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 Motorcycle Safety
 Physics and the theoretical
 Motorcycle vs Car tire and bead design...
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The Meromorph
Male Moderator
834 Posts
[Mentor]


White House, TN
USA

BMW

R1100RT
Peer Review: 1

Posted - 01/15/2014 :  4:16 PM                       Like
I just found this and wanted to share it for those who are interested.
It's a (somewhat ) less technical explanation.

http://www.goldwingfacts.com/forums...im-tire.html

rayg50
Male Moderator
2082 Posts
[Mentor]


NYC, NY
USA

Honda

Shadow Spirit 750DC

Posted - 01/15/2014 :  7:24 PM
Excellent, post by the writer. I thank you for sharing the link. I will say that my brain got full about half way through and I zoned out, so I will have to go back and reread it.

One question did come to mind regarding the contribution of weight. He mentions that leaned over the weight is the same (agreed) but (you knew that but was coming) I have always felt that leaned over the weight on the contact patch would be less because gravity would pull straight down and not along the axis to the patch. Is there any merit to my thinking or is my thinking backwards?


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AMJIce
Male Standard Member
123 Posts


Laguna Hills, CA
USA

Suzuki

DL650K9

Posted - 01/16/2014 :  3:50 AM
Wow! Thank you for that link.

I only read about 10% of it before my eyes glazed over. I have bookmarked it and will definitely soldier on. The technical aspects appeal to the nerd in me.
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SkootchNC
Male Advanced Member
1060 Posts
[Mentor]


raleigh, north carolina
USA

Harley-Davidson

road glide

Posted - 01/16/2014 :  4:25 AM
Great post..... followed by pages of "yeah? well I ride on a CT, and know better"... replies.

Some folks... BELIEVE... and science won't change their belief
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Gryphon Rider
Male Junior Member
45 Posts


Calgary, Alberta
Canada

Honda

Valkyrie Tourer

Posted - 01/16/2014 :  3:36 PM
quote:
Originally posted by SkootchNC

Great post..... followed by pages of "yeah? well I ride on a CT, and know better"... replies.

Some folks... BELIEVE... and science won't change their belief


But is it really science when it's 100% theory and no empirical evidence? Or when empirical evidence from hundreds (maybe thousands now?) of different testers provides a different result than predicted by theory, yet theory isn't revised or expanded to match the results? FYI, I don't want to convince anyone to run a car tire on their bike, but just to offer a little common sense in an atmosphere of fear-mongering.
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The Meromorph
Male Moderator
834 Posts
[Mentor]


White House, TN
USA

BMW

R1100RT

Posted - 01/16/2014 :  4:19 PM
In Theory, Theory and Practice should show the same result.



In Practice, They do not...

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Andrew Dressel
Male Standard Member
244 Posts


Milwaukee, WI
USA

Moto Guzzi

California Special

Posted - 01/18/2014 :  10:20 AM
quote:
Originally posted by rayg50

He mentions that leaned over the weight is the same (agreed) but (you knew that but was coming) I have always felt that leaned over the weight on the contact patch would be less because gravity would pull straight down and not along the axis to the patch. Is there any merit to my thinking or is my thinking backwards?


I believe you do have it backwards, as you have already guessed.

1. If you consider only the vertical component of the force in the contact patch, often called the normal force, it must equal m*g (the weight of the vehicle) and is independent of lean angle, as you agreed. The fact that the center of mass is not directly over the contact patch makes no difference in this equation.

2. If you consider only the horizontal component of the force in the contact patch, friction, it must increase in a turn and equals (m/r)*v^2 (for mass m, radius r, and speed v). With a little algebra, it can be shown that for a bike leaning in a turn, the friction force equals m*g*tangent(lean angle).

Thus, the total force generated in the contact patch, the vector sum of these two perpendicular components (the square root of the sum of the squares), actually increases in a lean. The direction of the resultant vector is approximately aligned with the mid-plane of the bike and so the rims, axles, suspension, the seat of your pants, and your kidneys merely experience an increase in "weight". A little more algebra shows that this "weight" equals m*g*secant(lean angle). At 45 degrees, the "weight" is 1.4142 times the weight experienced when riding upright in a straight line.

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Andrew Dressel
Male Standard Member
244 Posts


Milwaukee, WI
USA

Moto Guzzi

California Special

Posted - 01/18/2014 :  11:04 AM
quote:
Originally posted by The Meromorph

http://www.goldwingfacts.com/forums...im-tire.html

If you switch to tires with a better coefficient of friction, you'll immediately notice that stickier rubber is also softer; it wears out much more quickly. Motorcyclists accept the need to replace high-performance tires more often than touring-oriented rubber, but the auto types have another option: They can use wider tires to spread the wear over more rubber. And there, finally, is the reason high-performance auto tires are wider. It isn't to get better traction. Better traction comes from stickier rubber. The tires are wider to get acceptable wear from the stickier, softer rubber.



I have read this elsewhere, and it seems to make sense (except that wider tires are an option only for "auto types").

I have recently come across a competing theory, that you might find interesting. In his book The Racing & High-Performance Tire (published in 2003 by SAE), author Paul Haney explains that "a shorter contact patch at the same slip angle begins to [slide] at roughly the same distance from the leading edge as the longer contact patch." Since wider tires have wider contact patches, they simply have more non-sliding rubber in contact with the pavement than narrow tires do, which "means more total grip."
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rayg50
Male Moderator
2082 Posts
[Mentor]


NYC, NY
USA

Honda

Shadow Spirit 750DC

Posted - 01/18/2014 :  11:55 AM
quote:
The fact that the center of mass is not directly over the contact patch makes no difference in this equation.

Andrew thank you.
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alaskaal
Male Junior Member
38 Posts


Chugiak, Alaska
USA

Kawasaki

Vulcan Classic 1500

Posted - 01/22/2014 :  10:13 AM
That is an extremely interesting read. Thank you for posting!
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MotoGG
Male New Member
21 Posts


Murfreesboro, Tennessee
USA

Suzuki

GS500E

Posted - 07/01/2014 :  8:23 AM
Great post indeed !
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