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Discussion Starter #1
Tyres seem to be an emotional topic so I'm going to stick this on its own. It is purely about stability and unexpected factors that influence wobble, weave and dynamic stability (not traction and nothing on aerodynamic factors)

It won't interest many people but if you want more than google offers or just curious what a vehicle geek gets ip to, its here and there are individual bits/formulas etc that you can use to solve/explain other tyre issues you might run into.

There is a bit of maths

General tyre properties v cornering
http://sem-proceedings.com/02s/sem.org-2002-SEM-Ann-Conf-SEM059-Identification-Motorcycle-Tire-Properties-by-Means-Testing-Machine..pdf

Tyre pressure effect on stability
http://www.researchgate.net/profile/Matteo_Massaro/publication/261834253_The_effect_of_the_inflation_pressure_on_the_tyre_properties_and_the_motorcycle_stability/links/54b3ccec0cf26833efcf5396.pdf
 

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That tire testing machine could quickly measure the effective tire circumference at different loads (rider weights).
 

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After perusing through all of that I am still going to use the manufacture's recommended tire pressure posted under the seat. Then if I begin to have wobble or weave problem I will look to see if my suspension is set properly for the riding conditions. These papers almost could lead you to believe that tire pressure alone is the main control for wobble and weave. To me the tires only introduce the bad vibrations. I understand that you can limit some of the vibrations with proper tire pressure. Bike geometry and suspension can overcome a whole lot of this. A holistic overview somehow has to be considered.
 

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Another thought, perhaps the bike introduces the wobble and weave to the tires. This is mind numbing. Way above my pay grade.
 

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BRAIN CRAMP! my brother can assimilate the math. I'm too thick headed for the paperwork and formulas. Thanks for the post.........Mike
 

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Discussion Starter #9 (Edited)
You are absolutely right Gappy, use the manufacturers tyre pressure gappy and absolutely correct about the geometry.
The manufacturers have already done all the work.


I posted this as data for people who like to mess with tyre choices and go with options the suspension and geometry were not designed to cope with and those who are curious about kinematics or the design/research world.

Putting science in other people's posts seems to always get a bad reaction so I put it here instead.

--------------------------

On the question of what causes wobble and weave, its part of being on two wheels and there is another mode known as capsize.
It all gets a bit complex when you get into the detail of it and there are lots of different causes and combinations. Messing up your geometry is part of it but so is aerodynamics which is how I originally got involved.

Apart from the surprising effect of road camber and general curiosity, I wouldn't worry about it if your bike is standard.

I am glad some of you got some use out of it, I expected the post to disappear without trace :)
 

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It is better for working out tyre wear due to road camber/crown ;)
By all means, if you can distinguish the negligible camber of actual normal roads from horizontal.

Riders are taught to occupy their lane, by riding where they would be if sitting behind the wheel of a car, near the center, where the road is even flatter than near the edge of the asphalt. Roads aren't usually pointed.
 

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Discussion Starter #12 (Edited)
Not if they are taught properly
Position for Safety then view and grip

Camber angle was measured with a simple gizmo fitted to the back of a vehicle that was already surveying "actual normal roads" for another purpose. My judgement wasn't a factor.


Edit: there are 2 excellent publications that cover road positioning in great detail.
Advanced Motorcycling by the Institute of Advanced motoring
Motorcycle Roadcraft (police riders handbook) published by TSO
 

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Discussion Starter #14
Nope
The curvature, cant/superelevation etc of the road can be modelled in a simulator and output as an actual route or a generic class/composite or altered to see what difference changes make to drive the test rig.
Modern roads are built using comparative geometrics and standard formulae so its the older ones that add most of the variation.

The simulation can also drive a motion platform to produce a bump road or it can reproduce aircraft runways, sidewinds and general test awesomeness.
 

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The camber (transverse/cross slope) of the roadway has nothing to do with uneven motorcycle tire wear.

The uneven wear (left side in the US) is instead a factor of the way motorcycles lean in turns (in the direction of the turn), and that in countries where one drives on the right side of the road the left side of the tire has more miles on it than the right.

How can that be you ask? Simple: It's because left turns are longer then right turns.

Consider a 45° turn in a 20 foot wide two lane road, with a 100 foot radius at the center line. If I enter the turn turning right and stay 3 feet to the right of center the radius of my path will be 97 feet; however if I enter it turning left, now 3 feet to the left of center, my turning radius will be 103 feet. Therefore turning right, leaning right with the right side of the tires in contact with the road doing the work, I will travel 76.2 feet making the 45° turn,

However turning left, leaning left with the left side of the tires doing the work, I will travel 80.9 feet--4.7 feet and 6.2% further. Consider also that we tend to drive faster in left turns than when turning right.

That is where the rubber goes...

This is a wonderful article about motorcycle tire wear.

From that site:

 

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Discussion Starter #18
No, but science does.

If the article is correct. I can ride just as easily around the outside of a wall of death as I can on the inside, that clearly isn't true.

While I totally agree that the major cause of laterally uneven wear is due to greater distance travelled etc., the angle of the road surface relative is also a factor. It is smaller but it is still there.

If you take the longer distance/speed out of the equation for a moment. , is there anything else to cause wear? Things like slip and relaxation length?

Of course there are. So are these things symetrically aplied?
The wall of death scenario says they aren't.
Consider an exaggerated camber of 45 degrees and follow it around an S bend at speed. When the road turns one way you are pressed against like a banked race track, grip is excellent.
When the bend turns the other way there are forces lifting you off the track and grip is less and the faster you go the worse it gets.

Which tyre wears faster, the one scrabbling for a grip or the one pressed firmly onto the road?


But the camber isn't 45 deg! True, but it isn't zero either so it hasn't completely disappeared.


The article also says camber can't be a factor because it doesnt contact the wheel at the point where the wear is - so does the wheel suddenly float in there at that point or something?
It assumes that the camber argument is something to do with the point of contact with an upright wheel. It isn't, it is about scrubbing in the corners - exactly the point he is trying to make but failing to follow to its conclusion.

Every biker should already know that a positive camber = more grip and negative camber = less grip. Every good rider should be using it to there advantage.

Not saying camber is "the" reason, only that it exists as a minor factor easily proved/disproved in a lab by making left and right corners the same length
 

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I believe you have misread/misinterpreted the article, perhaps deliberately it might seem from your terse rant.

The author is asserting the road camber does not contribute to uneven tire wear when traveling in a straight line, which is the most common "conventional wisdom" explanation for left side (or right side in the UK) tire wear.

This photo illustrates his point regarding the relativity of road camber, lean angles and tire wear when traveling in a straight line:



Road camber does of course affect wear when cornering, however the effect of a 1° (mild) to 3° (rather steep) transverse slope is just a minor contributor as compared to that of 20° to 45° lean angles and the added distance traveled on "outside" turns...
 

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If the article is correct. I can ride just as easily around the outside of a wall of death as I can on the inside, that clearly isn't true.
English is my second language, please point out where it says so in the article.

Just like Helium and the other noble gasses are part of the atmosphere, road camber contributes to tire wear. Their presence can even be measured.
 
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