Sliding spread axles?

why is having them both slide dumb? danger? redundancy?

 

2 words

Bridge Law

 

As others mentioned closing the axles is important for running loads into Canada. You can load 17000 k (approximately 37450 lbs) on tandem axles but only around 20000 lbs on spread axles.

Another reason that nobody has mentioned is that closing the axles redistributes the weight of the load. If you're loaded heavy on either end of the trailer, you can sometimes correct it by opening or closing the axles.

On the new Western trailers the front axle slides and the rear axle is fixed. Not sure why anybody thought that was a good idea.

 

I have a friend with a 45' Wilson flat. The front axle slides so that it can be used as a spread or a closed tandem. I believe Jessup Trucking out of Gilroy has 53' reefers that have both axles slide. They can run as spreads, closed tandems and adjust for bridge laws.