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  1. #1
    Join Date
    Sep 2010
    Location
    Nova Scotia
    Posts
    831

    Tire Hardness and Aging

    I bought myself a little toy from Amazon and it arrived yesterday. It’s a Durometer and I wanted it to test tires.



    I think I should have researched it more as using the results are not quite what I expected. Mind you, it was very inexpensive ($32 Cdn) and I’m having fun with it, so that’s good. Plus I am learning things, so that’s fun too.

    Here’s the situation. This durometer reads rubber hardness on the Shore A scale. So I can check my tires. Softer ought to mean better grip. Unfortunately tire manufacturer’s do not seem to list a Shore rating for their tires. Oddly, many manufacturer’s of Radio Control car tires do. That’s where I got the idea. Hmmm…..

    What it is useful for, is to use it on a brand new tire, and then monitor its hardnesss as it ages (and is heat cycled by driving).

    Research

    I tried doing some research, and here’s some things I found:

    1/ According to an old document I found on the net, my BFG Radial TAs have an initial Shore number of 62

    2/ From a Corvette Forum:

    Mid 50s to 70ish--anything above that & things will get a bit slick, especially on the rears

    3/ From a Research Paper:

    During a tyre's lifetime, the rubber hardness of individual tyres may increase by up to 15 Shore A, which is equally large as new tyres may differ in hardness due to construction and material design.

    4/ From the same source (my interpretation of a chart/table):

    Increase in Shore number for tires made in 1990 (with a new Shore rating of 58 ) and stored for 10 years is an increase of 0.9 per year. This was for some unknown model of tire. Other brand tires, or made with newer (or older) technology, or with a different new Shore number would likely vary from this.

    5/ From PitStopUSA.com:

    I learned that rubber doesn’t have a set shelf life. When stored properly, tires (rubber in general) can last a very long time. Tires can degrade over time but what degrades a tire the most is exposure to heat and light. So if a tire is stored in a dark, cool place it shouldn’t show much signs of aging.

    I have been told for most of my life that “Tires get old and should be replaced every five years no matter how they look and how much tread is left.” I have also been told that as a tire ages it gets harder and looses traction. These two things don’t necessarily jibe with what I learned to during my research. Confirming or dispelling what I have been told for so many years seemed relatively simple. Measure the hardness of older tires and compare them to newer tires.

    I believe that old tires don’t necessarily need to be discarded just because they are old. I also think I dispelled the myth that older tires get harder as they age. If stored properly tires can have a very long service life. It is not the age of the tire itself that causes problems but extended exposure to the sun and heat that degrades it. Certainly, years of exposure to sunlight and blistering temperatures will ruin a tire and cause it to get hard and crack.


    Testing

    Before I start, it must be stated that Shore readings increase the colder a tire is and really ought to be measured at room temperature (somewhere I read 23 degC). So my testing doesn’t mean all that much this time of year.

    At any rate, I did some testing outside (zero degC), some inside my unheated garage (7degC) and one test at room temp (about 20degC).

    First, my BFGs which I bought around 1996 and still look like new due to low mileage and being stored in a dark garage, came in at 78. Even when the summer heat comes around, I doubt I’ll be anywhere close to the “new” value of 62. So they are harder than new, and that means less grip.

    Interestingly, using that 0.9 per year figure, mine could be at almost 83, but perhaps lack of sunlight helped. The other source lists a max increase of 15, so that would bring mine up to 77... almost bang on 78.

    The 78 number is high based on the Corvette Forum limit of about 70.

    I then tested the Michelins on my Toyota, which was outside in the cold and got 62.

    It just so happens I had a brand new winter tire inside in the warmth and it measured 58. I then put it outside for about 2 hours, not enough to really get it cold, but enough for the Shore number to increase to 60.

    So…. At this point I’m thinking I either better purchase new tires, or drive more like Aunt Martha.

    In the meantime, I’m having fun with my little durometer.
    John

    “A prudent person profits from personal experience, a wise one from the experience of others.”

