Announcement

Collapse
No announcement yet.

Truck rack " whistle " Advice needed

Collapse
X
  • Filter
  • Time
  • Show
Clear All
new posts

  • scott-n-montana
    started a topic Truck rack " whistle " Advice needed

    Truck rack " whistle " Advice needed

    I'll try and make this simple. The crossbar that goes over the top of the cab makes a whistling sound when you hit about 45 mph. I figured it would because it had happened to me years ago using a round bar. On my last truck I had the bar out in front of the cab. Now that I have a 4 door though I don't want to extend the rack out that far. There are 2 bars over the cab and the front one is a little higher off the cab than the 2nd one. I have the rack down at the powdercoaters now, but would go down there and cut off the 2nd bar if I knew it would stop the noise. Also the top part of the rack is only bolted on to the bottom part so most of the time I will not even have the extension on. Does anyone have any info on this and how far the bar would need to be above the cab to stop the noise. Thanks to any advise. Scott
    Attached Files

  • Bert
    replied
    Originally posted by tasslehawf View Post
    I would think that with sq. tubing, the folds would be stronger than the flat sides, therefore the flat sides are a weak point; whereas with round its all the same shape so no weaker areas.
    That's my thought!!!!!!!!!
    FusionKing, I agree with you if you used different shapes to each one's advantage, but I think it would look like cr@p on one truck rack!!!!
    Would be nice to have some side money, to get a round sched 40 pipe and square with the
    same wall thickness, then put the same load on them and compare...
    Last edited by Bert; 04-06-2008, 11:25 PM. Reason: adding to post

    Leave a comment:


  • tasslehawf
    replied
    I would think that with sq. tubing, the folds would be stronger than the flat sides, therefore the flat sides are a weak point; whereas with round its all the same shape so no weaker areas.

    Leave a comment:


  • FusionKing
    replied
    Whether using square or round tubing both need to be designed around the advantages that the shape brings to the table.
    You can simply take a 25 ft piece of pipe and square tube of varying thicknesses and shake them around and learn a lot.
    25 ft pieces of sch 40 6063 t-4 aluminum pipe is very floppy in all directions.
    Using steel square tubing and bending it with a bender could cause the square to become disadvantaged compared to round because of the collapsed sides from the bending process. Slight bends on the round can make it much stonger as well.
    The perfect rack would implement a variety of shapes each serving its own purpose and used to its best advantage

    Leave a comment:


  • DSW
    replied
    Originally posted by FusionKing View Post
    I'm sorry but I don't buy it

    I would think if you start digging then you will find strength to weight ratio is better but not ultimate strength as in weight bearing strength over a span.
    I agree with you on this. I know in a vertical aplilcation pound for pound round tube will beat other profiles. An alum soda can will support most peoples weight if loaded straight down. That a lot of psi on a thin thin wall. In horizontal loads an I beam is strongest for the weight. The taller the I web the more load is taken by the top and bottom cords and the more efficient. However the taller it is, the weaker it becomes when loaded latterally from the side. Hence why Wide flanges replaced I beams, and why the W profile is almost square in many applications.

    I don't have any horizontal load tables for pipe, so I can not back this up. But why would the use a W beam instead of round pipe for most structural apps? Ok its got a flat surface, but I bet you could work around this if it was substantially better. I do know that an arch is one of the strongest ways to transfer loads to the ground as opposed to a flat beam. So the idea that a tube may self cancel some load may have merit.

    Leave a comment:


  • FusionKing
    replied
    Originally posted by Bert View Post
    FusionKing, yeah, I thought it should be just as stong also, but I've talked to a lot of old timers, and they all say that because the pipe is round, then it's stronger. More even weight distribution......
    I'm sorry but I don't buy it

    I would think if you start digging then you will find strength to weight ratio is better but not ultimate strength as in weight bearing strength over a span.

    Leave a comment:


  • DSW
    replied
    Originally posted by tasslehawf View Post
    Why is it SOO much higher than the roof of the cab?? What does that rect. tubing/mesh end-plate do in terms of wind noise?
    The height of the rack over the crew cab was determined by the height of the back uprights. If I remember correctly they are 4' to the underside of the horizontal members. This was done so that stuff in the bed wasn't jammed against the lumber on the rack. You can't see it in that pict but we have 3' and 4' pins standing up in the back, a jumping jack and a fuel tank with pump. We also wanted to be able to get in the back without killing ourselves on the rear bar. Thought about making it removable, but it almost always has forms on the top.

    Click image for larger version

Name:	IMG_0032a.JPG
Views:	2
Size:	62.9 KB
ID:	500948

    Click image for larger version

Name:	IMG_0031a.JPG
Views:	1
Size:	140.6 KB
ID:	500947

    We retro fitted the flat bed to the CC and deliberately kept the bed up to bypass some fuel fill problems that we have seen on flatbeds in the past with low bodies. That may also be part of why it seems so high.

    As far as noise the old 7.3 non turbo diesel makes a racket as it is and all the metal pins don't help. I've also never seen the truck do more than 55-60 but never noticed any whistle. The greenish utility body I have pushed. That truck has run past 85. Trust me at that speed a whistle is the last thing on your mind! I don't remember it having one however.

    Alot of thought went into the CC rack and I would be happy to answer the reasons why we did what we did on it.

    Leave a comment:


  • tasslehawf
    replied
    Why is it SOO much higher than the roof of the cab?? What does that rect. tubing/mesh end-plate do in terms of wind noise?

    Originally posted by DSW View Post
    Actually I have a friend with two at work that go all the way up to the bumper permanently.

