (I've done it before.) Remember that you must check mileage under identical conditions as much as possible. Adjust speedometer readout downward as needed and use odometer corrections.

Ernie Rogers

[bwilson4web]

Originally Posted by Ernie Rogers

Wow, Bob, that's a fantastic idea! I can see it! You put the tire on a loose wheel, pump it up to pressure, then measure how high it bounces when you drop in on a smooth concrete surface! Or, see how the bounce changes with the kind of pavement. Lots of possibilities here.

Someone should sit down and work out the math, to see how you convert. . . .

I was thinking more along the line of a Rockwell hardness tester approach only using a ball instead of conical tip:
Rockwell hardness testers in portable, bench and automatic digital hardness testers

The idea is to measure the tread material elastic recovery to get an idea of the hysteresis loss. But Michelin did a similar demonstration a year or so ago.

They had two large cars, one with low rolling resistance tires and the other without. They set them on identical "U" tracks in neutral and started them rolling. The low rolling tire car stopped last.

Bob Wilson

[Ernie Rogers]

Ohhh, okay,

I guess that's how serendipity works.

Ernie Rogers

Originally Posted by bwilson4web

I was thinking more along the line of a Rockwell hardness tester approach only using a ball instead of conical tip:
Rockwell hardness testers in portable, bench and automatic digital hardness testers

The idea is to measure the tread material elastic recovery to get an idea of the hysteresis loss. But Michelin did a similar demonstration a year or so ago.

They had two large cars, one with low rolling resistance tires and the other without. They set them on identical "U" tracks in neutral and started them rolling. The low rolling tire car stopped last.

Bob Wilson

[MetroMPG]

Originally Posted by CapriRacer

I'm with Ernie on this issue of load carrying capacity: Use the largest size tire that will fit in the fenderwells. Larger tires are directionally towards lower coefficients.

However if that tire is also wider, you could be trading Crr against CdA:

http://ecomodder.com/forum/showthrea...g-cd-7475.html

And if it's taller (raising the ride height), drag may increase further.

[snowfish]

I'm seeing a bunch of theoretical speculation here. Do we have any real world, home brew, life test, experiences where the rubber really hits the road? Not talking test track here. I mean back and forth to work, to the store, the kids softball game, etc.

[theunchosen]

Originally Posted by snowfish

I'm seeing a bunch of theoretical speculation here. Do we have any real world, home brew, life test, experiences where the rubber really hits the road? Not talking test track here. I mean back and forth to work, to the store, the kids softball game, etc.

225/60R17 mpg 26
180/55R14 mpg low 30 high 50(I might have been tailgating a semi. . .

The turtle provides enough low pressure to pull the front of my car. My average is 35.

I used the 17s for a year until they wore out and then swopped in for 14s and new tires.
The 17 tires were hard as a rock. .22 cal had trouble solidly penetrating both sides while most of my other old tires its a non-issue.

[Frank Lee]

Tire Tech Information - Tire Rolling Resistance Part 3: Changes to Expect When Switching from Worn-Out to New Tires

here's one for ernie

[Ernie Rogers]

Thank you , Frank,

For showing me that article. It's hard to know for sure what the effect is unless you measure it yourself. I personally did not notice any change on my last tire replacement.

I think the author forgot to mention an important point. When you get the new tires, you will probably drive faster--if you keep the speedometer at the same position as before since the tire diameter is greater. This change in speed would have a greater effect on mileage than the effect from having thicker tread.

Ernie Rogers

Originally Posted by Frank Lee

Tire Tech Information - Tire Rolling Resistance Part 3: Changes to Expect When Switching from Worn-Out to New Tires

here's one for ernie

[Ernie Rogers]

Hello,

Has anyone heard about this?

I bought two tires today, from Sears. (Michelin Energy MXV4 Plus-- they were on clearance because they are a discontinued tire.)

Oh, that's not the news The manager said they had new "energy" tires coming from Goodyear, called "Goodyear Assurance Fuel Max" tires. So far, they have to be special ordered but should be in stock soon.

Ernie Rogers