Wheel travel tests performed on the rear suspension

the end region of the test. Due to the fact that the bump stops will come into play some variability in the calculations will be induced, this is seen from the oscillations that are present in the final parts.

Figure 5.19: Roll centre vertical position as wheel travel changes over the two tests

this is due to the fact that the solid axle suspension at the rear will be more rigid than the double wishbone employed at the front axle.

Figure 5.20: Vertical force experienced by the rear suspension in function of wheel travel

Figure 5.21: Total Rear Track Variation in function of wheel travel

Contact points positions in Figure 5.22 and 5.23 define how much the wheel moves when the suspension changes its travel, calculations are done on the left wheel.

Figure 5.22: Contact point along X-axis in function of wheel travel

Figure 5.23: Contact point along Y-axis in function of wheel travel

Parallel travel will have a small variation in position along the Y-axis but a large envelope in the variation of position along the vehicle’s side. Opposite travel will show a large variation in the Y-axis displacement, variation in X-Y-axis is relevant but less pronounced than the parallel wheel travel case, from these tests it is possible to understand that wheel travel will move the wheel in side-view,

changing the wheelbase as an effect.

The roll centre variation will be linear for the parallel wheel travel and almost constant with a parabolic trend for the opposite travel case, this is clearly shown in Figure 5.24.

This parameter follows what was found for the wheel track, the opposite wheel travel condition will make the roll centre position balance itself as the two wheels show a travel that has opposite trends between them.

Figure 5.24: Roll centre variation for the rear axle

To conclude the analysis on rear steering an analysis on the Anti-lift during braking was performed in Figure 5.25 comparing the two vehicle configurations.

Anti-lift is a characteristic that evaluates how much a vehicle resist to the motion of the vehicle that during braking will make the nose pitch down and the rear of the vehicle to lift, an anti-lift of 100%

at the rear will mean that the vehicle is flat during braking.

The two configurations react similarly between them, the highest difference come from positive wheel travel conditions, near neutral travel, especially for negative values the two characteristic almost overlap.

To conclude, it is important to know that the rear suspension also reacts to static excitations like the ones present in this study, by comparing the graph between the front and the rear axles it is possible to see how much difference there is between the two suspension systems.

Alignment parameters such as toe are not evaluated for the rear axle, due to the fact that a solid axle will have a negligible variation in toe and the variation in camber will be better explained in paragraph

6.1, the main difference comes from the contact point distribution and the fact that anti-lift is almost the same between the two vehicles.

Figure 5.25: Anti-Lift characteristic during braking in function of wheel travel

Figure 5.26: Anti-Squat Characteristic for the rear suspension during acceleration

The graph passes from positive values to negative values, this changes the characteristic to a pro-lift, it means that the suspension geometry will induce lifting in the suspension, and not counteract it,

during braking, the compression of the suspension largely affects the instantaneous centre location and this leads to a change in sign for the characteristic.

Figure 5.27: Camber angle variation on the rear suspension in function of wheel travel on the left wheel, the right wheel characteristic will be the same

Since the vehicle is rear wheel driven, it is also interesting to check the anti-squat characteristic of the suspension, this resulted in the graph in Figure 5.26.

This characteristic expresses how much the vehicle will counteract the squat that will happen when the vehicle accelerates: In acceleration the torque applied on the rear wheels will induce the rear suspension to compress and lower themselves resulting in a nose-up of the vehicle. An higher anti-squat percentage will mean that the suspension will counteract this motion more, a negative anti-anti-squat will favour the squatting motion of the suspension. This characteristic will be positive only towards negative wheel travel points, the difference between the two configurations is clearer for positive wheel travels, the shorter vehicle will have a higher slope compared to the long wheelbase vehicle.

To end the discussion on the rear suspension an analysis on camber angle is performed, mind that camber angle is expressed in relation to the body vertical line, as explained in Chapter 2.

Parallel travel will show almost no variation in camber, while opposite travel will show high variations, this is mainly due to the fact that a suspension like this will not have camber recovery. A twist of the suspension system showed by an opposite wheel travel motion will induce a camber variation, that will be almost symmetric between positive and negative wheel travels, the variation will also be affected by the fact that the vertical line from which camber is evaluated will also change

in tests like this, that basically induce some roll angle to the vehicle, this will amplify the difference in the case of the opposite wheel travel test. Results are shown in Figure 5.27.