Interesting Physics Lesson - Kawasaki Versys Forum
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post #1 of 33 (permalink) Old 02-22-2012, 02:42 PM Thread Starter
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Interesting Physics Lesson

I was a mechanical engineering major before switching, and got through several physics classes, including this topic, although not nearly as interesting.

http://www.stevemunden.com/leanangle.html

So, if I'm understanding this correctly, since the V has a pretty high center of mass (COM) it should actually outperform the supersport bikes with lower COM, provided their running on equal pavement, equal rubber, and have the exact same weight? This would explain why a supermoto is faster than pretty much anything in the tight stuff; they are extremely light and tall, with equal rubber.
If that is true, then why are supersports COM's so low? Is it only for transitional stability?
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post #2 of 33 (permalink) Old 02-22-2012, 03:22 PM
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[QUOTE=Toxigenegoober;187850If that is true, then why are supersports COM's so low? Is it only for transitional stability?[/QUOTE]

I left school when i was 15 so my guess is it all about looks for the super sports
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post #3 of 33 (permalink) Old 02-22-2012, 03:41 PM Thread Starter
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I left school when i was 15 so my guess is it all about looks for the super sports
See that's the thing. I respect the performance of the supersports, but that Hotwheels toy motorcycle look doesn't do anything for me. The only one I really like is the BMW S1000RR; it's got a functional look, like an M4 assault rifle.
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post #4 of 33 (permalink) Old 02-22-2012, 03:41 PM
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"What's the real lean angle?

The concept of the lean angle is not as trivial as one would imagine. If we had infinitely thin tires then it'd be obvious: Just draw a line from the center of mass to the contact point and measure the angle between that line and the horizontal or vertical. But we have fat tires. The actual lean angle must be measured from the center of mass to the center of the contact area, which will be to the inside of the tire. So the apparent lean angle — using a line parallel to the forks, say — will be greater than the actual lean angle, using the center of the contact area of the tire. Note that this means that a motorcycle with a lower center of mass will lean more than a motorcycle with a higher center of mass, for a given corner radius and speed."

Not sure how much an improvement in cornering a higher center of mass (COM) makes in the real world. Remember the height of the center of mass is measured in feet and the contact patch only moves a few millimeters off center when a bike transitions into a corner lean - so a difference might only be measurable at 1 degree or two. It also makes the bike slower to transition into a turn due to the need to overcome more sideways momentum. Race bike designers work hard to get a low and centralized COM. This allows the bike to transition faster from one turn to another and be more "flick-able".

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post #5 of 33 (permalink) Old 02-22-2012, 03:54 PM
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If that is true, then why are supersports COM's so low? Is it only for transitional stability?
Reduced wind resistance. Keeping everything in a low, tight package, with the rider leaning horizontal into the wind will help reduce drag and turbulence. A tall bike with big radiator scoops and the rider sitting straight up acts more like a sail in the wind. It's less about COM and handling, and more about reducing cross section and drag for those high speed straights.
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post #6 of 33 (permalink) Old 02-22-2012, 07:04 PM
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"If that is true, then why are supersports COM's so low? Is it only for transitional stability? "

You need to multiply everything by the Coolness coefficient that help sell bikes.

Low bike, cool = more sales. Tall bike not so cool = less sales.

Seriously

Aerodynamics. I do not think I would be able to sit up on a tall bike @ 200 MPH.

Same argument can be made for fairings. The add weight and improve aerodynamics. They also creates a revenue generating surface for the sponsors.
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post #7 of 33 (permalink) Old 02-22-2012, 08:14 PM
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I have to agree with the less drag and less turbulance also..speed equals low as you can go without scrapping steel is what I've always said..Nascar and Indy cars are built to be low for less drag especially on the super speedways...