  2. #2
    Join Date
    Jan 2006
    Location
    Chelmsford Essex
    Posts
    985
    Interesting read.I had Bf Goodrich tyres. Car is stored in the garage but I noticed discolouration of the tyre going light brown which is the rubber leakage. When this occurs the rubber hardens. My tyres when 15 years old but I decided to changed them two years ago and what a transformation. Tyre technology moves on and I was always very concerned on wet roads but not now. I went for Galaxy which are v rated.

  3. #3
    Join Date
    Apr 2012
    Location
    Wrexham
    Age
    47
    Posts
    541
    And im close to buying new ones because of 13 yrs old....
    Interested to see what mine would be but new ones this winter are the xmas prezzi.
    Regards
    Gav
    AK Ls1/t56
    Body on April 2014
    Passed IVA March 2017
    Registered April 2017.

  4. #4
    Join Date
    Apr 2012
    Location
    Wrexham
    Age
    47
    Posts
    541
    Galaxy? What are these? Interested!
    AK Ls1/t56
    Body on April 2014
    Passed IVA March 2017
    Registered April 2017.

  5. #5
    Join Date
    Nov 2004
    Location
    West Sussex
    Age
    63
    Posts
    186
    Galaxy radial t/a tyres are supplied by North Hants tyres and are good economical tyres. I replaced my BFG's with them and had no problem with them.

  6. #6
    Join Date
    Apr 2012
    Location
    Wrexham
    Age
    47
    Posts
    541
    Hi,
    Economical with cobra?? I want the best grip with dry and wet balance i can get. Pilot sport 4 255 45 17 are on the cards for me atm as per my other thread.
    Regards
    Gav
    AK Ls1/t56
    Body on April 2014
    Passed IVA March 2017
    Registered April 2017.

  7. #7
    Join Date
    Jan 2006
    Location
    Chelmsford Essex
    Posts
    985
    Gav,

    The Galaxy R1 GT are for 15" tyres and not 17". I think Eggbert having BFG Radial TAs he would be running 15".

    Regarding Michelins Pilot sports .I have just replaced my Pilot sport 3 on my daily running down to 2.1mm but they had tread cracks just 2 1/2 year old tyres. If you look about on the forums there is a lot of talk of this issue with these tyres. GM and Corvette owners had big issues. They statement back was they are summer tyres and due to cold climate below 20f ! I ended up going with Goodyears as they were great in the reports.

  8. #8
    Join Date
    Apr 2012
    Location
    Wrexham
    Age
    47
    Posts
    541
    Ahhhhh nooooo,
    More decisions.......
    Regards
    Gav
    AK Ls1/t56
    Body on April 2014
    Passed IVA March 2017
    Registered April 2017.

  9. #9
    Join Date
    Jun 2004
    Location
    Northampton
    Posts
    1,599
    Every day’s a school day with you John! Keep it up chap
    Dek

  10. #10
    Join Date
    Sep 2004
    Location
    Bressingham
    Posts
    1,332
    Many years back I took my old Dax to a track session shortly after it was commissioned.
    I was very disappointed with the amount of understeer I was getting. In fact I pretty much killed the front pair of BFG's that came with the kit.
    I replaced these with a pair of firestone firehawks i think. This gave a huge increase in the grip and by far the biggest improvement over the other settings that were trialled. I ultimately ended up cutting off the front of the chassis and replacing the setup to a more up to date geometry but that is another story.

    That left the rear BFG's which seemed OK. That was until i added more horsepower.. They were undoubtedly the major contributor to my first Cobra off road experience...
    So I then ended with what was a common fitment on all four corners in the Pirelli (P400?). They served me well until the car was sold.
    Of course I have no idea as to how old the BFG's were as i bought the kit as an abandoned project but i think keeping the rubber up to date is worth it for safety and peace of mind.
    A
    A S motorsport Ltd. 01379 688356 mob; 07909531816 web; asmotorsport.co.uk email \"andrewsoar@yahoo.com\"

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