What is my "true" duro?

Cakalac

Member
I've asked a few guys this and I've gotten a few different answers so I'm putting it out to see what the group says.

Tire Set A:
I have a set punching 58 and it's 50 deg outside. I set my air pressures hit them with the torch and add my prep before going to grid. My durometer now puches 51 after the prep dries and soaks into the tire with the heat. What is the correct duro I should be using for that tire? Am I truly going to grid with a 58 duro tire or 51?

Tire Set B:
I have a set punching 58 and it's 50 deg outside. I sit them in the sun for an hr and they are punching 53 with nothing done to them. What is my correct duro number?
 

JWD

Member
It doesn't matter because you aren't racing durometers. Just be consistent with your method in your notes.

Make your notes, Track condition was x. Temp was x. Tire was a 58 wiped and torched to 51. Track condition was y, temp was y. Tire was 58 dropped to 53 in sunshine.

Tire B is obviously going to have less bite than Tire A, primarily because of the prep because both tires have been heated.
 

CarlsonMotorsports

Premium User
I always figure durometer at race pressure and temperature (at the start of the race.)
I do not even bother with punching a tire with a durometer while it is still hot (you know it's going to read lower than you''ll race at.)

Like Joey said....Be consistent.
And remember....just because someone says that you need a tire punching 50d doesn't mean it will punch 50 on YOUR durometer and your method of measuring.


-----
Thanks and God bless,
Brian Carlson
Carlson Racing Engines
Vector Cutz
www.CarlsonMotorsports.com
28 years of service to the karting industry
Linden, IN
765-339-4407
bcarlson@CarlsonMotorsports.com
 

Ragnar

Member
Cakalac - I have a similar question below.....not trying to hijack your thread.

How do you (or do you) compensate for changes in ambient temp when adjust duro during the week? For example next week I know it will be 15-20 degrees warmer than race day due to a cold front moving through. I suspect the set I have punching now at 50 will punch higher on race day when the high will only be in the 50's
 

CarlsonMotorsports

Premium User
That's where using a hot box (or in your case a fridge/freezer) can tell you exactly what the duro will be at that temperature. :)
Really, after a while you get a feeling or experience how much it will harden as the temps drop. For the most part, I'm not as concerned with duro as I am bite and the prep that I used. Yea, sure, duro is still a factor, but I think it's overemphasized by some. Then again, I'm one of those who pays attention to tire temperatures on dirt and some folks think that's a waste of time. See, it's all good data, you just have to take each into account.
 

W5R

New member
Don't focus so much on duro, but focus on what is wiped/applied and how many wipes....to me that is more important than the durometet, especially with maxxis. You have to keep notes of what and how much is wiped and go from there....loose, wipe more, tight then wipe less
 

Cakalac

Member
That's where using a hot box (or in your case a fridge/freezer) can tell you exactly what the duro will be at that temperature. :)
Really, after a while you get a feeling or experience how much it will harden as the temps drop. For the most part, I'm not as concerned with duro as I am bite and the prep that I used. Yea, sure, duro is still a factor, but I think it's overemphasized by some. Then again, I'm one of those who pays attention to tire temperatures on dirt and some folks think that's a waste of time. See, it's all good data, you just have to take each into account.
This is going to be my focus matched with internal cc's
 

Cakalac

Member
I wasn't getting hung up on duro as much as curious as to what I'm putting on my kart in regards to duro. If I heat a 58d tire and put on my kart and its now punching 51 and I push to grid ...what am I racing on? A 58 or a 51? In my mind if duro can be grip related that should make a difference but maybe not...idk. It's why I'm asking.
 

W5R

New member
I go by what the tire duro's at ambient or room temp, if I check the duro at all. If its cold out ill heat them up lightly and check the duro, usually around 100* or less is where I want to check duro
 

JWD

Member
I wasn't getting hung up on duro as much as curious as to what I'm putting on my kart in regards to duro. If I heat a 58d tire and put on my kart and its now punching 51 and I push to grid ...what am I racing on? A 58 or a 51? In my mind if duro can be grip related that should make a difference but maybe not...idk. It's why I'm asking.
You're on neither. You prepped the 58 so it's softer than that and you added heat to get to 51. It will cool off so it's harder than that. If I had to guess, I'd say you're on about a 56, but that's all it would be is a guess.

What we're all telling you is that it does not matter. A durometer is a tool that measures hardness or softness. It does not measure grip.

In general a softer tire will produce more grip than a harder tire. But two tires punching the same durometer may grip completely differently based on what chemicals are in the tire or the structure of the tire.

Long story short if you need a properly treated 51d tire, the tire that was punching 58 at home that you've now prepped and heated to 51 trackside is not going to work. It's going to be too hard.

A few things about a durometer. It's completely useless on a hot tire. It measures density. A hot tire expands making it less dense. It's almost completely useless in cold weather for the same reason. A cold tire contracts and is therefore more dense.

If you want to situate according to durometer, take them all in the kitchen, let them sit for an hour or two then duro them and mark your results.
 
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