How does varying wheelbase during automobile design affect the properties of the vehicle that is going to be built (both two-wheelers and four-wheelers)? I know that greater wheelbase means less maneuverability (or maybe it's the other way around). Based on what factors will the wheelbase be finalized and manufactured? What figures of wheelbase are considered ideal, and why?
There are two concepts to understand (which I think you might already get to an extent). As the wheel base length grows, stability is gained, but you lose maneuverability. You also risk the greater chance of the vehicle becoming high-centered (ground rubbing the center of the vehicle) when traversing bumps in the road unless you increase the ride height of the vehicle or in some way gain more ground clearance, but then you lose some stability due to a higher center of gravity. Conversely, as the wheel base length shrinks, stability is lost, but you gain in maneuverability. Some of the stability can be regained through widening the wheel track (distance between the tires on a given axle).
There are many different reasons why a manufacturer would adjust the wheel base on a vehicle.
- Use: If a vehicle is to be used off-road (4-wheel drive) purposes, the wheelbase will not be made as long as the longer it is, the easier it will be to get high-centered. If a vehicle is meant for high speed cornering, the vehicle will be lower to the ground and the wheelbase will be longer, with wheels set more forward and back relative to the end of the vehicle.
- Aesthetics: How does the designer want a vehicle to look when it's put together?
- Manufacturing Costs: When you lengthen a vehicle, costs (such as frame/suspension strengthening and stiffening) come into play, which can drastically change cost.
- Viability: Does the vehicle actually need a longer wheelbase to function properly? This goes hand-in-hand with what was said earlier.
- Interior Space: As you lengthen the wheelbase, the interior space can be increased.
- Weight Distribution: Wheelbase has a great affect on weight distribution, depending on where the axle centers are located in the vehicle.
- Weight: As you lengthen a wheelbase while keeping the same distance in front/back of the wheels, your vehicle weight will increase to "fill in the gap" between the wheels, as well as what is needed to strengthen the vehicle to be able to handle the extra forces put on it to support it. If you do not overall lengthen the vehicle when increasing the wheelbase, the weight will not increase, but you will lose in other areas, such as trunk (boot) space in the rear.
One other thing with relationship to motorcycles:
- Torque Stability: If the wheelbase is not sufficient where there is an excess of power/torque, the front tire will always want to raise during a power filled takeoff. To counter act this, longer trailing arms will be added which creates a longer lever with the same amount of weight, thus giving the bike more stability on takeoff. (This is counteracting the want of the bike to do a "wheelie" during takeoff).
These are the basic reasons for selecting a wheelbase by a manufacturer, but there is no magic "formula" for a wheelbase. A manufacturer must decide for itself why it would want to use a wheelbase of a certain length. They will take all of the factors into account and use what it determines as best for the vehicle design, use, aesthetics, viability, and cost factors.
The first and most important criteria is what the intended use of the vehicle will be and where it will be operated.
Two British Prime Ministers being very tall, Jim and Ted, my department 'stretched' vehicles for them to have extra leg room in the back of the vehicle. When a British University was going on an field trip to the Himalayas, we provided LandRovers with really high ground clearances. Mrs T wanted more 'office space' in the back.
The directional stability was maintained by a front suspension re-jig which held the vehicle true to the Ackermann Theory. This ensures that the rear wheels will follow the direction of front.
The length of the vehicle on nearly all vehicles is irrelevant because it it not extreme, until you get into the sphere of the 'stretched limo'. Then you drive on the highway as if you were driving a semi-trailer.
The length of the wheel base will always be decided by its vehicle use.