Discussion on tire efficiency

[ConnClark]

Yes air does return more energy than rubber and steel. However the less it is compressed or disturbed the less energy lost. The same holds true for rubber and steel, the less it is flexed the less the energy that is lost.


hard rubber looses less energy.

http://www.vittoria.com/index2.php?o...=358&Itemid=71

From the box on the second page.

"Rubber compounds affect rolling resistance because they absorb different amounts of energy. In rough terms, thick, soft rubber usually absorbs more energy than thin, hard rubber. "


Caster Wheels - Performance TPR Wheels - Soft Rubber Wheels - Hard Rubber Wheels - Mold-On Rubber Wheels - Elastomeric High Tensile Rubber Wheels

From the comparison of types of caster wheels. Read the descriptions of the Soft rubber wheels and the Hard rubber wheels.

"Soft Rubber Wheels are a good choice for those applications where the average load is light with occasional loads using the full capacity of the wheel. Soft Rubber Wheels are manufactured of quality materials with a resilient rubber tread bonded to the hard rubber core."

"Hard Rubber Wheels are used where low cost, easy rolling wheels are required. Hard Rubber Wheels offer good floor protection, are quieter than steel wheels, and are strong and chip resistant."



Occasionally someone makes an advance in material science like adding silica to tire rubber allowing softer rubber to have a lower rolling resistance and better wearing characteristics. This is the exception and not the rule. It can be added to harder rubbers too but they won't grip as well.


My father designed tires. I learned a lot from him.

[Ernie Rogers]

Hello, Clark,

I appreciate the effort you have put into this subject. The ideas you present are good ideas. Your fundamental points here are--

1) Stiff load-bearing materials take less energy because they deflect less

2) Strong plates take less energy in bending because they are thinner.

You have to be careful about applying these rules to pneumatic tires--

1) The load bearing material in a tire is the air, not the rubber. Making the air stiffer (higher pressure) helps because the tire deflects less. But, in this case lowering the stiffness of the rubber also helps because it absorbs less energy (bends easier). The tire deflection (contact patch) is almost exactly the same no matter how hard or soft the rubber is. For a solid rubber tire, the conclusion is the opposite because the rubber supports the load.

2) A "soft, thick" tire wall is bad because the energy for bending goes up as the fourth power of thickness. The ideal tire wall is soft in bending but very strong and stiff in tension. That is the purpose of the cords, allowing great tensile strength in a thin, flexible tire. And, of course steel would do this best.

Ernie Rogers

Originally Posted by ConnClark

Yes air does return more energy than rubber and steel. However the less it is compressed or disturbed the less energy lost. The same holds true for rubber and steel, the less it is flexed the less the energy that is lost.


hard rubber looses less energy.

http://www.vittoria.com/index2.php?o...=358&Itemid=71

From the box on the second page.

"Rubber compounds affect rolling resistance because they absorb different amounts of energy. In rough terms, thick, soft rubber usually absorbs more energy than thin, hard rubber. "


Caster Wheels - Performance TPR Wheels - Soft Rubber Wheels - Hard Rubber Wheels - Mold-On Rubber Wheels - Elastomeric High Tensile Rubber Wheels

From the comparison of types of caster wheels. Read the descriptions of the Soft rubber wheels and the Hard rubber wheels.

"Soft Rubber Wheels are a good choice for those applications where the average load is light with occasional loads using the full capacity of the wheel. Soft Rubber Wheels are manufactured of quality materials with a resilient rubber tread bonded to the hard rubber core."

"Hard Rubber Wheels are used where low cost, easy rolling wheels are required. Hard Rubber Wheels offer good floor protection, are quieter than steel wheels, and are strong and chip resistant."



Occasionally someone makes an advance in material science like adding silica to tire rubber allowing softer rubber to have a lower rolling resistance and better wearing characteristics. This is the exception and not the rule. It can be added to harder rubbers too but they won't grip as well.


My father designed tires. I learned a lot from him.

[ConnClark]

Regardless of what the load bearing material is be it air, hard rubber, steel, or even stone, the softer rubber still is caught between it and the ground. It still will be compressed and create rolling resistance by increasing the contact patch area.

Lets take the the tire flex out of the equation entirely. Roll a large ball bearing on a large sheet of soft rubber and a large sheet of hard rubber. The soft sheet of rubber will induce a higher rolling resistance on the ball bearing.

