Originally Posted by Heatwave

Your link doesn't work but unless it shows a GPS reading I can assure that a 2006 bagger's speedo is off (light) by 4-5mph at 120. So strap a GPS on that sled and then come back with your readings.

Originally Posted by Heatwave

Yep...I have several degrees in fact but this debate doesn't require a college degree. My HS Senior son could have taught you alittle something from his AP Physics class that you must not have taken.

So here's your "proof of theory":

The force which will be balanced by the bike's peak horse-power (gearing setup is set for top end speed matching peak hp) is,...

F = 1/2*CdA*p*v^2 + CrW ,... where,

Cd = Coefficient of drag for the bike.
Cr = Coefficient of rolling resistance for bike.
p = Density of air,.. A = Cross sectional area of the bike,...W = Weight of the bike,...v = Velocity.

As you can see, the first term which involves air drag, increases as the square of the velocity, while the second term involving weight is independent of velocity.

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Incidentally, the hp required to go a certain velocity is,... hp = F*v/550

Also since air drag is the largest factor here, the condition of that air makes a significant difference, probably more so than the weight at high speed. The air density above (p) can be estimated as follows;

p = P/(T*R) ,... where,

P = air pressure (surrounding air not tire pressure, although tire pressure is a variable on rolling resistance)
T = temperature
R = gas constant (1718 ft-lb/slug)

But the equation doesn't tell the whole story when it comes to bikes, weight and terminal velocity. The reason being that generally a heavier bike is also going to have a higher coefficient of drag because if a bike is heavier it also has a higher x-section. The x-section is generally larger due to a larger rider , larger front x-section or both. So separating out the impact of aerodynamics from weight in their impact on terminal velocity is nearly impossible without a windtunnel.

SO....

If Bike A has 100 HP and weighs 1000 lbs. - Power to weight = .1hp/lb.
If Bike B has 100hp and weighs 500 lbs. - Power to weight = .2hp/lb.

Bike 'B' will only be slightly faster than Bike 'A', (talking about terminal velocity) and this, only because of the added friction from the drag on the tires, bearings, sprockets etc. assuming bike A & B have the same Cd even with a heavier rider or bike or both.

Granted, the impact of weight is far less than the Co-efficient of drag but it is a variable. And in the bike world, higher weight almost always means a larger x-section (Cd) of both the bike and the rider.

The theoretical answer is that the heavier bike will have a slightly lower terminal velocity (1-2mph) with the same hp when you are in the 120mph range. But the practical world answer is that the terminal velocity of a 2x heavier bike could be far less than a lighter bike if the Cd of the heavier bike and rider is significantly larger than the lighter bike. In the real world case, the combination of additional weight plus higher Cd could reduce terminal velocity by 2-5 mph in the 120mph range with the same 100hp.

Are you sure you graduated High School?

Originally Posted by Heatwave

But the equation doesn't tell the whole story when it comes to bikes, weight and terminal velocity. The reason being that generally a heavier bike is also going to have a higher coefficient of drag because if a bike is heavier it also has a higher x-section. The x-section is generally larger due to a larger rider , larger front x-section or both. So separating out the impact of aerodynamics from weight in their impact on terminal velocity is nearly impossible without a windtunnel.

SO....

If Bike A has 100 HP and weighs 1000 lbs. - Power to weight = .1hp/lb.
If Bike B has 100hp and weighs 500 lbs. - Power to weight = .2hp/lb.

Bike 'B' will only be slightly faster than Bike 'A', (talking about terminal velocity) and this, only because of the added friction from the drag on the tires, bearings, sprockets etc. assuming bike A & B have the same Cd even with a heavier rider or bike or both.

Granted, the impact of weight is far less than the Co-efficient of drag but it is a variable. And in the bike world, higher weight almost always means a larger x-section (Cd) of both the bike and the rider.

The theoretical answer is that the heavier bike will have a slightly lower terminal velocity (1-2mph) with the same hp when you are in the 120mph range. But the practical world answer is that the terminal velocity of a 2x heavier bike could be far less than a lighter bike if the Cd of the heavier bike and rider is significantly larger than the lighter bike. In the real world case, the combination of additional weight plus higher Cd could reduce terminal velocity by 2-5 mph in the 120mph range with the same 100hp.

