billyk
Guru
I am often enough wrong, and don't mind being corrected.
But I think @Henri and @JerseyJim are talking about something entirely different than gaining extra power by using your arms/hands/upper body (the big selling point of Cruzbike, and the reason these bikes are better climbers than other recumbents). They're talking about balancing pedal steer, which is minor and becomes automatic in the first few weeks of riding. It requires little force (as shown by the fact that many of us can ride these bikes no-hands). Sure you can balance pedal steer by either pushing or pulling on the bars, but it seems of small importance.
If we're talking about the CB advantage by engaging the upper body, @benphyr said it well above: The only way the bike is propelled is by exerting a forward force on the pedals with your feet. To do that you need a countering force that braces your feet pushing forward, otherwise they would just push your body backwards (Newton's 3rd law).
How can we gain that countering force? It has to be directed forward. There are two ways to do it:
1) Push against the seat back (the seat balances the leg push)
2) Pull with your arms (the handlebars balance the leg push)
Either of these results in bracing your legs so your feet can push strongly on the pedals. A traditional recumbent allows only the first.
In practice we use both methods: for easy cruising the first is fine, but when you want to accelerate, or climb, or sprint, add the second. That's the CB advantage.
In no way can pushing forward with your hands on the bars balance pushing forward with your feet. It has no effect on the force you can exert with your feet. All it does is try to push two relatively immoveable objects apart: the bars and the seat back. It's like standing in a narrow hallway and pushing against both walls: a useless waste of energy.
The design of CB bikes (the front triangle and strong handlebars) is all about being able to use your whole body to gain maximum push forward with the feet against the pedals. Those of us who've been through a few generations of CBs saw the early Quest models evolve to strengthen that front triangle, explicitly to make it more effective to pull on the bars to add extra power.
That's why the boom now connects directly to the bars with a big beefy tube: you get to pull directly against the bottom bracket. And why CB handlebars are thicker and stronger than those needed by traditional recumbents, which can be quite flimsy because they are just holding the brakes and shifters convenient to where your hands are (note the fold-down handlebar stems on many Bacchetta bikes). Both of these add weight, but are worth it by allowing this new form of usable power.
If you doubt the power that the arms and upper body can put out, consider rowing a boat (or a racing shell). The motion is to lean back and pull with your arms; as long as the feet are braced it's a very powerful motion. It's like what we do in reverse. Now try rowing a boat without bracing your feet: you will find that the power goes right away. That ability to use the feet to brace the arm-and-back pull in a boat, or the arms and back to brace the foot-push (on a CB bike) maximizes the strength of the human body.
But I think @Henri and @JerseyJim are talking about something entirely different than gaining extra power by using your arms/hands/upper body (the big selling point of Cruzbike, and the reason these bikes are better climbers than other recumbents). They're talking about balancing pedal steer, which is minor and becomes automatic in the first few weeks of riding. It requires little force (as shown by the fact that many of us can ride these bikes no-hands). Sure you can balance pedal steer by either pushing or pulling on the bars, but it seems of small importance.
If we're talking about the CB advantage by engaging the upper body, @benphyr said it well above: The only way the bike is propelled is by exerting a forward force on the pedals with your feet. To do that you need a countering force that braces your feet pushing forward, otherwise they would just push your body backwards (Newton's 3rd law).
How can we gain that countering force? It has to be directed forward. There are two ways to do it:
1) Push against the seat back (the seat balances the leg push)
2) Pull with your arms (the handlebars balance the leg push)
Either of these results in bracing your legs so your feet can push strongly on the pedals. A traditional recumbent allows only the first.
In practice we use both methods: for easy cruising the first is fine, but when you want to accelerate, or climb, or sprint, add the second. That's the CB advantage.
In no way can pushing forward with your hands on the bars balance pushing forward with your feet. It has no effect on the force you can exert with your feet. All it does is try to push two relatively immoveable objects apart: the bars and the seat back. It's like standing in a narrow hallway and pushing against both walls: a useless waste of energy.
The design of CB bikes (the front triangle and strong handlebars) is all about being able to use your whole body to gain maximum push forward with the feet against the pedals. Those of us who've been through a few generations of CBs saw the early Quest models evolve to strengthen that front triangle, explicitly to make it more effective to pull on the bars to add extra power.
That's why the boom now connects directly to the bars with a big beefy tube: you get to pull directly against the bottom bracket. And why CB handlebars are thicker and stronger than those needed by traditional recumbents, which can be quite flimsy because they are just holding the brakes and shifters convenient to where your hands are (note the fold-down handlebar stems on many Bacchetta bikes). Both of these add weight, but are worth it by allowing this new form of usable power.
If you doubt the power that the arms and upper body can put out, consider rowing a boat (or a racing shell). The motion is to lean back and pull with your arms; as long as the feet are braced it's a very powerful motion. It's like what we do in reverse. Now try rowing a boat without bracing your feet: you will find that the power goes right away. That ability to use the feet to brace the arm-and-back pull in a boat, or the arms and back to brace the foot-push (on a CB bike) maximizes the strength of the human body.
