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Discussion Starter #1
Tires:

A Little word that you can write volumes about:

Where to start? In these Forums, a tire thread usually goes on for 4 pages with nothing more than subjective opinions or old wives tales centered on Brand loyalty. Nobody seems to have even a modicum of knowledge about tires.
I thought that some hard facts may help you when you think about tires or handling problems.
Were going to keep in Layman’s terms here not scientific stuff or formula.

First let me say this: There isn’t a bad or dangerous tire out there in the aftermarket. At least not in North America. Even the stock tire that everyone derides will give good service. Until you wish to push the parameters of “good service” almost anything you can buy will be fine. If you think you want more than that continue reading below.

Traction: hey that’s what tires are all about right? Part of the traction a tire gives is simply the CF (coefficient of Friction) that a particular compound gives. This can vary slightly. There is virtually no difference in CA of any compound normally used in street tires.
Most of the differences in traction of various rubber compounds comes from the hardness of the rubber. This is measured by indenting the rubber with a spring loaded devise and measuring the depth of the indentation. This “Depth” is then transcribes on a Durometor Scale There are several scales, the one that covers tires it the “D” Scale. A given tire rubber compound will measure from around 50 to 100 D. The higher number the harder. You won’t find the number on any tires but most car tires have a Wear factor number that runs from 100 to 1000 with the higher being the longest wearing. This number is not solely a hardness number alone, but that’s most of it.

Why the hardness of a tire relates so much to the traction limit of that tire is because most of the grip of a tire on the road is from the rubber deforming around the road surface irregularities. Not the CF of the rubber. So the softer the rubber the more it deforms, the more grip. It’s not hard to imagine that there are real limits to how far you can go in either direction. Too soft and the tire wears rapidly or chunks, too hard and it doesn’t grip at all. BTW this is why motorcycles can lean past 45Deg.

Construction: Ok up to now we haven’t talked about tire construction. This is also related to traction. (Well hell everything about a tire (except white walls) is related to traction).
There are three fundamental types of tire constructions. The cross Bias, The Belted cross Bias. And the Radial.

The difference lies in the way the strengthing cords are arranged (all tire have cords)
Cross Bias: this is the oldest type. The cords run from one bead or edge to the other on an angle and each layer crosses the first in the opposite angle. This produces a tire that flexes uniformly across it entire surface.

The Bias belted: Constructed as the Cross Bias, with the addition of a stiffer circumferential bead or Breaker. This give a tire with Dual flexing rates. The breaker stiffens up the tread to reduce it deformation under load, but the side walls remain more flexible

The Radial: In this tire the cords are laid at a 90 degree angle in respect to the centerline of the tire and there is no crossing, Then a strong Breaker (usually steel Mesh) in laid under the tread, virtually eliminating any tread flexing at all. The side wall must then be very flexible.

Slip Angles: This is the angle of the difference between the direction the wheel is pointed in and the actual direction of travel of the machine. Or a fair estimate of the degree of sliding.

First let me say that this is not a racer thing or something confined to hard riding near the limit of adhesion. Every tire on every machine generates a slip angle when turned. A couple of forces cause this. The natural histories of the rubber (you know, the spring back) and the construction of the tire cords. Bias tire have more self aligning torque than radials and conversely generate greater slip angles.

Tire pressure can increase /decrease the slip angle of a given tire
Watch NASCAR? When you hear the commentators talk about the car’s pushing, or is loose/tight. Then he went up/down ½ lb. in the rear to fix it. What they were doing is adjusting the slip angle of the tires with tire pressure.

OK on any vehicle: a rear with a greater slip angle than the front will tend to tighten a given turn. If this is severe the thing could be un rideable. This is the reason that you’ll always be warned that it is un wise to mix tire brands. Especially Radial and Bias types.

There are a few thousand more points that affect how tires perform, but they are off into the area we don’t need to get to.

Think about all of the above the next time you’re buying tires or have a handling problem, some of it may help.

FOG
 

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Great Info, FOG.

