Tire rubber durometer rating -- stability

[gusss]

Hello; I import karting tires from Taiwan , while reviewing a sample tire sent for inspection for our order, I noticed a change in spec. of Duro rating . We spec. them at 65-75D ,this sample came in at 60-65D ..here is the factory response=
Hi Gus,

The tire factory explained that the tire compound is no changed so far. But the tires are getting harder after by sea. One month transportation under the Sunshine and the tires are harder. This time, you received the tire which is by air and just several days to arrive to your hand. Please kindly understand it. The tire factory has no change for spec of the compound. Please don’t worry it. Thanks

Please some Poly engineer, give us some ammunition to call this "bull"
any help much appreciated , gus.. (www.vintagespeedtires.com)

 

[anorlunda]

If you don't get a good answer here under materials, I'll move it to M.E. Automotive. Perhaps better answers there.

 

[ChemAir]

Can you read a date code, or other traceability mark on the tire that indicates its manufacture date? This would clarify the timeline. DOT (US Department of Transportation) requires this, and most race car tire manufacturers (Goodyear, Mickey Thompson, Hoosier, Firestone, Goodrich, etc.) do this as well. I'm not sure non-DOT imported tires are handled like this.

Tire temperature, UV exposure, O₂, O₃ can influence hardness over time, among other things. https://pubs.acs.org/doi/abs/10.1021/ie50360a009?journalCode=iechad I'm having trouble finding a good article on vulcanized rubber oxidation that isn't behind a pay wall. Tires will degrade faster in the sun, or at elevated temperature, so there's at least a grain of truth there.

As far as ammo--I wonder how much sun those tires see while in a closed container in the middle of a container ship. More likely, the inventory control is poor, especially if they have no traceability or date codes on the tires. It seems unlikely the tires were cost-effectively transported by plane, but I could be wrong. You may be able to ask a few questions about the shipper to see if the story holds up, and learn if they are going to keep shipping by air in the future, or if it will be random as required to explain QC issues when they occur.

 

[jrmichler]

Wait a month and test again? Inventory is expensive, but you could easily use up that month arguing about it. And I would start looking for a different supplier.

 

[gusss]

Thanks ChemAir; Yes these tires have a date code ..The sample tire airmailed to us was just made, normally we ocean ship, and that time line is about one month, this was airmailed for a OK to expedite production.. I find it hard to believe one month in a container would raise the Duro 10 points on Shore A scale..
These tires go on vintage racing karts, and because of earlier frame designs, a to soft compound will incur frame binding, and karts can flip over.. I've had other problems with this factory ,and usually with enough counter ammo they rescind. I'm not a Poly chem guy ,so I was looking for some good data to counter . Being such a niche market I'm limited for small production..thk/u. for your info and time ..gus..