Buying motorbike tyres.

After almost 9000 kms on tarmac roads the dirt tyres (very knobbly) that came with my bike were well past their best. They were great on the rough stuff - even in sand - but on tarmac roads, apart from being incredibly noisy, they were not that good. The "knobbles" translated a lot of vibration through the handlebars, in the wet the lack of surface contact made riding a bit slippery (not a nice feeling round hairpin bends in the Andes!), and I felt that the top speed, acceleration and fuel economy were also probably adversely affected.

"Oli" the Ronco, showing dirt tyres

I decided to leave buying new ones until my return to Peru in March this year (seemed silly to put new rubber on and then store it for 6 months), and that also gave me plenty of time to research the best options. And this is where I hit a huge snag - Oli has 17 inch wheels front and rear, and I was unable to find any manufacturer (let alone one that had representation in Peru) that made a front 17 inch "mixed" tyre! There are plenty available that are dirt tyres, or road tyres, but not in a dual-purpose format, which is what I felt I needed. I trawled the internet looking for a solution, and joined a couple of forums ("fori"?) asking for advice, and nothing sensible was forthcoming ("You bought a what?"), although one suggestion was that I bought a rear tyre and used it on the front.
Now I feel here I must include some technical stuff about tyres and what they do. The rear tyre comes into it's own during acceleration, putting maximum grip to the road when you open the throttle, and conversely the front tyre does most of it's work during braking, or deceleration, when it need maximum grip and control to stop you. OK, there is a lot more to it that this, but this explains the need for a different tread pattern front and rear. Tyre construction is made up of layers, running in different directions, and the joins being "glued" together depending on the wheel rotation - most tyres have an arrow indication which way it should be mounted. Thus it is potentially possible that a rear rotating tyre could de-laminate if rotating forwards - it is highly unlikely and more probable on high performance, high speed machines, but still not something you would want happening - and most manufacturers stress this on their websites. I did, however, find one or two, who did acknowledge that you could use a rear tyre on the front - "as long as you reversed the rotation", i.e. ignored the "arrow"! Unfortunately neither of these manufacturers made a suitable 17 inch rear tyre (or rather they only did one size, and it is better to have a narrower front tyre).
I have Pirelli MT60 tyres on my Honda 150 in Brazil (17 rear and 19 front), and they are very good on tarmac, and adequate off-road, and Pirelli do different widths in 17 inch tyres.

Pirelli MT 60's on a Honda 150

So I emailed Pirelli, and followed that up with a message on their Facebook page - and 3 months later I am still awaiting their response! As I know from my Honda that the front and rear tyres have identical tread patterns - other than they face in opposite directions - I decided to see if I could get a set upon my return to Peru. I started in the Ronco dealership, and the motorbike salesman there gave me all sorts of advice (they didn't stock MT60, but could order them - delivery schedule unknown!) - including mixing tyres from different manufacturers (a big no-no!) and massively different tread patterns (a bigger no-no!) - I think he was just trying to sell me a pair of tyres he actually had in stock! 
I left him still trying different combinations and walked a few yards down the road to a motorcycle spares shop, who had MT60's in stock - and different sizes - and asked for a pair. The salesman even explained that they were both "rear" tyres, which impressed me - the first time I had come across someone who seemed to know about products he was selling! But I took them anyway, and then had a long argument with my mechanic about mounting the front tyre with the arrow reversed! He finally agreed and I after 300 kms I am extremely pleased with the result. The road noise has vanished and so has the vibration, though I will need to run the bike for a few more miles to tell if fuel economy, top speed and acceleration are improved. 
Is it safe? I honestly don't know - I do know that the tread patterns are mounted correctly (even with a direction arrow pointing the wrong way!), and most of my riding will be done at gentler speeds (it is after all a dirt bike I am using as a tourer!) and on halfway decent roads, so only time will tell!