tire size for xr200

I have a 1990 xr200 and need a new rear tire. I want to order a dunlop or maxxis. What is the correct tire size to order. There is a cheng chen or something on there now and it is 4.6 x 17, not how the others are listed.

Not many choices out there for a 17" rear tire.

Well I found the answer, figured I'd put it here in case anyone else needs to know.
The regular tire size for the rear is 100/100x17. Two manufacturers make them. IRC makes the VE33 and its considered an Enduro tire. Bridgestone make the ED08 and it too is an enduro tire. The IRC runs about $50 and the Bridgestone runs around $100. These are not easy to find, thats for sure.