Suspension & Steering Project 

Objective — Learner will work in a team to develop an understanding of the meaning of turning angle through discoveries made in determining the turning radius of a vehicle.

Project Description:

Scenario —A customer has complained that her vehicle’s tires make a squealing noise when she turns corners at low speeds.  From information you, the service technician, gather from her, the problem has just started, she has not replaced the tires, and she ran into a curb recently. You suspect that the vehicle was damaged when it hit the curb. This caused a change in the toe angle of the tire and the tire began to squeal on turns.  Have students use tire- size information printed on tires and a formula to determine the diameter of the tire when properly inflated.

Mathematics— Review tire- size information with emphasis on section width, aspect ratio, and rim diameter. The following formula can be used to find the diameter of the tire when properly inflated. 

d_t = (SW)(AR) x 2 x d_r
                            2540

where d_t is the diameter of the tire
                            SW is the section width (mm)
                     AR is the aspect ratio (%)
                     d_r is the diameter of rim (in.)

Have the students find five tire sizes in advertisements. Have them interpret the meaning of each part of the tire- size nomenclature. Use the students’ answers for assessment purposes. 

The vehicle referenced here will be used again for a later activity in this project. Have students read and record the tire-size information from this vehicle and measure the diameter of the tire. Students will calculate the tire diameter and compare their measured and calculated values. Have the students explain any differences.

Make sure the vehicle is the same one that will be used in the activity to determine the turning radius of the tires and vehicle that follows later. Students will use the formula from the previous activity to calculate the diameter. Differences may be the result of excessive tread wear, under- or over inflation, measurement error, calculation, or other cause. 

Have students calculate the circumference of the tires and the number of revolutions they will make in one mile. 

Mathematics— Students will use the formula for the circumference of a circle (c = π d, where d is the diameter of the tire. Use 3.1416 for π ). To find the number of revolutions per mile, students should convert one mile to inches and divide this value by the circumference of the tire.

Have someone drive a vehicle in an arc that is more than a quarter- circle but less than a semicircle. Students will determine the turning radius of the vehicle, the turning radius of each wheel, the distance each wheel travels in a full circle, and the number of revolutions each tire makes during a full circle.

Mathematics— Students will construct perpendicular bisectors of chords of the arcs to approximate the common center of the arcs. They will then measure to find each radius. Students will use the formula for the circumference of a circle to find the other values. Use locally prescribed safety procedures for this activity.

Students’ answers can be used for assessment purposes.

Have students relate data gathered in the previous activity to show an understanding of the turning angle (toe- out on turns) of a vehicle. Have students relate tire squeal to turning angle. 

Students should demonstrate an understanding of the following:

1. The circular paths followed by the front wheels have a common center. Thus, they are arcs of concentric circles.
2. Concentric circles have different radii. Thus, the turning radius of each front tire is different.
3. If the radii are not equal, their circumferences are not equal.
4. Since all of the tires have the same diameter and the circumferences of the circular paths are not equal, each tire must make a different number of revolutions when driven in a circle.
5. Since each front tire has a different turning radius and makes a different number of revolutions, the turning angle of each tire is different.
6. A different turning angle for each front tire means the inside tire must turn at a larger angle than the outside tire, thus resulting in the tires being toed-out in relation to each other.

If the turning angle of a tire is not correct according to the design of the vehicle, the tire will be turning too slowly or too fast on turns, which may cause it to make a squealing noise even on slow turns.

Have the students discuss why the rear tires can move along circles of different radii and make a different number of revolutions and there not be a turn angle for the rear wheels.

Before starting this activity, go over the safety procedures to follow when using the alignment machinery. Students will measure the turning angle (toe- out on turns) for each front wheel of the test vehicle and find the difference in the angle measures. Have students replace one of the steering arms with a steering arm that is bent. Students will again measure the turning angle for each front wheel and subtract the angle measures. Have the students report their results and draw a conclusion regarding the effect of a bent steering arm on the turning angle of a wheel. Have the students relate this finding to a probable solution to the customer’s complaint.

Have an automotive technician visit your class to talk to students about the procedure for measuring turning angle and factors that can cause the turning angle to be altered. During the visit, ask the technician to discuss the automotive technician career major, educational requirements, benefits, and other interesting facts about a career as an automotive technician. Facts might include impact of the career choice on family and personal lifestyles; balance of career, family demand, and leisure time; and probability of steady employment. Use the assessment instrument of ICS G13 Consequences of Career Choice.

Have students write a descriptive paper explaining toe and turning radius (toe- out on turns). Have students measure toe on a vehicle.

Use similar triangles as a mathematical model to illustrate why correct toe alignment is critical in the correction of excessive tire wear.

Mathematics— Have students use similar triangles to show that, if the toe of a wheel is off a very small amount, it causes tire wear that is equal to the tire being shoved sideways.

Source: AYES