[orange4boy]

More interesting tire info. Especially if you want to drive on the Autobahn.

Link: Tire Tech Information - Air Pressure/Load Adjustment for High Speed Driving

The European Tyre and Rim Technical Organization (ETRTO) establishes the standards for tires sold in Europe, and recognizes that the tire's deflection must be minimized and controlled in order to surpass high speed driving stresses. In order to accomplish this, the tire inflation pressure recommendations and the tire's rated load capacities are customized when speeds exceed 160 km/h (99 mph) for all tires up to and including a V-speed rating, and when speeds exceed 190 km/h (118 mph) for all tires that are Z-speed rated and above.

The Autobahn's unlimited speed opportunities explain why many German vehicles identify alternate tire inflation pressures to accommodate higher than North American highway speeds and heavier than typical two-passenger loads. In order to accommodate higher speeds, the tire size and inflation pressure recommendations are tuned beyond what is branded on the tire's sidewalls. These increases in recommended tire pressure are usually determined by agreement between the vehicle and tire manufacturers. In the absence of such an agreement, apply the following:

Beginning with the vehicle manufacturer's recommended tire pressure for normal highway conditions, tire inflation pressures are initially increased and then the tire's rated load capacities (branded on the sidewalls) are reduced as speeds climb.

In our example shown below, the vehicle manufacturer's recommended 35 psi for a 225/45R17 91W Standard Load tire installed on a vehicle initially rises in 1.5 psi increments for every 10 km/h (6.2 mph) increase in speed until the inflation pressures max out with an increase of 7.5 psi when the vehicle's top speed has increased 50 km/h (31mph). Then as the vehicle's top speed continues to climb, the rated load capacity of the tire is reduced in 5% increments for every additional 10 km/h until the vehicle's top speed has increased an additional 30 km/h (18.6 mph). In this case the 225/45R17 91W Standard Load size's rated load capacity of 1,477 lbs. is reduced to 1,255 lbs. when applied to a vehicle with a 270 km/h (168 mph) top speed.

For W-Speed Rated Tires
Vehicle
Top Speed Required Tire
Pressure Increase Tire Load Capacity
% of Branded Maximum W-Speed Rated Tire
35 psi O.E. Example
mph km/h psi bar % of value branded on sidewall psi lbs.
118 190 0 0 100% 35.0 1000
124 200 1.5 0.1 100% 36.5 1000
130 210 3.0 0.2 100% 38.0 1000
136 220 4.5 0.3 100% 39.5 1000
143 230 6.0 0.4 100% 41.0 1000
149 240 7.5 0.5 100% 42.5 1000
155 250 7.5 0.5 95% 42.5 950
161 260 7.5 0.5 90% 42.5 900
168 270 7.5 0.5 85% 42.5 850

NOTES: Never exceed the maximum cold inflation pressure branded on the tire's sidewall.

I assume these cars are not stopping at the side of the road on the Autobahn onramp to adjust their tire pressures. It must be considered safe enough to drive with the higher pressures than OEM recommended for the balance of the trip below the insanely dangerous speeds of the Autobahn.