Navarra D22-2009 twin tyre racks

Submitted: Monday, Jul 21, 2014 at 09:43
ThreadID: 108819 Views:1364 Replies:4 FollowUps:6
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I am looking to get a twin tyre rack for my Navarra D22 2009 but would prefer to have it towbar mounted so that I can remove when not required. Can anyone steer me towards a supplier or manufacturer. I am SA based but will go anywhere to get it?

Cheers Pete
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Reply By: Ross M - Monday, Jul 21, 2014 at 15:33

Monday, Jul 21, 2014 at 15:33
G'day Jackson
Can't help with the supply aspect.
The associated weight of the carrier system, whatever it may be, will be another wheel of weight at least, so in reality it will be at least three wheels added to the very back end of the chassis. Possibly even further away than the chassis.
All that weight well behind the rear axle and combined with tow weight if ever/also towing sometimes, would place a high degree of bend stress on the chassis in the region behind the cab. ie, before the upward curvature and rear spring hanger.

Many Navara's have bends in the chassis because of loading behind the rear axle. While other vehicles are also subject to the same, there seems to be more N's than others with bent chassis, whatever the cause.
May be Ok if used on road ie, smooth roads, but where sudden high forces caused by off road use, as a result of the mass of load and "rear gear", especially if the loading on the rear axle bottoms the suspension, I would be careful with the fitment.
A raised and compliant, non bottoming suspension may be the way.

Just being cautious.
AnswerID: 536370

Reply By: Jackson - Monday, Jul 21, 2014 at 18:22

Monday, Jul 21, 2014 at 18:22
Thanks for the insight
AnswerID: 536378

Follow Up By: Member - Dough Boy - Monday, Jul 21, 2014 at 20:13

Monday, Jul 21, 2014 at 20:13
Hi there , there is a company that sells on ebay(amongst other places)
based in Ballarat that make a replacement rear bumper for the d22 with a twin spare wheel holder, I purchased one a couple of years ago for my previous truck (2010 d22 ) as I remember they are called Powerful 4x4 , was a bit of weight on the back of the truck and as such caused a little sag,even with a old man emu suspension kit on it , then sorted with the installation of air bags
Hope this helps
Cheers
DB
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FollowupID: 820473

Reply By: 671 - Monday, Jul 21, 2014 at 21:46

Monday, Jul 21, 2014 at 21:46
Pete

Don't ignore the advice given by Ross, it could easily save you from a lot of inconvenient and expensive chassis repairs.

The section of the chassis, plus the tub or tray, that extends back behind the rear axle is a lever. If you keep adding things to it, it will eventually force the rear end down and and lift the front wheels off the ground as the chassis pivots on the axle. If you actually did try doing that, the chassis would bend while you watched it somewhere between the front hangers for the rear spring back to the area above the axle.

In practice nobody puts that much weight onto their cars but the vast majority seem to forget that the situation changes dramatically when whatever they have behind the axle is in motion.

Your wheels would weigh at least 30 kgs each. The mounting bracket would most likely be over 20 making a very conservative total of 80 kg. Your tow ball would be around 1200 mm behind the axle.The tub or tray could go back a bit further. The wheels would be off the end of that making them at least about 1400 mm back. That is a long lever. As your rear wheels fall into a depression in the road, the chassis will fall suddenly. The forces generated by those falling wheels will increase by the square of the distance they are behind the axle. That works out to a force of 157 kgs if my maths are correct. On top of that you can add to it the forces generated by whatever else you have behind the axle.

A split second later your car wheels might come back up out of the depression quickly. The falling material in the back will have to be caught by the end of the chassis and heaved up instantly. Imagine what this is doing to the end of the chassis.

The same thing is happening when your front wheels rise and fall. The rear end of your chassis is going up and down in the opposite direction. The chassis is heaving the weight up and catching it when it comes down.

This makes it very difficult to load these type of cab/chassis utes without over-stressing the chassis. The handbook for mine for example (not a Navara) says a WDH must be used for any tow ball weight exceeding 90 kg. A WDH is not a spring but a lever that picks the rear of the chassis up and transfers weight forward to the front wheels. If I was to mount two spare wheels on the back of my car, I would have more than 90 kg hanging out past the tow ball but I could not use a WDH to move some of that weight forward because I am not towing anything. Herein lies the big problem. Owners can carefully load their utes making sure the car is not over GVM, or the axle load limit, but have so much out the back that the chassis is way outside the factory design limits. This is why countless utes of all makes have bent or cracked their chassis.

The problem can not be fixed with a heavier suspension. Aftermarket springs may make the car sit up a little higher and look better but the weight is still out the back and still generating the same forces as the chassis moves up and down.
AnswerID: 536390

Follow Up By: Ross M - Monday, Jul 21, 2014 at 22:41

Monday, Jul 21, 2014 at 22:41
Endorsement of 671 reply x a factor of 10.

If the chassis is forced up suddenly by the wheels on the terrain that 90kg may become 200kg or more in an instantaneous situation.

That is why a compliant suspension ie, long travel ability and not too stiff may be the only saviour.
The weight will cause Porpoising to despite good shocks..

Best to carry the heavies near the front of tray/tub and the bed roll and biscuits at the rear.
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FollowupID: 820485

Follow Up By: 671 - Tuesday, Jul 22, 2014 at 20:09

Tuesday, Jul 22, 2014 at 20:09
I am not so sure about the compliant suspension Ross. The weight is still out there flexing the end of the chassis up and down.

Just out of curiosity, I picked up my daughter's 3.6 kg sledge hammer last night. She uses it as a training tool in her job as a personal trainer. I had no trouble holding the head with the handle in a horizontal position out in front of me. When I held the handle and tried it, the thing was hanging down at about 45 degrees with my wrist strained to the limit. I was still holding only 3.6 kg though. The only change was the greater part of the material in it was now further away from my hand.

If only people would understand the effects of leverage on the rear end of a chassis and the forces generated by mass (the amount of material in something) in motion, there would not be any damaged chassis.

You can't load a car proprely while concentrating on static weight only.
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FollowupID: 820518

Reply By: olcoolone - Wednesday, Jul 23, 2014 at 09:04

Wednesday, Jul 23, 2014 at 09:04
Just a question... why two spare tyres?

Most who think they need two spares never end up using them, a good tyre monitoring system and plug kit is all we use.

You could try this mob.....

http://www.bigo4x4.com.au/
AnswerID: 536455

Follow Up By: Member - mechpete - Wednesday, Jul 23, 2014 at 10:13

Wednesday, Jul 23, 2014 at 10:13
one sharp rock through the sidewall an your plug kit is not worth
a cracker ,
mechpete
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FollowupID: 820557

Follow Up By: Jackson - Wednesday, Jul 23, 2014 at 16:47

Wednesday, Jul 23, 2014 at 16:47
Mechpete exactly why two spares are in my plans & also thanks to olcoolone. I do get the plug kit & will be carrying this as well. To all that have replied so far & after this thanks for all your ideas & opinions all are relevant.
I will look at other options maybe even carry off the front. More thought required = more beers & red wine + spare time to think. cheers all.
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FollowupID: 820577

Follow Up By: Bob Y. - Qld - Wednesday, Jul 23, 2014 at 17:40

Wednesday, Jul 23, 2014 at 17:40
Jackson,

These photos have aired on this, and other forums, a number of times.





Ol' mate seemed to do everything right, but still had this misfortune.

Bob

Seen it all, Done it all.
Can't remember most of it.

Lifetime Member
My Profile  My Blog  My Position  Send Message

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