May I add that temperature is also plays an important roll in performance as well as tire wear. Cold tire -> less traction. Too much heat -> wear faster/chucking. What I hear is that bike manufactures and tire manufactures always try to keep up with each other because the suspension/chassis and tires work hand-in-hand.

NT
 

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Discussion Starter #3
Yes tire temperature is factor in tire performance. Worth another 2 pages. But to describe anything more factual that what you said is difficult without being very specific. This was not in the scope of the piece I wrote.
Incidentally your comments are just the sort of vague Statments I was referring to in my introductory paragraph.

FOG
 

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Pirelli wasn't interested in what suspension set up i had when i asked them for tire performance data a few months back.  All they were concerned about was that when you peal off the track that your tire pressure be 34.5-35 psi front and back; they didn't say a word about tire temperature other than it's not that important i know about it.

I have a quick question regarding putting heat into tires on a cold track to bump pressures. Say i'm tracking on a cooler day and for whatever reason i can't seem to get my tire pressure to come up. is the corrective action to decrease pressure slightly to put more heat into the tire so your pressure comes up to what it's supposed to be when "hot"? The reason i ask is that i am noticing a few posts here and there talking about their chocked tire pressures being in the high to mid 20's (depending on tire manufacture and brand) so that when they get their first set of laps in their pressures comes up quicker. is this the case? Will lower tire pressures generate more heat so that on a cold track your pressures are spot on? Is it better to start out a little on the high PSI side or Low PSI side in order to dial in the tire for the track/temp?
 

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Discussion Starter #5
To answer you last question first. Yes lower starting pressure will cause the tire to heat more quickly. This is a point I didn't get into in my article because it is too complicated for the scope of that piece. Tires are self regulating to some extent, A underinflated tire will flex more and build up heat rapidly to the point where the pressure is almost normal then it will level off as the increased pressure reduces the flexing friction. This automatic feature has some limits. If you start with too low a pressure, the pressure rise will never reduce the flexing enough to stop the heat buildup and the tire will overheat. The opposite it also true.
All this temp stuff is based on constant use, IE: consistant lap times. The goal is to end up with a properly inflated tire to maintain the contact patch shape at a temp that softens the rubber enough to achieve maximum grip.
Amature riders are not expert enough to utilize the full potential of race tires because they cannot ride consistently at the limit. Most Race tires develop max grip when spun at 110% of road speed. Unless your name is Hayden or Rainey or Swantz you can't do that often enough to keep the tire at it Max grip. The best you can hope for is to get reasonably close to the average point where you are operating within the "Normal envelope" that the tire designer built into that tire. Street tires have a very broad tolerance for temperature variations, That's why the Pirelli guys didn't care about the tire heat. Track day guys place far too much emphasis on all this equipment stuff and not nearly enough on their ability.

Things like tire warmers are silly for a track day guy as the tire probably will cool down on the track. I never used tire warmers in my intire race career yet I was consistently in the first 3 at turn 1 even when starting from the back rows. Our class was DOT tires.

FOG
 

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I would like to point something out here. If an amateur is buying tires on the strength of which top name endorses them...be aware that they don't endorse them for free.
Nicky Hayden told me in '96 that he was getting a minimum of $10,000USD per race to run Dunlops.
Hell, for that kind of money EVEN I WOULD RUN DUNLOPS.
Goodyear advertises that until about '98 every car that won the Daytona was on Goodyear tires...what they don't tell you is that Goodyear was a major sponsor of the Daytona and you couldn't get on the track with any other tire.
The same with Firestone and the Indy.
Goodyear sponsored a stock car class and made Goodyears the "spec" tire. If you ran the class you got three sets of tires for the weekend, FREE. Then found the front runners painting Goodyear on the sidewall of Hoosier tires... 'CAUSE GOODYEAR COULDN'T MAKE A DECENT SHORT TRACK TIRE.

I run Avon tyres, exclusively, because I get them CHEAP! If I was paying full pop I would probably run Chein Shing or Maxxus.
 

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Discussion Starter #7
That's all well and good but, If their winning on those tires, maybe their not so bad. Point 2 : A champion like Nicky Gets to choose which tire Co he takes the money from.

