[frobotz]

In a vacuum on flat roads your are correct, But with outside forces, IE unlevel ground, resistance and gravity, Weight does affect top speed. Dont care how you cut it. Put a 350 LB rider on your bike and see if goes as fast. Believe me, it wont. Its part to do with aerodynamics, but partially responsible due to weight. bare bones, It just takes power to move weight. More weight, More power that is required

 

[stevelm]

Newton & Galileo proved centuries ago that neglecting air resistance, ALL objects (REGARDLESS OF WEIGHT) fall at the same rate. This same law applies to objects going down an incline (read hill). High School Physics 101. F=ma. The F may will be larger due to larger mass. a=F/m so the F is larger with direct proportion to m, so a is always constant!

As a graduate engineer with a PE. (If you don't know what a PE is, I fear that your knowledge of physics will be anecdotal instead of empirical) I can tell you without doubt, weight has no effect on ultimate top speed. Period. (It will have a great effect on acceleration, no doubt.)

 

[jimnet518]

falling with no wind resistance yes, but this is on a bike, the extra weight will create more drag and require more force to counter the drag at the same speed, so when you dont have more force then you wont have the same speed (unless they reach terminal velocity), but im sure you know this as a graduate engineer and i defer to your higher education, but a bike with 2 passengers in a real world scenerio will have a lower top speed (ever notice how vehicles carrying more weight have worse gas mileage? because the added weight needs more power to cruise at the same speed and more power means more fuel consumption), remove outside influences and the top speed is the same. and i will also repeat, the differences in top speed may be so small as to be unnoticable with just a passenger, but why dont you find a nice stretch of road, run your bike up to top speed, adn then try to tow a car with the bike, the add bulk will not let it get to anywhere near the same speed

 

[stevelm]

I agree, that in most all cases, added weight will equate to added a drag (but it does not have to).

However, the statement about added weight and its negative effects on fuel economy is simply due to the added power required to accelerate the added mass, over & over again in daily driving. And yes, lifting a greater mass (up a hill) requires more work. But I thought we were talking about ultimate top speed (implying straight & level).

Did you know that when studying physics, especially ballistics, the vertical motion has no effect on the horizontal motion. Vertical motions and horizontal motions are completely independent of each other (neglecting air resistance).

Here's a cool fact: (Neglecting air resistance) A bullet fired horizontally from a rifle will hit the ground at the exact instant as another bullet that is dropped at the same height and time the fired bullet left the rifle barrel! The horizontal action of the bullet is independent of its vertical action.

Two riders on one bike simply has greater aero drag. Same thing with the car towing a trailer...the trailer adds huge amounts of aero drag.

I love redkow97's statement about a train. The rolling resistance of a steel wheel on a steel rail changes an infinitesimally small amount with regards to weight. Virtually zero change in rolling friction. Yes, with pneumatic tires, rolling friction increases with weight, but again, this change is negligible in ultimate top speed. It's all drag limited

No more beating the dead horse!

We all are passionate about riding! (I just happened to be passionate about physics too!)

Steve

 

[frobotz]

Newton & Galileo proved centuries ago that neglecting air resistance, ALL objects (REGARDLESS OF WEIGHT) fall at the same rate. This same law applies to objects going down an incline (read hill). High School Physics 101. F=ma. The F may will be larger due to larger mass. a=F/m so the F is larger with direct proportion to m, so a is always constant!

As a graduate engineer with a PE. (If you don't know what a PE is, I fear that your knowledge of physics will be anecdotal instead of empirical) I can tell you without doubt, weight has no effect on ultimate top speed. Period. (It will have a great effect on acceleration, no doubt.)

A motor pushing weight down the highway isnt falling, There is a huge difference, the motor has to overcome the weight and wind resistance to move the object. One it fails to do so then thats the top speed. Add more weight and the motor cannot push it as fast.

 

[frobotz]

I aree to your statemtn about ballistics also. But we are not talking about falling objects. We are talking about horsepower trying to overcome weight.


Speaking of trains, Hook a train car to the back of your 12HP riding lawn mower. I bet it has a new slightly lower top speed. Thast not wind resistance, Its weight.

Not arguing, But your talking ballistics adn terminal velovity. We are talking about horsepower trying to overcome weight. Completely different animals.

 

[dad1]

Here's another way of looking at it.

At Bonneville, flying start, wide open, two vehicles race and tie. Both reach a top speed of 200 MPH. Then one vehicle's weight is doubled and one vehicle's aerodynamic drag is doubled for another run. Which one do you bet on to win, hands down, no doubt whatsoever?

 

[knightslugger]

Here's another way of looking at it.

At Bonneville, flying start, wide open, two vehicles race and tie. Both reach a top speed of 200 MPH. Then one vehicle's weight is doubled and one vehicle's aerodynamic drag is doubled for another run. Which one do you bet on to win, hands down, no doubt whatsoever?

too easy, but i'll stay for the show.

 

[SWIFTY]

Here's another way of looking at it.

