Technical Data...Center of Gravity?

# Thread: Technical Data...Center of Gravity?

1. ## Technical Data...Center of Gravity?

Hey Guys:

For those of you who have engineering experience or just some very in depth motorcycle knowledge,

How the the Center of Gravity calculated on a motorcycle?

Generally a lower center of gravity is benefitial to riders...which is why the newer style moto GP exhausts are nice to see on the 06 r6 as well as GSXR600-750.

Are V-twins generally higher or lower center of gravity? What is the formula for calculating the C of G? I know with aeroplanes its something like your moment in inches multiplied by your gross weight that gives you your C of G in inches....

Does anyone know?

2.

3. Cof G is basically hanging the bike on an imaginary point and adjusting the bikes location until it balances itself at that point.

Most software (AutoCad packages) can do this for you automatically.

I dont remember the exact formula but CoG is calculated by allowing for the sum of all the acting torques to = 0. Torque equals the moment arm (distance) times the force (newtons).

Note that CoG is a static attribute only, engineers are also concerned about the polar moment of inertia.

I dont think that vtwins are much different CoG wise.

4. Well....thanks? In order for me to get that the I would have to transfer a exact replica model of the bike in ACAD which i don't have (replicas of bikes). ?

Or

Can I just add the dimensions and have it work the C of G from there? I understand thats its static and thats why I am concerned with how to establish that point.

Wow, I really didn't expect an intelligent answer, hopefully you can help me further =)

5. What you can do is figure out the weight of the components indivdually (wheels, engine, tank, muffler) measure their distance from your arbitrary point and get a rough estimate that way of the torque of each item. Obviously items to the left (or right) will be negative torque and vice versa.

BTW I am not an engineer and I'm sure someone will put this together better for you.

OR you can ask the manufacturer of the bike the same question, I woundlt think its that secretive.

6. Originally Posted by REVELATIONS
What you can do is figure out the weight of the components indivdually (wheels, engine, tank, muffler) measure their distance from your arbitrary point and get a rough estimate that way of the torque of each item. Obviously items to the left (or right) will be negative torque and vice versa.

Ok no, Im not about to do that for every bike out there, hahaha...

Ask the manufacturer eh...humm theres an idea...wonder if they have a C of G 1-800 number...hah...it would be quite humorous to ask a salesmen that question, just to see what kind of bullshit he comes up with....

7. What exactly are you planning to do with this information?

8. Originally Posted by REVELATIONS
What exactly are you planning to do with this information?
Add it to my bank of knowledge in my brain?

Not a lot really...just be intrested to know which bikes have lower C of G's. And see what influences that, such as engine style, exhaust style (undertail, GP or standard) , seat height and such...

Also on other hand be curious to know which bikes have lowest C of G's for stunting and such...as lower center of gravity lowers the balance point quite a bit...which has obviously results for stunters.

9. Remember that bikes are awesome stunters for WAY more than just having a low CofG.... ie the Honda CBR900 has (had?) one of the shortest wheelbase of modern sportbikes, can you say wheely machine??
Anyway, its the sum of all parts that makes for a sweet stunt bike, like the Suzi SRAD for instance. Ask the stunt guys if you want more info. They have this down to a science.

10. Originally Posted by REVELATIONS
Remember that bikes are awesome stunters for WAY more than just having a low CofG.... ie the Honda CBR900 has (had?) one of the shortest wheelbase of modern sportbikes, can you say wheely machine??
Anyway, its the sum of all parts that makes for a sweet stunt bike, like the Suzi SRAD for instance. Ask the stunt guys if you want more info. They have this down to a science.
Had...yeh the 1000rr is terrible for stunting cause it has a extremely high C of G, i know there is alot of other factors that also effect stunting such as toque and wheelbase even adjusting your tire pressure makes a huge differnce... Suzi SRAD or TL?You can stunt almost any modern sportbike as good as the next if you know what your doing...curiousity is all...

11. I've got a calculator that can give CoG.

You need 2 x scales, a big heavy block, and a bunch of strong friends.

Measure front and rear wheel radius plus wheelbase.

Put one wheel on each scale, hop on and get in your riding postion while the bike's held up just like you were setting sag. Get the #'s off the scales.

Now put one scale on the block, and lift the bike so the rear wheel's on the block. Same deal, get in your position and get the 2 readings, and measure the height of the block(the higher you get the rear wheel the better).

And no, I won't send you the calculator since I paid for it, but I'll punch the #'s in and it's also going to give weight distribution to the wheels.

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