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post #8 of 33 (permalink) Old 02-22-2012, 08:19 PM
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My wife's cruiser is low to ground like a fat pig so it should eat up the twisties, NOT.
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post #9 of 33 (permalink) Old 02-23-2012, 03:34 AM
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Phil, I am sure the fat pig enjoy these Twisties

http://en.wikipedia.org/wiki/Twisties

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post #10 of 33 (permalink) Old 02-23-2012, 03:36 AM
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Phil, I am sure the fat pig enjoy these Twisties

http://en.wikipedia.org/wiki/Twisties
Yep its looks like the pig had more than its share of those twisties
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post #11 of 33 (permalink) Old 02-26-2012, 08:36 PM
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Back on topic.
A lower CG will is huge for accelerating and decelerating in a straight line. A 200 hp bike would wheelie in 6th gear if it were as tall as a dirt bike. And actually, alot of deticated SM bikes are lowered.

For turning, its all a compromise. Lower CG may mean a slight bigger lean angle for a given speed but it also means quicker transions like you said. The bike cannot be too low of coarse since it needs enough ground clearance.

There is no exact answer for your question. Every bike is slightly different and will likely have specific tweaks to complement other designe desions done on that particular bike. And the guys that are making those desitions are not going to be givingg away their secrets for free.
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post #12 of 33 (permalink) Old 02-26-2012, 08:55 PM
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Sportbikes strive for "mass centralization" along their "roll center". It is not the same as COG. Being taller, the Versys has a tougher time with it than a sportbike. But no matter. Remember 33BHP?
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post #13 of 33 (permalink) Old 02-26-2012, 09:35 PM
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That's right... Being taller may give Versys more room to lean, but more lean is required to overcome its higher COG, so also increased lean transitions when changing direction. The higher COG also results in higher levels of weight shifting, and extra leverage and upsetting effects on balance and suspension, grip, etc.
It helps to be aware that you always control your direction be means of countersteer. The more you try to turn your handlebars to point your front wheel to the right, the more you'll lean to the left and turn left.

Last edited by invader; 02-27-2012 at 01:40 AM.
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post #14 of 33 (permalink) Old 02-27-2012, 12:46 AM
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here is a site that is filled with basic design on Motorcycles;

http://www.tonyfoale.com/

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post #15 of 33 (permalink) Old 02-27-2012, 03:07 PM
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Supermoto fun...

The pro supermotard bikes are around 250 lbs. and 60 hp. Our Versys is around 450 lbs. and 60 hp. The road race bikes are around 380 lbs. and 200 hp. big difference in power to weight ratio...
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post #16 of 33 (permalink) Old 02-27-2012, 03:13 PM
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Basically, Sportsbikes can outperform their tires anyways, i.e. their corner speed is limited by the tires, not by the lean angle. Therefore, a higher center of gravity will not help them corner faster.

You might also notice that you need less lean angle when cornering at your usual speeds when carrying a passenger.

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post #17 of 33 (permalink) Old 02-27-2012, 03:51 PM
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When I go to Loudin NH to watch local racing, Eric Wood smokes most of the race prepped sportbikes sliding around on his motard but he is an expert.
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post #18 of 33 (permalink) Old 02-27-2012, 06:20 PM
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Sport bikes can easily overpower their tires. They can't over lean them. Pegs and bodywork will scrap before the tires let go.

Motards are fast because they are light. Weight is the enemy among race machines.
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post #19 of 33 (permalink) Old 02-28-2012, 10:54 PM Thread Starter
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The pro supermotard bikes are around 250 lbs. and 60 hp. Our Versys is around 450 lbs. and 60 hp. The road race bikes are around 380 lbs. and 200 hp. big difference in power to weight ratio...
I've seen a video with guys leaning motards like that. Crazy!

And, I do want to read that book now. I'm a nerd and like that kind of stuff.
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post #20 of 33 (permalink) Old 02-29-2012, 07:50 AM
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High COG lets you lean better, all things being equal. But low COG lets you flick from side to side better. Also can you imagine riding your Versys at 200mph? You want low and very aerodynamic for that.

So yeah, a Versys or motard will beat the pants off a sport bike in slow twisty sections because it can carry more corner speed. But the sport bike will be able to transition left to right easier, and will blow the doors off a Versys or motard in the straights.

I'd rather be riding.
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