If you're looking for a long life knobbly try a Michelin Desert. I've been getting about twice the mileage from them compared to MT21's on my XR600 and now a CCM600.
They do cost twice as much as the MT21's so the cost per mile is about the same and all you're saving is the extra tyre change but on a long trip that matters.
The down side is they whine much louder than the MT's and don't have the MT's wet grip but much tougher construction means less likelyhood of damage when running low pressures

i tried a set of tkc's on the AT during my trip recently and only got about 3000 miles out of my rear! front is still great!do they come in different compound's? maybe i had a soft compound? i was fully luggaged and 2'd up with some off roading involved but was really dissapointed in the mileage! maybe try something else next time.

I'm with Matt and JMo. The Pirelli RallyCross is great in the soft stuff and smooth (and long-lasting) on the pavement. Went over 10,000 km http://www.freewebs,com/shanperu/ on them, much on pavement and the rear was only 1/2 used at the end of the trip.

Toby

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http://www.aroundtheblockmotoadventures.com/
'We build the bike (in Peru) for your Epic Ride of South America.'

Well, I bought that XR650R, and did 6500 miles in the USA, pretty much equally spread on TKC80's initally, then Pirelli MT21's (both 140 rears)...

The TKC's were great in the dry dusty dirt road conditions of Nevada and California, and up into Oregon -plenty of highish speed (60-75mph) highway use too. The rear was totally bald by 3200 miles however, although that was after plenty of off-tarmac/gravel road use, followed by a blast down highway 101.

I swapped them for a pair of MT21's and ended up with much the same wear (I guess rough roads are always going to shred tyres, and especially on a big single with no cush drive), and in dry conditions no discernable difference in grip, although I actually preferred the front TKC in loose gravel on top of a hardpack surface, the MT21 would occassional feel as if it was about to let go, athough it never did.

However, the TKC's (front particularly) did start to vibrate as they wore down which was irritating at highway speeds. Typically every other knobble on the front of both tyres wore unevenly, although the front MT21 didn't vibrate so much despite looking like a cog after 3000 miles.

In summary, for a big(ger) bike in primarily dry dual-sport conditions, I'd happily recommmend both and buy them again, athough don't expect either to last much more than 3000 miles of combined on and off-road riding.

Hope that helps...

JennyMo xxx

trying out a set of karoo's at the moment but i've done only 1300 miles and it aint looking good! this is on my own without luggage! about half left/gone already and they're very noisy. good handling in the dry i find but like the others dodgy in the wet. what to try next:confused1: