Is 235/65 the stock tire size on the 17" alloy?
 

Before i make the leap and downgrade to 17" alloys , is the 235/65 the tire size default as used on x5s with 17" original rims? been told many that 255/60 would be more suitable although speedo would be slightly out but still within the 3% limit of max difference btween stock and replacement tire size that is permitted....any feedback would be great before i bite the bullet

having just replaced tires on my 17 inch alloys, 235/65 was the stock default size listed.

I believe 235/65 is correct size - you can always check the drivers side front door
there is a label on it with recommended sizes of tires & rims etc etc

Both are listed at Tire Rack, but more availability of brands for the load range for the 60's. Speedo is definitely low here on 60's, but not a bad idea for us, lol.

235/65/17 to a 255/60/17 is a .51mm over all difference in tire diameter a .69% change in tire size. You're not really going to see any difference in the speedo.