Time for opinions and controversy - K-Bikes.com - Excellence in Motion
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post #1 of 25 (permalink) Old Oct 7th, 2010, 1:06 pm Thread Starter
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Time for opinions and controversy

Okay here is the question.

When trying to manuever slowly a lower CG is better. I think we all agree on that.

So???

1) To get this lower CG I say that one can stand up (on the pegs) which then lowers the CG because now your weight is all being transferred through your feet, thus creating easier manuevering versus staying in the sitting position.

2)Others contend that standing only makes the weight at a higher level thus raising the CG.


I'm in the "1" camp.
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post #2 of 25 (permalink) Old Oct 7th, 2010, 1:36 pm
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I'm with the others.

All you're doing by standing up is raising the bulk of your body, ergo a higher
center of gravity.

But, WTH do I know, I'm on a K12RS

tim-----still on the right side of the frostline

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post #3 of 25 (permalink) Old Oct 7th, 2010, 2:57 pm Thread Starter
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I understand that the weight is higher but the bike only realizes the weight where it is placed.....the pegs. Thus lower CG.
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post #4 of 25 (permalink) Old Oct 7th, 2010, 3:18 pm
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Quote:
Originally Posted by kbmwrs
I understand that the weight is higher but the bike only realizes the weight where it is placed.....the pegs. Thus lower CG.
And that's all well and good, until you move your head or turn your body in some fashion.
Then all that weight way up high in the new center of gravity affects the machine.

It seems to me.

Or, putting your argument another way, where would you prefer the gas in your bike to be? Up high, or down as close to the pegs as possible ? Once you start tossing it in corners the weight of your load shifts, affecting your center of gravity, affecting the quality of your ride.

Your example may work, but only if the weight is unmovable.

tim-----still on the right side of the frostline

you can't stop the signal

Last edited by shook sez; Oct 7th, 2010 at 4:28 pm.
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post #5 of 25 (permalink) Old Oct 7th, 2010, 6:25 pm
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CG is the point of balance in the bike Ėit doesnít matter where or how weight is attached, as long as itís attached. Think of it this way: when sitting, your hips are attached to the seat, the seat is attached to the frame, the frame is attached to the pegs. So how is that really any different than standing, with your hips attached to your legs, your legs attached to your feet, and your feet attached to the pegs?

I believe weight high up makes slow maneuvers more awkward because that weight acts on a longer lever arm to the contact patches, so any lean tends to pull the bike more strongly over. You, the rider thus have to exert greater counter-torque to keep the bike from falling over, making handling more difficult. It doesnít matter how the weight is attached as long as the lever arm is the same length.

When you stand on the pegs like a dirt rider, you still have a weight up high (the CG is raised), but now _you_ control the weight, so you can take advantage of the long lever arm to increase your control Ėit takes less lean to achieve the same counter-torque for whatever the bike below you is doing. Thatís probably why you feel more control by standing on the pegs.

Standing on the pegs also makes it easier to shift more weight. You can put almost 100% of your weight on one side very quickly. When seated, you have to hang off to get the same effect.

Iím an engineer, but not a _real_ engineer.
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post #6 of 25 (permalink) Old Oct 7th, 2010, 6:28 pm
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Yeah, this question comes up every so often, especially in dirt bike circles. So here's the one true and correct answer:

Standing up on the pegs raises the combined center of gravity of the bike and rider. Yes, it does.

It may "feel" easier to maneuver that way, but that is due to one simple consideration which is often overlooked here: the bike and rider are not a single, rigid body.

Sitting on the seat effectively ties your butt to the bike which limits your movement in relation to the bike. And your main body weight is lower, so the combined CG of bike and rider is lower.

Standing on the pegs moves your weight higher (and thus raises the combined CG), but makes it easier for the bike to move a bit beneath you due to your legs bending and shifting and thus your main body mass moves easier in relation to the bike.

So no real controversy here, just an oversimplification of the forces at work leading to an incorrect conclusion that "feels" right.

Ken
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post #7 of 25 (permalink) Old Oct 7th, 2010, 6:33 pm
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OK, now my head is starting to hurt.

tim-----still on the right side of the frostline

you can't stop the signal
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post #8 of 25 (permalink) Old Oct 7th, 2010, 6:55 pm
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As a long time dirt bike rider and former MX racer, I can tell you that on tight single track, you'd better be off the seat and on the pegs. Standing puts your weight low on the pegs. Sitting on the seat puts the weight high up on the seat.
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post #9 of 25 (permalink) Old Oct 7th, 2010, 7:06 pm
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Quote:
Originally Posted by kbmwrs
I understand that the weight is higher but the bike only realizes the weight where it is placed.....the pegs. Thus lower CG.
+1

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post #10 of 25 (permalink) Old Oct 7th, 2010, 7:39 pm
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Quote:
Originally Posted by JM1200GT
Standing puts your weight low on the pegs. Sitting on the seat puts the weight high up on the seat.
And that only works because it allows the bike to move around underneath you. But the total CG is still higher than if you were sitting.

Again, you and the bike are not one, single rigid body here.

Quote:
Originally Posted by Fergie
+1
Sorry, still incorrect, even if it "feels" right.

Ken
Pacific NorthWet
'13 Dark Graphite Metallic K16GTLD, 24K miles and counting...
'09 Magnesium Beige Metallic K13GT, 60K miles miles and counting...
'02 Mauve Metallic K12LTC, 106K miles and sold
BMWLT#145, IBA# 366, MOA# 111996, SCMA# 24032

All lower 48 states plus Alaska on the K13GT in two weeks . . .

Some people see the gas tank as half empty. Some see it as half full. All I care is that I know where the next tankful is coming from...
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