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| An example of suspension working to provide stable ride |
What’s ride?
By the word ‘ride quality’ or ‘ride comfort’ one actually means the feeling that one gets while car’s moving over rough terrain or is under the affect of braking / acceleration. How comfortable or uncomfortable one feels while sitting in a car is termed as perceived ride quality.
The perceived ride quality gets affected by a majority of factors like suspension design, weight, wheelbase, track, tyres etc.
Can a suspension system affect the ride?
Suspension system alone does not affect the ride quality, but is one of the major contributing factors to the ride quality of the car. As humans are sensitive to certain vibration frequencies more than others, it makes perfect sense to isolate the cabin from them. Extremely high frequencies originating from driveline and tyres are taken care by the rubber mounting on which the suspension components are mounted.
A suspension system uses a spring and damper unit. The function of spring is to absorb the shock which damper helps settle the spring to original position after it has absorbed the shock.
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| Damping and settlement time |
The static deflection rate of the suspension system (without the damper) is an important factor in determining how comfortable the ride would be. That is, the deflection that the spring undergoes with weight. Damping affects it in a way that over-dampening reduces ride quality dramatically. Therefore, in order to reduce the affects of over-damping at light loads, some degree of under damping is usually accepted when the car is fully loaded and it does provide a comfortable ride. Since suspension does not work in isolation, factors like laden weight, weight bias with luggage load, ride height under laden weight etc. are other parameters that affect the ride quality. Suspension systems are designed to achieve a best compromise and keeps all such factors is mind.
Does alloy wheels / wheel size / tyres have an affect on ride?
Effective wheel size affect the ride to a great extent and larger wheels generally provide a more pliant ride quality as they are able to absorb the shock created by larger crevices without the need to climb over them. Wheels of smaller diameter react more violently to potholes and undulations.
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| Wheel diameter affects ride quality |
Tyres with high aspect ratio (the ones generally found on SUVs) are generally more comfortable to ride on as they have the inherent capacity to absorb more shocks.
It’s worth noting that a car has sprung mass (comprised of chassis, occupants etc.) and unsprung mass (suspension components, wheels, brakes etc.). The disturbance from road is filtered by suspension systems and should ideally not be experienced by the sprung mass. The ratio of weight of the sprung mass to unsprung mass also affects the ride quality to a great extent, because as the speed of the car increases, the effective vertical force acting on the suspension increases (force=mass x acceleration). Therefore, with lighter wheels and lesser unsprung mass, you should be able to improve the ride quality considerably.
While people use alloys wheels in hope that it would improve ride. And they can, unless they weigh the same as steel wheels. If alloy wheels weigh the same as steel wheels, they serve only an aesthetic purpose and do not improve ride.
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| Pitch axis and Roll axis |
Can wheelbase / height of CG affect ride quality?
A car with smaller wheelbase would pitch more than a car with comparatively longer wheelbase. Similarly a car with wider track would roll less in comparison to the car with narrower track. But since all the forces are assumed to act through CG (Centre of Gravity) via tires, the overall height of the car also has an effect on the ride quality. It is for this reason you feel that SUVs roll more around a corner and may feel less comfortable than sedans.
With current generation of cars that adopt self-levelling and adaptive suspension, role of physics is somewhat reduced and it is for this reason we see cars like Macan perform more like a sports car and not like a typical SUV.
