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Old 07-11-2006, 04:54 PM   #1
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The Motorcycle Tire Bible - Good Info

Everything you might want to know about motorcycle tires but were afraid to ask...

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http://firebladers.bikenet.gr/articl...echnology.html

One of the most important factors of today’s proper bike handling is tires. After all there wouldn’t be such a “rubber” war in the GP scene, if you are from the people who closely watches the GP scene (I think few people reading this article are not watching it) you will have encountered numerous times teams checking on new tires, tire companies trying to retrieve the most out of them…even bike transformations due to them.
Let’s be honest it takes little experience to understand that one of the most important motorcycling aspects is the tire itself. How many times have you complained about the tire not being what you expected, or how many times you have bragged about the cool set of tires you just bought?
Although not a tire expert or even the rider with tons of experience I will try to put down as much valid information I have crossed while searching and discovering.


Tire Construction

Mixing

Tire construction is really complicated opposed to what you see tires may not be mechanical or high tech looking gadgets but are definitely a huge process and years of research.
Although a tire consists of natural rubber (but in really small amounts) there are many more ingredients that finally produce a “synthetic” rubber. The creation of synthetic rubber contrary to natural rubber is necessary to produce the proper characteristics that we demand.

* Carbon black forms a high percentage of the rubber compound. This gives reinforcement and abrasion resistance.
* Sulphur cross-links the rubber molecules in the curing process.
* Accelerators are complex organic compounds which speed up the curing.
* Activators assist the vulcanisation. The main one is zinc oxide.
* Antioxidants prevent sidewall cracking, due to the action of sunlight.

The raw rubber, whether natural or synthetic is called the polymer. The process of combining this with the other ingredients is called mixing. Within the industry, the terms mixture and compound are synonymous. This may seem strange, but the mixing and subsequent curing of the rubber and its ingredients is analogous to baking a cake.
Tire Construction Process
Tire Construction Process
The rubber polymer used to be mixed with the other ingredients on a series of open mills. However, modern tire factories use large internal mixers. The Banbury Internal Mixer manufactured by Farrel is typical of these.
Mill mixing comprised a series of machines with pairs of large steel rollers, rotating with a small gap between them, called a "nip". As the rubber was forced through the nip it provided shearing forces to masticate and work the rubber. Natural rubber required the input of a lot of energy to break it down, so it was first fed into a mill with corrugated grooves cut into it. This is called a "cracker mill". Carbon black for mill mixing was normally obtained as a master batch (pre-mixed with rubber) from an external source, to avoid the handling problems of the fine powder. The curing ingredients are added as late as possible, to avoid the compound curing up.
With Banbury mixing, the process is better controlled. The mixing is done in three or four stages to incorporate the ingredients in a logical order.
The carbon blacks are delivered to the factory in tote bins and are stored in hoppers above the Banbury tower.
The finished rubber compounds are sheeted off and stacked on pallets waiting subsequent processing.

Calendering

The raw carcass materials made of textile or steel are coated with rubber. This is done by passing them through a machine called a calender which has a series of rollers in a stack, normally four. The rollers are called boles. The fabric passes between the middle rollers and rubber is fed from above and below. The thickness of the rubberised fabric is controlled by the gap between the rollers. This gap is called the nip.
The profiled slabs of rubber which go to make up the tread and sidewall of the tire are produced using an extruder. This machine forces the green rubber through a die to give the required shape. After mixing and extruding is finished then the process of actually constructing the tire takes place.

Beads

At each edge of a tire is a wire bead, around which the plies are wrapped, and this bead holds a tire on its rim. In a method similar to calendering, a number of individual, copper-coated wires are wound in a jig, and the resulting matrix-or bead wrap-is rubberized to hold everything together while the tire is being constructed. Even this part of the process can affect a tire's performance, as the shape of the bead wrap determines the fold over of the various plies and how they wrap back into the sidewall.

Assembly

First stage building is assembled on a flat collapsible steel building drum. The tubeless liner is applied, then the body ply which is turned down at the edges of the drum. The steel beads are applied and the liner/ply is turned up. The chafer and sidewall are combined at the extruder. They are applied together as an assembly. The drum collapses and the tire is ready for second stage.
Second stage building has an inflatable bladder mounted on steel rings. The green first stage cover is fitted over the rings and the bladder inflates it, up to a belt guide assembly. The steel belts are applied with their cords crossing at a low angle. Often a nylon zero degree belt is applied above the steel belts, to make the structure work more efficiently.
The tread rubber is then applied. The tread assembly is rolled to consolidate it to the belts and the green cover is detached from the machine.

