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Old 06-22-2009, 04:16 PM   #1
chimchimm5
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Default Tire durometer - when is a used tire "too hard"?

I understand that this is subjective, but just need experienced insights.

I ran some old tires at the track this past weekend (actually I've just been using them and they are getting towards the end of their life). They were in usable shape so I was cheap/lazy and just used them. They worked, no problems.

Except, having done a couple track days before AND running them on the street they've gotten rather hard compared to new. The hardness really affected my traction and this was a damper on the day. I know I could carried more speed within my talent if the tires gripped better.

So I'm thinking of buying a Longacre durometer to be used to (check various things and) to read the duro of the new tire, vs broken in, vs whenever; so I can make a better decision if I want to run them again.

So because this was an HPDE, and not a competition, it's all about what you're willing to run. So...

How much harder does a tire typically get as it ages and is used? (in duro numbers and % delta)
Does it depend on compound?
About how many track days can you get out of a set (with caveats) before it's too hard?


I'm regretting now for not putting on the RE01R I have waiting in the garage, instead of running the old summer tires.
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Old 06-22-2009, 06:05 PM   #2
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I'm thinking, for an HPDE it doesn't matter.
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Old 06-22-2009, 07:37 PM   #3
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Quote:
Originally Posted by MasterKwan View Post
I'm thinking, for an HPDE it doesn't matter.
Of course it doesn't "matter" from a "competition" standpoint. But that's not what I was asking.

I need a feel for how much tires get hard and how much that affects the traction so I don't have to trial and error a half a dozen sets before I start to get the idea myself.

In this particular case, had I known that the tires would perform so significantly worse than their previous performance I would have switched to the next set I had waiting instead of being slower than necessary at this track day; ie I wouldn't have been so cheap/lazy had I known this. I'm not rich enough or abundant in free time enough to do a dozen track days a year and I need to pick the brains of those more experienced so that I can make my own decisions as if I had more experience than I did.

This is a balancing game of economy of time/money/resources
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Old 06-22-2009, 08:17 PM   #4
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My new sets are at 50 - 55 and they are no good after three 15 minute sessions. They get to low to mid sixties and they go off by a half second per lap.

But this has nothing to do with your question because we are running different tires on different cars.

Just get some RA-1s and drive them till they cord.
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Old 06-22-2009, 08:33 PM   #5
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How are you planning on factoring in tire temp? Tires get soft when they get hot so, hard cold might not mean hard hot.

Check these out. I haven't ordered any yet but, at $85 each, they're cheaper than street tires even.

https://www.fossport.com/product_view.aspx?cat=9
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Old 06-22-2009, 09:28 PM   #6
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Quote:
Originally Posted by MasterKwan View Post
How are you planning on factoring in tire temp? Tires get soft when they get hot so, hard cold might not mean hard hot.

Check these out. I haven't ordered any yet but, at $85 each, they're cheaper than street tires even.

https://www.fossport.com/product_view.aspx?cat=9
You know... I may have asked the wrong question, but I think you just gave me the right answer. Thanks.

Are these essentially Hoosier A6 tires?

EDIT: ok waitaminute... I avoid R-comps because I need a super gentle break away for my less-than-expert talent.

I'm looking to stick around the RE01-R type of tire... street legal and forgiving and can get me to/from track if necessary.

Last edited by chimchimm5; 06-22-2009 at 09:35 PM.
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Old 06-23-2009, 12:00 AM   #7
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Quote:
Originally Posted by chimchimm5 View Post
You know... I may have asked the wrong question, but I think you just gave me the right answer. Thanks.

Are these essentially Hoosier A6 tires?

EDIT: ok waitaminute... I avoid R-comps because I need a super gentle break away for my less-than-expert talent.

I'm looking to stick around the RE01-R type of tire... street legal and forgiving and can get me to/from track if necessary.
The koni challenge tires are actually harder than R6's. They are designed to last longer, but have a bit less overall grip. I wouldn't call breakaway progressive on any slicks though, so if thats what you need then street tires are the way to go.
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Old 06-23-2009, 12:03 AM   #8
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Quote:
Originally Posted by boost junkie View Post
The koni challenge tires are actually harder than R6's. They are designed to last longer, but have a bit less overall grip. I wouldn't call breakaway progressive on any slicks though, so if thats what you need then street tires are the way to go.
back to square one then
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Old 06-23-2009, 04:30 AM   #9
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Perhaps the answer you're looking for is to just get a 2nd set of wheels, and have your new tires on them. If you hit the track and the old ones feel like crap, swap the new ones on and don't look back.

-Mike
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Old 06-23-2009, 05:07 AM   #10
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Originally Posted by grippgoat View Post
Perhaps the answer you're looking for is to just get a 2nd set of wheels, and have your new tires on them. If you hit the track and the old ones feel like crap, swap the new ones on and don't look back.
Simple and effective. I had thought of that and will be doing it.

Just hoping to gain the scientific way as well.
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Old 06-23-2009, 11:50 AM   #11
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Just do what all pro racers from F1 on down do, when your laptimes start to go off either pull in for new tires or check them to see if you can run a bit longer before they cord, then if you are on a budget just keep running them until the cords are showing. There are so many rapidly changing variables to consider that it's just not worth chasing it scientifically.

A pyrometer to measure temps across the tire is a better way to use scientific analysis than a durometer. That's a good subject for another thread: What the pyrometer reads and what adjustments you should make to adjust....
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Old 06-23-2009, 02:28 PM   #12
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Yeah, tire pressures did make a huge difference. I'd gain +6psi in some cases.

The other thing I shoulda done was pulled off to the hot pits earlier to check tire pressure and release air after they got hot.
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Old 06-23-2009, 05:23 PM   #13
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Quote:
Originally Posted by boost junkie View Post
The koni challenge tires are actually harder than R6's. They are designed to last longer, but have a bit less overall grip. I wouldn't call breakaway progressive on any slicks though, so if thats what you need then street tires are the way to go.
*Koni challenge tire guy chiming in*

The Grand Am Koni Hoosiier tire is an A5 construction with a harder rubber compound. They also are definitely not the most forgiving as far as break away is concerned, even when compared to other R-compound tires.

+6 psi is actually not very much tire pressure buildup. Even when running nitrogen to minimize tire buildup, 8-10 psi is much more common for most 17"ish 245/40ish tires
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Old 06-23-2009, 05:50 PM   #14
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Yeah, I see 10 psi.

How do they grip compared to an RA-1?
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Old 06-23-2009, 07:08 PM   #15
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Quote:
Originally Posted by MasterKwan View Post
Yeah, I see 10 psi.

How do they grip compared to an RA-1?
Initial grip for the first 2-3 heat cycles is slightly better than an RA1, heat cycles 4-6 are about the same as an RA1, and after that, the RA1 has better grip. The RA1's are also slightly more forgiving, and come back a bit more quickly than the Cup tires do if you get to sliding and overheating them.

For all intents and purposes, for a HPDE tire, the two are close enough that they are basically interchangeable. Buying them new strictly for HPDEs, I'd buy the RA1s first, but buying them used [cough]Icansell225/45-17's,245/45-17's,and275/40-17'sused[cough] it's basically a draw, and used Koni Challenge tires are generally easier to find.
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