Building a Scania V8 R500 - Part 1. Chassis

I`m building a Scania R500 - from a 1:24 scale kit produced by ITALERI.

I`ll be discussing aspects of truck construction as I go along, hopefully highlighting some basic truck technology.  It`s easy to think that modern vehicles bear no resemblance to those of the past, but that`s not true.  Suspension and steering; engine, transmission and final drive; and tyres are all there to maximise the laws of physics, and have retained the same configeration since diesel replaced steam.  Cost and natural performance limits have meant that the chassis abandoned long ago in car design is still used in truck manufacture.   Yes, your truck is computer controlled and a modern marvel;  but so is the modern cruise liner - which is still a Titanic underneath.   

Building a Scania  R500    Part 1. Chassis



Channel `C`  section chassis offers good resistance to bending stresses.  All chassis are subject to bending and twisting as  load and road inputs produce opposing and irregular stresses.  Section depth resists bending and flanges counter bending and torque.  The top of the rail will be under compression, the bottom under tension.  The horizontal centre is neutral.  When holes are drilled or cut into a chassis rail (sometimes to lighten the structure), the centre line is the best location due to this minimal stress.   





Ladder rail chassis construction has been around since the year dot - if it works, why change it?  Simplicity, ease of manufacture and, therefore, cost make it the most efficient platform for truck bodies. (The components in this chassis will appear across the Scania LGV range of vehicles.)  For non-independent suspension systems, the twisting that will inevitably occur in the chassis is not too critical and can be catered for by the dynamics engineer




Components are either riveted or bolted to the chassis.  Welding forms a solid piece and causes stress in the join as the chassis twists and bends.  Used as a stress barrier,  riveted and bolted joins allow for movement.  All chassis flex - even though not necessarily visible to the naked eye. A few years ago, I saw a Scania beaver tail, six-wheeler plant rigid that had been converted from a tractor unit.  The chassis had been lengthened with the support of strengthening flitch plates but every annual test necessitated the replacement of some of its body fixing bolts.  The chassis was twisting enough to sheer them.  The vehicle had been re-plated correctly and always passed its test.   

 

Chassis widens at the front, where the engine is positioned.  A narrow chassis at the rear, aligned with the 5th wheel mounting,  fully supports the 5th wheel load (at least 20% of the trailer`s weight).  As the trailer rolls when cornering, a torque is applied to the tractor`s chassis.  This torque is resisted in part by the greater force moment capability of the spread chassis at the front - being wider, the front of the chassis provides greater stability. 

Next - Part 2.  Suspension (drive axle)