Rubber!

I'm an enthusiastic but wildly incompetent mountain biker. I cycle locally across Forestry Commission land, which is the site of a wind farm. My normal route is a 30 mile loop, and is not technically demanding. Nevertheless, I fall off regularly. On one occasion, I simply fell over when the cumulative rattle of cycling over frozen tyre tread indentations left there by the local farmer's tractor gradually and gently robbed me of control. Still clipped in, and holding the handlebars with a rigor mortis grip, I lay tipped onto my side. More spectacularly, I frequently get launched head first over the handlebars on steep descents. This incompetence has led to an immoderate fascination with off road tyres. They are the point of contact between me on the bike, and the ground. Their choice has a bearing on how successfully I maintain that contact. I generally cycle singlespeed. I enjoy the simplicity of it, having, so to speak, only two gears: sitting down, and standing up. When I come to a steep hill, I stand up. When on the flat, or descending a not-too-bumpy hill, I sit down. Foolproof. Gears, 21 of them on my 'geared' mountain bike, can be confusing and distracting. So long as the terrain is not to hilly, or the route too long, I default to my On-One Inbred. This bike is also fully rigid: it has no suspension at all. This is also a preference, as a rigid fork steers and tracks more accurately. A suspension fork has lateral 'flutter'. It also has the unnerving habit of altering the bike's geometry as it compresses or rebounds through it's travel, and shifts your body weight forward and back over the bike. I find a bike without suspension more predictable, and as I am not a freerider or downhiller, my riding rarely exceeds the capabilities of such a simple bike.

On my singlespeed I use a WTB Weirwolf 2.1 up front, and a 1.9 Nano Raptor on the rear. This size of Nano Raptor is no longer available, I bought 10 of them as new old stock. They are very light, 380g on my scales, and have a low rolling resistance due to the raised centre line. Their lightness is ideal for singlespeeding because it reduces the rotating mass of the wheel. The difference tyre weight makes to the effort it requires to pedal is masked on a geared bike, on a singlespeed it is readily felt. Hills I can climb on this bike with these tyres are insurmountable if I swap to heavier tyres.

What I also like about these tyres is the flexibility of the carcass. I run them at 30psi, and this allows them to conform to the terrain. Their low profile tread has many working edges, and these provide a surprising amount of grip as the tyre moulds to the ground

Up front, I use the 2.1 WeirWolf because of it's aggressive array of teeth along the shoulder of the tyre. If your rear wheel slips, it generally isn't disastrous: you can catch the slide, or, at worst, you find yourself having to put a foot down or crashing onto your bum. If your front wheel slides from under you, the resultant crash tends to be much heavier and head forward. The Nano Raptor wouldn't work up front because it's shoulder tread is puny. The WeirWolf is designed to rail into corners and actually increases grip when tilted.

I have these in a massive 2.5 downhill version, and out of interest fitted them to my singlespeed to see what difference they would make to the effort needed to get up my local hills. I washed out on most of them.

I generally prefer tyres with low profile tread, and run them at low pressure, 30psi rear, 25psi on the front, thinking that the amount of deformation a tyre undergoes as it moulds itself to the contours of the ground is the best source of grip. [Unless, of course, you are dealing with mud.] Tread patterns that consist of knobs can sometimes feel fidgety over loose terrain, especially if the lugs are weak. They tend to rebound and deflect off stones and other loose rubbish, making handling unpredictable. There is also the issue of lugs folding suddenly if you lean into a corner, which is more likely to happen if you run tyres at low pressure as I do. My two favourite tyres with knobs are the WTB Stout, which avoids some of the above criticisms by having it's lugs squat and well spaced out, and Panaracer's Cinder, which has a stepped lug pattern and an especially grippy compound. The side knobs on both tyres are well supported at their base and unlikely to fold.