I think they're all too skinny. But that's just my personal opinion. Unfortunately the 705's do not come in a proper size for our bike. You can get a 130 and 140 in 17 but they don't offer one in 18 so we're out of luck. The MT90's is a good recommendation, that's the tire that comes on the 990. I don't think they're cheap but they're a good tire. A variety of rear sizes will fit, some are just more appropriate that others, and yes, the tread width and height varies by manufacturer for a given size. I ran out 3 of the Michelin T63 rears in 130 and finally got tired of them being just too skinny. Handling and traction was good however, not very long lived (under 2K miles). They were cheap and that was good. LOL. If I was going more road focussed I would look close at the 705 front and a 244 rear, even better get the Kenda or IRC version of the 244 (K270, GP1) The kenda K270 in 5.10 is a decent looking tire, good performance on and off. You could even run the matching front but the 705 is a better road tire. Another excellent combo but little more money would be the Heideneu K60, 140 rear and 90/90 front. Great mild dualsport pattern. Extremely popular with the bigger ADV bikes. Keep in mind any of these front tires will wash out on dirt, so if you still plan for anything more than smooth dirt roads I would stick with a good road knobby like the t63, Karoo II, or even TKC. For full on road I wouldn't know what to suggest without going on a search. The problem here is finding a matching set with the 21 front and 18 rear. There are tires for both but not always in appropriate sizes. Like the Conti Trail Attack - great tire, there's a 21 but no 18. Same for Anakee, Tourance, any number I can think of. The new Anakee 3's would be worth a shot, but similar tread spacing of a K60.
