[Paul_E_D]

Here's some info that was shared on a 125 site about Dunlop race tires. Some of it is 125 specific, but much of it apllies to other tires.

This DOES NOT apply to street tires.

Here are the long awaited factoids that I learned from Steve Brubaker at Race Tire Services (Dunlop's distributor East of the Big Muddy). Much of this, many of you already know, but there may be some interesting details:

1. Dunlop does not recommend an optimal heat range for 125 tires. Steve emphasized that it is more important that you have proper tire pressure (27, I recall) front and rear, than to let air out just to increase the temp. (My experience has been that at cool tracks, I've run 24 or 25 with good stiction!). He feels that when people let air out, the bike just handles funny.

2. Nitrogen is an acceptable substitute for air. It's more stable because it holds less water, which is what expands when heated.

3. 10% higher pressure when warm is a myth. DO NOT GO BY THIS! As previously mentioned, air holds differing amounts of water depending on the source. As many of you painters know, compressed air creates moisture. So, actually, a "bicycle pump" would give you more stable air. (I tried nitrogen last year and didn't notice much real difference, except my credit card was warmer and it's a biotch to load and unload in the van! Surprisingly, I still noticed a pressure increase when warm.)

4. Much discussion about heat cycles. Steve feels, and I concur via experience, that the real tire killer is rapid cool-down. What this does is brings the tire's inherent oils out to the surface (ever notice "bluing"?) and makes the rubber carcass less elastic. Picture a hard skin forming on pudding made the "old school" way. His advice is to get the unplugged tire warmers onto the tires ASAP after coming in. The warmers themselves act as insulators that let the tire cool down more slowly - so, too bad for those folks that have to do post-race tech!

5. What about tire warmers? Well, Steve likes them, if used properly. Only plug them in 30-45 minutes before use. Leaving them on longer is just cooking the performance out of them. (I've heard it rumored, but not scientifically confirmed, that you have more heat in your tires right off the warmers, than you do as the race progresses. Bickle says that you've got the first three or four laps to be a hero.)

6. How long do tires last before the performance drops off? Steve says that hotshots like Miguel DuHamel use tires only twice, then bin them. He also says that a guy like me in his first year can use them down to the wear bars - which is a WHOLE season! He says that performanc drops off dramatically in the first two short sessions (or in one long race) as they lose 5%-10% in these first two cycles or in a long race, then levels off to a straight line gradual descent over time.


7. How long does it take to "scrub-in" new tires? One decent lap, Steve says.

8. What do I have to do to get the "release agent" off the outside of the tire? Nothing. Dunlop does not use a release agent. DO NOT USE BRAKE OR CARB CLEANER ON THE TIRE, AS IT WILL BREAKDOWN THE STICKY COMPOUNDS! Use them straight up!

9. What's the deal with "cold tearing"? Steve says that cold tearing happens both with a a cold tire on hot tracks as well as a hot tire on cold tracks. Temperature differential creates a desire in the rubber to attach to the track, instead of itself.

10. Got gummy balls? Forget Tinactin. What's happening is that those little gooey balls on the edge of your tire are from the track, not from your bike. They mean nothing, except there's a lot of rubber on the track.

11. What compound to use? That's up to you. Ostensibly one uses a harder compound for higher track temps. I generally use soft, but might begin to play with mediums just for comparison when it gets hot and sweaty out.

[legalspeed]

Thanks for the info Paul, It certainly confims the warmers/heat cycle thing. I measure the rubber compound with a durometer (calibrated every six months). The tires's performance charactaristics drop off at 68 (for my tastes).

10.) I completely disagree. I had those all the time, thought everything was, as it should be. Then I FINALLY went to Pete Kates at GMD; my suspension was shite, twisted tripple, bearings sounded like a freight train, yadda yadda, Pete fixed it and I have never had little balls since. Well, not on the tire's edges anyway.

The ones that get plastered to my front tire, they are from the track.

Wizard (from gixxer.com) bought ten or eleven sets at the beginning of the season. I am thinking about this too, I have a cold storage area to keep them in which is better than the truck they are stored in at the track.

Do you agree with this? : buy one set of Dun's, Pirellis, and Mich, to try, then buy a few sets of the one you like.

