( long post coming up, but hey, it's winter and bass season just closed up here. If I'm the only one who reads through all this, I understand )
I agree that most people intuitively understand how the different gears on a bicycle help them on varying terrain, but the explanation above is technically incorrect. The power required to bike uphill at a certain speed is the same (neglecting friction loss), regardless of which gear ratio the cyclist is using. The difference is in the torque and RPM required to deliver that power. Higher torque with lower RPM for higher gear ratios, lower torque and higher RPM for lower gear ratios.
Friction doesn’t complicate things very much. Since my last post was talking about a chosen bait at a chosen speed, the drag from the lure is not a differentiating factor. For constant retrieve speed, lure drag and especially line drag will change depending on how much line you have out, but again, this is independent of your reel choice. Friction within the reel will sap a bit of power, but I think the difference between the same reel in high/low gear would be negligible. With faster moving parts in the low gear ratio reel (to achieve the same spool speed), the power loss would actually be higher.
The difference in IPT at the start/end of a cast is absolutely valid (demonstrated with actual measurements by @Team9nine). It’s a good point for the discussion, and it doesn’t conflict with any of the posted formulas/explanation (the effect is the same for reels of any gear ratio). Carrying on with the idea of “optimizing” gear ratio – if one was going down that unnecessary road, they would do well to use an average operating spool radius (and IPT) in their calculations, rather than the nominal radius/IPT at full spool capacity. Reel size would come into play as you said – an optimized, larger-spooled reel wouldn’t stray as far from to the “sweet spot” of comfortable RPM/torque at the start/end of the cast, but one would need to consider the disadvantages of large reels as well.
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What’s missing from my last post (…to be continued…) is an explanation of how to incorporate “required effort” into the calculations, and ultimately into the choice of gear ratio. This is related to the “required power,” but it’s not the same. The formulas in the last post show that for a chosen lure and chosen constant retrieve speed, the required power is independent of gear ratio, IPT, spool size, etc. On the other hand, required effort to achieve the same presentation DOES depend on these reel parameters.
To explain this, think of the angler as the engine in a car (the reel is the drivetrain). People who race cars (or play video games) might be familiar with visualizing engine performance by plotting the torque generated at full throttle against the engine RPM. Multiplying Torque x RPM on the same plot would give you a power delivery curve (power vs RPM). You could make the same plots for an angler operating a reel, except instead of the torque/power generated at full throttle, you’d be interested in the torque/power generated at a given “effort” or “comfort” level.
Like engines, no two anglers are the same, and these curves would be unique to each person (they’d also depend on reel ergonomics, crucially the handle length). Even for different anglers though, the curves would share similar traits. I’ve drawn a conceptual version of what these curves might look like (below, left), showing torque/power output for “low effort/high comfort” (black), “medium effort/medium comfort” (green), and “high effort/low comfort” (red).
You can imagine similar curves for any effort level between or above/below these ones. For fishing a crank-n-wind type of lure all day, the idea is that you want to expend the least possible effort by operating on curve that is as low as possible on the chart. The second image (below, right) shows the same power curves, with a horizontal line added which represents the power required to reel your chosen lure at chosen speed (Pcrankbait = [lure drag force] x (retrieve distance) ÷ [elapsed time]).
All of the power curves intersect the Pcrankbait line, which in practical terms means that you could achieve the same presentation at any effort level by changing the handle RPM (ie: changing the gear ratio of your reel). I’ve indicated hypothetical cases on the chart, where too high or too low a gear ratio would leave you operating on the med or high effort curves, rather than the low curve.
Conveniently, the Pcrankbait line intersects the “low effort” curve near its peak. If it didn’t intersect at a peak, remember that these are just three curves drawn for example, you could infill the chart with curves for any effort level.
The RPM at the intersection with the peak of the lowest effort curve (call it ωopt, in angular velocity units) is the optimal cranking rate that would let the angler fish this crankbait at the desired speed with least effort. From here it’s simple to calculate the OPTIMAL GEAR RATIO (Gopt) the angler should select:
Gopt = (ωspool) / (ωopt)
Where ωspool is the angular velocity of the spool at the chosen lure speed, calculated as:
ωspool = 2*π*(lure speed) / (spool circumference)
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