Originally Posted by bxr140
Yeah, that's a really good point that I never considered. It's significantly easier to swap a front tube on the trail for a big ADV bike, and it takes significantly less space to carry the spare...
I'd like to point out how stupid I think the 17/21 combo is. Early on I convinced myself that it was a good compromise, but in reality, it's the mullet of wheel sizes. (Technically a reverse mullet I suppose, but I digress). With the meaty 17 out back, it really should have a 19" front. Few, if any people would really notice the ~3/4" smaller radius front tire off road (especially with proper suspension), and the bike would be SOOO much better on the tarmac. Or, with the skinny 21" up front, a narrow 18" in the upskirt would bring much more balance to the force on both surfaces, while really only significantly impacting the on road performance for a couple percentile of riders.
Well, it depends on the view point. The big adventure bikes, cannot put their power down with anything less than 3.5 rear. For me, 17 or 18 is only a matter of tyre choice. If you are happy with with what you can find for your intended use in 18, then there is no reason to change. Otherwise the handling characteristics are not night and day. The front is a different story.