Lift Axle weights - single axle with drop axle bridge law

Discussion in 'Trucking Industry Regulations' started by Mach, Aug 25, 2020.

  1. Mach

    Mach Light Load Member

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    So long story short, I have a truck thats being built as a single axle but with 2 10K drop axles on a 40' straight truck. The first drop will be a pusher spaced at 96" ahead of the drive axle. Bridge law states that a single axle is good for 20K lbs. Thats not a problem since that axle will carry at most 9K lbs. The second drop axle will be right behind the drive axle in a tag configuration. it will be as close as it can to that drive axle which is about 56" from hub to hub. Now The single drive axle has a 23K lb capacity and the tag axle at 10K capacity. With the axle up, I will only be legal for 20K on that drive axle. But with the tag axle down, will that axle group technically be considered a tandem group at 34K permissible? I ask this because if the truck is weighted down to max capacity on the rear, the drive axle may be 21 or 22K while the tag axle sits close to its max capacity (estimated 8 - 9K). So would this be legal since it is technically under 34K lbs for tandem bridge law? Or will DOT still see that drive axle as a single axle and can not weigh more than 20K even though it is rated to 23K.

    It would be rare that the truck sees a max weight like this but should I come across it, I obviously want to know my limits.
     
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  3. Roberts450

    Roberts450 Road Train Member

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    It should be looked at as a tandem rated for 34k.
     
  4. Mach

    Mach Light Load Member

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    Thats what im thinking but i just wonder if Im going to get that one picky dot officer one day that decides to measure the individual axles in the group and say that im over weight lol
     
  5. magoo68

    magoo68 Road Train Member

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    Hopefully you don’t see snow often . That combo would spin everywhere .
     
  6. Roberts450

    Roberts450 Road Train Member

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    Is the axle actually rated at 10k or is it a 13.2k axle? What size tire will it be running and is it a steerable one?
     
  7. Hammer166

    Hammer166 Crusty Information Officer

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    Anything 8 feet and under is defined by the Bridge Formula as a tandem.

    So in your case, both the drive and pusher as well as the drive and tag combos would be considered tandems when calculating bridge weights. And the 3 together would need to be under 45,000 pounds.
     
  8. Mach

    Mach Light Load Member

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    It would be rare. The idea of this set up is to be lightweight and fuel efficient. And at the weight I'll be running at most of the time, even a 6x4 will be a nightmare in snow.

    It's a 10k lb steerable drop. Will run a 235/65/19.5 tire. I think that's what it will be

    Cool. Sounds like I'll be alright then.
     
    Last edited: Aug 26, 2020
    magoo68 Thanks this.
  9. roshea

    roshea Road Train Member

    In most states that drive axle would be limited to 20K regardless if considered a single axle or part of a tandem. This is info for Tennessee which specifically mentions no axle in a tandem group can exceed 20K

    Tennessee Axle Weight Limits
    Maximum Legal Weight Allowed
    Axle Group

    Maximum

    Single 20,000 pounds

    Tandem 34,000 pounds

    Gross Vehicle Weight

    80,000 pounds (except that freight motor vehicles operating on interstate highway system shall not exceed the lesser of 80,000 pounds or the weight produced by application of the formula set in T.C.A.)

    Maximum Permit Weight Allowed
    Conditions for Permitting Overweight Movements
    In general, the maximum allowable axle weights by special permit are as follows:

    • Single Axle: 20,000 pounds;
    • Tandem Axle: 40,000 pounds; and
    • In no case shall a single axle in a tandem group exceed 20,000 pounds.
     
    Mach Thanks this.
  10. Mach

    Mach Light Load Member

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    Ah I was afraid of that. And then I'd also imaging thAt pretty much all other states will likely follow that same principal. Oh well it still works. Thanks man!
     
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