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  1. #1
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    Default Info needed on Single versus Tandem axle aerial device

    I am doing some research in to the various aspects of a single axle ladder versus a tandem axle. I have searched all of the internet and all of the publications and have the pros and cons for both. I am looking for some more information relating to these two subjects, especially comparing wheel bases and maneuverability. I would also like to know some history on what apparatus out there on single axle chassis relating to maintenance and reliability over the long haul. I have contacted the City of St Louis to find out about the reliability and out of service time for their quints they run with the TQC concept, but have not had any response. Any articles or information you can get me about this subject would be fantastic and I would really appreciate it. I have not had a lot of luck and am really trying to compile somoe good information and need everyone's help. Thanks.


  2. #2
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    Your question depends on how you plan to run the apparatus. As a quint to replace a traditional pumper, I would stay with a single rear axle for 2 reasons: Lower operational cost and increased maneuverability.

    If the apparatus is to run it as a truck company, then I'd lengthen the aerial ladder and go with a tandem rear axle.

    The last thing I want to do is incite a quint debate here, but I have seen more than one department start out designing a single rear axle quint. By the time they lengthen the ladder, add more compartment space and equipment, what started out as quint to replace a pumper has morphed into an aerial apparatus.

    C6

  3. #3
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    What size and type of aerial are we talking about? Your response will dictate my response.

  4. #4
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    I agree with command.

    If you are going to run it like an engine company that happens to have a ladder on the top then single axle.

    If you are going to run it as a dedicated truck company then make it more capable and go double axle.

    You mentioned St. Louis and the TQC. I live about 30 mins from St. Louis and two independent sources (one STL firefighter and one apparatus sales person covering STL) have said that they will be moving away from the TQC. I imagine it is because of the cost of replacing so many ladders. As far as I have been told they will still have one quint and one ladder or tower per battalion with a total of six battalions, save the airport.

    I have the engineering drawing of their current 75ft. quint. Its very small, 195" wheelbase if I remember.

    There are so many options when it comes to an elevated device you can get a 50ft. snozzle or a 114ft. bronto skylift. All depends on what your needs are.

  5. #5
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    Default tandem versus single

    The truck will run as our first out EMS response vehicle and the busies truck in the city. It will be used as an all purpose vehicle, and they are looking at a 75' stick. It will serve all purposes. My concern is the maintenance of a single axle stick, being overloaded the first day out the door or at least almost overloaded, less compartment space, better ride with the tandem, better braking, etc. I am pushing for a tandem due to the weight issues and lack of compartment space with a single axle. I have read a lot of bad about the single axle not holding up over the life of the vehicle, and realize the cost of tire scrub and tire replacement with a short wheelbase tandem. I should be able to achieve a decent turning radius with a shorter wheelbase tandem.

  6. #6
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    Default single versus tandem

    Another reason I am pushing for the tandem is to gain compartment space. I have read quite a bit about the single axle not even being able to carry the ISO complement of ground ladders, and the truck barely being able to hold a full complement of what we would call and engine company. In my opinion, a 75' stick is pretty much useless to us, but that is the direction they are going. I have heard a lot about St. Louis's single axle problems and the trucks not holding up over time and the rear suspension having issues in a short perior of time. You also reduce braking and the ride of the truck with the single. Trying to prevent overloading the truck with equipment when it comes to weight the first day out the door. Brake replacement can be very frequent as well.

  7. #7
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    Suggest you delete the similar post in the Engineers Forum. I'll repost my reply here.

    Robonel:

    Experience with both single axle and tandem (current) axle aerials on a light duty station. Original (1967) Mack cab forward with a 75 ft. Snorkel single axle. Slow (43 mph) response with the thermodyne diesel. Very maneuverable with very little problems when off highway (dirt roads). Set-up was quite fast and we did not have many issues with ground support. Weight of vehicle was 43,000 lbs with 25,000 lb on rears and 18,000 lb on front. This loading required radial tires in 1967 to meet the axle rating for the front. Snorkel was transferred to another Mack MR commercial chassis in 1992 after a complete rebuild at Snorkel in St. Joe, Mo.

    Mack – Snorkel was replaced with a KME Quint 100 ft tower in 2007. This is a tandem axle with a Gross Weight Loaded of 79,500 lbs. This was a big change for our drivers due to the weight and maneuverability. A tandem has a tendency to push on the corners especially in wet or winter weather. There is absolutely no going off paved roads when the frost is coming out or after prolonged rains. Major problems are weight on the tandems (56,000 lbs) causes the front end to push on corners even when on dry roads. The rear overhang opposite side swing keeps the driver busy watching both sides of the truck on turns. You must stay at least 2 feet from signs or cars on the side opposite the direction of turn to keep the “rubber dinky” light from hitting on the off side. This forces you toward the inside of the turn and makes for trouble when trying to clear the cab on the turn. The increased weight and the total suspension of the rig on the stabilizers prevents any set-up on grass or sidewalks. 40,000 lbs on the pads and outriggers is a very large load for normal soil especially when wet or recently thawed.

    You asked for comparison, but I do not wish to leave the impression that we are not happy with the new rig. The additional reach and features more than compensate for the increased set-up time and restrictions caused by the additional weight. The single axle required an engine next to the Snorkel for adequate water supply. The quint has a 2,000 gpm pump and can supply up to 1,600 gpm from the 2 ½” solid stream nozzle. (water tower only – no personnel in the basket).