    [ATTACH]13745[/ATTACH]
    [ATTACH]13746[/ATTACH]

    The 1st I helped build when I worked with him, and is sort of what I am using as a jump off point. Mostly having to do with tie downs and the over the cab portion. We found that just wraping straps around the rail wouldnt work well for single items or rebar. The truck has loops on the uprights so that the straps can be longer and we wouldn't run into the buckels or the ratchet when tieing down stuff. The second truck is somewhat similar to the new truck, but the new one is taller. It was the truck we used to base the rack on the truck in the 1st pict on.

    I was sort of looking for other options. But I appreciate the offer. Actually I just got done sending you an email or pm (I forget which) about the ceriated tungson question.

    Leave a comment:


  • DSW
    replied
    Actually I have a friend with two at work that go all the way up to the bumper permanently.

    Click image for larger version

Name:	IMG_0027.JPG
Views:	1
Size:	33.0 KB
ID:	500945
    Click image for larger version

Name:	IMG_0039a.JPG
Views:	2
Size:	42.8 KB
ID:	500946

    The 1st I helped build when I worked with him, and is sort of what I am using as a jump off point. Mostly having to do with tie downs and the over the cab portion. We found that just wraping straps around the rail wouldnt work well for single items or rebar. The truck has loops on the uprights so that the straps can be longer and we wouldn't run into the buckels or the ratchet when tieing down stuff. The second truck is somewhat similar to the new truck, but the new one is taller. It was the truck we used to base the rack on the truck in the 1st pict on.

    I was sort of looking for other options. But I appreciate the offer. Actually I just got done sending you an email or pm (I forget which) about the ceriated tungson question.

    Leave a comment:


  • Bert
    replied
    DSW, wow! never though of the drip thing, as I've never had a truck rack before!! THANKS! I guess I'll be extending mines out a little furthrer like you did though!!!
    Far as your "front rack" thing. I see a few guys here that make a frame off their bumper (bolted on to the bumper), and that helps support the piece. If I see one again, I'll send you a pic.

    Leave a comment:


  • DSW
    replied
    Originally posted by Bert View Post
    Rule #1: Don't have your bar shorter than the top edge of your front window, sticking out a little is better. If it is exactly above it might be ok, but just a little behined, it'll start to whistle.
    One thing you might think about. If your rack extends past the front of the top of the windshield by much you can expect it to drip on the windshield all the time. Especially if you make a solid top like some have. We have one at work this way and it is annoying to say the least. Looking back at it, just a little bit farther forward and it would drip on the hood rather than the windshield.

    I'm looking at building a new rack for my truck so have kinda been keeping an eye on this. Noise shouldn't be a problem as the body is at least 18" over the cab. I am thinking about going over the roof so I can get at least 14-16' on the rack (11' body) but hate the way I think it would look. My first thought is to use 3" alum channel. Anyone ever make a rack that telescopes out sort of like what some of the chopsaw tables do? I don't need to hold a lot of weight, just support long items like molding, light steel bar in full lengths or PVC pipe. Any suggestions on what alum sq tube sizes slide in/out togther well? My other thought is to make a removable rack that would go all the way to the front bumper. The 9' 6" height to the top of the body makes installing this a PITA by myself. Any suggestions and picts would be appreciated.

    Leave a comment:


  • Bert
    replied
    Originally posted by FusionKing View Post
    I agree with about everything here...it sounds plausible enuff except the part about round being stronger than square...a piece of square the thickness of that sch 40 pipe would be awfully heavy duty
    FusionKing, yeah, I thought it should be just as stong also, but I've talked to a lot of old timers, and they all say that because the pipe is round, then it's stronger. More even weight distribution......

    Leave a comment:


  • FusionKing
    replied
    Originally posted by Bert View Post
    Gonna build my first truck rack in 2 or 3 weeks (when my pipe bender comes in). My union instructor showed me things to look out for (all the racks on their trucks are all schedule 40 round pipe, round being stronger than rectangle or square stock):

    Rule #1: Don't have your bar shorter than the top edge of your front window, sticking out a little is better. If it is exactly above it might be ok, but just a little behined, it'll start to whistle. Funny this thread came up about that! He said the air coming off the windshield hits the pipe and makes it whistle. You could make it higher, but we both agreed it doesn't look nice... He makes all his around 3" above the top point of the cab...
    my .02 (pick it apart, but that's what I was told, and that's how I'm going to make my 1st pipe rack)
    I agree with about everything here...it sounds plausible enuff except the part about round being stronger than square...a piece of square the thickness of that sch 40 pipe would be awfully heavy duty

    Leave a comment:


  • monte55
    replied
    Originally posted by Bert View Post
    Monte, what kind of "round bar" do you have that has sharp edges????
    lmao!!

    Monte is probably right, but I also think it's a HUGE difference too, of where you place it!!

    -bert-
    p.s. Monte, package shipped as you requested. This time, I put air holes....
    Hope she faires better than the first one did!!!!!!!
    Did you bury the body yet???
    My chisel
    I didn't know if it was round or square. Even small round can create noise at certain speeds. When relative wind hits a an object it splits and speeds up to meet at the trailing edge and depending on the shape will dictate how much turbulance as in an airfoil. Even aircraft wings make noise as they slip through the air.

    PS I thought it was going to be two months...air holes will be great

    Leave a comment:


  • Bert
    replied
    Originally posted by monte55 View Post
    Whistling is generally caused by fast air movement over sharp edges.
    Monte, what kind of "round bar" do you have that has sharp edges????
    lmao!!

    Monte is probably right, but I also think it's a HUGE difference too, of where you place it!!

    -bert-
    p.s. Monte, package shipped as you requested. This time, I put air holes....
    Hope she faires better than the first one did!!!!!!!
    Did you bury the body yet???

    Leave a comment:

Working...
X