Tire rolling resistance in the draft calculator

Hello everyone.

Since my car feels somewhat more sluggish when going downhill and coasting with the new summer tires compared to the old, worn-out ones, I repeated a series of measurements for rolling resistance today:
Push the vehicle forward while the transmission is in neutral, release it, and measure the distance (s) and time (t) it takes to come to a stop.
A measurement series consisting of approximately 20 runs with varying speeds can roughly compensate for measurement errors.

The delay can be expressed as a = 2s / t². To calculate the rolling resistance, multiply the rolling resistance coefficient by the vehicle's unladen weight, and that's the calculation.

My initial impression was correct: the new tires (Pirelli P 6000) have a rolling resistance of approximately 137 N in the middle of the measurement range, while the old Conti SportContact tires had a rolling resistance of 111 N.
Converted to top speed, the Pirellis consume almost 2 horsepower more than the Contis.

In the rolling resistance calculator, the rolling resistance is calculated in field G 21 using the simplified formula "weight x 0.1". The conversion factor of 0.1, which relates weight (in kg) to rolling resistance (in N), is based on my measurements using the old Conti tires.

Since it's apparently not the case that all tires roll as "easily" as the aforementioned Contis, it seems appropriate to change the conversion factor to 0.11 to 0.12 (simply overwrite the value in G 21).
The difference between 0.1 and 0.12, even for the calculation of the 81 kW Golf 3, amounts to about 0.05 seconds – well...

My main takeaway: there might actually be something to these new "fuel-saving" tires. Apparently, the P 6000 models are not included yet.

Or could it be that the new "high-profile" tire blocks lose even more internal friction, causing worn tires to generally have lower rolling resistance than new ones?

Hi Ulf,

When I bought new summer tires last year, I initially thought my Golf looked bulkier. I'm upgrading from Dunlop SP2000 tires, size 195/50, to...
Switched to Goodyear Eagle F1 tires, size 195/45. I'm glad there's some truth to it. (Apparently, Goodyear tires are supposed to be more fuel-efficient than Dunlop tires, although...)

Regards,
Thomas.

Volkswagen Golf 3 - AFN engine - 1997.

*excavate*

Currently, I am working on expanding the DZR (presumably a specific tool or software) to be an alternative torque curve estimation tool. Instead of just calculating the time for the 2000-4000 rpm range, this expanded tool will break down the overall acceleration into segments of 500 rpm width. These can then be compared with log data, from which the corresponding individual times are interpolated and stored in a separate .xls file.
To determine the torque curve, the Nm table in the dynamic load reduction (DZR) calculation is adjusted until the calculated 500 rpm interval times match the log data as closely as possible.

Essentially, it's a kind of K-Power for manual operation, but without the logged run-in phase. Generally useful for people whose reachable measurement distances are sufficient for the acceleration phase, but which do not offer an accurately matching subsequent deceleration distance due to the presence of inclines/declines, curves, etc.


To determine the losses during acceleration as accurately as possible, more information about the course of the rolling resistance would be helpful.

Based on what I've read so far, it's 99% likely to be about...

Fr = Fn * Cr

with Fr = rolling resistance force, Fn = gravitational force, Cr = rolling resistance coefficient, approximately 0.013 for passenger car tires on asphalt.

From this, the reference value for the rolling delay, which is already included in the DZR (German Road Traffic Regulations), of 0.13 m/s² can be derived. Multiplying this value by the vehicle mass yields the rolling resistance – and this is completely independent of the speed.

Conversely, the slightly downward-sloping torque curves observed in roller dynamometers suggest that there is at least one non-linear component involved, meaning that the braking force increases with speed. While this could potentially be caused by the mixing performance of the transmission oil, it might also originate from the tires.
If the rolling resistance force actually increases with speed, I would appreciate a brief explanation of the underlying principles and a formula that can be used to describe the relationship between rolling resistance and speed.

Because a loss factor, for example, in the order of approximately 10 kW (necessarily calculated independently of speed) for a 1.3-ton vehicle at 200 km/h, arguably warrants being treated with the utmost precision in the dynamic resistance model.