FOG
 

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FOG said:
... Track day guys place far too much emphasis on all this equipment stuff and not nearly enough on their ability...

FOG
That is SO true... except for these 500's. Re-spring and raise the ride height but that's all that's necessary to get around well.

Any of the tires generally accepted as decent track rubber will work VERY well for the novice... and beyond. Seat time and learning how to use what you've got is where it's at and there's a TON there. The equipment's the last few seconds once the basics are well executed.
 

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FOG said:
The best you can hope for is to get reasonably close to the average point where you are operating within the "Normal envelope" that the tire designer built into that tire. Street tires have a very broad tolerance for temperature variations, That's why the Pirelli guys didn't care about the tire heat. Track day guys place far too much emphasis on all this equipment stuff and not nearly enough on their ability.

Things like tire warmers are silly for a track day guy as the tire probably will cool down on the track. I never used tire warmers in my intire race career yet I was consistently in the first 3 at turn 1 even when starting from the back rows. Our class was DOT tires.

FOG
Cheers to that!
 

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dad said:
FOG said:
... Track day guys place far too much emphasis on all this equipment stuff and not nearly enough on their ability...

FOG
That is SO true... except for these 500's. Re-spring and raise the ride height but that's all that's necessary to get around well.
also true to a point, but not so much for people just starting out. My EX is sprung correctly for me, but the rear ride height was WAY too low... lower than stock... but I still managed to win a good number of novice races on it like that before I adjusted it properly.
 

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Discussion Starter #11
Well I'm not being a smartass but winning novice races " CAN " be an little like winning at the Special Olyimpics. But as I said the riding is far more important than almost any bike set up. Jeff could beat you if you took off the front wheel.

FOG
 

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haha, oh trust me, I know... I occationally guest instruct at Tony's Trackdays & when he introduces all the instructors to the attendees he always adds in the fact I won my first feature race (PTwins)... although I'm proud of the fact that I did that, it doesn't say much for the NV Ptwins class. I mean hell, I did that w/ a 1:29.3 being my best lap time. :D

Although it WAS a great race between myself, Tom Joyce, his son Connor (till he crashed out) and my buddies Mike & Chad. The 4 of us all crossed the finish line w/in 1.5 seconds of eachother, it was great.
 

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Discussion Starter #13
Just to give a little insight to what I mean: in 2000 in the last race of the season when I was up in the points. I had my shifter fall apart on the warm up lap. I was able to screw it back together but only by hand. It falls apart again on the first lap. Stuck in 4th gear, I have to continue as even the finishing points will give me second in the PT Championship. I turned consistint laps at 1:27. actually passing all the juniors that got by me at the start while I was fixing my shifter.

FOG
 

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hehehe, nice. I totally know what you mean, can't say I'm suprised to hear that story, that's pretty funny... although, if you look at the Novice results lately, across the board, you might be suprised w/ some of the times. Alot of veteran racers say that the novice ranks have picked up a bit & many think that the popularity of trackdays has had a big impact in that.

I'm not sayin Novices are all that now cuz they're not, it's definitely still "little league"... but it's made some pretty decent progress, which is good to see. You've got alot of novices in the 600 classes that are breaking into the 22's and guys in the PTwin class like myself & my teammate that are gettin into the 26-27's before they're eligible fo AM. Hell, my teammate & I both did 24's before we got our 10 NV races in & I haven't seen any times like that anywhere in the LRRS results that are posted online... but yeah... NV is still the "special olympics" on the grand scale of things :D

... but now we're gettin WAY off topic ;)
 

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Discussion Starter #15
... but now we're gettin WAY off topic

OK back to tires.
there is no question that Armature times have fallen, and I don't mean that, at slower than the fastest times that your not really racing. Only that as a gage to judge the effectiveness of a chassis setup, anything but the fastest times could be misinterpreted.
I know that the development of tires since I started racing Exs in 1989 has knocked off 10 seconds of time at Loudon. Track changes have accounted for some of that too. My son one what was the PT class in 1991 &1992 and never turned a lap below :25. The bike hasn't changed (much) enough to make any difference.

FOG
 
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