The fancy blue Kevlar reinforced ones...
I have them on my Subaru, and in this really cold weather they (seem to) have started slipping, both on the alternator and the PS pump.
Anyone else run into issue with these and the cold? Do they need way more tension than rubber or anything?
Gearhead_42 wrote: The fancy blue Kevlar reinforced ones... I have them on my Subaru, and in this really cold weather they (seem to) have started slipping, both on the alternator and the PS pump. Anyone else run into issue with these and the cold? Do they need way more tension than rubber or anything?
Are they Japanese style groove, or North American style groove? Jap belts are a larger cross section V, and an American belt designed for an American car will never drive correctly.
First things first...have you re-adjusted the tension on it? I've read that aramid (Kevlar) actually grows as it gets colder, unlike most materials (negative thermal expansion). If you're checking the tension after it's warm, then in theory it would loosen up when it gets colder. Probably not much, but worth bringing up.
Bryce
Negative thermal expansion coefficient of Kevlar. facepalm
Why didn't I remember that! [turns in engineering degree in shame] Combined with the very looooong tensioner adjusters in the Subaru the 80 degree swing between installation and now was enough.
I tightened up the belts and the charging system is happy again! Thanks Bryce!
Now to remember to readjust before temps are back in the 90s and I start killing bearings 
It's so tiny an effect as t obe non-existant.
http://www2.dupont.com/Personal_Protection/en_GB/assets/PDF/Automotive/Technical%20Guide%20for%20Kevlar%C2%AE%20in%20Mechanical%20Rubber%20Goods.pdf
And according to Gates, they're polyester anyhow, not Kevlar.
http://www.gatesracing.com/belt.cfm
Hmmm... we're both right. #2 cords are polyester, but #4 cords are Kevlar (aramid) 
Well, regardless, belts were looser than is good, tightened belts and charging system happy.
Think I need to design automatic tensioners for Subarus 
A squirt does wonders on my ol slipping belt Buicks.
While Kevlar is an aramid, by no means does aramid mean Kevlar. It can mean quite a few other others. Sorta like Polypropylene and plastic. Polypropylene is a plastic, but not all plastics are Polypropylene.
The undercord doesn't get tensioned, that's the job of the tensile cord or cords. The undercord is there for friction and lifespan. Sorta like the woven fabric you see on the sides of a high load v-belt. It doesn't provide tensile strength to the v-belt, it does let it live a lot longer.
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