U.S. sales of medium- and heavy-duty trucks rose modestly in August, ticking up 3.0% on a daily rate basis mainly on the strength of Class 8 demand.

Volume totaled 29,579 units, up from 27,649 year-ago, and pushed to-date 2012 sales to 232,206 vehicles, 22.3% ahead of like-2011’s 189,840.

Heavy-duty demand inched up 5.3% in the month to 16,497, from 15,085 in August 2011. Daimler accounted for most of the Class 8 gain, with deliveries rising 29.3% to 6,220. Its Freightliner brand enjoyed a 26.3% spike, while sales of its Western Star more than doubled.

The only other Class 8 truck maker to post positive results was Volvo Truck, as a 50.8% jump in Mack volume resulted in a 10.7% increase overall. International’s heavy-duty truck sales slipped 14.2%, while PACCAR posted an 8.4% decline.

Through the first eight months, Class 8 sales totaled 132,164, up a healthy 32.1% from like-2011’s 100,038.

Medium-duty deliveries rose fractionally, gaining 0.3% in August to 13,082, compared with 12,564 year-ago. The performance left sales 11.4% ahead of like-2011 through the first eight months, with volume totaling 100,042 units.

August saw only one medium-duty sector gain substantial ground, as Class 5 sales rose 16.7% on a daily rate basis to 4,014. Ford (up 11.4%) and lower-volume Chrysler (19.2%) and International (94.6%) accounted for most of the added units.

Class 7 sales were dead-even with year-ago on a daily basis, though volume of 3,939 was 144 units higher. International’s 24.1% plunge in deliveries took most of the bite out of the segment, which saw gains by most other truck makers.

Class 4 sales fell 15.3% to 846 units. Isuzu was the only Class 4 truck maker to post a gain in August.

Class 6 demand also slumped, albeit by a more modest 8.2% to 4,283 trucks. Ford sales spiked 124.5% to 627 units, but that wasn’t enough to offset steep declines for higher-volume players such as International (29.4%) and Daimler (14.0%).

More than 1,000 units of Class 8 inventory was taken out of the system in August, as unit stocks fell to 41,151, equivalent to a 67-day supply. That’s still well ahead of year-ago’s 29,698-unit, 51-day supply.

Medium-duty truck makers ended August with 42,621 units in inventory, an 88-day supply. That compares with 31,007 and 64 days’ in like-2011.