Dot wrote:Ok so Russell has one and I know it has something to do with wheels and axles etc but what do they do etc???

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and do not say you pick em)

Well that wrecked a good come back line.
When two axles share a common suspension component it is generally refered to a as boggie axle system, maybe there's only one g in it / Googled it and it's a Bogie axle

In Russell's case the second axle has no drive and is behind the drive axle so it's known as a 'tag' axle, it tags along behind, if the axle was in front of the drive axle it's called a pusher axle, usually seen on a prime mover with a single drive and no room behind for another axle. The second axle is usually to share the weight although sometimes it's to get by the over hang rule on a rigid chassis.
There should be heaps of terminology in that lot to ask a whole heap more questions Dottie
T1 Terry