So I was looking @ the Dunlop D803, Pirelli MT43 and Michelin Trials tire when a co-worker told me to go with the pirelli because it was bias ply...
Ok I've read all the bias vs radial arguements and articles online but get this;

he said that the older bikes that came with bias ply tire should stay with those because of how they were built and that a radial tire may cause some harm... He's been on allota bikes outa the 70's onward and admits that he could be wrong and that radial ply tires may have changed since then so it is nologer a concern BUT to atleast look into it first to see if there was ever any truth to this...

so what you guys think? is a newer tech radial ply safe for my 1979 XT500?
Mostly street use...

The DOT certification on any street legal tire will make sure they are safe to use.

Try again, I just found this;
"While radial tires perform better than bias tires, some older motorcycles can't be fitted with radial tires because of differences in rim profiles. ..."
Source; http://www.timberwoo...aintaining.html

Bump.
Anybody know how to find out if the xt500 rims are compatible?

If you're riding on road, the MT43 is the only DOT approved tire on your list. Problem solved? Besides that, on road use will pretty much trash an 803 or x11 in short order. The MT43 will hold up a lot longer under those conditions.

Yes you can put a radial trials tire on an XT500 (rear 4.00x18). That is a different question as to whether you will like the result. Those tires you mentioned are trials radials built to run low pressures and run in conjunction with a trials front tire also. The only one that doesn't fit that category is the MT43 which is a DOT knobby.
I think you would find that you have to run more air pressure than the tire really likes with the radials just to get the stability that you are used to. They will also wear out really fast on pavement and will give the bike an odd moving around feeling and some strange braking charachteristics. I think you have the best tire in this group mentioned for DS use already.....the MT43 Pirelli.

Also if you price out true trials tires you will see that they are very expensive. Too expensive to experiment with.

Mt 43 it is then. thanks guys, this is also the most afforable of the 3. I'll see if I can get one to day to replace my rear tire; a rotted out cheng shin POS.