STITES DESIGN PRODUCTION BLOG

Golden Ratio for Truck Trike = about .25 !!

July 9th, 2010 by Bill

There is a golden ratio for vehicular efficiency, that is, vehicle weight / cargo weight.  A typical truck that weighs 8000 lbs., and often carries 2000 lbs. of cargo around town, comes in at “4″.  That’s obese!  One wants to get the ratio below “1″, where the cargo weighs MORE than the vehicle.  Who’s the king of the golden ratio?  the cargo bicycle, the cargo trike, or maybe the electric cargo trike??

Honoring the ‘golden ratio’, we can achieve high levels of efficiency.  The Truck Trike is coming in around 215 lbs.  That’s just where we wanted to be, in the 200 – 250 range.  And there’s the ambitious cargo load – 800 lbs.  Then there’s the rider’s weight, and batteries.  If we include the batteries in the vehicular weight, and the rider in the overall payload, we could easily see 250 / 1000.  That’s 1/4 or .25   Excellent.

Bringing in electric assist allows the rider to move these heavy loads at a reasonable pace.  Using dual electric drive motors, with the right gearing, allows us to power total vehicle weight that can top 1,000 pounds – yeah, that’s a 1/2 ton!

So, the flip side of the power coin, is stopping all this mass.  We have spec’d some new motorcycle/scooter level hydraulic disc brakes on the rear, and I am presently working on the custom hardware to mount these components.

One Response to “Golden Ratio for Truck Trike = about .25 !!”

1. Tony D says:

Bill, I think you are way ahead of the curve with the Truck Trike’s weight. Here’s how I see the numbers on vehicular efficiency.

Vehicles are intended to move things from one place to another and thus their efficiency is defined by how much energy is required to move a given amount of payload (passengers and cargo) a given distance. To a first-order approximation, the energy required to propel a vehicle is proportional to the vehicle’s total weight (ie. vehicle + fuel + passengers + cargo). To calculate the relative energy efficiency of a vehicle, the weight of the payload is divided by the vehicle’s total weight. Thus an ideal, weightless vehicle would have an efficiency of one (100%). If the weight of the empty vehicle equals that of its payload then the efficiency drops to one half (50%). Some typical vehicle efficiencies:
Automobile – 10%
Jet airliner – 30%
Bicycle – 90%
Saturn Rocket – 1%

[A short diversion]
Like Pi, the Golden Ratio (Phi) is one of the universal mathematical constants passed on to us by the ancient Greeks. It is defined as the number to which you add one and then invert to get the same number again (approximately 0.62). It shows up all over the natural world and is a fundamental of Renaissance aesthetics. Its relevance to the topic at hand is that it sits at the sweet spot of vehicular efficiency – a vehicle that weighs 62% of its payload has an efficiency of 62%. Further reducing vehicle weight quickly reaches the point of dimishing returns in efficiency and comes at the cost of a host of other parameters like safety, convenience, range, and speed.

Your Truck Trike comes in at an enviable 80% efficiency. You could more than double the weight of the vehicle and still hit the Golden Ratio! That leaves a lot of room for hydraulic brakes and other safety/convenience features. Nice work!