[Paul_E_D]

I just bought three sets to use up some contingency money that would expire this month. Storing them in a garage is fine. As you say, probably better than on a truck.

The info was passed along from the Dunlop tire provider for the east coast.

As for the balls, I don't really think it's a set up thing. I notice that my tires pick up a lot of crap after the cars have been out there, or in the summer when it's hot. I assume it's some combo of rubber from the track and from the tire.

Funny wear patterns and tearing can be set-up related. I don't know exactly what your tires looked like. A bike that's well set-up will have a nice even and smooth wear pattern (regardless of balls).

[legalspeed]

Not a garage, an environmentally controlled rubber storage area.

I work in R&D for Total Fina; Hutchinson Sealing Systems Inc. USA. We extrude rubber, make sealing strips for cars, turcks, computers, etc.

We analyize rubber compounds, vulcanization, thermal plastics, bloom, Compression Load Deflection, and do extensive finite element work.

I'd like to discuss this with you at the track sometime, I'll be the one measuring my tires with a durometer.

Does the durometer really work? Yes, it gives confidence.

[Paul_E_D]

I've used a durameter occasionally. I couldn't feel the difference between riding hard and soft slicks, so I gave up on it. Plus, the hardness was different at different points on the tire making the info a little hard to interpret.

I can say this, the front tire on my racebike work hardens a lot faster then the rear tire does.

Have we met? I'm really not up on screen names. Anyway, I'd be up for a little more durameter testing. Bring it on over.

[legalspeed]

I think we met casually, at the track. We'd recognize each other by face.

I measured across the tire, in four places, and at three different radian points (I used the spokes for reference); to get an average. It's not what your reading now, you have to build a database, but more where the rubber was when it was new, compared to what is is reading at present, and how the tire performed at say 45 (new) as compared to now when it's at 75. 70's start an unpredictable slide, one that kicks out (for me).

So, I know when the Dragons start to get to 60, time to bestow some deneiro on Miles.
Experienced riders prolly don't need this. I was a rookie when I started using the durometer, needed to know when my tires were toast. Everyone said "When they start to slide unpredictably"
I wasn't comfortable with that answer, I started measuring.

[R7]

The ones that get plastered to my front tire, they are from the track.

I was under the impression that the globs of rubber always stuck on the front tire came from the tire itself under hard braking? If it gets picked up from the track, why is there never any globs stuck to the rear tire?

Good post Paul
I never put my warmers on for a slow cooldown when i come in from practice or a race but now i know to do that when i come in

Not that i'd do it but at the theory of using a race tire until it hits the wear bars, i'd get 2 seasons out of a set of tires.... though i'm hoping bumping up this year will pull me along faster so i'm sure the tires will cook a little faster

[Paul_E_D]

why are there never any globs on my rear tire?

Because the front already picked them up! I think we're talking about different things here. There are the globs picked up on the surface of the tire, and globs hanging off the edge of the tire.

The fact that we're even discussing them leads me to believe we are becoming somewhat delusional in our withdrawl from this highly addictive sport.

I just read about some fork internals that made me

I'm sick I tell you, SICK!

[Kip]

I got a idea !!!!! Ride the bike as hard as you can and if the tires are holding you back then you must be flying out their.

[Paul_E_D]

Who's to say I haven't done that already?

It is a good idea though. I never really worried about tires much until I was in the hunt for expert race wins and championships. Now I'm curious to know a little more to gain any advantage I can while keeping my expenses down.

[hessogood]

I'm sucking in the info around here. I got a billion questions but I don't want to be posting 6 topics a day, I'll figure it out on my own or ask around up at the track.

[legalspeed]

Originally posted by R7
I was under the impression that the globs of rubber always stuck on the front tire came from the tire itself under hard braking? If it gets picked up from the track, why is there never any globs stuck to the rear tire?

I think it is becaue the front is subjected to different extreme conditions. The rear tire does little heavy braking, while the front offers no acceleration.

The front seems to grind the stray rubber into it's tread, while the rear seems to pick them up and fling them, that's why I have a difficult time believing
the rear tire's balling rubber is being picked up from the track. I believe these little rubber balls are formed by the sanding effect of rough surface contact
with the track, plus, oh, just a little heat.

If they are formed by the rear picking them up, then A.) where are they coming from?
B.) why is there any left after a few hundred bikes run the course during a day of competition?