Curing and Finishing

The green covered are moulded in a curing machine also known as a vulcanizer, or a press.
Cure is often called vulcanization or cross-linking. It is an intermolecular reaction caused by the introduction of chemicals (usually sulphur and zinc oxide or Morfax) which link or tie independent chain molecules together causing the polymer to form molecular networks. These chemical cross-links between polymer chains may be chains of sulphur atoms, single sulphur atoms, carbon to carbon bonds, polyvalent organic radicals, or polyvalent metal ions.
The critical parameters relating to the curing process are:

* The time elapsed before the curing process starts.
* The rate at which the process occurs.
* The extent to which the cross-linking occurs.

There must be sufficient time before the process begins to allow the mixing of all of the ingredients of the rubber compound, the forming of the ultimate product and the molding. Thereafter, the process should be rapid, but controlled. Accelerators (such as zinc oxide) reduce the time required for cure while at the same time resisting premature vulcanization (called scorch). Retarders, on the other hand, inhibit cross-linking or delay cure. It is desirable for a retarder to inhibit cross-linking at processing temperatures, but not at curing temperatures, thus providing more processing time without affecting the cure rate. It is the compounder's task to choose the proper cure system ingredients to accommodate the time required for mixing, forming, molding, and processing the selected polymer into the product or component being manufactured, while at the same time minimizing the time necessary to cure the material to its optimal physical properties. A strong background in chemistry (preferably rubber chemistry) is a highly desirable qualification for a compounder.
The cover is placed over a butyl curing bladder expands the cover to meet the mould surfaces as the press closes. Here the tread pattern is moulded onto the tire. Originally, tire moulds were in two halves. With radial tires, the tread elements are split into segments to avoid distortion to the steel belts as the mould is closing. The sidewall plates are engraved to provide the inscriptions of size etc. on the cured tire.
The tire is cured with high pressure hot water inside the butyl bladder. This has replaced steam as the curing medium, since pure steam at the pressures required would give too high a temperature for an even cure. The mould sidewall assembly is fixed to steel plates which are heated by steam.
Ater curing the tires passes to the finishing department, where they are inspected for defects. After which they are run on balance machines and the heavy spot marked. They then undergo other uniformity controls on a force variation machine. This measures the tires for radial run out, lateral run out and conicity.

Reading the tire codes

190/55ZR17M/CTL 75W

What do this numbers mean?

190 Stands for tire width

55 is the aspect ration (check 180,190,200 Hide and Seek?)

R stand for Radial

17 is the rim diameter in inches

M/C Means for Motorcycle Only

TL stands for Tubeless

75 is the Load Index. The load index (75) is the tire size's assigned numerical value used to compare relative load carrying capabilities. In the case of our example the 75 identifies the tires ability to carry approximately 387 Kilograms.

W is the speed index in our example it means the tire is capable performing at speeds up to 270Km/h.
For more information check the corresponding chart with explanation of its code.

Soft & Hard compounds.

Compounds are often described in terms of their "hardness" or "softness". This does not mean literally how hard the tires are to touch, but describes how the tires behave on the road or the racetrack.
Harder compound tires allow more mileage but offer less grip in relation to soft compound tires which offer less mileage but more grip. What makes a tire soft or hard is specified during the Curing process (check tire construction) and it’s a result of the number of sulphur cross-links between the long rubber molecules.
The hard compound tire has a greater number of cross-links between the long rubber molecules (introduced by Curing). This restricts the length of the rubber molecule that can interact with the road surface. Less interaction between the rubber molecules and the surface means that the tyre has less grip on the road.

Why race tires are not water friendly?

Although many people believe that race tires are not water friendly because of the lack of grooves it is not the only reason.
Lack of grooves does affect tire performance on water (hydroplaning) but another reason of race tire problems in wet conditions is the use of less Silica in the compound. As we described earlier in tire construction there are different ingredients consisting the tire, one of them is Silica. Silica is responsible of traction during wet conditions but is also responsible to provide better heat dispersion, Street tires generally work in a wide range of temperatures compared to race tires, this is achieved with the use of Silica something that race tires do not include in big quantities.

