I was wondering if anyone has ever fitted 320mm disk to XT660R?
I would just need front break caliper extenders and a 320mm disk from XT660X?
Who makes the caliper extenders or where could I get those?
Look at this picture: http://www.the-larkins.com/Picture%20124.jpg
I would need something like that.

I also wonder about the brake lines, if they would be too tight after this mod?

I understand that the X version is a supermoto and better breaking performance is needed, but why the R version doesn't need better performance? Is there something that speaks against fitting a larger front disk to an enduro bike?

Someone who has access to both bikes (X and R), could confirm that the X front disk matches the R front wheel.

I would think it's just not practical - a bigger disk is going to be in the crap, getting hit by rocks, pabbles, grass, ice, and other stuff, and you really want to keep the disks as dry and clean as you can whilst off road. The more holes in the disk the worse it performs in the mud & wet as you get alot of crap being taken into the caliper, in some case's it improves brake performance by using solid disks.

Also, the grip off road isn't anything like the tarmac, so I couldn't really see the point in more stopping power - you'll just slide along!!

Maybe that's why?

That said, it would look monsterous on a road going R...... .

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Thanks Gas_Up_Lets_Go, a good point there. Bigger disk is more close to the ground. I think i'll try the wavy disk with different brakepads first.

Also, making the front end stiffer (wilbers springs +15w oil) helped a bit already.