At this point in the diagnosis, the vibration has gone through the following analysis:

Automotive vibrations are usually related to the rotating speed of a component. Calculate the speed of these components using either an engine speed method or a vehicle speed method. Use the engine RPM readings taken during the road test in order to diagnose the vibrations that are sensitive to engine speed.

If the vibration is sensitive to vehicle speed, determine the rotational speed of the tires. As long as you operate the vehicle at a constant speed, the tires will operate at a constant speed. This speed is measured in rotations, or cycles per second. The reading is then compared to the frequency of the vibration, which is also measured in cycles per second.

The EVA program is designed to perform targeted frequency calculations on a suspected vibration source. The tire size, axle ratio, number of cylinders, vehicle speed and engine rpm are factored into a calculation that determines the predominant vibration frequency, amplitude and the suspected vehicle system producing the vibration.

1. Use the EVA to determine the speed at which the vibration occurs.
2. From the EVA main menu, select Auto Mode, then press enter; select Vehicle Speed, then press enter.
3. Enter the vehicle tire size information with one of three options:

•	RPS at 5 mph -- Refer to the Tire/Speed table below for the Hertz value at 8 km/h (5 mph) for that tire size.

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Database -- Select the tire type and tire size from each selection screen. Tip: when browsing the tire size or axle ratio list, press a number key to go to a related point in the list; for example, press 1 to go to the top of the list; press 4 or 5 to go to the middle of the list; press 9 to go to the bottom of the list.

•	Manual Entry -- Select Manual Entry to enter tire size directly. Enter the tire width (100-500 mm), aspect ratio (0.30-1.50) and rim diameter (10.00-25.00 in).

4. Enter the driveshaft configuration (skip step 5 if vehicle is front wheel drive).
5. Enter the axle ratio, refer to the Axle Ratio screen or table below,(2.00-9.00) from the Axle Ratio selection screen. Note: Axle Ratio is not applicable if front wheel drive (FWD) is selected.
6. Select the vehicle speed units in miles-per-hour (MPH) or kilometers-per-hour (KPH).
7. Enter the vehicle speed at which the vibration is felt.
8. As the test is run, the vehicle speed must be manually adjusted to match the actual vehicle speed:

•	Select the incremental step you want to increase/decrease vehicle speed, then press enter.

•	View the frequency ranges applicable for the speed selected, press enter to go to the active data screen or exit to go back one screen.

•	Press the up or the down key to adjust the on-screen vehicle speed on the live data screen to match the actual vehicle speed.

9. Data is displayed as averaged (A is displayed) or instantaneous (I is displayed). Press average (avg) key to toggle. The amplitudes of the vibrations detected are displayed in descending order beginning with line 2. Repair the strongest vibration first. One to three sources of vibration are identified:

•	TIRE 1,2,or 3 (1st, 2nd, or 3rd order tire/wheel system concern).

•	PROP 1 or 2 (Propshaft concern).

•	OVERLAP (overlap of Tire 3 and Prop 1 frequencies).

•	UNKNOWN (vibration source is unknown).

10. Data is received through input A (A is displayed) or B (B is displayed). Press key 4 to toggle.
11. The vehicle speed (V) is displayed in mph or kph. Press the down or up key to manually adjust this figure to match actual vehicle speed.
12. An identification letter symbol displays during record (R) or playback (P).
13. During record or playback the event and frame numbers are displayed. If an event is not selected, a question mark (?) appears. During record or playback the frame number cycles from 0 to 9; for example, 0:0, 0:1, 0:2-0:9.
14. Amplitude of the signal is displayed in number of G forces (G).

Steering and suspension assembly vibrations are the first level of testing for low-frequency vibrations that are sensitive to vehicle speed. The symptoms of a steering/suspension first-order vibration are a shimmy or a shake. This is usually felt in the steering wheel or in the seat. Inspect the following components for wear or damage: