Sadly three-wheelers have a bad name that they do not deserve, this mainly comes about because of jokes about the Reliant, the truth however is the steering on a three-wheeler is far more responsive than on a four-wheeler.
Steering Response Time
To discover why the steering is more responsive on a three-wheeler than a four-wheeler we need to compare the Yaw response time.
Yaw response is the time it takes after a quick steering input until the vehicle reaches a steady state.
Three-Wheelers have a very rapid yaw response time, so rapid that a well-designed three-wheeler can have a yaw response time of just 0.10 seconds.
The average four-wheeled car has a yaw response time of 0.30 seconds.
So the yaw response time is 33 percent less than the average car, even sports cars can not match the yaw response time of a three-wheeler. Most sports cars having a yaw response time of about 0.15 seconds.
Why is the Yaw response time quicker
While we have been pointing out the difference between three and four-wheeled vehicles the yaw response time has nothing to do with the number of wheels.
The quicker steering response is, in fact, a by-product of having fewer wheels. Fewer wheels equal less weight, less weight equals less mass so less polar moment of inertia.
Why does responsive steering matter?
Having more responsive steering means the vehicle will respond quicker, turning quicker means you can quickly avoid other vehicles and avoid accidents.
When I was a Truck driver I saw many accidents and many close calls, what I started to notice was the ones that were managing to miss the accidents were the smaller lighter cars, the bigger heavy cars seemed unable to turn in time to miss them and just ploughed straight into the vehicle in their path, where the small ones often could turn in time. The reason for this is the smaller cars have more responsive steering.
Note: This only applies to symmetrical three-wheelers, other forces come into play for non-symmetrical three-wheelers and motorcycles with sidecars.