Advantages of third axle placement

3 singles vs a Tri.

 

Don't quote me but I believe in Michigan the 3 singles (Over 9' ) is good for 18,000/axle.
Anything under a 9' spacing is only 13,000/axle.
On the Michigan specials anyway.

 

It's all about bridge weight,spreading the weight evenly across the axles so as not to damage the road surface and bridge floors. Keeps the DOT off your 6.

 

The first picture you posted of the tridem are 60" Canadian spreads. In Canada they can gross more on that 60" than a 40". I think it goes up to around 16,000 per axle on a 60". Here anything under 9' is 13,000.

 

Canadian Legal tri-axle weights:
9' front to rear (4'6" ea) is 23,000kgs/50,700lbs
10' front to rear (60" ea) is 24,000kgs/52,900lbs
12' front to rear (72" ea) is 25,000kgs/55,100lbs

Canadian Permitted tri-axle weights:
9' f to r is 25,000kgs/55,100lbs(some exceptions)
10' f to r is 27,000kgs/59,500lbs
10' f to r in BC is 29,000kgs/63,900lbs
12' f to r, I dunno. Don't know anyone who runs this spread anymore

 

I remember IL wouldn't permit me as a 3 10. They wanted the axles closer together.