Top 5 most fuel efficient tires (Lowest Rolling resistance: LRR)

[Ernie Rogers]

Hello, Racer,

For bending of a flat plate (let's say the undertread), the strain energy is proportional to the plate thickness squared. Your story fits perfectly with the theory.

That leaves open the question of exactly how the grooved tread participates because the strain is mostly taken up in the groves where no work is required, or at least much less.

Since the wear of the tire is in the grooved part, we would expect thickness change there to have somewhat less effect--and it could depend on the the tread design.

Well, heck, you could probably teach us a thing or two about how tread design affects tire rolling resistance.

Ernie Rogers

Originally Posted by CapriRacer

Anecdote:

You may be aware that I work as an engineer for a major tire manufacturer - who will remain nameless. Background to this story: At least one major vehicle manufacturer requires tire suppliers to monitor the RR of the tires being supplied - and that task is assigned to a QA engineer.

I was once asked to document all the changes made to a particular tire - and I ran across an entry where a new tread die was made to bring the tire back into RR compliance. I asked the QA engineer in charge what was with that - and he proudly whipped out a graph showing the RR by date and a gradual upward trend. He stated that the die used to extrude the tread component wears over time and gradually the tread gets heavier (and thicker). By making a new die, the tread was brought down in weight and the tread thickness decreased, and the RR was reduced.

BTW, the mold doesn't change so what would be measured as tread depth would not change. All the change in the volume of rubber in this anecdote is between the bottom of the groove and the top of the casing. This dimension is commonly called undertread.

Ergo: Change in tread rubber weight (volume) = Change in RR

I've encountered this principle in several studies of RR, but it's usually expressed as a "throw away / background" comment - as though this is so fundamental that it doesn't need validation. Perhaps it is because the studies that back this up are quite old and out of print.

[CapriRacer]

Originally Posted by Ernie Rogers

Hello, Racer,

For bending of a flat plate (let's say the undertread), the strain energy is proportional to the plate thickness squared. Your story fits perfectly with the theory.

That leaves open the question of exactly how the grooved tread participates because the strain is mostly taken up in the groves where no work is required, or at least much less.

Since the wear of the tire is in the grooved part, we would expect thickness change there to have somewhat less effect--and it could depend on the the tread design.

Well, heck, you could probably teach us a thing or two about how tread design affects tire rolling resistance.

Ernie Rogers

Here's the deal about the tread elements - the opposite of the grooves.

When you bend a flat plate, the surfaces are either put in compression or tension. In the case here, the "plate" is being unbent, and the base of the tread elements is being compressed.

But there is another factor to consider: Pantographing. That's the word that is used to describe what happens because of the cords in the tire.

If you consider the individual cords to be attached to the adjacent layer, what you have a a series of parallelograms. So as the tread enters the footprint, the undertread "unbends" and gets shorter (it is traveling along the "chord" and not the "arc" of a circle), so the width gets wider.

That means that not only is there movement in the radial direction (We're calling it "bending") and movement in the circumferential direction (because of the "chord" effect), but there is also movement in the lateral direction.

Another thing to consider is that compared to the cords, rubber is very flexible. So changing the tread rubber has an unusually high proportional affect on the energy not returned, compared to its effect on stiffness.

[NeilBlanchard]

Thanks for posting! I feel like I'm starting to get a better feel for RR.

Q: In an ideal world, how would one design the lowest rolling resistance wheel/tire?

Anything is possible; including no air inflation, and no need for any suspension function! (The suspension would need to be redesigned to work with this new tire/wheel.) You would want to have smooth aerodynamics, and good traction on "normal" paved roads, in wet and dry conditions. (We'll leave the snow and ice for another tire/wheel.)

[Ernie Rogers]

Thanks, Racer,

So, I conclude that all else being equal (including coefficient of restitution or internal friction), I can reduce the strain energy and therefore the energy loss by using softer rubber (lower elastic constants) in both the casing and the tread material. Of course, thinner components are also desired.

I am over my head here-- adding a second phase to the rubber, such as colloidal silica, could act to "pin" movable elements in the small-scale (e.g., molecular) structure thereby reducing internal friction. (This is called dispersion hardening in metals.) While hardening may occur, this could actually be detrimental.

Comments?

Ernie Rogers

Originally Posted by CapriRacer

Here's the deal about the tread elements - the opposite of the grooves.

When you bend a flat plate, the surfaces are either put in compression or tension. In the case here, the "plate" is being unbent, and the base of the tread elements is being compressed.

But there is another factor to consider: Pantographing. That's the word that is used to describe what happens because of the cords in the tire.

If you consider the individual cords to be attached to the adjacent layer, what you have a a series of parallelograms. So as the tread enters the footprint, the undertread "unbends" and gets shorter (it is traveling along the "chord" and not the "arc" of a circle), so the width gets wider.

That means that not only is there movement in the radial direction (We're calling it "bending") and movement in the circumferential direction (because of the "chord" effect), but there is also movement in the lateral direction.

Another thing to consider is that compared to the cords, rubber is very flexible. So changing the tread rubber has an unusually high proportional affect on the energy not returned, compared to its effect on stiffness.