Grip & Traction

Grip = indentation + adhesion

Tire Friction
Tire Friction
The phenomenon of indentation accounts for 70% of the grip provided by the tyres and results from the interaction between the molecules of asphalt and the molecules of rubber. In the world of circuit racing, it is possible to match the compound perfectly to the track by analysing the surface and the roughness of the asphalt employed. In rallying, engineers are obliged to find a compromise for the differing characteristics of the surface from one stage to the next, and even from one portion of a stage to another.
Adhesion accounts for the other 30% of grip and results from the attraction between the molecules of the elastomer and those of the asphalt, a phenomenon known as the Van Der Waals forces, after the eminent Dutch physicist. Adhesion is therefore dependent on the quality of the bond between the molecules in question. This can be demonstrated by the experiment of pouring a drop of water and a drop of alcohol onto a pane of glass. Unlike the water, the alcohol will tend to spread out over the glass. In other words, the adhesion of water is superior to that of alcohol. The same applies to the bond between the tyre's elastomer molecules and the molecules of the asphalt and the mission of the chemists is to achieve maximum adhesion.
Adhesion is a property of rubber that causes it to stick to other materials, as we see with adhesive tape.
Tire Adhesion
Tire Adhesion
Adhesion is generally thought to be the result of momentary molecular bonding between the two surfaces. If bond strength is the same at all the bond sites the force that resists sliding is proportional to the total of all the minute areas of contact. If the two surfaces were perfectly smooth the true area of contact would be the same as the observed area of contact, but this is not the case. Real surfaces are actually very rough on the molecular scale and contact is limited to the highest protuberances on each of the two surfaces. The true area of contact depends on the surface profiles, properties of the materials, and the contact pressure.
Tire Identation (Hysteresis)
Tire Identation (Hysteresis)
Adhesive friction is the major contributor in tire traction, but it requires intimate contact between the two surfaces. Adhesive friction forces decrease drastically when the road surface is lubricated by dust, water, or ice. That's when deformation friction becomes more important. Here’s where another interesting property of rubber, viscoelasticity (Indentation), comes into play. Rubber is elastic and conforms to surface irregularities. But rubber is also viscoelastic; it doesn't rebound fully after deformation. Press your thumbnail into a street tire and the rubber rebounds. Press it into a racing tire and the mark stays there, recovering only slowly. This is a simple but crude test of hysteresis, or energy loss, in rubber. Low-hysteresis rubber rebounds quickly; high-hysteresis rubber lags in rebound after deformation.

Heat cycles, cold tearing and tire manipulation

If you are a rider who has some track experience or has spoken a few times with racers he has heard of different kind of tire wear and problems.
Rubber in tires undergoes cyclic stress (and mostly at very high levels). As we all know from Physics a work produces energy loss so the work done from the rubber is transformed into heat generation. The combination of high stress and temperature generates mechanical and chemical changes in the rubber.
Some elastomers, and rubber falls into that category, exhibit stress softening and permanent set. Stress softening has been attributed to displacement of polymer network junctions and entanglements and/or the incomplete recovery to original positions of those junctions and entanglements after stress deformation. The presence of fillers [carbon black and silica] introduces possible additional softening mechanisms, including breakage of rubber/filler attachments, disruption of filler structure, or chain slippage at filler surfaces. When intermolecular structures are irreversibly disrupted or reform in new positions while the polymer is extended, the result is permanent deformation.
A rubber compound is a mix of many materials, including chemically active agents. An excess of certain kinds of active agents can provide an opportunity for a disrupted or broken bond to repair itself by rebonding at the same location or in a new location.
Another mechanism for tire give-up is simpler. The tire might wear to a tread thickness too thin to generate enough heat and the tire temperature falls out of the range for max grip. A thick tread, even a slick, deforms and the resulting hysteresis generates heat. A thin tread deforms less, generating less heat.
Rubber is a mixture of materials and chemicals manufactures with mechanical processes and various heat and pressure cycles. When in use the rubber is under mechanical work and at elevated temperatures similar to the process when it was born. This process multiplies the effect of Curing (check tire construction) which changes the tire characteristics.
You are wondering why do racers use the tires and change them even when they look new. Race tires material when new is semi-stable but if the tire is raced then it enters a new cycle of curing, curing makes the tire harder thus it becomes less effective in race terms.
The first heat cycle of a tire is called scrubbing (break in) from there on every heat cycle changes a tire to some degree in the direction of harder, less flexible and less adhesive. Race tires can loose effectiveness before the treat wears enough if they go through many heat cycles. For some tires three cycles is too many! While other show a performance drop off initially and then maintain a good level of performance until the tread is worn off.

