A wider track width is where the wheels are offset more than before, or more than another set of wheels. For example; the go kart in the image below has a wider track width on the rear set of wheels than the front set of wheels do.
Increasing track width can have a variety of effects on the handling and stability of the vehicle, both in a positive and negative manner.
Increasing track width may have the following effects on a vehicle.
Reduces weight transfer
Reduces body roll
Softens spring rate
Increases surface area and drag
Increasing the track width will widen the tyres contact patch. This will reduce a vehicles weight transfer significantly. This reduced weight transfer will also lead to a reduced amount of body roll.
Not only that, assuming the shocks and springs stay in the same location, the effective spring rate will be reduced, this is due to a change in the suspension geometry. To put it another way, the wheel has more "leverage" on the springs/shocks.
Basically, it means less spring movement will happen for a given amount of vertical wheel movement.
Widening the track width may also increase the total surface area of the vehicle, increasing drag.
One other thing to note is a slight increase in weight due to the wheel spacers or longer control arms, whichever is used to increase the track width.
There are key benefits to increasing the track width of a vehicle, as listed below.
Widening the track width reduces weight transfer and body roll, increasing vehicle stability, especially at high speeds.
The effect of a reduced spring rate will also improve grip.
You can also have different track width setups, such as wider on the front track or wider on the rear track. Depending on your goal and preferences, you can gain specific advantages from these setups.
A wider track width on the rear will allow drifting to be easier as the rear of the vehicle will be less stable and more inclined to rotate.
Increasing the front track width improves forward stability, decreasing the risk of rotation at the rear of the vehicle. This is the usual setup for most road cars as it is safest.
There are some major drawbacks of a higher track width, such as listed below.
Increased turning circle
A wider track width will result in a larger turning circle, this can make tighter turns more difficult and the car will be less agile.
As mentioned further above, an increased track width will result in increased surface area of the vehicle, increasing drag and therefore reducing top speed and even acceleration.
Wider Front Track Width
A wider front track width, as seen on most stock road cars, is the safest setup as it increases forward stability, reducing the likelihood of a spin out.
This causes less weight transfer on the front wheels, increasing body roll in the rear and weight transfer onto the rear tyres, having the secondary effect of increasing the likelihood of understeer (especially on front-wheel-drive vehicles).
Wider Rear Track Width
A wider track width on the rear of a vehicle will allow the rear of the car to slip and come out of line with the front wheels more easily. This is great for drifters.
Widening the rear track compared to the front increases load on the front wheels during cornering, increasing the ability to steer and corner if properly setup. However, it also increases the risk of a spin out and oversteer.
When turning, the track width has an impact on weight transfer. The wider the track, the less weight is transferred from one side of the vehicle to the other.
The height of the centre of gravity, the cornering force, and the average track width all affect total weight transfer.
However, since the larger end of the vehicle transmits a lesser portion of this total, the vehicle 'leans' diagonally towards the end with the narrower track.
Because more load on a tyre results in a greater slip angle, a wider track at the rear will cause the vehicle to lean on its outside front tyre, causing understeer, whilst a wider track at the front would cause it to lean on its outer rear tyre, causing oversteer.