At Bonneville, flying start, wide open, two vehicles race and tie. Both reach a top speed of 200 MPH. Then one vehicle's weight is doubled and one vehicle's aerodynamic drag is doubled for another run. Which one do you bet on to win, hands down, no doubt whatsoever?

I'll go with the heavier vehical, but I'm only guessing.

 

[jimnet518]

1. thats very interesting about the bullet

2. yes we are beating a dead horse, it sounds like we agree that weight alone doesnt necessarily make a lower top speed, but the fact that the weight changes other factors does create a lower top speed in real world conditions.

3. the bonneville question, it could depend on how much weight and aerodynamic drag we are talking about, a vehicle that has virtually no aerodynamic drag but weighs a hell of a lot would get slowed down a lot more doubling the weight as opposed to doubling the aerodynamic drag for example, if the original aerodynamic drag caused it to slow down by 2mph compared to in a vacuum and the weight caused it to slow down by 5mph compared to vacuum, than doubling it would cause the aerodynamic drag to only slow it by 4mph and the weight to slow it by 10mph. but that is an impossible scenario, although i have been saying that weight effects the top speed, i have also been saying it doesnt effect it much, but aerodynamic drag effects it a hell of a lot, thats how chutes on dragsters are able to slow them down, chutes dont weigh very much, but when opened they create a lot of drag, so the heavier car would beat the less aerodynamic one

 

[solar-ex]

plus weight adds resistence to the tires, in terms of roll resistance.

the verdict: in a real world scenerio of a person on an EX500R trying to reach the max top speed weight is a bad thing, so loose as much as you can.

 

[SWIFTY]

the verdict: in a real world scenerio of a person on an EX500R trying to reach the max top speed weight is a bad thing, so loose as much as you can.

That's what I'm going for.

 

[dad1]

... would it help if the drag on one was only increased by only half while the weight on the other was still doubled? :-\ Gentlemen, place your bets. ;D

How a boat goes through water is full of the same principles.

 

[solar-ex]

a boat going through water and a bike rolling on the ground are completely different..

 

[dad1]

a boat going through water and a bike rolling on the ground are completely different..

... while a boat going through water and a bike going through air are basically 'zackly the same. Place your bets! ;D

This is an open book test, BTW. 8) Google is your friend.

 

[stevelm]

I promised I was not going to beat this poor horse anymore, but I can't help it!

The remark about the 25hp mower pulling the train is so wacked-out, I don't even understand how it relates.

"would it help if the drag on one was only increased by only half while the weight on the other was still doubled?"

Here's the answer: The drag increases by velocity SQUARED. Drag is the killer, weight is negligible.

For those of you who read "Car & Driver" magazine, their road tests provide top speeds. They indicate either one of two things: 1)Top speed is Drag limited, or 2)Top speed is governor limited. I will bet my life that they will never say Top Speed is Weight limited!

The Tour Du France bicycle races:
When they are racing the standard or mountain courses, they use the lightest possible bike: for acceleration & climbing.
When they do the time trials: they use heavier bikes, but the are much more aerodynamic. Top speed is what they want. (Acceleration & climbing are not of concern)

Poor frigging horse!

 

[Guest]

I'm amazed this thread has lasted so long. The horse is a bloody pulp at this point.

 

[dad1]

OK, last chance. ;D

A five percent increase in drag vs: twice the weight. 200 MPH, two identical vehicles that had tied at 200 MPH at Bonneville. Make 'em Busas to fit the theme of the board. Which one will you bet on? :-\ ;D

See if this link helps. Try using a .6 coefficient of drag and 6 sq. foot frontal area, both fairly realistic for a bike. I hate to see my compadres lose money. ;D

Then play with the numbers again around 60 MPH. Remember when we had a national speed limit at 55 MPH after the seventies gas crunch? In the interest of conserving fuel? Maybe this will shed some light on the science behind that decision.

http://www.rbracing-rsr.com/aerohpcalc.html

Requires less cypherin' than a mortgage decision at World Wide. Enjoy! ;D

 

[stevelm]

Hey dad:

Excellent link! Thanks!

To others: Try adding weight whist keeping other variables constant; notice how little the HP required changes!

Now change Cd, keep others constant: Big HP change, same thing when changing frontal area & speed.

AMEN! Horse can now RIP in horse heaven!

 

[dad1]

To others: Try adding weight whist keeping other variables constant; notice how little the HP required changes!

Now change Cd, keep others constant: Big HP change, same thing when changing frontal area & speed.

AMEN! Horse can now RIP in horse heaven!

That was kinda' the point. You can double the weight and still beat a bike with just 5% more drag. It's actually close at only 1% more drag. At speed, drag's where da' money zat, hands down. 8) The line for only 5% more drag vs: twice the weight is crossed somewhere around 55 to 60 MPH. The faster you go, the more aero means, as originally stated. 8)

And yes, it's the same principle with a boat going through water. Gases are considered a fluid when talking about aerodynamics and aero tests can even be performed under water with meaningful results.