[Ernie Rogers]

Hello, Clark,

You are missing something. The deflection of the tire is only related to the tire pressure. Another way of saying it: the contact patch area is the same size whether the rubber is hard or soft.

It takes more energy to deflect hard rubber by a specified amount. That's why soft rubber works better.

Most of us have noticed a decrease in fuel economy in winter. One explanation for that is that the tire rubber gets harder when cold.

Ernie

Originally Posted by ConnClark

Regardless of what the load bearing material is be it air, hard rubber, steel, or even stone, the softer rubber still is caught between it and the ground. It still will be compressed and create rolling resistance by increasing the contact patch area.

Lets take the the tire flex out of the equation entirely. Roll a large ball bearing on a large sheet of soft rubber and a large sheet of hard rubber. The soft sheet of rubber will induce a higher rolling resistance on the ball bearing.

[NeilBlanchard]

Hi,

I don't think that is the reason for worse mileage in the cold:

Longer warm up time, so longer on rich mixture
Cold air has more drag -- ~6.8% more drag at 30F than at 60F
Bearings etc. have more friction due to cold lubricants

[dcb]

Certainly tire warm up is not the only reason for reduced winter FE but it does seem to be a contributing factor " Cold tires can have as much as twice the rolling resistance than when they are warmed"

It is a bit counter-intuitive too, since we tend to equate (right or wrong) cold tires with less traction, and thus less resistance. But there ya are.

[tasdrouille]

Take it this way, the rubber is gonna deflect the same amount anyway, so it's better have one easy to flex. Less energy will be spent flexing the softer compound than the harder one.

Connclark, your ball bearing on rubber sheet analogy would be the equivalent to solid rubber casters on a concrete floor, in which case you would be right to say a harder compound will have less RR, because on solid wheels that rubber would be holding the load. On car tires though, the air pressure is holding the load and afaik the rubber compound hardness does not change the deflection of the tire much (contact patch size at same pressure/load).

[ConnClark]

Whether its a pneumatic tire or a solid tire a harder tread compound gives lower rolling resistance.

From page 40 http://www.geax.com/vedit/18/immagin...2009_EN_LR.pdf

" Sticky Soft compound on side knobs and ARAMID RACING 3D on the central ones. That's the best compromise you can get from both the compounds: cornering grip and braking performances keeping low the rolling resistance. Soft side knobs guarantee a strong bite in turns and excellent grip in all situations whilst the central (harder) compounds with aramidic particels makes for lower rolling resistance reducing wear and tear to acceptable levels. It's the ideal solution for racing tyres"



Note on this page that all the low rolling resistance tires have a hard compound

MAXXIS TYRE TECHNOLOGY

[bgd73]

The lower rated tires ought to be extincted, as well as 13 inch and even 14 inch wheel sizes. All one needs is miles and years and big to small cars to figure this out.
T rated and above (above is very hard, it is a test on balance of drivetrain) and would be annoying for all FWD as they are never content. I like T-rated on an old subaru for example. 1 tire can take the weight of the whole car, which ought to ba an international law bankrupting the rubber reef makers with there low rated excuses from humanity forever.

Alloys vs steel wheels is another big think. Alloys win, they are genious.

[Ernie Rogers]

Excellent argument, Clark,

But I notice at the MAXXIS site that the tread rubber designed for racing is NOT the hardest--

>>>>
57a Silica based compound created specifically for our Road Racing line.
• Enhanced grip
• Low rolling resistance
>>>>

And note this statement on casing construction--

>>>>
120 TPI Casing used in our Road Racing line, Cross Country eXCeption series, and BMXception series.
• Lightweight
• Smaller gauge cords
• Highly supple casing
>>>>

Don't I see a consistent pattern of greater flexibility in the racing materials?

Ernie

Originally Posted by ConnClark

Whether its a pneumatic tire or a solid tire a harder tread compound gives lower rolling resistance.

From page 40 http://www.geax.com/vedit/18/immagin...2009_EN_LR.pdf

" Sticky Soft compound on side knobs and ARAMID RACING 3D on the central ones. That's the best compromise you can get from both the compounds: cornering grip and braking performances keeping low the rolling resistance. Soft side knobs guarantee a strong bite in turns and excellent grip in all situations whilst the central (harder) compounds with aramidic particels makes for lower rolling resistance reducing wear and tear to acceptable levels. It's the ideal solution for racing tyres"



Note on this page that all the low rolling resistance tires have a hard compound

MAXXIS TYRE TECHNOLOGY