IFS, Yes More Letters for the Alphabet Chassis Soup

I was doing a seminar the other night and we kind of got into it about the advantages or disadvantages of IFS, your know independent front suspension. Now these guys were all professional technicians who had been working on heavy rigs most of their lives. We were just bringing them up to speed on the alignment procedures of the Freightliner chassis that features IFS. To be honest it was like smashing rocks with a watchmakers hammer to get through the mentality of “solid axles is for big trucks and independent front suspension for small cars.”But in the trades we saw the same mental block with the advent of alternators, electronic ignition in gas engines, and computerization. However time and technology march on.

Back when the wheel was invented it would appear that the next `invention was the axle. As long as Gronk was satisfied with a two wheel cart steering was not a problem. But when the four wheel cart appeared in the cart dealers showrooms then steering became an issue. A pin through the cart somewhere near the center of the front and extending loosely through the axle allowed the axle to pivot and the cart to negotiate corners. By the way that is also the principle of the 5^th wheel concept.

Around 1870 a Munich carriage maker named George Lankensperger invented an axle that would allow the front wheels to pivot at the outer ends of the axle and be connected together with tie rod linkage. Just like today when agents get in the mix the device was granted an English patent by Ackerman the agent and became knows as the Ackerman Steering system.

The Ackerman steering with the solid beam front axle sitting on leaf springs became the norm for the early auto and truck design. As the cars got more powerful using long straight eight engines mounted in the front of the machine a problem surfaced. The problem was that to make the car lower and appealing to the eye as well as a lower center of gravity for safety, the front axle had to be moved forward, in front of the engine , to allow for up and down motion when going over bumps. As such the long front hood of the Deusengergs, Packards, and other big cars graced the highways. In the early thirties the independent front suspension was developed to get the cars lower and a bit shorter. Trucks and Henry Ford clung to the solid axles for several more decades.

Today all light trucks, up to one ton, sold in the USA have IFS as well as all cars. Vans, when first introduced in the early 1960’s, had straight axles and slowly converted to IFS through the next decade as the engineers looked to move the engines forward out of the passenger/load compartment. GM took the IFS into the P-30 chassis which became a popular motor home chassis. IFS has been pretty much standard on class C and class B rigs. While the solid axle has been the norm on the DP and super C machines. But that is changing as Spartan and Freightliner are offering IFS on the big chassis. Next week we will check out the big WHY as certainly lowing the rig appears not to be the reason. See you next week.

Brad Sears