I'm going to buy new set of excel/talon wheels from OTR. Rear rim is 18x2.50, what meens that I should not go beyond 130. Ideally would be 120/90R18 or 130/90R18. According to this calculator https://www.tacomaworld.com/tirecalc...0r17-130-80r18 120 is 3,3cm more in diameter than stock setup, and 130/90 5,2cm more. Has anyone tried such a combination? If this is to much, than what would be max diameter of the wheel? Thanks for help.

I take it you have changed the OE silencer? 18" wheels regardless of tyre will foul it on 3/4 compression. The actual maximum diameter depends to a degree on what aftermarket exhaust you run. All the single-sided systems will be fine, but be wary that the 'Y' pipe arrangements on some twin system will still get in the way of an 18" wheel.

On a 18 x 2.50 rim, a 120/90 is the default tyre size.

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Thanks Pleiades. I was in touch with Talon, and seems that OTR setup is not an optimal solution for an adventure bike like xt660z. In fact this is LC4 hub (lc4 is 70 kg lighter then xt660z), and as you have said - 120/90R18 is the right size. Eventually I can use 130/80 (130/90 would be better, but most probably there will be problem with swingarm clearance), what limits dual tyries selection to Michellin T63.
The other option I have is to use 17x3,50 on the stock hub. Do you have any exeprience with such a setup? This way or another, I need new rims for next season :-(

I've held back on changing my rear rim because a 2.50 is too narrow for me and 2.75/3.00 are not available from Excel.

A 2.50" rim is ideal though for off road use, but really narrows your choice of dual sport and road tyres.

A 3.50 is going to be too wide. It will physically fit, but anything less than a 150 section tyre is going to leave the rim exposed off road and pull narrow tyres into a flat profile and be very unforgiving in terms of side wall flexibility.

Building off an LC4 hub is definitely the way to go though.

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Well, seems there OTR is back in game...and T63 is not the worst tire for adventure riding ....
Thank you. You have helped me a lot.