Center of Gravity

henryroten · 12-20-2012, 05:06 AM

I am considering lowering the suspension on my 990R and was wondering if by doing so the COG is effectively lowered? Or is the COG a relationship between the weight distribution of the motorcycle in relation to the sitting position of the rider (does that make sense?)?

Thanks just curious.

anotherguy · 12-20-2012, 05:15 AM

There4's the vehicle COG and the bike/rider COG. Generally when a bike is lowered both follow. There are variables and unusual situations but they are exceptions.

LuciferMutt · 12-20-2012, 05:38 AM

In before the huge argument about if standing on the pegs raises or lowers the CG.

Yossarian™ · 12-20-2012, 06:22 AM

Quote:

Originally Posted by LuciferMutt

In before the huge argument about if standing on the pegs raises or lowers the CG.

Me too. I want to get a good seat.

slide · 12-20-2012, 06:39 AM

Quote:

Originally Posted by anotherguy

There4's the vehicle COG and the bike/rider COG. Generally when a bike is lowered both follow. There are variables and unusual situations but they are exceptions.

What do you hope this will accomplish? Better handling? Or what?

pretbek · 12-20-2012, 06:51 AM

Yes the COG is lowered.
But effectively? As in: with noticable effect on handling? I doubt it.

The effect of any geometry change (rear lower than front, mess with the fork to change rake/trail) will be much greater.

Oh, and lowering will very effectively reduce your ground clearance.

SRG · 12-20-2012, 10:18 AM

Pretbeck - I think you are right, the actual distance that the CG would be lowered is not a large amount (wouldn't it be equal to amount of lowering? i.e. if you drop the rear 1" and drop the front 1" then the CG drops 1").

However, lowering the CG a seemingly small amount may have larger effects that one might suppose. I know my Husaberg is quite sensitive to changes in the amount of rear sag and position of forks in the tripleclamp.

The only bike I ever tried lowering links on was a 640 Adv. I don't think it effected the handling much, but it did allow the underside of the rear fender to contact the tire under full compression of the shock. Made a cool barking noise when it did

.

DAKEZ · 12-20-2012, 11:05 AM

The lower the mass the lower the COG period. Thread over.

Double H · 12-20-2012, 11:22 AM

Quote:

Originally Posted by DAKEZ

The lower the mass the lower the COG period. Thread over.

wait, what?

randyo · 12-20-2012, 11:24 AM

Quote:

Originally Posted by LuciferMutt

In before the huge argument about if standing on the pegs raises or lowers the CG.

it does both

lowers COG of bike but raises COG of rider

what does it do to the combination bike rider COG

depends on the bike and the rider
an average rider on a GS, it will lower the COG
a 6'4" 265lb rider on a Rebel, it will raise the COG

pretbek · 12-20-2012, 11:32 AM

Yay! Here we go.

Quote:

Originally Posted by randyo

lowers COG of bike but raises COG of rider

How does standing on the pegs lower the COG of the bike?
In my opinion (and that of physics in this universe), it makes no change to the COG of the bike.

Yossarian™ · 12-20-2012, 11:45 AM

Quote:

Originally Posted by randyo

lowers COG of bike but raises COG of rider

We've got a live one!

randyo · 12-20-2012, 11:48 AM

Quote:

Originally Posted by pretbek

Yay! Here we go.

How does standing on the pegs lower the COG of the bike?
In my opinion (and that of physics in this universe), it makes no change to the COG of the bike.

weight that was on the seat is now on the pegs, doh ! but as I said, your body COG is higher

slide · 12-20-2012, 11:53 AM

Quote:

Originally Posted by randyo

weight that was on the seat is now on the pegs, doh ! but as I said, your body COG is higher

How about I stand on the pegs but in a sitting posture with my ass is only .0001 mm off the seat.

Now what?

High Country Herb · 12-20-2012, 12:00 PM

Quote:

Originally Posted by pretbek

Yay! Here we go.

How does standing on the pegs lower the COG of the bike?
In my opinion (and that of physics in this universe), it makes no change to the COG of the bike.

The COG (actually center of mass, to be exact) of the bike is unchanged by standing on the pegs (or getting off and walking away for that matter). The COM of the bike+rider raises a bit, because some of the mass (the rider) has moved up. If you stood on a 10 foot tall (weightless) ladder attached to your bike, it would be raised significantly. It doesn't matter where/how the two bodies of mass are attached, the issue is simply the center.

Along those lines, lowering the bike lowers the seat, which also lowers the rider. COM has been lowered. This doesn't mean the bike will be less likley to fall over, though, because now the COM is closer to the point of rotation (where the tires meet the road) and will rotate faster. (more flickable?)

I think the only major benefit to lowering the bike would be making it easier to get your feet flat on the ground when stopped. That will make it less likely to fall over.

12-20-2012, 05:06 AM	#1
henryroten ^OP Gnarly Adventurer Joined: Sep 2011 Location: God's Country Utah Oddometer: 174	Center of Gravity I am considering lowering the suspension on my 990R and was wondering if by doing so the COG is effectively lowered? Or is the COG a relationship between the weight distribution of the motorcycle in relation to the sitting position of the rider (does that make sense?)? Thanks just curious.

12-20-2012, 05:15 AM	#2
anotherguy Beastly Adventurer Joined: Jun 2009 Location: in the foothills now.... Oddometer: 4,314	There4's the vehicle COG and the bike/rider COG. Generally when a bike is lowered both follow. There are variables and unusual situations but they are exceptions. __________________ When injustice becomes law,resistance becomes duty. Thomas Jefferson

12-20-2012, 05:38 AM	#3
LuciferMutt Rides slow bike slow Joined: Aug 2008 Location: New(er) Mexico Oddometer: 9,554	In before the huge argument about if standing on the pegs raises or lowers the CG. __________________ You couldn't hear a dump truck driving through a nitro glycerin plant! Cobbie Award Winner

12-20-2012, 10:18 AM	#7
SRG SRG Joined: Nov 2004 Location: Charlottesville, Virginia USA Oddometer: 893	Pretbeck - I think you are right, the actual distance that the CG would be lowered is not a large amount (wouldn't it be equal to amount of lowering? i.e. if you drop the rear 1" and drop the front 1" then the CG drops 1"). However, lowering the CG a seemingly small amount may have larger effects that one might suppose. I know my Husaberg is quite sensitive to changes in the amount of rear sag and position of forks in the tripleclamp. The only bike I ever tried lowering links on was a 640 Adv. I don't think it effected the handling much, but it did allow the underside of the rear fender to contact the tire under full compression of the shock. Made a cool barking noise when it did . __________________ Lazy Traveler

12-20-2012, 11:05 AM	#8
DAKEZ Beastly Adventurer Joined: Mar 2007 Location: U-gene, OR. Oddometer: 17,989	The lower the mass the lower the COG period. Thread over. __________________ "Be who you are and say what you feel, because those who mind don't matter, and those who matter don't mind." — Dr. Seuss “Watch out for everything bigger than you, they have the "right of weight" Bib

12-20-2012, 06:51 AM	#6
pretbek Studly Adventurer Joined: Oct 2008 Location: West Chester, PA Oddometer: 501	Yes the COG is lowered. But effectively? As in: with noticable effect on handling? I doubt it. The effect of any geometry change (rear lower than front, mess with the fork to change rake/trail) will be much greater. Oh, and lowering will very effectively reduce your ground clearance.

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