But the main thing this helps determine is what the viscosity is <i>at the bearings</i>. A higher HTHS will always give you better wear protection but at a higher viscosity price, which as well all know, is not smiled upon by the CAFE crowd. I think the bear minimum for HTHS is something like 2.5 or 2.3. As mentioned above, the HTHS will decrease as the oil shears down. So you have to keep in mind the VI numbers as the HTHS will decrease as the oil shears which is in a relationship with viscosity. Look at the 0W40, high VI, but pretty good HTHS. Do you think that HTHS will be the same after 4K miles? For something more shear stabile, look at the differences among the X-30 weights. 5W30 has a lower HTHS, but a VI of 167 versus the 10W30 higher HTHS but lower VI at 147. Seems the 10W30 would be more shear/HTHS stabile. But look at the 15W50, really high HTHS and relatively modest VI. Pretty nice, but look at the viscosities at different temperatures. At 40C, it's still pretty thick, even though it shows a pour point of -45. I sure wouldn't want this in my engine up in Canada during the winter without an engine heater.