I thought this article by Michael Graham was concise and simple. Post mark it for your discussions when comparing Delta's to Tadpoles, and some about front wheel drive vs rear.
Link (here) , Article in full below:
By Michael Graham, mechanical engineer and blogger at EngineerDog.com
I asked myself the same question before I designed a new solar powered race car chassis in college.
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Yea, I thought I was so damn cool.
To answer your question, we should first define the different three-wheeled vehicle designs:
Delta: One wheel in front, two in back.
Tadpole: Two wheels in front, one in back.
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Now lets compare the two designs for a few different desirable vehicle design characteristics.
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 designing a chassis, we can choose how the car will react when turning too fast. One of two things will always happen: either the car wheels will slip relative to the ground, or the vehicle will tip over. Obviously, slipping is the desired outcome. Keep this in mind for the moment.
When the car does slip out of control on a fast turn, we can design it in such a way that we know whether the front or rear wheels will slip first. This is important because if the rear wheels slip first, the vehicle runs the risk of spinning out of control (oversteer). If the front wheels slip first (understeer), you wont 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 all commercial cars. Which wheels will slip first is a simple matter of weight distribution and weight transfer.
The problem for delta vehicles is how to distribute their weight and control their weight transfer during a turn to avoid undesirable outcomes. If you design the weight distribution for a heavy front bias to achieve understeer, you increase the risk of tipping over. If you increase the weight distribution on the rear tires, the vehicle will oversteer in hard turns.
We also need to consider nose diving, which is exactly what it sounds like. When you slam on the brakes as hard as possible, the vehicle will either skid to a halt or the rear wheels will lift off the ground. This is also a function of weight distribution and weight transfer. It would seem that the delta design has an advantage here because it naturally lends itself to having a rear biased weight distribution. But in the real world, a hard stop doesn't always occur when traveling in a straight line. If you stop hard enough while turning with a delta vehicle, the weight will transfer to the front wheel enough (despite suspension designs to prevent this) to cause the vehicle to flip over at an angle. See the Reliant Robin video below.
Category Winner: Tadpole
Braking:
The front wheels on any vehicle provide the majority of your stopping power (something like 60-70%). The delta is at a disadvantage considering the weight distribution issues discussed above and the fact that it has one less front tire to brake on.
Category Winner: Tadpole
Simplicity of Design:
Steering is definitely easier to design for the delta. No special considerations need to be taken into account to avoid lateral wheel slipping on turns. The tadpole design has to incorporate extra linkages to approximate Ackermann steering geometry, as seen below, to prevent wheel slippage.
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Front suspension design is definitely easier on the delta. The best choice is the telescopic fork. The rear suspension design can be any number of options.
The reverse is true of the tadpole. Multiple choices are available for the front suspension, while the rear suspension is much easier to design (the swing arm being the obvious choice).
Imagine designing a toy tricycle for a child. Have you ever even seen a tadpole design for this?
Category Winner: Delta
Aerodynamics:
The tadpole design lends itself better to the aerodynamic tear drop with the correct length/width ratio more easily than the delta. (The ideal teardrop width/length ratio being 0.255) The image below shows how poorly the correct shape fits the delta design. Plus, you would have to encase more empty space with the delta.
Category Winner: Tadpole
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Powertrain:
The delta design has more disadvantages when selecting your drive wheel. If you go with front wheel drive, you risk putting too much weight at the front of the vehicle. If the you choose the back, you need to add a differential gear to the rear wheels. Even an electric motor is troublesome. If the motor is on the front, you don't want the heavy batteries up there for weight reasons. But if the batteries are in the back you have to run the main power cables to the drive motor a long distance and through to the passenger cabin. Either way you have a disincentive to have too much weight on the front driving wheel, so you miss out on potential traction.
A tadpole with rear wheel drive gets the best of both worlds. No differential is necessary and you can keep a good 30% of the vehicle weight on the drive wheel to maintain good traction.
Category Winner: Tadpole
Conclusion: For most vehicles the tadpole is clearly the best option on three wheels. However, the delta will always have value for niche applications...
