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Discussion Starter #1
I have a K8 Burgman 400. My wife does not feel safe sitting so high up. Does this make the bike top heavy? We have rode a lot of motorcycles but this is the first scooter. Thanks for any help.
 

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I have a K8 Burgman 400. My wife does not feel safe sitting so high up. Does this make the bike top heavy? We have rode a lot of motorcycles but this is the first scooter. Thanks for any help.
Of course it does. And at the risk of offending, the magnitude of the increase is a function of your wife's weight.

Advise her to sit still and not attempt to "help" you balance and all will be well. Her doing that will raise the center of mass and make the scoot more stable at lower speeds--not when stopped, but when maneuvering at lower speeds.

A while back I was asked by a fellow forum member why his Honda NT700V felt more stable when coming to a stop, despite it's being noticeably more "top-heavy"--here is my response.

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Any two-wheeled (inline wheels) vehicle, when moving at all, behaves as an inverted pendulum--this is just like when you attempt to balance something on a fingertip, with the classic example being balancing a broomstick vs. a pencil. If you have ever done that you know that it is far easier to balance the broom than the pencil; this is because the higher center of that mass (CoM) of the broom swings through a longer arc allowing more "time" for correction, and therefore a less frantic and more controllable correction, when an imbalance occurs.

So as long as the bike is moving and corrections can be made by moving your "finger" (the tire contact patch) to be beneath the center of mass, and all else being equal, the bike with the higher CoM will be easier to balance. The overall higher mass helps too as the heavier bike will naturally have a higher moment of inertia (MoI), making it more resistant to changes in its rotation velocity about the CoM.

In the instance of the 400 vs. the NT700 the latter has both a higher center of mass and higher overall mass. This is why Harley guys can cruise around parking lots at 0.05 MPH with such ease.

What makes it counter-intuitive (inverted) is when bikes are stopped you can no longer easily move the tire contact patch (your "finger") so as to be under the center of mass. Everything changes and the bike with the higher mass will be less "stable", or more correctly less forgiving when it does go off balance.

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When a passenger swiveling all about at the hips trying to help you balance is thrown in it destroys stability because their moving about makes the CoM a moving target. The overall higher mass and MoI issue will also take a hit if the passenger is not sitting still as the shifting mass and inertia of their body will once again serve to upset the apple-cart...
 

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I feel it makes it quite a bit top heavy and the passenger seat is too high. I ride 2-up 85% of the time, but frequent start and stops is the only place it gets a little tougher. I put a passenger backrest on mine 1st thing and she felt much safer, then I added a drivers backrest and she liked it even more being cradled in between. So I guess for me, it's just a little tougher taking off with out weaving from a stop. (I'm 5' 10" @ 180 lbs, and she's about 5' @ 130 lbs.)
 

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My wife absolutely had to have something behind her on my old 400. We tried one time without the top box and she was a nervous wreck. With top box she felt more 'secure'. As far as being so high up, I am unable to compare between bikes, as the 400 was my first ever bike (minus a 50cc), and now my 650 is my second. However I can say that at stops, do agree that her 'squirming about' does take some effort. This is why that whenever she had to do a "position shuffle", she had to tell me first so I can firmly plant my legs. But when riding, it was no problem. With the 650, this is almost a non-issue now. Reason for that I am attributing is its almost 200lb's heavier and that weight is low. Which basicly is how cliffyk's explaination is. With the 400 being a light bike, with high mass up high, at stops it feels unbalanced and takes effort to keep it straight. But when riding its no problem at all.

All this experience I give is from 2 riders whom's combined weight was pretty much at the weight limits of the 400.
 

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I am so lucky to have the best pillion rider ever IMHO.

SWMBO and I have thousands of happy miles together , she gets on, sits very comfortably and relaxes. Often times she reads a book while we are riding.
What makes it so effortless is that she trusts me and my riding skill. This has come from years of practice and adjustment .

True she does not ride long distances that often anymore ( me either for that matter)but when she does we enjoy it.

As the pilot , you have the responsibility to make sure you are comfortable in as many situations as you can come up with and not do anything to upset her equalibrium and balance. Your confidence and skill are what determines how she enjoys the ride.
 

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Discussion Starter #7
Thanks for all the imput. I'm just going to give her a little time to think about it and maybe she will come around some day but in the meantime I'll just continue to ride and enjoy myself. Thanks again everyone.
 
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