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  1. #1
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    Default Wheelbases on apparatus

    I recently had the opportunity to check out a new 2500 gallon pumper tanker built on a 4-door Peterbilt 357 chassis. The truck looked great, but I have a question about the wheelbase. The truck has tandem axles and has a wheelbase of 283 inches. That is pretty long. Does anyone out there have any experience on driving a piece of apparatus this long? In rural areas, I would suppose it would be fine. I do not know about driving it in the city. The Tankers went to Crosby, Texas. They bought two of them. They look like great trucks.

    http://www.crosbyvfd.org/


  2. #2
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    Black Hawk VFD, South Dakota
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    Default

    Check the manufacturer's specs on turning radius to see if a wheelbase will work for your situation.

    Some of the larger chassis actually have a pretty short turning radius for their length. Our 96 Pierce/Freightliner four door on a 232" whellbase actually turns shorter than our two door 81 FMC/GMC pumper that is built on a 200" wheelbase.

    We are currently writing specs for a light duty rescue. We found that on a 200" wheelbase, the International chassis has a 40' turning radius. The Ford F-550 has a 78'turning radius. The larger chassis has a better cramp angle.

    Stay Safe

  3. #3
    Senior Member Dalmatian90's Avatar
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    Default

    You know, some rural areas and some cities aren't that much different!

    Cities may end up with congested, narrow streets -- we may end up with narrow driveways that are more difficult to make the swing into than some roads, and when the house is a 1000' up the driveway, you don't got an option. The big tankers may stay on the road and pump up a driveway lay though, but even there we have roads with "Y" intersections Aerials & Big Tankers are gonna have a difficult time in certain directions making the swing.

    IIRC, there are actually two "Turning Radius" numbers to be concerned with. (Correct me if I'm wrong)

    The most common is "Wheel-to-Wheel" which is the radius of the turn made by outside rear wheel.

    There is also the "Curb-to-Curb" which is the minimum width the whole truck -- from front bumper to back bumper -- needs to turn. The more space in front of the front axle, and the more behind the rear the bigger the turning area.

    Wheel-to-Wheel defines your minimum hard surface. Curb-to-Curb may be more forgiving if you're just swinging over a low curb and over grass. But if you're making a turn into a driveway bordered by Stone Walls or manuevering around cars, it's important.

    Length is important.
    Cramp angle (how hard the front wheels cut) is important (and depends on body style, front axle weight ratings, tires, etc)
    Overhangs are important.

    Most important is balancing all three with your district & your needs and what is acceptable for turning.

    Matt

  4. #4
    Forum Member colfireman's Avatar
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    Default

    Our department is actually going the other direction. Our last engine has a 165" wheelbase and the Saulsbury unit were waiting for will be 170".i believe the cramp angle is 50 degrees. Overall length is 30'4". with our 1400 gallon tanker were are looking at possibly getting a short wheelbase tractor and putting the tank on that to keep it short and tight.

  5. #5
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    colfireman,

    Be careful in using too short a wheelbase for your tanker.

    A short, close coupled chassis with a relatively high center of gravity is a real handful especially in wet or icy conditions.

    We run a tender/tanker with 1500 gal tank that will turn shorter than the type 6 brush trucks due to cramp angle. It is on an 177" wheel base. Check the chassis manufacturers specs for turning radius. As dalmation90 pointed out there are actually two types of turning radius. The easiest one to compare is the curb to curb. A 45' curb to curb means that you could make a "U" turn on a four lane street if the lanes are 12' wide.

    If you elect to build the tanker yourself, make sure you have the proper weight distribution between the front and rear axles. THe weight should be distributed rater than concentrated.

    Stay Safe

  6. #6
    Forum Member TCFD12's Avatar
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    Default

    Our Tower has as 275" wheelbase and an overall length of 49' 5 1/2". Due to the increased cramp angle of the front axle, it actually turns better than the truck it replaced, even though it is significantly bigger. We operate in a suburban area with both residential and commercial areas. The size of the truck has not been an issue for us at all. In fact most drivers say that they feel more comfortable driving this truck than our first due engine. Sometimes by shortening a wheelbase, you create a truck that may feel "tippy" in the corners. Our new engines are going to be 215" WB to try to eliminate this feeling.

    I think there has to be considerations of the area you are protecting and identifying any potential problem areas. Just don't be afraid to go with a longer WB, you may be surprised on how well they will handle.
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  7. #7
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    Default



    Not sure if I ever heard of Dalmation's wheel to wheel turn radius but it is an interesting measure of the width of the pathway required for the apparatus to make a turn. It is obviously wider than the track of the vehicle so it provides a useful measure of the OUTSIDE dimension required to turn the vehicle. It sounds like wall to wall turning radius. With extended bumpers and large compartments behind the rear wheel, this measure tells us what objects taller than curbs we are likely to clip in a turn. It can be measured by making the tightest turn circle possible and dropping a traffic cone at the front or rear outside corner (whichever sticks out further) of the apparatus every 10 feet or so.

    My definition of curb to curb is different too. Curb to curb is simply the INSIDE distance required for the vehicle to turn. It is the radius of the circle carved by the inside wheels of the vehicle in the tightest turn possible. You can measure it by simply turning the steering wheel of the vehicle as far as possible and measuring the diameter of the circle the inside tire tracks leave on the pavement. There WILL be tire tracks because of the scuffing of the tires in such a tight turn. Go around the circle a couple of times to make sure the steering wheel is really hard over.

    By the way, wall to wall and curb to curb numbers are not always the same in left and right turns. Left and right cramp angles sometimes differ due to steering mechanism or suspension geometry.

    Don't forget the radius is half the measured diameter. Sales folks like to quote radius numbers because they are smaller numbers and sound better.

  8. #8
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    Default

    Cramp angle is very important. Also you don't want to
    get it too short. All that stuff has got to go somewhere
    and if you don't make it long you gotta make it tall. Have
    you considered looking at a Pierce Allsteer? That will
    for sure make your turning radius very small.

  9. #9
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    Jul 2002
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    Default

    The Crosby pumper tankers perform just fine in their environment. They get along perfectly. I guess that is the key design what you need for your environment. For every issue a longer wheelbase vehicle creates like Y turns or backing up to finish a turn the reality of the GEE WIZ new fangled steering axles have other built in problems that are much harder to solve like the tire scrub issues, the 4 to 5 thousand mile tire replacement costs, the All-Steer and Twin Steer complexity, driver training and accident issues of a swing out rear end and $40,000 additional cost of the G wiz systems.

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