Browsing through the rather good Peterbilt truck gallery website I have encountered this super shots of their 365 and 367 bonneted rigid models which as Biglorryblog readers can see are perfectly suited for mixer and tipper operations. The small set of wheels tucked up around the back of the mixer barrel normally run on the road when it's loaded. I assume it's something to do with axle loadings although I'm sure my anorak army (US chapter) will let me know if it's for something else!
Click through here for some more bonneted beauties...
Although the standard US tipper, or dump truck as they like to call it, is the bonneted 6x4, they often add-on smaller wheels in-between the steer axle and double-drive bogie in order to help meet local axle loading regs. I'm sure Martin P can expand on their use. Last but not least here's one with a body on it too...
The non-steering wheels in front of the 'bogies' are called "pusher axles" and wheels behind the 'bogies' are called "tag axles". They are single wheels. And they are for wieght regulations.
If there are three drive axles in a row they are called a "tridem" instead of 'bogie'.
A truck with a second steer axle is called a "twin steer".
-John
And the axle shown in the raised position on the mixer is called a "booster" and uses hydraulic suspension for additional capacity when the drum is loaded. Pushers and tags are popular in many States but are seen in considerable numbers in Ohio, the Pacific North West and California.
i have lots of sweet petes on my site!
http://www.roadtransport.com/blogs/big-lorry-blog/2008/02/pimp-my-rideok-pimp-my-truck-biglorryblog-on-some-awesome-asian-waggons.html#more