Currently, i've Schwalbe Dureme in 2" and i think they are good on asphalt road.
<nods> I have found them to be a very good all-'round tire for pavement and use on mixed surfaces.
Where I have found them to be problematic is while riding on the very rough, sharp-edged ballast rock used on logging roads in my area. They are irregular in shape, ungraded, and tend to collapse around the tire. The Dureme's sidewalls are a bit fragile for this sort of thing. Not a real failing given the overall mission of the tires. i like them enormously and have found them to be an ideal compromise. However, I do make sure I ride with care on that particular surface. "Regular" gravel and bad roads have not been a problem for me.
I had really good luck with the 2.0 Marathon deluxe tires fitted to the Raven Tour kindly loaned me by Forum member AndyBG for my 2014 tour. Their sidewalls seemed a bit more robust than the Duremes', but they rolled well under load. I only had one flat in ~9,000km; it was caused by a long roofing stable I picked up outside Giurgiu, Romania. Not a bad thing, it caused a chance meeting with the homeowner whose lawn-edge I was using to make repairs. We became friends immediately and I have stayed in online contact with his lovely daughter.
If i'm planning to go in Africa on dirt roads for example, "Marathon Mondial" tires will be a good choice i think but..
Should i stay in 2" or 2.15 ? or more wide ? ( i didn"t find a biggest size than 2.15 for the Marathon Mondial tires)
The Marathon Mondial is sort of the definitive expedition tire, and for good reason. It is very durable, but it is also heavy and this can be noticeable when riding unladen...not so much when loaded to the gunwales.
If you go too wide on your tires, you may have problems with mudguard/fender clearance when traversing actual mud -- it can cake onto the tires and cause rubbing that will slow or stop your progress, as it did me in Romania and again in rural Belgium and Germany. It was not so fun getting off the bike and into mud well over my shoe-tops to remove enough mud for the wheels to turn...only to repeat the operation 100m later. Pushing the bike doesn't really help that much. My hat is off to Shimano for making pedals and cleats that reliably dis/engage in such conditions. If you find yourself in such conditions, use a stick instead of fingers to clear the mess, 'cos the edge of the mudguards is sharp against wet fingers.
Remember also, tire profiles are roughly 1:1, so a wider tire is also a taller tire. If you fit fatter tires, you will likely need to raise your mudguards by removing some spacers. The tightest point for mud clearance will generally be under the mounting bolt heads, inside the mudguards.
So, the takeaway here is if you fit larger tires, make sure you have adequate mudguard clearance for use in really poor conditions.
A general caution: Though the Nomad is capable of carrying enormous loads reliably and well, cycling is always more pleasurable with "less". I speak as someone who introduced a visiting Dutch friend to cycle-camping. He had not really camped and wanted to carry all the amenities with him (we had a folding kitchen sink, so yes we took that as well...and his Dutch Army tank driver's boots for hiking, and...). Well, why not? The fully provisioned bike with us aboard and the trailer in tow weighed in at 272kg/600lb. My homemade trailer weighed 57kg/125lb alone. We did fine riding even on steep grades on gravel Forest Service roads using 26x1.5in road slicks. It would have been more pleasurable grinding uphill if we had also fitted a winch...or carried less.
I rarely load my Nomad with cargo weighing above 25kg for "normal" tours, but when desert touring for extended periods, then I add the 26.5kg of water and extra food, because there is little fresh water available and no stores for resupply. It is not practical to pre-cache supplies thanks to the heat and animal predation. For the occasions when I have taken a full load, the Duremes proved both wide enough and strong enough for my needs.
Even so, the desert heat demands I carry more stuff...a folding, vented Korean fisherman's hat for shade when stopped, and a folding chair to get me off the scalding hot pavement at lunch breaks. Pulling off hot tar that has solidified on the skin is no fun...the skin comes off with it. Lycra shorts melt, too. You have to carry what you need for the demands of a given tour.
Of course, terrain, riding style, user preference, and a hundred other variables come into play, but the general maxim still holds -- carry less to enjoy more.
I remember riding on my last long tour and realizing that at any given moment, I was *not* using ~95% of my carried items. The trouble is, the ~5% I did use varied, sometimes within the hour as weather changed.
All the best,
Dan.
