When it comes to trikes there are several parameters that change the trike dramatically. The main one is the wheel configeration because it affects the balance of the trike. There are two main options when considering a three-wheeler, Two wheels Front and one wheel rear (2F1R) which is known as a TADPOLE and the other is One Front Wheel and Two Rear Wheels (1F2R) which is known as a DELTA configuration.
For the purpose of this blog I will leave out of the equation what happens when you build the trike to lean over in the same way that you would lean a motorcycle. The reason I want to leave it out is that “leaning” the trike changes everything and in some ways makes either configuration work to an acceptable level, overcoming most of the shortcomings. But in this post I want to stick to the basic designs to try and unearth which is the BEST starting place.
3 Wheelers Are Not A New Idea
From the very earliest days of motoring, engineers have toyed with three-wheeled automobiles. In fact, the Benz Patent Motorwagen, generally considered the first motorcar, rolled on three wheels.
Many companies have had a go at getting the 3-wheel concept right but they have never really lasted.
Out of the Tadpole and the Delta configerations, it is the tadpole that is more common because having two wheels up front greatly improves stability and braking and the design typically offers excellent aerodynamic efficiency.
Why Would Anyone Build A Trike?
Often, it comes down to economics. They can be cheaper to build than a conventional car, especially if you’re a boutique builder or startup, because they’re classified as motorcycles and therefore not subjected to rigorous (and expensive) crash testing and other regulatory hurdles.
They offer greater protection than a motorcycle and lower operating costs than a car, which made three-wheelers like the BMW Isetta and Messerschmitt KR-series, popular in Europe and Japan after World War II.
Messerschmitt bubble car
A great help to me when starting to understand aerodynamics is that aquadynamics (water) follows very closely to aerodynamics. This is good because there are a number of large marine animals that benefit well from having excellent aquadynamics and these shapes can be used when developing things that need to pass through the air as well.
The engineers at Airbus got a lot of their ideas from a whale because of the relative ease with which it moves underwater, even while weighing tons and having a large body. So they incorporated the whale’s body structure and ran aerodynamic simulations.
Tadpole fits into aerodynamic flow
As you can see, the whale body shape is basically just a version of the Tadpole shape.
This is the most important part of the Trike experience because we have come to love the trike for its ability to be cheaper to develop due to the fact that it is more often categorised as a motorcycle and not a car. (Cars in most countries have much more detailed, which equals expensive, conditions to adhere to.)
So handling is all important because what use is a pleasure vehicle if it can’t handle well. We want speed, handling and comfort otherwise we may as well stick with the more rudimentary 4 wheel design.
Dynamic Stability: When a vehicle is said to be dynamically stable it is meant that it reacts safely and predictably under various driving conditions.
When we look at designing a car, we have to choose how the car will react when we try to turn the car at too high a speed. One of two things will always happen: either the car wheels will slip across the ground, or the vehicle will try to (or actually) flip over. Obviously, slipping is the preferred outcome as it gives us more opportunity to fix in the moment whereas flipping is pretty permanent and damaging to car and driver.
So now the choice is, do we want the front wheels to slip out (understeering) or the back wheel/s (oversteering)?
If the front wheels slip first (understeer), you won’t spin out and it is easier to regain control. Understeer is considered a safe dynamic response to slipping in a turn and is designed into almost all commercial cars. Which wheels will slip first is a function of weight distribution and weight transfer during turns.
The problem for Delta three wheel vehicles is how to distribute their weight and control their weight transfer during a turn to avoid oversteering. If you design the weight distribution for a heavy front bias to achieve understeer, you increase the risk of tipping over. Alternatively, if you increase the weight distribution on the rear tires, the vehicle will oversteer in hard turns (aka 911 Porsche rear engine), which is also bad.
So the Delta has the problem positioning the weight just right. Have a look at this video from Top Gear about the Reliant Robin After you have stopped laughing think about how bad that is for a sports vehicle.
With the Tadpole design we get to have more options to overcome some of these weight based issues. The first being braking. Most braking power comes from the front wheels in a normal car (60 to 75%). When we brake hard, we throw a lot of force into the front wheel/s. If it is a Delta setup then we have less rubber on the road which will make stopping harder and if braking hard into a corner we risk the weight transfer flipping the car altogether.
In both cases of the Delta Trike and the Tadpole Trike, we want to keep them as low to the ground as possible. Centre Of Gravity is easiest to control if the weight is kept low to the ground. However this of course brings in a major problem. Visibility.
We need to be able to use this vehicle in the day to day traffic of a city and that requires two types of visibility. Other cars seeing us and us seeing over/around other cars.
When you build a car too low to the ground (or the drivers head position) you immediately restrict the visibility of the driver in both the above cases. So that is why we are seeing the new crop of “Sit Upright” trikes coming where the drivers head is level with a car driver’s head and the centre of gravity is addressed by keeping all the batteries (weight) for these electric trikes low.
With the Delta shape you need to position the driver and passenger as far back near the rear wheels as you can. This of course means that you end up with a very long nosed vehicle. The Tadpole (especially for a single seat car) provides a much easier layout to get the weight balance right. With the whale shape (Tadpole) being more aerodynamic this seems to me to be a more obvious choice.
Driving the wheel/s
The next issue to consider is driving the power from the engine or motor into the wheel/s. This is obviously MUCH easier on the tadpole trike as we only have the one wheel to drive. It only needs to be supported by a swingarm (which we can get off the motorbike that is donating its engine to us.
On the other hand, the Delta has a couple of options which can get quite complicated. If you only drive one of the rear wheels (which is cheaper) it throws off the balance of the car and can cause different issues in extreme circumstances. If you drive both the rear wheels then you are adding extra wieght just where you need to have people sitting.
I think from my research that to make a trike or 3-wheeler based on anything but the Tadpole configuration is just asking for trouble. We know that making the trike lean into the corner (as a motorbike does) will help erase any of these problems BUT why start with problems in the first place.
I know for me. The Tadpole will be the start. Cheers.
Hello, I am Jonathan, a lover of vehicles that spark the imagination, make your blood boil and take you to a place where time stops and the moment is everything. Hence my love of trikes.