| which are not based on data. Which is what everyone else is doing as well. You seem to be doing the same. No sir, I am not. For example, you state:
- If the protection is damaged (cracks) then the belt needs to be replaced
I believe this is stated explicitly in the service manual. As such, this is not an assumption, I state as fact this is what is in the manual. - the fibers do not age appreciably without use, and are good for 60k How do you know that? This follows from the manual. If you don't believe it, it would be interesting to hear your theory on how fibers degrade with time. They are not exposed to UV or to oxygen, or any other pollutant, unless the rubber is cracked. Let's hear it, chief. Yes, the rubber is exposed to oxygen and to grime, but the fibers are not. You also assume that whatever the data suggests is exactly what made it into the manual. You cannot say for sure that there is no time limit for changing the belt, you can only say that Nissan deemed it appropriate to put that in there based on whatever criteria they find important. I'm sure there was a balance of cost and reliability.
If you are arguing that after 1000 years pollution makes it to the fibers, I would ask you for evidence. I see no reason that UV or oxygen or any pollutant would make it to the fibers unless the rubber cracks. I think the only tradeoff here is on how long it takes the fibers to micro-abrade to failure, which is maybe 4-sigma longer than 60k. (If that sentence makes no sense to you, I can only apologize.) I have made no claims either way, I'm just saying that I believe you are doing the same thing, drawing some conclusions without data? You are certainly entitled to your opinion, but I don't think I am doing anything of the kind. I in fact do have experience with making calls about reliability and cost in an engineering setting, using data as a guide. I also have experience with accelerated aging of materials. I'm not saying you are wrong, I'm just saying that you seem to be doing the same thing, just in the other direction. Perhaps I'm wrong. I appreciate that you acknowledge the possibility you are wrong. This is always a possibility, including with what I say, both on average, and for specific cases. But I am not wrong at all in quoting what the manual says, and stating that the manual was not just pulled out of a marketing guy's ass; the manual is based on a lot of engineering know-how, from the very same guys that designed our cars.
- John
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20:48:40 12/11/09
