So I'm wanting to upgrade my tires and I'm wanting some dual sport tires. I'm not sure how to match them exactly to the correct size knowing the back rim is a 16 and the front is a 18. Where can I find the right size tubes after buying the right tires? I'm wanting the tires to look exactly like the bike attached: http://bikebrewers.com/wp-content/uploads/2016/01/Suzuki-GN-125-Street-Tracker-18-1024x683.jpg Thanks for everyones help 
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