Are you sure you graduated High School?

Originally Posted by coolerman69

You my friend have an answer (excuse}for anything that proves you wrong. You are the authority on EVERYTHING! I guess when my $12k EG blows by your $40k+ ego bike time after time there would be some unknown fact that would prove me the looser! I bet you ride alone A LOT!

Originally Posted by mtclassic

proof positive that my theory is correct once again..........................guys that say they have several degrees are usually wrong when it comes to the real world. This is a real world fact regardless of what your formula say, my 2011 RGU will go ~120mph per gps and my speedo is actually spot on at 85mph per gps as I have a tts mastertune and messed around with the vss until it was spot on. I weigh ~200 in gear and driving solo I can attain 110 very quickly and then it creeps to 120 at which time the road runs out so I slow down. Now here is the real world thing....I add the weight of my wife ~150 geared up so. So figuring my bike weighs around 880 fueled up my wife only increases the weight of the bike + me by about 12-13% so in the real world adding 12-13% to the overall weight of the bike +rider will not allow said bike to get anywhere near 120mph...............and that is not based on theory or formulas that is based on fact.

Originally Posted by Heatwave

So let me get this right...even when you read the real world math and the practical implications of weight (and any reduction of Cd from that additional weight) you still disagree.

Ok.... I guess there are natives in New Guniea that think the world is flat too! They probably can't be convinced that we live on a globe either. Time to move on when the natives prefer to believe they live in a flat world.

Originally Posted by Deuuuce

Thank you for the dissertation on aerodynamics which wasn't even the discussion nor needed whatsoever. Power to weight is for acceleration, not top speed.

And a heavier rider in full tuck may have no difference in cross area AND doesn't mean airflow past the windshield is negatively effected. Also a heavier rider may lower the bike, decreasing drag as well.

You're grasping at straws because the Cr is so minimal with a heavier rider on an identical bike that it will make virtually no difference. A 150lb rider vs. a 200lb rider will have the same top speed. 300lb rider if the same cross section won't have any appreciable difference.

Your "real world" example of 2-5mph is ridiculous because you're comparing two different bikes.

Bottom line identical bikes one rider heavier than the other is going to have a top speed differential that is insignificant for comparison purposes.

Let's use cars, an area I'm an authority on, for your ridiculous 1,000lb differentials. It's aero, gearing and hp that makes the difference, Cr is MINIMAL.

Like a C6Z and E60 M5. The Vette weighs 1,000lbs less. Yet the BMW, due to the vastly more significant factors, has a higher top end.
Or a ZR1 vs. a Bently Super Sport. Roughly the same hp? 1,500lb+ difference? Basically the same top speed.

Weight differential for the same bike is meaningless for this discussion.

Originally Posted by mtclassic

My theory has proven itself again. damn and I am not even high school educated. I had to drop of school in the 3rd grade to go to work to help the family out both my kids needed new shoes and the wife was pregnant again but I digress. You are way too smart and did not even read my post. If you were not so educated with your sevral degrees you would figure it out like most of the guys with common sense would do/did and got a chuckle out of it besides. P.S. go back and read the last sentence of both your posts 2782 and 2787 now go read the start of post 2794..

Originally Posted by mtclassic

well in post 2794 you say you don't do personal attacks but in 2782 and 2787 you take a jab at whatever poster was disagreeing with you. And you proved my theory in two posts by lacking a certain common sense that many of the higher educated people have...in simple terms when my wife is on the back of my bike a certain thing called friction comes into play....it is her fists digging into my kidneys telling me if I go faster it is going hurt more, I am willing to bet the majority of republicans and tea partiers got this joke but the dems and libs are still scratching their heads cause they is so much smarter lol. Anyway I am just having fun so put your pocket protector way. I do believe friction via heat or other wise is going to cause some differences in top speed when it comes to much greater weights between two similar vehicles as in the real world we do not run in vacuums and we do not have unlimited time spans, perfectly flat roads etc to do top speed runs.