chassis moounted roof racks

Submitted: Monday, Nov 04, 2002 at 01:00
ThreadID: 2288 Views:2716 Replies:4 FollowUps:5
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Hi folks, I'm wanting to carry a 10ft 6in punt, about 60kgs, on top of a 98 rodeo dual cab4x4, but do not want to have any of the roof racks that mount directly onto the cabin roof, as they will cause dents. We are intending going out for 12 months, and have Gove , Kimberleys and the centre on our list, so are expecting rough roads. Is there anyone with experience of how to mount the racks to the chassis, and whether steel or ali is best? I also want to carry a basket above the cabin. I'm concerned about the twisting between the ute body and the main cabin, what effect it might have on the integrity of the racks.
Any points or suggestions greatly appreciated
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Reply By: OziExplorer - Tuesday, Nov 05, 2002 at 01:00

Tuesday, Nov 05, 2002 at 01:00
The only roof rack system partially mounted from the chassis, would be front and rear. The front would have to come from the chassis mounts in the front, and you would need to mount two frames in your well type body. One would need to go down to the floor in the back, with the other that could be mounted on the top of the well type body immediately behind the passanger compartment.
You would want to use Grade 350 Extra Light Gal or black pipe. The most important thing is that there is sufficient bracing and diagonal bracing. I used to make these when I had my steel manufacturing business, and never had any that let go or broke. Aluminium would cost a small fortune.

The punt over the top provides a great sunshade.
Hope you are aware of the instability of a punt and how easy the flip over. Once they start to go, there is just no stopping a punt. Personally having had a punt and a conventional tinnie, I much preferred the normal tinnie.
AnswerID: 8196

Follow Up By: Sails - Tuesday, Nov 05, 2002 at 01:00

Tuesday, Nov 05, 2002 at 01:00
Hi OziExplorer,
thanks for that info, especially about the stability of the punt.Does the problem occur when you are under way, into a chop or cross swell, or is it from getting the weight all on one side and over she goes?
You mentioned the chassis mounts in front. Do you mean the very front of the chassis, or the rear cross beam that supports the gearbox? It is conveniently located towards the front of the front doors, so a bracket could be fitted to allow the pipe to go in front of the doors and then follow the windscreen pillars
Grade 350 extra light gal; what is the recommended wall thickness and pipe diameter you would have used? Would it be any different for black pipe?
I neglected to mention that I have a chieftan canopy which is 100 mm higher than the cabin roof. I am considering suspending a basket over the cabin of the car, and so the ring frames would be perfect to support it; and the 100 mm depth probably becomes 150 mm by the time the rear bar is in place, which gives enough space for the basket.
Now its time to draw up some plans. Do you know any one in the Sydney region that does this kind of work professionally?
Once again, many thanks for the info. It is much appreciated.
FollowupID: 3925

Reply By: OziExplorer - Wednesday, Nov 06, 2002 at 01:00

Wednesday, Nov 06, 2002 at 01:00
Sails, punts are that dangerous they should have warning stickers on them. If you are in a smooth lake, and you are highly aware of the instability problems of a punt and you make sure you remain seated eavenly, then a punt can be good. However, yes HOWEVER, when you go to land a fish and you have somebody else in the boat, the tendancy without thought is to go and assist - and whoOPS over the punt goes without *any* warning. I have seen punts go over from the wash from other boats, and in a swell, they are even more dangerous. When I was in North Queensland they used to have 'Tinnie Boat Safety' demostrations, and used to demonstrate how easy it is to tip a punt in four different ways. While I am not into making laws to protect people from themselves, I really think that it should be law life jackets should be warn at all times in punts. Only in the last few months in the Murray River, there have been at least three drownings from punt accidents.

Now, I will go back and re-read your roof rack and then answer that one.
AnswerID: 8256

