When looking to purchase used 20ft tri-axle or 40ft tri-axle chassis there's something you should know - you may get a tandem chassis which has been modified to a tri-axle.
Modifications are done in several ways:
* A 48ft tandem chassis is cut down to 40ft and a 3rd axle is installed
* A 3rd axle is installed to a 40ft tandem chassis
* A 3rd axle is installed to a 20ft tandem chassis
These modified tri-axles may cost less than the originals but their reliability can also be lower. The lighter steel construction of the original two axle chassis may not be suitable for stresses of three axles and hence, lead to premature failures. Keep in mind that you will be hauling overweight containers.
Not to mention that the modified design may not comply with the US bridge formula and weight laws. For example, a modified 20ft tri-axle chassis may not be long enough or the axles not spaced properly on the 40ft modified tri-axle.
Needless to say, make sure you are getting original tri-axle chassis by asking the right questions and/or using an experienced container chassis surveyor.