Graining

Grainining is the result of aggressive riding with a soft compound before it reaches its proper working temperature. Tires as we know need a specific temperature range to work properly, stressing them lower that range or higher will slowly destroy the tire. Graining is often called “cold tearing”. When a new rubber sample is continuously abraded in the same direction, the rubber develops an array of nearly parallel ridges at right angles to the abrasion direction. During sliding, deflection waves in the rubber turn into peaks which are bent over, exposing the upstream side to abrasion. The peaks wear thinner into teeth and the tips are eventually torn off.
Tire Graining
Tire Graining

Sliding on smooth tracks does not always produce abrasion. Abrasion is generally initiated by local stress concentrations at the contact between track asperities and rubber. Abrasion intensity depends on shape rather than size of the asperities. Experiments have shown that road surfaces exhibit wide variations in abrasion characteristics. Lab experiments with abrasion in an inert atmosphere-nitrogen-show less abrasion than the same process in air. This leads to speculations that antioxidants in a rubber compound can make it more resistant to abrasion.
Unfortunately, once a graining pattern is worn into the surface of a tire it's difficult to wear the pattern away. The ridges tend to perpetuate as wear continues. Even worse, since the tread is not evenly loaded after it has been grained, the tire loses grip. It's just another way for a rider to mess up. That's why experienced riders are so valuable.

Blistering

Reversion happens when tires get way too hot. When you see a rider lock up a tire the smoke tells you something bad is happening. The resulting flat spot is caused by frictional heating of the tread rubber causing reversion. The overheated rubber softens and is scrubbed off the tire.
Another, less severe, form of reversion is blistering. Too high cold inflation pressure or too much pressure build-up during use caused the tread to overheat. The heat is generated at the interface between the belt plies and the tread and the rubber melts, causing a local blister (when you do burn-outs you are experiencing a massive tire blistering).

Tire oxidation, sun and oxygen effects

The main causes of rubber aging in tires are Ozone, Heat and Deflection. To protectrubber from aging, Antioxidants and Waxes are generally used in the rubbercompounding.
Antioxidants come out to the surface of the tire where chemical reactions take place with the attacking ozone. Thus ozone is rendered inactive to age rubber.When you find the tire surface "reddish", this means Antioxidants have come out to the surface and effectively fought against ozone.
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Old 07-11-2006, 05:32 PM   #2
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Great info.



People are still going to put race tires on their streetbikes no matter what.
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Old 07-11-2006, 05:59 PM   #3
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Somebody sticky this one.

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Old 07-12-2006, 01:36 AM   #4
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wow.. a lot of information
thanks a lot supertireguy.. i'll make sure to read up on it when i get the time ...
i might hit up your place if i need to change tires
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Old 07-12-2006, 08:04 AM   #5
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Nice post...thanks!
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Old 07-12-2006, 05:37 PM   #6
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wasn't that same article in a Sport Rider eon's ago?
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Old 07-10-2009, 11:56 AM   #7
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Old 05-01-2010, 02:02 PM   #8
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Bump.

Mods maybe make this a sticky thread.
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Old 05-02-2010, 03:46 PM   #9
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Old 05-02-2010, 06:38 PM   #10
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Quote:
Originally Posted by mototireguy View Post
Too high cold inflation pressure or too much pressure build-up during use caused the tread to overheat. The heat is generated at the interface between the belt plies and the tread and the rubber melts, causing a local blister (when you do burn-outs you are experiencing a massive tire blistering).
Huh? I though low tire pressures=higher tire temp?
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Old 05-02-2010, 09:18 PM   #11
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Good find, Robbie.
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Old 05-03-2010, 10:46 AM   #12
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is there a 'how its made' episode on the building or a tire? that would be interesting to watch

great info
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