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Old 10-11-2009, 01:33 PM   #1
maxgs
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Keith Code on Race Tires

This is an interesting read from Keith Code. In this article he says some very curious things about:

-tire warmers & heat cycles
-the importance of tires "shedding"
-tire footprint when leaned over


http://forums.superbikeschool.com/in...?showtopic=877


The Bands of Traction

If you saw the last GP in Portugal this past weekend you couldnít help but be impressed with the traction capabilities of the tires. The corner speeds, lean angles and how quickly the riders could flick the bikes is astounding. Clearly, that level of riding can only be achieved by those who are able to trust the tires. How do you arrive at the point of being able to use current tire technology?

The Edge

Anyone would like to be able to read and sense traction at a pro level. That would mean something like: to always know when you were at the edge of traction and feel comfortable enough to bring it there when and if you wished to.

For a professional rider that ďedgeĒ has to be pretty wide. Think of it this way: you must be able to ride in that band of traction or you donít get paid. That is a different perspective than most sportbike enthusiasts have on the subject of traction.

Bands of Traction

Feeling in control of tire grip would mean reading the signs of losing grip and knowing what those signs meant. If there was a nice long, tapering curve to losing traction, where the signs of it ramped up very gradually from a squirm to a little slip and then to a slip & grip and then on to a nice, clean, power-on slide weíd all be traction masters. The fact is, tires do have signs and signals just like that but talking about it doesnít make it any more real or comfortable without some personal experience to back it up.

Reading the Signs

By questioning a track day or club race rider you could pretty well figure out what lap times theyíd be able to turn by what traction signals they had experienced and were comfortable with. You would find most riders stuck right at the ďsquirmĒ band of traction.

Not too bad really, providing that the riderís basic riding techniques were firm, he could go quite quick at the squirm band of riding. This would typically give lap times that were within 8 to 12 seconds of AMA Pro 600 Supersport times. The squirm band starts right when the rider has enough pressure on the tires to get a decent sized footprint on the pavement, which is the technological magic of radial tire design.

Many riders think there is less rubber on the ground when the bike is leaned over but it is the opposite, there is more. They think that because they canít add gobs of throttle when it is leaned over. In actual fact, as we bring the bike up we can add more throttle because the tires do not have to deal with the leaned over side-loading from the cornering. When the bike is straight up it has the least rubber on the ground but no side loading to take away from the available traction.

Technical Skills

Having good technical skills is the only sane route to mastering the bands of traction and reading their signs. In other words, without a firm grounding in basics, itís easy for riders to misidentify what they think is a loss of traction when it isnít or because of poor technique they may skip a band or two and get themselves into trouble.

Sloppy throttle control gives a false sense of tire grip. Using lean angle in the wrong part of the turn for the wrong reasons gives a distorted feel for it. How the rider sits on the bike can have a huge effect on it. Confusing inputs into the handlebars is another classic way of misreading the signs your tires can give you. All of them will set you up to miss the signals completely.

These, and others, are all technical aspects of riding that can be adjusted by the rider without having to touch the bikeís suspension. Being coached through these points is the way to go and leads to control of the mysterious traction questions riders have.

Tire Technology

Riders know that 21st century motorcycles and tires are better than they are. Fine. What security does anyone have that this is true beside the thin hope that if they do get into trouble the bike and tires will save their bacon?

One aspect is tire warmers and the security they seem to give riders. Tire warmers are a fact of life these days even at track day events. What many riders fail to realize is that by the time they get around a lap or two the tires can actually cool down.

Tire temperature is based on tire usage. The higher loads the hotter they get. If you arenít in the band of traction that will take you over the tire warmer temp you really are looking at a security blanket that isnít totally real. For sure it can save a rider from the embarrassment of a first lap, cold tire crash and that is the good news.

New Skins

Aside from crashing, tires are the single most expensive, consumable cost riders have for track days and racing. Tires do wear out and that wear is part of the key to their ability to grip.

Take the tireís viewpoint for a moment. They are willing to stick provided there is rubber covering the cords; the temperature is up to the loads being demanded by the riderís speed; lean angle; braking and drive off the corners. Tires wear out just like skin. As the outer layer becomes dry it is swept away by friction. On your clothes when it comes to skin. On the pavement when it comes to tires.

Tires, like skin, dry out from age or from heat. Exposing the next layer of fresh, pliable rubber underneath to the road is critical to performance. If the dry rubber remains on top, traction isnít as good. To expose the new, fresh rubber, enough load must be put on the tires to ďcleanĒ them. It has been theorized that 10% tire slippage is the ideal situation for tires because it keeps the temperature up and at the same time ďcleansĒ them.

Heat Cycles

How many heat cycles a tire has gone through, theoretically, has a huge effect on how well they work. The heating and cooling is supposed to reduce their grip by changing the chemistry that holds the rubber together and riders sometimes worry about it.

The Dunlops on our school coachís bikes are usually take-offs; theyíve already been raced on and often raced on by pro riders who can get them up to full temperature. We then use them for days of track riding and all the coaches can go quick enough to run club race lap times and most of them could qualify for an AMA Supersport race. While our coaches donít ride hot laps every moment of every day the tires do get a minimum of 30 heat cycles a day.

Hereís the point: The record for a front tire is 38 school days. The record for a rear is 18 days.
The average laps per day would be around 90. I think Dunlop knows something about tires and taking up the devils advocate, these are the stickiest, most expensive ones so perhaps, at least for the quicker riders, there is economy in buying the good stuff after all.

NOTE: We change the Dunlops on our í07 ZX6 student bikes every three or four days.

The Sticky Stuff

Everyone wants to have the stickiest rubber they can afford but it isnít sticky until they can put the big load on the tires. Most riders would do better and learn heaps more about traction with something lesser than full race, factory rider developed tires. Why? They donít have to put the big loads on the tires to start to experience the bands of traction as listed above.

Look at it this way. If you are using the tire at the bottom end of where it was developed by pro riders would it actually save you if you got brave for a moment? The answer is no. Pushing the loads on the tires up for a moment when the rest of the lap was at your normal pace will not give the tire enough time to warm up to the level you momentarily demand from it to handle the situation.

In other words, your potential and that of the tires have to come up together for you to take advantage of what the tire has to offer. To a large degree, the security of the stickiest rubber is false. Until you arrive at some consistency in your levels of speed and lean angle and throttle control and the other technical parts of riding it is no more then blind faith.

Trusting the Tires

In the end it isnít about the tires it is about the rider. Itís about using good technique and having good technical skills. Itís about gaining some consistency with them and knowing you can do it. After that, itís not so difficult to trust your tires because you trust yourself.


Keith Code
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Old 10-11-2009, 01:37 PM   #2
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Old 10-11-2009, 01:43 PM   #3
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Old 10-11-2009, 02:12 PM   #4
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very good read

i like this part a lot.

In the end it isnít about the tires it is about the rider. Itís about using good technique and having good technical skills. Itís about gaining some consistency with them and knowing you can do it. After that, itís not so difficult to trust your tires because you trust yourself.
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Old 10-11-2009, 03:17 PM   #5
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