Center of gravity or Centre of gravity

[Guest Swifty]

I'd like to know exactly where the centre of gravity is on the 86-93 Venture Royale. Obviously it's slightly forward of the centre stand but I'd like to know exactly. I can do the calculation if someone can just give me the weight on each wheel...no rider, nothing in the bags, full tank of gas. Does anyone have the numbers? (no smart comments, just the numbers, please)

[SilvrT]

(no smart comments, just the numbers, please)

 

Now, this really spoils it for me.... :crying:

[Venturous Randy]

I doubt you could do it with calculations, as the wheels are just a small part of the mass in question. The best way would be to find a way to lift the bike on a level plate on the bottom and have a round bar you could roll it foward and backward until it would balance. At that point, the centerline of the bar would be the center of gravity and you could measure to a reference point from there. As you could imagine, this would take a couple of people, or at least some way you could limit the movement of the bike.

RandyA

[MiCarl]

I doubt you could do it with calculations, as the wheels are just a small part of the mass in question. The best way would be to find a way to lift the bike on a level plate on the bottom and have a round bar you could roll it foward and backward until it would balance. At that point, the centerline of the bar would be the center of gravity and you could measure to a reference point from there. As you could imagine, this would take a couple of people, or at least some way you could limit the movement of the bike.

RandyA

 

What he's doing will work just fine. It won't be the Center of gravity though, just the vertical line it lies on. No way to calculate how high it is without more information.

[Squeeze]

Who am I, to teach a Teacher about Tech Math ?

[KiteSquid]

Maybe he is looking for the balancing point on the frame.....

 

 

Swifty, Why do you need this information?

[Black Owl]

Me thinks he is confusing the center balance point (which is constantly moving) with the center of gravity....

 

But then I'm just a dumb ol farm boy....

[E-Fishin-C]

Ive been told its just right behind the 1st gen Starter

[MiCarl]

Ive been told its just right behind the 1st gen Starter

 

Farther back than that. If I have a full fuel tank I can unbolt the front wheel and the back wheel settles to the ground. With a half full tank the nose falls down. That is with the normal amount of crap (2 helmets) in the trunk.

[YYZ]

Oh, I thought he wanted to know the correct way to spell centre.

[elmicko]

Oh, I thought he wanted to know the correct way to spell centre.

 

The spelling would depend on which continent he's on.

[BradT]

What he's doing will work just fine. It won't be the Center of gravity though, just the vertical line it lies on. No way to calculate how high it is without more information.

 

I agree and obviously the rider, passenger and load in the bags will change the Center of Gravity.

 

BRad

[Guest Swifty]

the center balance point (which is constantly moving) with the center of gravity....

HUH??? What is the heck is the center balance point, and why would it be constantly moving?

I calculated the centre of gravity on airplanes for 30 years and it never moved (only minimally as fuel was used up on a flight, and I never had someone leave the airplane in flight!) except when a new piece of equipment was added or subtracted from the airframe. AND the centre of gravity can be calculated based on the weight under each tire of the plane. I suppose you could find the center of gravity through the y axis but that wasn't what I was looking for, sorry for that part of the confusion. Anyways, it doesn't make sense to find it for the y axis if you are moving a motorcycle in a two dimensional plane on the x axis. Maybe a motocross guy could use that to see how "flickable" the bike is in the air but I'm not doing that...yet!

 

Randya is on the right track but I want numbers. I just want the weight under each tire...that's all, simple request...IF someone has them.

 

Sorry SilvrT, I'll let you loose after the fact.

[saddlebum]

Can't you just park it on two bathroom scales :think:

[BradT]

I'd like to know exactly where the centre of gravity is on the 86-93 Venture Royale.

 

I bet you were not far off here. If you knew the weight of the bike you could probably calculate the weight on each tire.

 

[86er]

Hell, Swifty can't even park it in his living room; and now U want him to park it on bathroom scales!?!?

 

Can't you just park it on two bathroom scales :think:

[Flyinfool]

Can't you just park it on two bathroom scales :think:

 

Unless you shop at stores for really big people, :stickpoke:most bathroom scales do not go up to the 500 lbs that you will need.

[KiteSquid]

Unless you shop at stores for really big people, :stickpoke:most bathroom scales do not go up to the 500 lbs that you will need.

 

You can use a lever and fulcrum to divide the mass going to the scale.

[TIMEtoRIDE]

All you have to do is put the bike on centre stand and weigh the front tyre.

Then measure the distance. Divide by the total "book" weight.

 

I'll make up some numbers- - If you found 50 pounds 3 feet ahead of the stand

on an 800 pound bike, the stand supports 750 pounds, and the fraction is 5/75 of 3 feet,

which is .19 feet forward of the stand. ( sound right guys??)

 

You would have to lay the bike on it's side to get the vertical CG, I think.

[TIMEtoRIDE]

And now that I thought about it- -

 

Tape a piece of cardboard to your side panel.

Do the above measurements, and draw a line using a plumb line.

Next, get 5 guys to help set the bike on a block, now rock the bike backwards to find the tipping point. Draw a vertical line to the mainstand pivot.

 

Where the 2 lines intersect is the EXACT CENTER of gravity.

Each line was the balance point at it's "level" or orientation.

[LilBeaver]

I'd like to know exactly where the centre of gravity is on the 86-93 Venture Royale. Obviously it's slightly forward of the centre stand but I'd like to know exactly. I can do the calculation if someone can just give me the weight on each wheel...no rider, nothing in the bags, full tank of gas. Does anyone have the numbers? (no smart comments, just the numbers, please)

 

 

As some have pointed out, there seems to be some confusion on what you are looking for. if you want the actual center of gravity on the bike you'll need two measurements (and one assumption). If you assume that the bike is symmetric about the centerline (front to back) one can assume that the center of gravity is located on that centerline.

 

For the other two dimensions (front to back and top to bottom) there are various methods you could use to measure out what you would need to actually compute it.

For the front to back, there seems to be some ideas out there already. The easiest one (with household items - ie. bathroom scale and a length measuring device) would be to put the bike up on the center stand and measure the weight on the front tire when at rest. If you assume the book is nominally close to the actual total weight for the bike you have enough information to calculate the front to back center of gravity.

 

For the location on the vertical plane, you will need a second measurement. My proposition, for the simplest approach would be to place a scale (of a suitable max weight) under the side stand and you will need to take a few measurements. 1) reading off of scale 2) distance from point of contact on 'foot' of center stand to the center line of the bike (if you were to draw a straight line down from the center of the bottom of the bike and intersect it with an imaginary line drawn from the center stand to the center-line of the bike -- ie all in the same plane). Now, vary the angle and repeat the measurements.

 

From there it is just a little algebra to solve for what you are looking for.

 

You said that you can do the calculation - but if you would like any clarification on this let me know. I'd be happy to help.

Sidenote: Qualifications - I am a Ph. D. student in Physics (M.S. earned last year) and I teach college Physics.

 

 

Happy measuring!!!