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Link (here) , Article in full below:
By Michael Graham, mechanical engineer and blogger at EngineerDog.com
I asked myself the same question before I designed a new solar powered race car chassis in college.
[Broken External Image]
Yea, I thought I was so damn cool.
To answer your question, we should first define the different three-wheeled vehicle designs:
Delta: One wheel in front, two in back.
Tadpole: Two wheels in front, one in back.
[Broken External Image]
Now lets compare the two designs for a few different desirable vehicle design characteristics.
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 designing a chassis, we can choose how the car will react when turning too fast. One of two things will always happen: either the car wheels will slip relative to the ground, or the vehicle will tip over. Obviously, slipping is the desired outcome. Keep this in mind for the moment.
When the car does slip out of control on a fast turn, we can design it in such a way that we know whether the front or rear wheels will slip first. This is important because if the rear wheels slip first, the vehicle runs the risk of spinning out of control (oversteer). If the front wheels slip first (understeer), you wont 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 all commercial cars. Which wheels will slip first is a simple matter of weight distribution and weight transfer.
The problem for delta vehicles is how to distribute their weight and control their weight transfer during a turn to avoid undesirable outcomes. If you design the weight distribution for a heavy front bias to achieve understeer, you increase the risk of tipping over. If you increase the weight distribution on the rear tires, the vehicle will oversteer in hard turns.
We also need to consider nose diving, which is exactly what it sounds like. When you slam on the brakes as hard as possible, the vehicle will either skid to a halt or the rear wheels will lift off the ground. This is also a function of weight distribution and weight transfer. It would seem that the delta design has an advantage here because it naturally lends itself to having a rear biased weight distribution. But in the real world, a hard stop doesn't always occur when traveling in a straight line. If you stop hard enough while turning with a delta vehicle, the weight will transfer to the front wheel enough (despite suspension designs to prevent this) to cause the vehicle to flip over at an angle. See the Reliant Robin video below.
Category Winner: Tadpole
Braking:
The front wheels on any vehicle provide the majority of your stopping power (something like 60-70%). The delta is at a disadvantage considering the weight distribution issues discussed above and the fact that it has one less front tire to brake on.
Category Winner: Tadpole
Simplicity of Design:
Steering is definitely easier to design for the delta. No special considerations need to be taken into account to avoid lateral wheel slipping on turns. The tadpole design has to incorporate extra linkages to approximate Ackermann steering geometry, as seen below, to prevent wheel slippage.
[Broken External Image]
Front suspension design is definitely easier on the delta. The best choice is the telescopic fork. The rear suspension design can be any number of options.
The reverse is true of the tadpole. Multiple choices are available for the front suspension, while the rear suspension is much easier to design (the swing arm being the obvious choice).
Imagine designing a toy tricycle for a child. Have you ever even seen a tadpole design for this?
Category Winner: Delta
Aerodynamics:
The tadpole design lends itself better to the aerodynamic tear drop with the correct length/width ratio more easily than the delta. (The ideal teardrop width/length ratio being 0.255) The image below shows how poorly the correct shape fits the delta design. Plus, you would have to encase more empty space with the delta.
Category Winner: Tadpole
[Broken External Image]
Powertrain:
The delta design has more disadvantages when selecting your drive wheel. If you go with front wheel drive, you risk putting too much weight at the front of the vehicle. If the you choose the back, you need to add a differential gear to the rear wheels. Even an electric motor is troublesome. If the motor is on the front, you don't want the heavy batteries up there for weight reasons. But if the batteries are in the back you have to run the main power cables to the drive motor a long distance and through to the passenger cabin. Either way you have a disincentive to have too much weight on the front driving wheel, so you miss out on potential traction.
A tadpole with rear wheel drive gets the best of both worlds. No differential is necessary and you can keep a good 30% of the vehicle weight on the drive wheel to maintain good traction.
Category Winner: Tadpole
Conclusion: For most vehicles the tadpole is clearly the best option on three wheels. However, the delta will always have value for niche applications...
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