Follow Up By: Oziexplorer - Wednesday, Nov 06, 2002 at 01:00

Wednesday, Nov 06, 2002 at 01:00
Yes, I meant the very front of the chassis. Once you put a bend in to come off the side of the chassis, it takes substantial bracing to take the side flex out of the unit. You are basically forced to use roof attachments to take out the side flex. The other issue today is that cabs are 'more' rubber mounted/flexible than previously, and that would need to be taken into account. No problem with the canopy, but you are going to be forced to drill some mounting holes in the rear. If you put hard sheet rubber underneath the mountings, when you remvoe it, the holes can be easily masked. Every mounting hole/plate needs to have a backing plate.
40NB Extra Light Gr350 pipe is from memory 2.3mm wall thickness. 40NB Extra LIght Gr350 is equivelent to a heavy wall in a Gr250. We used to bend a front and back bow in a large radius bend (6 pipe dia) and then proceed from there with lighter pipe for bracing and ancillary mounts. RHS cracks with flexing on vehicles, and pipe is far superior. I would highly recomend you make the basket to go under the tinnie. This means you can lock the tinnie on, and it will also keep the stuff in your basket safe. You can make the tinnie hinge up easily, so if you need to get into the basket, it will be quick. Having a basket out in the free air on its own will cost you a *fortune* in fuel consumption. If you keep the tinnie with nose down close to the top of the windscreen if possible, your fuel consumption hit will be minimal. A poor roof rack can cost you up to 3km per litre extra fuel consumption - amazing, but true.
FollowupID: 3939

Follow Up By: Sonny - Wednesday, Nov 06, 2002 at 01:00

Wednesday, Nov 06, 2002 at 01:00

I have to say that the extra light GR350 40NB is not equivalent to the heavy wall in GR250. The heavy wall is 73% stiffer, 26% stronger in bending and 76% stronger in axial loads. Even the normal wall GR250 pipe is still 46% stiffer than the extral light GR350 for only a little extra weight, and still has better load carrying than the extra light. Given that your going to be no where near the load capacities of the section, the more stiffness you can achieve from the section the better the rack will be.
FollowupID: 3958

Follow Up By: Sails - Friday, Nov 08, 2002 at 01:00

Friday, Nov 08, 2002 at 01:00
Hi OziExplorer,
thanks forthe reply, your cautions re the punt and info on the rack are much appreciated, and Its great to see the differing opinions that are coming out about the steel. I'll be taking the punt down to my local lake and doing some stability tests to determine if it is a risk that I want to carry, or maybe sell it and get a "V" bottom.
I'll take the details you gave to my local Steel Store and price it up and see what I can come up with in design.You dont have any plans sitting around for a '98 Rodeo roof rack ,do you??
Just an aside, while on the forum I came across an item relating to Rodeos cracking their chassis' which was a bit of a concern. I found another web site from a Subaru car club that did the Simpson with a rodeo dual cab in company.They called the rodeo the Pie truck,due to the ute load set up. there is a photo on the web site of the Rodeo with the rear end sitting on the ground at 45 degrees to the cabin; chassis broken clean in two.
So the weight that goes onto the vehicles really does have to be taken into account.
GM of course put it all down to vehicle abuse!!
FollowupID: 4006

Reply By: OziExplorer - Wednesday, Nov 06, 2002 at 01:00

Wednesday, Nov 06, 2002 at 01:00
Sonny, go to the Palmers website and download their PDF specification files. What you have failed to take into account is the extra weight and flexing moment of the Gr250 pipe. As for your statement of 'a little extra weight' suggest you check your dictionary what 'little' means.

Gr250 because of the extra weight, the flexing moment and causes the Gr250 to self destruct. The extra tensile strength of the Gr350 is significant because of the lighter weight, and the flexing properties of the higher tensile steel. I built racks for seven years and never had any break, while my opposition had plenty of breakages till they copied my racks. I just love you therorists that quote figures without any knowledge of how the product works. Go away and do your calculations in design.
AnswerID: 8275

Follow Up By: Sonny - Thursday, Nov 07, 2002 at 01:00

Thursday, Nov 07, 2002 at 01:00
And oziexplorer, we all just love the know it all. As I said, the additional stiffness of GR250 far outweighs its extra weight. And at only 1.7 kg/m, I do only call it little. If this additional weight causes GR250 to self destruct, than its not worth building a rack out of either grade cause what load could you put on it.

The opposition racks probably work caused they copied your layout and how it all fits together. Have a look at any item that fails. Its never the member, its always the connections and layout that lead to its failure.

I've probably been making things longer than you been around, so why don't you let everyone have their opinon and let the truth come out.
FollowupID: 3974

Reply By: sails - Friday, Nov 08, 2002 at 01:00

Friday, Nov 08, 2002 at 01:00
Hi sunny, thanks for the input . I wont get in the way of professionals discussing the merits of materials, but acknowledge that the failure of a product is usually due to the connections failing. Hence the need to get it done right the first time. As I am thinking of having a basket on top of the cabin, which will fit under the boat just for wet tarps etc, there will be a little more weight than the plain tinny, so I need to make sure the tube I use has the capacity to not sag from the effect of the corrugations on the load. If you have any design input you can share , it will be appreciated!!
AnswerID: 8331

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