Rolling resistance and tire size

The question might not be entirely relevant here, but the topic of rolling resistance always comes up when discussing electric vehicles.
Is there a calculator, Excel sheet, or formula available to calculate or estimate rolling resistance as a function of tire size? For example, how does the final speed (or fuel consumption) change if tires of size yy/zz x 16 are installed instead of y/z x 15?
Or is it simply impossible to answer, because factors like the type of tire have such a significant influence?

Greetings and thank you.
Rainer.

Hi.

Ernst S and I are currently working on an update to the DZR, which will also include data on rolling resistance measured using a stopwatch.
The aim is not to determine the rolling resistance with absolute precision, but rather to provide a more reliable method for calculating the actual motor power based on the wheel slip ratio.

However, the future calculation of rolling resistance (when Rainer makes the new version available online) will provide some information about the rolling resistance on the specific test track (in real-world conditions).
Unfortunately, the rolling resistance is again relatively low, meaning that even slight inclines and declines can practically distort its apparent value to the point of making it unrecognizable.
However, what matters in the intended application within the DZR is that these errors cancel each other out in the final performance calculation.

In practice, the rolling resistance varies significantly between different types of tires.
Here's an example from my experience: 195/60 R14 tires on a Golf 3. Used (worn) Conti SportContact tires result in approximately a 20% lower overall rolling resistance. Rolling resistance, equivalent to that of a new Pirelli P 6000 tire of the same size.

If you ever want to determine the rolling resistance yourself:
On a perfectly flat surface, push the vehicle to a speed of approximately walking pace, then release it and measure the time and distance it travels before coming to a complete stop.

The rolling resistance in Newtons is calculated as 2 * s * m / t², where:
* s = rolling resistance coefficient
* m = mass
* t = tire pressure
"dabei ist" translates to:

"it is included"
"it is available"
"it is present"
"it is there"
"it is also"
"in addition"
"along with that"
The rollout distance in meters.
vehicle mass in kg
"t" represents the rollout time in seconds.

Hello Ulf,
Thank you for the response and the suggestion about the rolling path.
After some consideration, I am also convinced that a universally valid, formula-based calculation is hardly possible.
I roughly estimated that the A3 needs approximately 70 kW to overcome air resistance at 200 km/h. With the same (incorrect) assumptions, an extra 1 cm of tire width costs around 0.6 kW, so it's not a significant factor. Different types of tires, tire pressure, and even factors like changes in the turbulence within the wheel wells are simply not quantifiable.
Best regards, Rainer.

In practice, the rolling resistance varies significantly between different types of tires.
Here's an example from my experience: 195/60 R14 tires on a Golf 3. Used (worn) Conti SportContact tires result in approximately a 20% lower overall rolling resistance. Rolling resistance, equivalent to that of a new Pirelli P 6000 tire of the same size.


I've also experienced that the Conti Sport Contact tires have extremely low rolling resistance. I haven't been able to achieve such high speeds with any other tire on my G3 with 195/50 R 15 tires, except for the Continental.

Best regards, Alex.

I haven't been able to achieve such high speeds with any other tire than the Conti, when using my G3 with 195/50 R 15 tires.

So, let's say the tire has 20% less rolling resistance, then that translates to approximately 3 km/h more speed that you can achieve due to overcoming air resistance. I repurposed Ulf's DZR for a different purpose.
At 3 km/h, the motor rotates approximately 70 RPM faster, which reduces the torque. So, depending on the torque curve, you can't actually achieve those 3 km/h.

Okay, I would say that when there's a significant change in top speed due to different tires, it's much more likely that the rolling circumference has changed, which can affect the speedometer. According to the German Road Traffic Regulations (DZR), a difference of up to 8 km/h is possible. And the increase in traction due to the smaller tires could potentially add another 3 km/h, if.
Best regards,
Ernst.