Test Drive: Air-Ride Axle on the Road in a T660

In line with an emerging trend to migrate air suspensions up to the front of the truck, Kenworth has introduced the AG130 for T660, T800 and T2000.

The four-bag air ride is intended - at least initially - for over-the-road trucks and tractors, to offer an even better front end ride along with some marginal weight savings. It is also compatible with disc brakes, responding to another likely trend.

I had the opportunity to take out for a few miles a T660 with the AG130 optional front suspension. It was a fun ride.

The AG130 is a smooth-riding alternative to the standard leaf spring suspension, mounting up to the same spring hangers. It could be retrofit to existing Kenworth models if an owner decides the upgrade is worthwhile.

The suspension has a few benefits apart from the usual ride attributes of an air suspension. It has a constant ride height by virtue of the height/load-sensing valve, it saves around 20 pounds over a 12,000-pound steel spring suspension, and it features what Kenworth says are low-maintenance bushings. The design includes easy access through an air spring retention clip for quick air bag replacement.

The axle is rated 12,000 and 13,200 pounds. The T660 here featured the lighter of the two and the truck was loaded to around 65,000 pounds for the drive. That may have been a mistake for offering real impressions of the difference in ride, because the T660 has a nice-riding, stable-steering front end anyway, especially under load. The air ride sacrifices none of this, and in back-to-back testing would likely demonstrate its better ride.

According to Kenworth Chief Engineer Mike Dozier, the slightly higher roll stiffness of the air ride also contributes to additional road feel and handling precision. In the few miles I covered, I noticed the truck steered well, with zero kickback through the wheel and no tramlining on road irregularities and seams. But the T660 is very good in this respect on its standard suspension, too.

The air bags carry around 75 percent of the load on the suspension, with the axle-locating light leaf carrying the balance. Shock absorbers are included. Dozier says the use of four air bags instead of two as found on other air ride front ends reduces vibration transmitted. He says it's the best-riding front suspension the company has ever offered. With two air bags per side, there is an amount of torque resistance built in, which should prove a major benefit with the adoption of high-torque drum or disc brakes that will become mandatory when the new braking regulations are finalized.

Kenworth customers may not feel the driver benefits worth the upcharge, mainly because the standard Kenworth ride is so good. But the low-maintenance design, lower weight and almost certainly higher retained value if sold to an owner-operator could make the investment worthwhile. If nothing else, it gives a trucking company bragging rights in driver recruiting, an issue that for the moment has gone away, but likely will return before it's time to trade in the new trucks bought over the next year.

From the August 2009 issue of Heavy Duty Trucking magazine.