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Old 01-05-2013, 02:46 PM   #51
icebox
Studly Adventurer
 
Joined: Sep 2008
Location: West Yellowstone, Montana
Oddometer: 988
Quote:
Originally Posted by ph0rk View Post
I'n not sure who cx is.

Ah yes, 40 mph headwinds at 7000 feet. Sure, that happens every day (outside of the Rockies and Sierras, not much at all in the US). My bike had plenty of power (sans headwind) around 5000-6000 feet on a steep grade, two up. Around here, elevations anywhere close to that and no wind would be only a headwind for long, and then you've got other problems, problems cars aren't immune to either (40mph side wind sucks no matter what vehicle you're in). Sustained winds that speed are rare here, are they an everyday thing where you live?

The same story is true with a Honda fit as with an accord, with even worse power numbers. You don't need more than 65 hp to tour at legal speeds unless you're ridiculously over the GVWR of the bike.


An engine is a pump, so power loss at altitude (temperature held constant) is just due to air density. Assuming the same air temp, you've got 781.858 milibars at 7k, and 1013.25 at sea level (of course, more like 984-998 where I live):

781.858/1013.25 = 77.163% of sea level air density, and thus 77.163% as much air can flow through the engine.

65hp * 77.163 = 50.156 (again, same air temperatures assumed),

I suppose if you lived at that elevation you might get bent out of shape about it, but the majority of the US land area is at far lower elevations.



Nothing wrong with wanting more power than that, but need it? no. I suppose if you want to sit at 95mph actual at 7,000 feet into a 40 mph headwind you need a busa, but otherwise...
In fluid dynamics, the drag coefficient (commonly denoted as: cd, cx or cw) is a dimensionless quantity that is used to quantify the drag or resistance of an object in a fluid environment such as air or water.

All that to prove I was off by 2.156 HP, 48 vs. 50.146, but maybe the barometric pressure was lower that day. I LIKE 650 Vee Stroms, nice bike, and capable of most anything with the right rider. And yes I live at 7000' and if you cross Wyoming or much of Montana 40 MPH head winds, tailwinds are a hoot, are not uncommon. In fact most days we ride we deal with strong winds coming home.

So what did the OP buy? I am jealous. Spending way too much time in the flea market, luckily new bikes are at least a hundred miles away.
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