Tire Rolling Resistance: Low & Efficient.

Hello everyone.

After switching from summer tires (195/60 R 14 Pirelli P 6000) to winter tires (175/65 R 14 Fulda Gravito), I was immediately surprised by how easily the car could be pushed around.
Subjectively, only half the force is needed to get it moving, and it also rolls much further.

I never noticed that before when I was changing tires.
It still seems related, because this summer I replaced the amazing 195 Conti SportContact tires with Pirellis, and around the same time, the average fuel consumption of my truck increased by about 0.3 liters.

Now I also understand why my wife's ALH Ibiza consumed a bit more fuel than my Golf: the Seat also came from the factory with the P 6000, which I liked so much in terms of driving comfort, handling, and price that I bought one myself.
While I'm still saving about 0.3 liters of fuel, the difference was more significant with the old tires.

Now that the winter tires are on, the Golf feels noticeably more "agile" even with just a little bit of throttle. Let's see how the fuel consumption develops during the winter...

Does anyone here know exactly what determines a tire's rolling resistance?
Do flip-flops consistently have more rolling resistance in addition to the increased air resistance, or is the same amount of work simply distributed over a larger contact area?

It's somewhat off-topic, but still relevant in some ways, for example, for the DZR (German Road Safety Council).

Hi Ulf!

'According to my textbook, the rolling resistance (fR) is mainly dependent on the tire design, vehicle speed, tire pressure, and tread pattern.'

'For a radial tire, I can see from the speed chart that the rolling resistance ranges from 0.013 at 20 km/h to 0.016 at 150 km/h.'

'Tire pressure has a much more significant impact... I don't have any usable values for fR, but increasing the pressure from 2 bar to 2.6 bar can reduce fuel consumption by approximately 10%, depending on the type of tire.'

Further influence: the ground... the harder, the better.

The geometry of the suspension has a significant impact: Negative camber can dramatically increase rolling resistance. A tire with a conical shape (causing it to run at an angle when driving straight) also increases rolling resistance.


It's not actually stated that wide tires necessarily have more rolling resistance. The 'shoulder' of a tire, which is the last part of the sidewall that curves into the tread, doesn't become larger with wider tires. I think I once read online that fuel consumption might even decrease with increasing tire width... although in practice, you often see the opposite because wider tires are usually not inflated as much.
Best regards, Ernst.

The increase in rolling resistance for wider tires is primarily due to the larger cross-sectional area. Despite all advancements, such a tire is inherently unaerodynamic and cannot be completely streamlined.
When performing record-breaking runs, "separator discs" are mounted, which are then heavily inflated to reduce the amount of soil compaction.
Christian.

In practice, you usually see the opposite because wider tires are typically inflated with less pressure.

Okay, so my summer tires (size 205/45 R16) are inflated to 2.7 bar, and my winter tires (size 185/60 R14) are inflated to 2.1 bar. I use Continental tires for both summer and winter.
Both were inflated by the tire dealer.

.... in practice, you usually experience the opposite because wider tires are typically inflated with less pressure.

Okay, so my summer tires (size 205/45 R16) are inflated to 2.7 bar, and my winter tires (size 185/60 R14) are inflated to 2.1 bar. I use Continental tires for both summer and winter.
both were inflated by the tire dealer.

I think it depends more on the cross-sectional area. The smaller the cross-sectional area, the more pressure is required.

Yes, something like that.

Overall, the correct tire pressure depends on the tire's aspect ratio, width, vehicle weight, and tire type. So far, I've only observed that wider tires tend to be less inflated when the other factors remain roughly the same. (For comparison, truck tires have 6 bar or more, even though they have a somewhat larger aspect ratio.)

Ulf can disregard the width aspect for rolling resistance, as the tread pattern (tire type) is more important. Wider tires increase air resistance.
And the most important factor for Ulf's analysis is tire pressure, as it has the greatest influence on rolling resistance.
Best regards, Ernst.

Bisher bin ich auch davon ausgegangen, daß Breitreifen mehr verbrauchen als Schmale (Aerodynamik, größere Aufstandsfläche, mehr Grip im Trockenen, aber geringere Walkarbeit). SowThat's the theory.
"I used to own a Bora Kombi TDI with 115 horsepower and 195/65 R15 ContiContact tires for approximately 15,000 km. The average fuel consumption was about 5.85 liters. After a total loss, I now have another Bora Kombi with better equipment and, therefore, probably a bit more weight. It has the same engine and I drive it the same way, but with different tires: 225/45 R17 Conti SportContact. The average fuel consumption has increased slightly to just under 6 liters. This increase in fuel consumption can be explained by the additional weight. Furthermore, I drove about 2500 km in Scandinavia with the old car, which resulted in fuel consumption figures of around 5 liters at times, naturally lowering the average fuel consumption of the old car."
I recently bought a set of Dunlop M3 winter tires, size 195/65 R15, and the fuel consumption has increased by about 0.3 liters to approximately 6.25 liters. I always set the tire pressure according to the manufacturer's recommendations, or slightly adjusted to suit my own needs, but the deviation is never more than 0.2 bar above the recommended pressure.
Since I travel between two locations and usually maintain a similar speed, the data is also comparable.

Thomas.

Hi Ernst,

Even after your explanations, my summer tires, which are difficult to start rolling, remain somewhat puzzling to me.

