Wheels and Tires - Diagnosis and Testing

Preliminary Inspection

1. 1
   Confirm the customer concern by performing a road test on a smooth road. If any vibration is evident, refer to Symptom Chart: NVH.
2. 2
   To maximize tire performance, inspect the tires for signs of incorrect inflation and uneven wear, which may indicate the need for balancing, rotation or front suspension adjustment.
3. 3
   Correct tire pressure and driving technique have a major effect on tire life. Heavy cornering, excessive acceleration and unnecessary hard braking increase tire wear.

Correct tire pressure and driving technique have a major effect on tire life. Heavy cornering, excessive acceleration and unnecessary hard braking increase tire wear.

Tire replacement must be performed according to the recommendations for:

• tire size
• speed rating
• load range
• tire construction type

Using tires/wheels of any other size, load range or type may seriously affect:

• ride
• handling
• speedometer/odometer calibration
• vehicle ground clearance
• body and chassis tire clearance
• wheel bearing life
• braking performance

New wheels must be installed if the vehicle wheels are:

• bent
• cracked
• dented
• severely corroded
• leaking
• have elongated wheel stud holes
• have excessive lateral or radial runout

Use only the tire sizes recommended on the certification label located on the driver's door or door pillar. Larger or smaller tires may damage the vehicle, affect durability, and require speedometer recalibration. Make sure the wheel size and offset match those recommended for the tire in use.

Inspect the tires for signs of uneven wear. The following descriptions identify the wear type:

Check the tires for:

• cuts
• stone bruises
• scrapes
• blisters
• embedded objects

Check the valve stems for:

• cracks
• cuts

Install a new valve stem if damaged or when installing a new tire.

Tread Wear Indicators are molded into the bottom of the tread grooves. Install a new tire when the indicator bar becomes flush with the tread surface, or is less than 2/32 inch.

Tire Wear

Tire wear is usually defined as the loss of tread depth. Tread wear is caused by friction with the road surface. The tread should wear evenly around the entire circumference of the tire and across the entire tread surface. When this is not the case, the tire may show abnormal or irregular wear.

Normal Tire Wear

Normal tire wear is defined as even wear across and around the tread. Because many factors (driving style, road surface, vehicle type, tire type) can affect tire wear, there is no absolute expected mileage for normal wear. A tire is considered worn when the tread is worn down to the tread wear indicators.

Abnormal/Irregular Tire Wear

Abnormal/improper tire wear is defined as tire wear that is not even across or around the tread, and which causes performance-related concerns.

Abnormal/irregular wear may be caused by many factors, including driving style (aggressive, passive), climate (hot, cold), road conditions, vehicle loading, and vehicle maintenance (correct tire pressure, rotation intervals, and balance). It is important to determine the root cause of the wear before performing repairs. Tires with abnormal/irregular wear may still be serviceable provided the minimum tread depth is greater than 2/32 inch and the tire does not cause vehicle performance concerns (noise/vibration).

Inner Edge/Shoulder Wear

Inner edge (or shoulder) wear occurs on the inner edge of the tire and is usually caused by excessive toe and/or excessive negative camber. If the tread depth of the outer shoulder rib is at least 50% greater than the tread depth of the inner shoulder rib, the tire has inner edge/shoulder wear. To determine if tires have this type of wear, visually inspect the tires. In some cases, it may be necessary to measure the tread depth of each rib and compare it to the shoulder.

Outer Edge/Shoulder Wear

Outer edge (or shoulder) wear occurs on the outer edge of the tire and is usually caused by excessive toe and/or excessive positive camber. If the tread depth of the inner shoulder rib is at least 50% greater than the tread depth of the outer shoulder rib, the tire has outer edge/shoulder wear. To determine if tires have this type of wear, visually inspect the tires. In some cases, it may be necessary to measure the tread depth of each rib and compare it to the shoulder.

Heel/Toe Wear

Heel/toe wear (also known as feathering) occurs on the outside or inside edge/shoulder of the tire. To determine if the tires have this type of wear, inspect the tires on both the inner and outer shoulder ribs. In some cases, it may be necessary to measure the difference in tread depth between the leading and trailing edge of each rib on the inner and outer shoulder ribs.

