here is what _Popular Mechanics_ had to say about tire thumping and nylon cords:

http://www.popularmechanics.com/cars/how-to/repair/1833626

I don't think we have to worry about this with our Vanagons, as all the tires I've heard of being used with them are radial, and steel with polyester.  DMc

---- Dave Mcneely <mcneely4@COX.NET> wrote:
> Nylon tires thumped.  Don't know about rayon.  Some newer tires have rayon, however.  I don't know why.  My brother tells me that radial cords smoothed out the thumping even more than the move from nylon, but I do know that nylon thumped.  DMc
>
> ---- Karl Wolz <wolzphoto@q.com> wrote:
> > My recollection is that nylon cords were introduced to get RID of the
> > thumping; it was rayon cords that had
> > "memory issues".  OTOH, I could be wrong - it's been many years ago.
> >
> > Karl Wolz
> > |
> > |From the link you provided, I see that the tire includes nylon cords.  I
> > |did not know that any modern tire included nylon in the construction.
> > |Perhaps because Hankook markets them as a "summer tire," they find nylon to
> > |be satisfactory.  Have you noticed the thumping phenomenon I mentioned?  Do
> > |you guys drive them year-round?  I would assume so.
> > |
> >
>
> --
> David McNeely

--
David McNeely