    The real question should be, “What do I need to adequately service my coverage area”, and then build the rig accordingly. The single / tandem axle question will resolve itself when you decide on the size of aerial you need to serve your coverage. (high rise, industry, town houses, etc)
    Kuh Shise

  8. #8
    Reliance
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    My question is. Why do you need an Aerial Ladder and/or Quint if most of the calls are EMS?

    That is a high fuel mileage vehicle on medical runs.

  9. #9
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    Can you consider purchasing a state bid SUV to run all those EMS calls and then you could have a double axle ladder to run the fire calls?

    If you have a budget its pretty easy to shave off 25k in a ladder truck and dedicate it to a separate purchase.

    You could run a jump company and save alot of wear, tear, maintenance, fuel by running a nimble SUV on the EMS stuff.

    Of course if you are union, you might not be able to do a jump company per what your contract says.

  10. #10
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    On the debate over single vs tandem axle trucks, the tandems have been more problematic by 2-3 times over the single axle setup.

    With 4 75' singles and 9 100' tandems, you will be happier with the single axle if your 100% sure you're getting a 75' stick. Ride and maneuverability is better with a single. As for braking, a tandem is slightly better, but you need to spec that both rear axles have spring brakes, otherwise only one axle will have parking brakes. As for maintenance and reliability, hands down, the single axle wins.

    Your wheelbase will be dependent on your OAL.

    If your OAL is the same with either, then get the single axle. You will get more compartment space and with ours, a full compliment of ground ladders that fit under the ladder.

    If you should happen to change your mind and get a 100' stick, then by all means, a tandem should be mandatory.

    FM1
    I'm the one Fire and Rescue calls, when they need to be Rescued.

    Quote Originally Posted by EastKyFF
    "Firemens gets antsies. Theys wants to goes to fires. Sometimeses they haves to waits."

  11. #11
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    when you say busiest truck in the city, how many runs are we talking? It busy means different things to different people. if the truck is only going to see 1000-2000 runs its not that bad. But if you're pushing 2000-3000 runs a year on a single axle quint that is overweight or just below, you might be better off re-examining your approach. You'll be putting a lot of abuse on an expensive piece of equipment. Especially if its going to be running a large percentage of EMS calls where a lot of the tools you are bringing to the party you don't need.

  12. #12
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    Just as FIREMECH1 said, you will be happier with a single axle 75,77 or 78. I have seen alot of newer single axle quints (with 500 gallon tanks) that have an enormous amount of comparment space and "real" ladder compliments.

    As for braking capabilities; ask to have your engine brake tweeked according to your needs. Have you asked about the possibility of including some type of driveline retarder with a jake? Just a thought.

  13. #13
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    I don't understand how you think you'll get more compartment space on a tandem. The ladder, for the most part, determines the overall length, if you add another set of wheels in there you have to give up compartment space. Miami Dade runs some very well designed single axle quints. And talk about busy trucks! Do a search, you find an article or two about them.

  14. #14
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    Yes, we have a vehicle available to do that, but the manpower is the issue. The QRV we have would suit the city best, but we cannot get another 2 personnel to cover that piece of equipment. We are way beyond that, so that is why I am trying to justify a tandem with a short wheel base versus a single axle that will have less compartment space, be overloaded the first day out the door or close, and will have more brake wear and suspension issues over the life of the vehicle, among other things.

  15. #15
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    We don't have that many runs, not in the several thousand category, but it will still be a busy truck and the single axle issues I have read about will be more problematic and require more maintenance. At least that is the research I have found.

  16. #16
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    Default single axle

    Quote Originally Posted by Reliance View Post
    My question is. Why do you need an Aerial Ladder and/or Quint if most of the calls are EMS?

    That is a high fuel mileage vehicle on medical runs.
    I agree, but they are looking at an all purpose vehicle due to manpower issues, the same story as other departments. I do not want to run it as a primary EMS vehicle, but have no choice at this point.

  17. #17
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    Default single axle

    Quote Originally Posted by VanIsleEVT View Post
    I don't understand how you think you'll get more compartment space on a tandem. The ladder, for the most part, determines the overall length, if you add another set of wheels in there you have to give up compartment space. Miami Dade runs some very well designed single axle quints. And talk about busy trucks! Do a search, you find an article or two about them.
    I will take a look and see what Miami Dade is running. I did just see a single axle ladder at Rosenbauer a few weeks ago and was only 3 years old and was there for a total refurbish, I couldn't believe it. If you have any other info or articles, pass them on to me. Thanks.

  18. #18
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    I agree with previous posts by VANISLE and FIREMECH.

    While I sympathize with staffing shortages, you may be disappointed with the multi=purpose "swiss army knife" style truck being proposed.

    Based on the described use, I recommend a single axle for these reasons:
    • Maneuverability.
    • Lower overall cost of operation.
    • If you need more equipment than this apparatus can carry, you probably need additional apparatus with more manpower.

    When you write your specs, consider stiff frame rails, air ride suspension, and auxiliary engine brake to address some of the concerns that were raised.

    Having just taken a truck out of service for several hours yesterday to have the tandems realigned, I can affirm that tandems are not a panacea.

    C6

  19. #19
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    I believe you can go up to 52k gross on a single axle, and 80k on tandems. So you can have a well equipted single axle truck that is heavy, and actually be under weight.

  20. #20
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    Miami Dade 75'
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