Plenty of decent road bias tyres out there for the XTR (and XTZ) in 90/90x21 and 130/80x17. I have used:

Dunlop Trailmax TR91

Bridgestone Battle Wing

Continental Trail Attack

Of the ones above, personally I rate the Dunlop Trailmax TR91 marginally the best, but all have been pretty good perfromers on tarmac, wet or dry.

There are others too such as Michelin Anakee III and Pirelli Scorpion Trail, but I've not tried them.

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