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Old 01-21-2008, 07:37 AM   #1
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Default Confused about Tire Durometer readings?

This last weekend, somebody borrowed my MAXMOD Tire Durometer.....When I got it back, a very well known World Champion sent it back to me with a message that it doesn't read correctly......HMMMMM

So, I tested it against a my tires, and sure enough, its reading of my Jaco 42's came up 52, on 2 different sets of tires, new and used.......

I went in search of finding where to send it to get it "factory" calibrated and couldn't find where it was made to send it back, but I came accross a post on Petitrc.com in the forms that was writen by Jack, (Jaco tires).

It reads:
If you have a Maxmod or similar durometer you will probably get a 5-10 point higher reading. This is fine, as long as you use the durometer to COMPARE the tires YOU run. Do not try to compare to other drivers or to our numbering system. The Maxmod is not consistent or accurate enough compared to a $600 Shore Type C. It does, however, serve it's purpose of grading your own tires in relation to each other very well.
So, I did some searching and found another of his posts that read:
Whatever you do, DON"T GO BY DUROMETER READINGS ALONE. They mean NOTHING when comparing tires from different "Families". I can give you 4 different tires that read 30 on the durometer. Only one will work on the rear... one will do donuts and spin out, one will make you push to the wall, and the other will wear out in 2 minutes. This is the most common misconception regarding tires I see.
Now that I'm still confused, but not as much, the only good use of the durometer is to match tires up, by shore readings, not actual shore of the tires.

Can anybody answer a few questions:
Do the tires have to be the same size to take readings?
Does "family" mean batch, or brand?

Does anybody know where to send the Durometer to get calibrated?
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Old 01-21-2008, 08:23 AM   #2
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Default Calibrate

I bought a maxmod tire durometer and it was off. You can calibrate it yourself. If I remember it has two setscrews on it that you need to loosen and it will slide up and down. Just play around with this until you get it to read correct. It's not very difficult to get right.
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Old 01-21-2008, 08:34 AM   #3
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"Families" of rubber mean are the tires made from natural rubbers, synthetic rubbers, blends? Any of these can have similar durometer readings but VERY different performance characteristics.

A durometer also needs a fair bit of "free" rubber (large tire diamter) so it doesn't "bottom out". If you compress mounted rubber with a durometer as the rubber compressed gets closer to the rim it acts more firm and has a definite effect on the readings. THIS is what is referred to when they talk about the MaxMod reading 10 or so higher. Problem is you can't really calibrate this out because it is entirely dependent on how much sidewall your tire has. When it's new there is less "error" on the part of your durometer than when the tire approaches the end of its useful life. For this reason the durometers are all but useless even on brand new 1/10 and 1/12 tires.

Makes 'em fairly doubtful comparing your own tires too unless they have pretty much the same sidewall height.

You have to remember that in the era of the MaxMod durometer we mounted our own 1/8 tires from donuts that were ENORMOUS. I also don't think there was the consistency in rubber quality, batch to batch, that we have now so you would check donuts as you mounted them and pair them up based on the readings. Still have my MaxMod durometer and truer. I really don't use either, but they are reminders of a LOT of fun back in the day.
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Old 01-21-2008, 09:35 AM   #4
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My MaxMod is very consistent with most tire brand's ratings. It is within a few points either way- generally the rears will read lower and the fronts higher...ie- 35 rears will read 33 and 35 fronts will read 37.

I only use it on freshly trued tires to match sets. I pull 10 new sets out and true them to within 1mm of my desired size. Then I match up my sets and finish true them to final size- I start the outer (generally left) tire 0.5- 1.0mm larger than the inside.
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Old 01-21-2008, 09:40 AM   #5
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...Check with Rob Murdock at WindTunnelRacingProducts.com

If I remember correctly - he does recal. on the MaxMod durometers...
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Old 01-21-2008, 10:40 AM   #6
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Scottrik: What you say about tire size, is what I was thinking and the "family" question is now clear......thank you.

I am only using it to "match" the tires at trued size now, much like when I use a caliper to match size.
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Old 01-21-2008, 10:59 AM   #7
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I have such a meter and personally I do not use it. I only use it to select tires from a shipment making new matching pairs.

Regarding the numbers, I trust the number on the box and know when to use harder or softer tires
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Old 01-21-2008, 04:30 PM   #8
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Can someone tell me whats the proper procedures on how to use a tire durameter, i get to many different ways on how to use it.

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Old 01-21-2008, 04:38 PM   #9
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Default Tire durometer readings

Originally Posted by Roelof View Post
I have such a meter and personally I do not use it. I only use it to select tires from a shipment making new matching pairs.

Regarding the numbers, I trust the number on the box and know when to use harder or softer tires
I "used" to trust the shore ratings on the boxes, but not any longer. I also had the Max style durometer, and seemed to get different readings. I now the the Ron Parris durometer, and it is very accurate.So much so that I gave my Max durometer away. I then started checking all of my new tires from the boxes, and they do vary quite a bit. What I do now is true all of my tires the same,<front or rear> match them with the new duromemeter and I know they will match. If you get a chance to pick up a good durometer, by all means do so.
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