Do you agree with me that hard compound tires are for soft terrain. And soft compund tires are for hard terrain.
?

Yes, that is typically true. There is also a difference in how the casing of the tire is constructed as well.

Brouder539, on 18 July 2012 - 06:16 AM, said:

No

Not always.  The terrain rating of knobbies refers to the soil type.  A "soft" tire like the MX31 is for soft terrain, and a "hard" tire like the MX71 is for hard pack.  Very generally, the hard surface tire would have a softer rubber compound in the tread than the soft surface tire, but in reality, it isn't that simple.  Most good modern tires will have from 3 to as many as 6 different rubber compounds mixed in at various layers, and while the outermost rubber in contact with the ground may well be softer on a hard surface tire to promote better adhesion, the core of each knob will be harder to resist squirming and rolling over under a load.  Soft surface tires can and do take several different approaches to the compound used, and most of what differentiates them as a class is usually a matter of tread design, having taller, but narrower knobs spaced farther apart to penetrate deeper into looser soils.  The tire body itself will be yet another compound to address the design parameters needed. Cheaper tires are usually simpler in this way.

Some "soft" tires round off the knobs very quickly, and some others don't.  And some will tear knobs off in a string if they so much as see a rock on the edge of the trail, while others can dig rocks all day without damage.

Brouder539, on 18 July 2012 - 06:16 AM, said:

As grayracer said, its usually harder compounds for harder tracks and soft compounds for softer tracks.

Soft/Inters work in more conditions then hardpack tires, which kinda suck in the mud/sand and are only partly good in loam.

There is a lot more going on with the different tires then what meets the eye. Hard pack tires have more, shorter knobs with less profile on the sides of the tires, to help keep the rider from leaning the bike over too much and tearing the knobs off. The carcass on hard pack tires is really the key, its more rigid and designed to absorb the impact differently then a softer tire. The softer tires have less but taller knobs. They have more profile (more knobs on the sides) and have a softer carcass with softer knobs then a hard pack tire. However, they're not really that soft, its just because the carcass is softer, they flex more. That added flex leads to damage if used on hard pack tracks. You'll get tearing and such if your not careful with a real soft tire.

Bridgestone 200 series tires are a great soft/intermediate tire.
Pirelli MX32's are a great soft/intermediate tire.
Dunlop MX51 rear and MX31 front for soft and MX71 front for hard, are a great intermediate tire.

I have yet to try the new Michelins...

Edited by tye1138, 18 July 2012 - 08:26 AM.

tye1138, on 18 July 2012 - 08:21 AM, said:

This typically is not true. Most hard terrain tires use softer compound knobs to help with traction, while most soft terrain tires use taller narrower knobs made of a harder rubber compound to dig into the soft soil deeper. This is why if you run a tire designed for mud and sand on blue groove clay you will often rip the knobs off because the tall knobs will want to roll and the hard rubber compound will tend to tear rather than flex.

Hard terrain tires tend to have wider, shorter knobs to maximize contact surface area and to minimize knob rolling. They also use a softer rubber compound in the knob to stick to the hard surface better since the knobs won't dig into a hard surface very far. Trials tires and dual sport tires use even softer knobs since these are designed to run on rocks and pavement, the hardest surfaces you could encounter.

tye1138, on 18 July 2012 - 08:21 AM, said:

That is not what I said.   Read beyond the first sentence.