Diagonal Wear

Diagonal wear occurs diagonally across the tread surface and around the tire circumference. To determine if the tires have this type of wear, visually inspect the tires to determine if the wear pattern runs diagonally across the tread and around the tire circumference. In some cases, the difference in tread depth of the diagonal wear pattern may need to be measured.

Symptom Chart: Tire Wear

Symptom Chart

The diagnosis in this manual assumes a certain level of skill and knowledge of Ford-approved diagnostic procedures.
REFER TO: Diagnostic Methods (100-00 General Information, Description and Operation).

Symptom Chart: NVH

Pinpoint Tests

For a description of the various tire wear patterns, refer to Inspection and Verification.

Pinpoint Test A: Inner Edge/Shoulder Wear

Possible Sources:

• Excessive camber
• Incorrect wheel and tire rotation

Pinpoint Test B: Outer Edge/Shoulder Wear

Possible Sources:

• Excessive toe
• Incorrect wheel and tire rotation

Pinpoint Test C: Diagonal Wear

Possible Sources:

• Incorrect wheel and tire rotation
• Excessive Toe/Feathering
• Incorrect tire inflation
• Loose, worn or damaged suspension components

Component Tests

Radial Runout

Radial runout is an egg-shaped deviation from a perfect circle, measured perpendicular to the circumference. On a wheel and tire assembly, this means measuring the center rib of the tire tread. The center rib indicates the condition of the tire as a whole. Total runout is the difference between the maximum and minimum gauge readings. The high spot is the location of maximum runout.

Radial Runout Measurement - Hunter Road Force® Loaded Method

1. 1
   Using tire chalk, mark the vehicle position on the inside sidewall of all 4 tires.
2. 2
   Remove the wheel and tire assembly.
   REFER TO: Wheels and Tires (204-04A Wheels and Tires, Removal and Installation).
3. 3
   Make sure the tire pressure is set to the correct pressure specified on the VC label.
4. 4

   NOTICE: Make sure the correct wheel balancer adapters are used. Improper installation of the assembly on the balancer or damage to the wheel may occur.

   Install the wheel and tire assembly onto a suitable wheel balancer using the appropriate balancer adapters, as shown in the illustration. Refer to the PTS website for the list of recommended wheel balancer adapters.

5. Measure the Road Force®.

• Temporarily mark the high spot and the Road Force® value on the tire sidewall. If the wheel and tire assembly Road Force® exceeds 9 kg (20 lb), perform the matched mounting wheel and tire assembly optimization procedure.
• If the wheel and tire assembly Road Force® value is 9 kg (20 lb) or less, permanently mark the high spot and Road Force® value on the inside sidewall of the tire for future wheel and tire service reference. Balance the assembly and install the wheel and tire on the vehicle using the wheel-to-hub optimization procedure.

Radial Runout Measurement - Dial Indicator Method

1. 1
   Make sure the tire pressure is set to the correct pressure specified on the VC label.
2. 2
   Using tire chalk, mark the vehicle position on the inside sidewall of all 4 tires.
3. 3
   Remove the wheel and tire assembly.
   REFER TO: Wheels and Tires (204-04A Wheels and Tires, Removal and Installation).
4. 4

   NOTICE: Make sure the correct wheel balancer adapters are used. Improper installation of the assembly on the balancer or damage to the wheel may occur.

   Install the wheel and tire assembly onto a suitable wheel balancer using the appropriate balancer adapters, as shown in the illustration. Refer to the PTS website for the list of recommended wheel balancer adapters.

5. Position a suitable dial indicator and place it on the center rib of the tread.
   
   1. Rotate the wheel and tire assembly (or wheel) to locate the low point.
   2. Set the dial indicator to 0.
   3. Rotate the wheel and tire assembly one full revolution to make sure the low point is found and the dial indicator returns to the 0 reading.

6. Slowly and continuously rotate the wheel and tire assembly (or wheel) while measuring radial runout.
   
   • Note the deflection (runout) from 0 on the dial indicator.
   • If the wheel and tire assembly runout reading is greater than 1.14 mm (0.045 in), temporarily mark the high spot and runout reading on the tire sidewall and perform the match mounting procedure to optimize the wheel and tire assembly.
   • If the wheel and tire assembly runout reading is 1.14 mm (0.045 in) or less, permanently mark the high point and runout reading on the inner tire sidewall for reference during future wheel and tire service. Balance the assembly and install the wheel and tire on the vehicle using the wheel-to-hub optimization procedure.