[Ernie Rogers]

Hello, Neil,

I will try to answer your question, and then Racer might add corrections.

1. Air is the ideal suspension medium for a wheel because it absorbs NO energy. Nitrogen doesn't add anything except maybe longer life.

2. General shape of the tire-- large diameter, fairly narrow, and high profile (aspect ratio). Tread is narrower than the tire. As light-weight as possible.

3. Soft rubber with least internal friction. Very strong cord material.

4. Tire pressure is fairly high, helped by narrower width and high profile.

A question I would have is, is it better (more efficient) to provide compliance (soft ride) in the tire or in the wheel suspension?

Is there an accessible book or paper to recommend?

Ernie Rogers

Originally Posted by NeilBlanchard

Thanks for posting! I feel like I'm starting to get a better feel for RR.

Q: In an ideal world, how would one design the lowest rolling resistance wheel/tire?

Anything is possible; including no air inflation, and no need for any suspension function! (The suspension would need to be redesigned to work with this new tire/wheel.) You would want to have smooth aerodynamics, and good traction on "normal" paved roads, in wet and dry conditions. (We'll leave the snow and ice for another tire/wheel.)

[NeilBlanchard]

Hi,

There are several issues with inflated tires:

You have to keep them properly inflated, and you have to worry about punctures.

They flex more at the contact point than would, say a steel hoop with a rubber tread.

I want the lowest rolling resistance possible! And I want to regain all the energy possible (via the suspension) rather than have it wasted as heat.

[Frank Lee]

Thinking extremes, you probably wouldn't want a solid hoop- say, steel for instance- because unlike trains, we need some conformity with the road to get an acceptable level of traction. So maybe we add a layer of rubber to the hoop where it meets the road. Gained some conformity for traction, also gained a bit of resiliance for bump absorption. Some r.r., yes, but what else are ya gonna do?

Take all the resiliance out of the wheel and stick the suspension with all that monkey motion, and you will have one busy suspension! It will be like adding a bunch of unsprung weight, even though it is partially sprung. It'll likely be too heavy to respond to higher frequency excitation- maybe big ol mushy suspension pivots can handle that.

Wonder what r.r. the Tweel has.

[CapriRacer]

Originally Posted by Ernie Rogers

Thanks, Racer,

So, I conclude that all else being equal (including coefficient of restitution or internal friction), I can reduce the strain energy and therefore the energy loss by using softer rubber (lower elastic constants) in both the casing and the tread material. Of course, thinner components are also desired.

I am over my head here-- adding a second phase to the rubber, such as colloidal silica, could act to "pin" movable elements in the small-scale (e.g., molecular) structure thereby reducing internal friction. (This is called dispersion hardening in metals.) While hardening may occur, this could actually be detrimental.

Comments?

Ernie Rogers

I think you will find that rubber plays a very small role in overall tire stiffness compared to the ply cord and steel cord - and those play a small role compared to that of inflation pressure.

For practical purposes, the rubber, especially the tread rubber, comes along for the ride - and the rubber's role in Rolling Resistance is large simply because of its volume percentage.

Rubber chemistry is not my strong point, but my understanding is that silica is a substitute for carbon black, and the RR improvment is due to less internal friction.

[Vekke]

new tyre test results:

following RR test values/numbers are from ADAC tire test: size is 185/60/R14

the lower the number, better the RR:
Value
Michelin energy saver 2,0 VR
Hankook optimo k415 2,0 rwr
Continental premiun contact 2 2,1 VR
Goodyear duragrip 2,1 R
Dunlop sp sport fast response 2,1 R
Fulda carat progresso 2,2 VR

Those are the tires which are good in rr and arent very bad in other tire test sectors.

VR=very recommendable
R=recommedable
RwR= Recommadable with regards

From these tires I would pick goodyeat duragrip or dunlop, because tyrewearwas as small as Michelin energysaver. In other tires the number were twice as much or more!

[blackjackel]

Originally Posted by Vekke

new tyre test results:

following RR test values/numbers are from ADAC tire test: size is 185/60/R14

the lower the number, better the RR:
Value
Michelin energy saver 2,0 VR
Hankook optimo k415 2,0 rwr
Continental premiun contact 2 2,1 VR
Goodyear duragrip 2,1 R
Dunlop sp sport fast response 2,1 R
Fulda carat progresso 2,2 VR

Those are the tires which are good in rr and arent very bad in other tire test sectors.

VR=very recommendable
R=recommedable
RwR= Recommadable with regards

From these tires I would pick goodyeat duragrip or dunlop, because tyrewearwas as small as Michelin energysaver. In other tires the number were twice as much or more!

I found the report you are talking about:

Tabelle Sommerreifentest 185/60 R14 H

I believe that neither the duragrip or dunlop would be the best choice when it comes to balancing wear and tread life, it seems that the hankook optimo would be the best bet since it has the same LRR as the Michelin energy saver while having a wear of 2,2 which is way better than energy savers 0,6 but a little less than dunlop's sport which is at 3,0.

I don't see why you recommended duragrip as their wear rating is only 0,8 which is only 0,2 more than the energysaver.