The suspension geometry (everything is original except for 15mm spacers all around) is the same as with the winter tires, and the tire pressure is practically the same as well (always around 2.7 bar).
Even the height of the sides is almost perfectly aligned.

However, summer tires often have very long, continuous contact patches in the direction of travel, while winter tires tend to have shorter, individual blocks.
If the tire is flattened in the area of the contact patch, it is my opinion that summer tires may develop greater internal stresses in the tread area. This is because the tread material, which is compressed in the circumferential direction, cannot "deform" elastically (forward and backward) into adjacent tread grooves everywhere, as is the case with winter tires.
Do you think this is a possible explanation?

Hi Ulf!

Okay, so the longer, continuous tread area is at least one reason why summer tires are quieter. I'm not sure how that affects the 'walking' behavior. A more stable sidewall (walking zone) of a winter tire would be more likely to be the reason for less 'walking.'

Two questions: Which tire will be compressed more under static load? You've probably already measured the static tire radius before.
Are any of your tires directional?

Best regards, Ernst.

Ernst S. wrote:

2 Questions: which tire will be compressed more under static load? You've probably already measured the static tire radius before. Are any of your tires directional?

Hi Ernst,

leider hab ich keine ausreichend genaue Meßmöglichkeit betr. Belasticity radius.
However, the rolling circumferences correspond quite accurately to the standard value, with the winter tires being a few millimeters larger. Therefore, they are theoretically compressed slightly less.

Only the winter tires are speed-rated.

Hi!

I don't know what your definition of 'minimal' is, but the amount of walking required depends on the depth of the impression.
For this reason, directional tires should have a higher rolling resistance again.

I don't think we can attribute the difference to any specific effect right now.
But you could try to reduce the pressure of the winter tires so that they are compressed the same amount as the summer tires. Then you might really be able to see the difference that the tread patterns make. (But I don't know how scientifically sound that is ).
Best regards, Ernst.

Ernst S. wrote:

I don't know how much your "minimal" is, but the walking behavior depends on the indentation... For this reason, directional tires should have a higher rolling resistance again.

Hi Ernst,

From my gut feeling (= without deeper consideration), I would guess that narrower tires, with the same load and tire pressure, would be compressed more - is that correct? (Thought experiment: TDI with bicycle tires at a tire pressure of 2.7 bar ).

195 to 175mm width is a "significant" 11% difference, so the larger circumference of the winter tires is likely due to an oversized carcass rather than the tire pressure. . .

I didn't mean to emphasize the extent of it.
But it's about the stability of the sidewall. And that's why I need to know the exact indentation (regardless of the circumference).

And hopefully, the winter tires won't be pressed in as much.
If not, then summer tires must really have a tread pattern that provides strong braking performance.
Best regards, Ernst.

Ernst S. wrote:

I didn't actually want to go into the details. But it's about the stability of the sidewall. And that's why I wanted to know the exact indentation. (Regardless of the circumference)

Hi Ernst,

I can't accurately measure the indentation right now because I don't have the appropriate tools.

However, I believe that the "stiffness" of the sidewall hardly contributes to the load-bearing capacity or reduces the sinking.

Imagine yourself sitting on a stationary, airless tire without a valve.
I claim (and this claim can be refuted) that even with a load of less than 50 kilograms, any airless car tire will completely collapse due to the "softness" of its sidewalls. Therefore, with a load of a few hundred kilograms, the sidewalls have little to no influence on the deformation or contribute significantly to the load-bearing capacity.

In my initial assessment, every tire will sink until the contact area multiplied by the tire pressure generates a counterforce that matches the respective wheel load. Therefore, given a specific load and tire size, the amount of sinking is largely dependent on the tire pressure.

Given that the contact area with narrower tires is initially smaller, narrower tires, in my opinion, are compressed slightly more (at the same tire pressure) to compensate, until the aforementioned equilibrium of forces between the internal pressure, the contact area, and the wheel load is achieved.

Therefore, the 175-size winter tires, at 2.7 bar, are likely to be compressed even further than the 195-size summer tires, even though the latter have a heavier rolling resistance.

Hello!

Yes, I think that's what's happening. And what's left are winter tires, which should actually be more difficult to roll, and they aren't significantly narrower, and they have the same pressure... I'm also completely clueless about what's going on. But I've heard from several people that they noticed more acceleration after changing the tires, even if the tires were the same width.

Best regards, Ernst.

Okay, and now I've figured out why summer tires have so much rolling resistance.

The indentation is the same size because the sidewall doesn't contribute to the load-bearing capacity...

The summer tire is considerably harder than the winter tire, even at the same temperature.
Unfortunately, I don't know how much the rubber compounds vary, but even at an outside temperature of 40°C (and even higher road surface temperatures), a summer tire shouldn't lose its grip, and a winter tire should remain soft enough at -15°C to maintain reasonable traction.

Let's assume someone is changing tires at an outside temperature of 10°C (50°F). The amount of force required to deform the tire's contact patch will be the same, but it takes much more effort to change a summer tire because it's already very hard at 10°C. A winter tire, on the other hand, is still very soft at 10°C, which is why it requires so little effort to change.

And if that's not true, then I'll blame it on the TDI winter tires.
Best regards, Ernst.