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There's a lot of confusion about why we use such big tires. It's commonly believed that a bigger tire has a bigger contact patch. This is incorrect. An ST1300 fueled up weighs about 700 pounds; the rider is about another 200. The tires are at about 40 psi. So, 900 pounds divided by 40 psi is 22 square inches. If the weight is equally distributed on the two tires, each tire has a contact patch of 11 square inches. That's it, tire width and diameter never entered into the calculation. A narrow tire will have an 11 square inch contact patch that's long and narrow; a wide tire will have an 11 square inch contact patch that's short and wide. If you drop the tire pressure to 20 psi (popular for on/off road bikes) then your contact patch doubles in size. If you find yourself in snow or rain, raising the tire pressure will shrink your contact patch and help you push through to the road.
 

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Good points all. Your contact patch will also get smaller as you go faster. I learned this one day while riding with some squidly friends while my rear tire was flat. We were riding stupid-fast on a curvy stretch of road above Borrego Springs called the Montezuma Grade. When we stopped for gas, one of them cracked a joke about me "running racing slicks." When he persisted in the lame joke, I finally saw that my back tire was flat and that the rubber had melted/revulcanized and was smooth, shiny, flat and stuck to the concrete pad of the gas station.
Because we were riding at 60-90mph, the centrifugal (or centripetal) force was enough to stand the tire up, even while doubling the posted speed limit around some of the corners.

But for some reason, riders with "skinny" back tires get some kind of gym-shower anxiety. And even though it makes a bike handle like a truck, I've seen impossibly wide tires forced onto narrow rims, with the tire's shoulder almost touching the chain. The price of looking cool, I guess.
-CCinC
 

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Last season I picked up a puncture on my Mean Streak. I opted to go with a bigger tire. A Michelin Pilot 200. Now I wish I had the old tire back. The 200 negatively effected the handeling of my bike. When this tire is gone I'm going to go back to the stock size.
 

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The size of your rear doesn't affect your the way handles. Most tires have the same contact area. An oval is still an oval no matter how wide it is. It still comes togther at a point. Center of gravity and weight distribution are the keys to a good handleing bike. My friend has a lowered 650 front and rear. That thing handles like a dream, it can almost go circles around my ninja and my GPz.
 

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nathan600r said:
The size of your rear doesn't affect your the way handles. Most tires have the same contact area. An oval is still an oval no matter how wide it is. It still comes togther at a point. Center of gravity and weight distribution are the keys to a good handleing bike. My friend has a lowered 650 front and rear. That thing handles like a dream, it can almost go circles around my ninja and my GPz.

Not true
 

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nathan600r said:
The size of your rear doesn't affect your the way handles. Most tires have the same contact area. An oval is still an oval no matter how wide it is. It still comes togther at a point. Center of gravity and weight distribution are the keys to a good handleing bike. My friend has a lowered 650 front and rear. That thing handles like a dream, it can almost go circles around my ninja and my GPz.
Here is a link that explains why this is not true...

http://www.sportrider.com/tech/tires/146_0206_size/
 

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Yes I know that it's better to have a wider surface to balance on than a smaller one, but the higher your bike sits the farther you have to lean it over and going over too far throws off your center of gravity.
 

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Actually in a corner you want your center of gravity to be as far inside the corner as you can. Thats why sport bikes center of gravity is higher than other types of motorcycles.
 

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Yeah I don't understand why they run like that. I've seen lowered bikes that can do the turns just as easily as the sportbikes, but they don't have to put that much effort into it.
 

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Sport bikes run high center of gravity because it makes it that much easyer to move the center of gravity to the inside of the corner. This is also why you lean off inside a corner. If it worked with other bikes you'd see them ripping up the pros who are running sport bikes.
 

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Just too much work for me to have to move around that much for turns. I prefer the lazy way.
 

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I love the rush of hanging only an inch from the ground thats going past at over 100mph.
 

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LOL I don't think I would try that on my ninja. Well maybe I would, maybe that would wear down the chops on the sidewall and make it round again.
 

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OK, I may be missing something, but if all the wide tires do is increase your unsprung mass and make the bike handle "like a truck," then why do the supersports have such wide tires? There must be some reason...
 

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Its cause they have a lot more power going to the rear wheel. They need more contact area to take advantage of that power. In a straight line a 600 can't touch a liter bike. On the track there ussually isn't alot of difference from a 600 to a liter bike in lap times. I can very though. Tracks with lots of straights that lack many tight corners a liter bike will run faster, but a track with chicanes, kinks, decreasin radius turns, etc... a 600 will have just as good or better times. For example, my favorite track's, Mid America Motorplex, record is held by a 600. It does have a couple nice straights but the 600s still make up for their power in the corners. Heres a picture of the track...
 

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nathan600r said:
The size of your rear doesn't affect your the way handles. Most tires have the same contact area. An oval is still an oval no matter how wide it is. It still comes togther at a point. Center of gravity and weight distribution are the keys to a good handleing bike. My friend has a lowered 650 front and rear. That thing handles like a dream, it can almost go circles around my ninja and my GPz.
Boy am I glad to hear this, cause my rear is quite large & getting bigger :-|
 

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bikeaholic said:
There's a lot of confusion about why we use such big tires. It's commonly believed that a bigger tire has a bigger contact patch. This is incorrect. An ST1300 fueled up weighs about 700 pounds; the rider is about another 200. The tires are at about 40 psi. So, 900 pounds divided by 40 psi is 22 square inches. If the weight is equally distributed on the two tires, each tire has a contact patch of 11 square inches. That's it, tire width and diameter never entered into the calculation. A narrow tire will have an 11 square inch contact patch that's long and narrow; a wide tire will have an 11 square inch contact patch that's short and wide. If you drop the tire pressure to 20 psi (popular for on/off road bikes) then your contact patch doubles in size. If you find yourself in snow or rain, raising the tire pressure will shrink your contact patch and help you push through to the road.
I'm completely sober, so why doesn't this sound right to me :confused:

It seems the shape and diameter of a m/c tire would have some bearing on the contact patch. Take the 800a vs the 800b, at the same front tire pressure it still seems the 800b would have more front tire touching the road. Maybe I'm thinking to much of the flat car tire :|
 

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nathan600r said:
Just too much work for me to have to move around that much for turns. I prefer the lazy way.
Then why ride a sportbike? Stick to a cruiser!
 

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Green Knight said:
Its cause they have a lot more power going to the rear wheel. They need more contact area to take advantage of that power. In a straight line a 600 can't touch a liter bike. On the track there ussually isn't alot of difference from a 600 to a liter bike in lap times. I can very though. Tracks with lots of straights that lack many tight corners a liter bike will run faster, but a track with chicanes, kinks, decreasin radius turns, etc... a 600 will have just as good or better times. For example, my favorite track's, Mid America Motorplex, record is held by a 600. It does have a couple nice straights but the 600s still make up for their power in the corners. Heres a picture of the track...
elr658 said:
Because on a properly engineered motorcycle, the setup is complimentary. Nothing overpowers anything else. The tire is sized to the rim, which is sized to the motor. All a big stupid tire does, is ruin the carefully planned balance of handling. Big tires make your stuff steer like a truck.
True, and true.

In layman's terms, the way it was explained to me by my mechanic (when I was going to opt for a wider tire) is this: The wheel is still going to be the same width, so when you *pinch* a wider tire into a smaller wheel, you're basically making it "bow" out more, essentially making your contact patch narrower. You actually LOSE traction and handling, not gain it.
 
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