we have mid roofs short nose short bunk real compact truck the cascadia that i have weigh about 3500 more than the prostar
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Pulling a 53' dry box, you can get away with not knowing much...that doesn't mean there isn't more to know, though.
Judging by that picture, I would guess the axle spread on that tractor is closer to 235"....give or take. Remember, you are measuring from the center of the 1st axle to the center of the 3rd....then consult the bridge weight formula table for the measurement you got for those 3 axles. That lets you know what you can put on your tractor, up to 54,000 because the tandems are limited to 34,000 and a single axle (i.e. steer) is limited to 20,000 or the axle rating or the tire rating...whichever is lowest. If you have a 12K axle, then 12K is your limit. If you have a heavier rated axle, but run tires that the pair are rated 12,380, then that is your limit.
The measurement from the center of the front drive tire to the center of the rear trailer tire lets you know in the 4-axle column how much you can carry on the drives + trailer, up to 68,000 because each tandem is limited to 34,000. Pulling 48-53' trailers, you'll be long enough to run 68K on those 4 axles....if you start pulling shorter trailers (39' trailers have me in the "exemption" that allows 68K despite being too short under the bridge law formula), you may need to run heavier steer axle weights or add extra axles in order to gross 80K...otherwise, you can't even gross 80K without being overweight!
The measurement from the center of the steer tire to the center of the rear trailer tire lets you know what you can gross when you look in the proper column. If you've got 5 axles, look in the 5-axle column. If you go to work somewhere else and start driving a truck that has more or less axles, look in the appropriate column.
That is nothing more than a recommendation from the manufacturer...in actuality it is a gimmick to get the buyer to pay extra for a "heavier rated" (recommended) axle. Also going over the rating by up to 500 lbs (12,500) will not effect warranty or make the vehicle illegal in any respect.
That's usually the best way to know. I guarantee it'll be more than 10-12' though.
Look at most any flatbed with spread axles....they need to be at least 10' apart in order to have 40K on the trailer axles. A 9' spread would only allow 39K, and an 8' spread would only allow for 38K. Anything less than 8' between a pair of axles and the limit is 34K, so there really isn't anything gained by spreading them anything less than 8'.
Not only that, but if there was only 10-12 feet between your front steer axle and your rear drive axle, you MIGHT have 2' of available frame rail space for the fuel tanks between the drives & steer....if you were lucky....but it would probably be less.
Now if you are talking that there is 10-12 feet between the rear of the steer tire and the front of the front drive tire, that's a different story. The tires are probably low profile 22.5's in which case they are roughly 40" tall. Most of the time, the drives will likely have a 52" (plus or minus a few inches) axle spacing between them...
20" (center of the steer tire to the rear outer edge of the steer tire)
+ 20" (center of the forward edge of the front drive tire to the center of the front drive axle)
+ 52" (typical axle spacing)
92"...or a little better than 7'
Add your 10-12' guestimate, and we're now at 17-19' spread on those 3 axles.
17' = 48,500# on 3 axles
19' = 50,000# on 3 axles
Now, 34,000# can be carried on your drives, which leaves 14,500-16,000# that can be legally carried by the steer axle under the bridge formula.
Next, look at the sidewalls of your tires. If they are low profile 22.5's with a load range G, they will likely be around 6150 max load each...or 12,300 for the axle. If that's the case, then 12,300 is all you can legally move onto the steers.
Now look at the axle rating on the door tag. If it says more than the 12,300 that is allowed by the tires, you are good. If it is only a 12,000 pound axle, though, then that's what you are limited to.
You cannot exceed the lowest weight rating for the road or your equipment...otherwise, you are overweight.ew2108 Thanks this.
Interesting in over 15 years of running....I have never been checked for steer axle over 12k....maybe whoever got the "overweight steer" axle took an attitude with the scale house "copper" and brought the situation down to...."I'm gonna find something, anything, to write you a ticket!".....and dumb arse driver wasn't smart enough to go to court and challenge the ticket after the fact.
The axle rating on the door sticker is a RECOMMENDED WEIGHT...check it with any scale coop.....I already have.....but you can read into any rule or reg and find someone who has a different interpretation of what the law reads and what is intended....just how old is the regulation in this issue anyway....some things change over time and aren't updated in the regs.
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