Section 86.508-78 - Dynamometer(a) The dynamometer shall have a single roll with a diameter of at least 0.400 metre.(b) The dynamometer shall be equipped with a roll revolution counter for measuring actual distance traveled.(c) Flywheels or other means shall be used to stimulate the inertia specified in § 86.529 .(d) A variable speed cooling blower shall direct air to the vehicle. The blower outlet shall be at least 0.40 m2 (4.31 ft2) and shall be squarely positioned between 0.3 m (0.98 ft) and 0.45 m (1.48 ft) in front of the vehicle's front wheel. The velocity of the air at the blower outlet shall be within the following limits (as a function of roll speed): | Actual roll speed | Allowable cooling air speed |
| 0 km/h to 5 km/h | 0 km/h to 10 km/h. |
| 5 km/h to 10 km/h | 0 km/h to roll speed + 5 km/h. |
| 10 km/h to 50 km/h | Roll speed ±5 km/h. |
| 50 km/h to 70 km/h | Roll speed ±10 pct. |
| Above 70 km/h | At least 63 km/h. |
(e) The dynamometer shall comply with the tolerances in § 86.529 .42 FR 1137, Jan. 5, 1977, as amended at 42 FR 56738, Oct. 28, 1977