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Discussion Starter · #1 ·
I have joined the Dark Side and find I like it.
But there is a ton of information about increasing contact patch.

By real theory contact patch does not change, or at least not enough to be of any notice.

A tire is an air spring, IF you are supporting 350 lbs and have 35 PSI in the tire, the contact patch is 350/35 or 10sq in.

I will pause while many go right through the roof.

The wider tire will have a shorter contact patch than a thin tire.
Same area, except for some effect do to sidewall stiffness, which is also a spring.

I refer you to these essays.

http://www.eng-tips.com/viewthread.cfm? ... 250&page=1

http://www.eng-tips.com/viewthread.cfm? ... 250&page=1

http://www.eng-tips.com/viewthread.cfm? ... 250&page=1

Sorry to stir the pot, but I just couldn't take it any longer.

This goes against instincts and urban legend but it is science.

I shall now duck for cover.


Larry
 

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Being a drag racer by heart, I totally disagree. I can air my tires up and down and change my contact patch. The first thing I do with new tires is mark the entire tread with shoe polish and do a quick burn out and see what is contacting the ground and adjust air pressure as required.

So you are telling me that when I have my street tires on my Chevelle the contact path is 800 pounds per rear wheel divided by 35 PSI =22.8 sq in. and with my cheater slicks (25 PSI radials) which are the same size the contact patch is 40sq in. No way. Both tires are BFGoodrich 275/40/17
 

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Speedsville,

A lot of it also comes down to the "quality" of the contact being made. All I know is, that after over 13,000 miles with a rear CT, riding hard, and lots of canyons, the back end has never broken loose on me once. So, even if the contact patch was half that of a MT (which it isn't), and I got the same kind of traction that I mentioned earlier, I'd still go with the CT. I had way to many "pucker" moments with my rear motorcycle tires, thank you very much. :shock:

Another urban legend is that motorcycle tires are inherently "stickier" than car tires. Not so, not so. Just ask twin1300 about the results he saw when he tested his CT against his MT with a durometer.

-S
 

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Speedville,

Send a pic of your tire and what brand and size do you have??????????


Plus what they do tell you is that if they had the same compound of rubber,....but the car tire is softer and more grip than the motorcycle tire, so you are not putting apples against apples. If both motorcycle tire and car tire had the same softness of rubber, then you might have something and they are correct about that.


...............twin


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speedsville said:
Just out of curiosity, why do you refer to "these essays" ie plural and then post the same link three times?

I agree with twin 1300 and others on the "three essays" :lol: posted above. Your formula is great in theory, but doesn't take into account compound stiffness and geometry of the tire. The air isn't the only thing supporting the load. I would agree if the tire was made out of 3 mil plastic membrane, but it isn't.
 

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Discussion Starter · #6 ·
1: of course if you change the pressure (change the spring) the contact patch changes

2: I am not discussing traction of compond.

3: I put on a GOODYEAR TRIPLE TREAD. I will have to get out my digital camera and get a few pictures.

4:When I copied the links. I must have screwed up.
I had 3 different sites. Here are the other 2.

http://www.tirerack.com/tires/tiretech/ ... ?techid=10

http://auto.howstuffworks.com/question506.htm

The air is the largest difference. But not the only factor, and could go either way.
And the sidewall ect. could go either way for more or less actual contact patch. Also look how fast Formula One cars are going with a smaller tire than they used a few years ago.

"A man convinced against his will, is of the same opinion still"

Larry
 

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I agree with you mostly, the contact patch won't be terribly different in area. I think most people assume that is what causes the difference in their traction and handling when it's really a lot of other things going on instead.

I think that the reason "why" it's different is really not as important as "what" is different. People compare two tires and evaluate the differences between them. If you're saying the differences are not due to contact patch difference, okay I'll buy that. Most really aren't all that concerned about the science behind it, it's just something they say to be able to talk about the differences they feel.

Is the contact patch area thing the only point you're trying to make?
 

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Discussion Starter · #8 ·
Verbatim,
Yes, it just drives me up a wall when people keep misstating an anti physics urban legend.
It mostly just comes from hearing others think there is more contact patch when it is no possible

I too thought the same, since we were kids arguing about Fords and Chevys, in high school we always thought that bigger tires meant bigger patch and more bite.

I didn't realize this until we were talking tires for the Mustang at Ford and another engineer pointed this out.
I too rejected the idea until I asked myself, "Self, if the contact patch changes, with the same PSI, tell me why."
I couldn't.

No other spring between the chassis and ground.

Now just listen the anouncers talk during a NASCAR race and they are always talking about making air pressure adjustments, to change spring rate.
Remember, it is PSI inside the tire.
POUNDS PER SQUARE INCH!

Larry
 

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I don't think it's too difficult a concept to grasp. Given that the load is unevenly distributed on the contact patch, however, I think the geometry of the tire and hence the resulting patch will be different enough to have an effect. The actual square inches will vary slightly based on the other things mentioned here.

Performance and traction will, in my opinion, be very different depending on the shape of the tire...whether the contact patch is the same or not. I think you'll agree, no? Naturally all the other things like compound, tread pattern etc will also have an effect.

Tell us what your opinion of your ct is. I know you said you liked it, but what about it is different than a mc tire?
 

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Discussion Starter · #10 ·
So far, and I believe it will only get better, I like the CT very much.

At first I went to a parking lot and drove figure 8's then rode up to a friends house. By the time I got there, I had adapted to any differences.

I do notice 2 things, she seems to spring up out of a turn a little easier, and driving in a rut I can feel the rear center up but very stable.

IT feels real good in higher speed sweepers.

Now if I can get 30,000 miles out of it :D

Larry
 

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speedsville said:
So far, and I believe it will only get better, I like the CT very much.

At first I went to a parking lot and drove figure 8's then rode up to a friends house. By the time I got there, I had adapted to any differences.

I do notice 2 things, she seems to spring up out of a turn a little easier, and driving in a rut I can feel the rear center up but very stable.

IT feels real good in higher speed sweepers.

Now if I can get 30,000 miles out of it :D

Larry

Congrats.......Just wait till you get caught in the rain.......Then you are going to see something awesome.


....................twin


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how are tight turns at speed? I'm considering a CT for my first change but am concerned about those floorboard-grinding turns. I've read about having to counter-counter steer on turns. Is this common or only for low speeds? Does anyone have any experiences/advice that they can share? Thx.

I ride a Metallic Blue 2005VTX1800N3. http://www.cruisercustomizing.com/mrrogercruz
 

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http://www.vtxoa.com/forums/viewtopic.p ... 4&start=50

Go to the bottom of the post of the pics where we are working on bikes and read the paragraph about our midnight run.


Counter steer is for speed....when you are going slow as in a parking lot or turning into a drive way, you turn the direction you want your bike to go. When at speed excess of 25 mph I guess you use counter steer...turn right to go left and vice versa.

Counter steering will save your life and make riding 100% more fun. I think it would be good advice to take a motorcycle safety course.


..................twin

ps....let me know if this answers some of your question.


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