Mc Pherson Strut - Wheel and Ride Rate Modifications

MDI _ Mc Pherson Front Suspension Adams Model

Wheel Rate of the baseline suspension system

Wheel rate at 0 wheel travel is 32.77 N/mm 

The target wheel rate is 20 N/mm

Baseline Motion Ratio = 0.93 

Ride Rate at 0 wheel travel is 28,16 N/mm 

Motion Ratio = sqrt(28,16/32,77) = 0.93  (Adams found the same) 

Required wheel rate is 20 N/mm 

So ride rate should be = 20 x 0.93^2 = 17,298 N/mm

Changing the spring stiffness around the same percent from 50N/mm to 30,7 N/mm doesnt change the wheel rate at rest position but it increases in both bounce and rebound. 

Wheel rate at 0 travel is still 32.77 N/mm

20 N/mm is reached with the following adjustments

New ride rate is 18,5 N/mm more than what we calculated with formulas. Because we can not predict the motion ratio shift when we change the installed length. Thats why we need softwares as ADAMS

Now we try to achieve the same wheel rate from baseline by just modifying the hardpoints not spring characteristics

 Different Modifications are tested. 

With mod_7 21 N/mm Wheel rate is achieved. But this installation is not plausible. Thats why we have to play both spring and hardpoints. 

 Changing HP and Spring characteristics

Wheel rate achieved = 20N/mm

Ride_rate = 18.16N/mm

If we arrange the motion ratio = 1 we would get the same ride rate as wheel rate in theory.