Modifications & 'How to' Guides

[jcubed]

Hi Jimbomort,

Regarding the spare wheel on my avatar, it is something which I developed myself out of neccessity, but the attached article should explain the how and why.

As I explained to arctra, with whom I communicate from time-to-time via email, the article had been taken out of context somewhat, by ignoring the contents of my covering letter, which pointed out the following:

A number of reader's letters published in Leisure Wheels magazine, contain personal measurement criteria of how that specific writer would go about selecting a soft/off-roader. As many authors, as many opinions, but they generally all start with a comprehensive list of just about everything available, and then start crossing off the ones that in their opinion would not be a) affordable and b) capable off-roaders. A common reason for disqualifying throughout, is a space-saver spare wheel.

In my letter, I agreed that the latter was a no-no for off-roading, but explained that potential buyers should perhaps reconsider their criteria, and rather pick a vehicle where the things that CANNOT be changed are right, e.g. overhang, but the things that CAN be changed, like too large rims/low profile tyres, too litte ground clearance and yes, a space-saver spare wheel, weighted with lesser severity.

The submission of the article below was evidence that I am not speculating here but that it is indeed do-able. Please excuse the fanfare with which the leading paragraph announces taDAAA!, but that is editorial license.

If you have any more questions or want to see more pictures, I can upload.

[Transporter]

Hi mate,
Could you please post close up pictures of that spare wheel carrier. I would like to make one when we get our Tig. It would save me and others the time.

Great posts! Thanks.

[jcubed]

Spare Wheel Carrier

Hi Transporter,

Attached a few images that I had on my PC. I saw that I did not take any clear pictures of the mechanism and how it attaches the spare wheel to the cycle rack - which is an off-the-shelf Thule 970 Express - but I'll get round to it over the week-end.

Not to discourage you, but I attached the parts list to give you an idea of the magnitude of the excercise. The bottom line is that unless you can do the machining yourself - which is what I did, using an industrial milling machine and lathe at work after hours - it is going to be horribly expensive. The main part has to laser cut, for which a minimum set-up cost is payable, adding to the cost.

The existence of the parts list was the outcome of a feasibility study to see whether I could make and sell these things as a hobby, but the amount of work per unit is of such a nature that by the third one, you'll be completely fed-up with the process. Prices are in ZAR, at the time - 18 months ago.

So it was one of those obsessive things you only do for yourself, in the vein of "I'll get this thing to work, if its the LAST thing I do".

But if you decide to try anyway, I have discovered a few shortcuts during the process which I don't mind sharing with you.


The above detail is key to the modification to convert the fixed mechanism to one that folds down, and is the "before" picture.

This image illustrates how the installation leans forward in order to get th CG as close as possible to the hitch. The new clamping feet is also visible, as is the "driver awareness" black rod sticking up above the wheel.

Spare_Wheel_Carrier_Shopping.doc - ImageHost.org

[Pullstarter]

Nice work! Love custom fab jobs!

[jcubed]

Retrieving the spare wheel from the vehicle

In response to some PM requests for more details on the Spare Wheel Carrier with a view to home manufacture, this summary describes HOW to remove the wheel from the rack in order to swop it with a flat, as it is not quite as straightforward as opening the boot, removing the floor, undoing a wing-bolt and then lifting the spare wheel out.

This should give readers an idea of whether they could be bothered with a device like this. Depending on the interest level, this will be followed by a post describing WHAT has to be done in order to convert the cycle rack into a spare wheel carrier, in order to give a further indication of whether a project like this is within readers' capabilities or perhaps that of someone they know.

HOW this WHAT is to be done, with background as to WHY, will probably be done by way of PMs, as those not mechanically inclined will be bored stiff once the talking gets down to pitches, threads, tolerances, machinery, materials etc, as it inevitably will do in this section.

In sequence, the images below apply:

Disconnect the lightboard then Unlock and remove the padlock

;

Undo the latch and close the arms, then lift the rack off the hitch. Depending on where you are, the wheel may be quite dirty, so if you have one, get your teen-age son to do this. Next place the assembly number plate down on a covered surface to prevent scratches to the number plate light. Remove indicated bolt fully. The lightboard will drop away from the wheel onto the (covered) ground.

;

Lift and flip the wheel over, then Unscrew the two wheel nuts and spacer and lift the wheel off the rack.

;

You now have one full size spare wheel ready for fitment. Simple enough, or not?

[jimbomort]

......This should give readers an idea of whether they could be bothered with a device like this....

jcubed sounds like making the rack is a big job, well done.

I can see its main application as being a specific offroad trip or the like as it would seem a hassle dropping the spare wheel carrier down each time for regular unloading of the boot (eg for the weekly shopping etc) or am I missing something with the way it works?

[team_v]

It is a good idea to have an external full sized spare.
It also allows you to drop the floor in the boot giving you even more boot room (of which some find limiting) as well as the extra functionality of having the full sized spare.

I would hate to be caught out in the sand and only have a space-saver to rely on.

Does it impede the rear hatch opening much?
I would probably end up just putting the spare in a caged cargo hold on the roof racks to allow easy access to the rear of the car.

[jcubed]

More on day-to-day usage

Hi last two posters,

Jimbomort, my description above is to get the wheel off the car for fitment in case of a flat.

For day-to-day use, it's no more effort to flip it down than opening a door. There is no unlocking or disconnecting to be done. Reaching over the spare wheel from the rear, the black plastic handle visible in some of the images is lifted - it has a finger-operated latch which automatically locks when closed, but which upon pressing, releases - which opens the hitch clamp partially, allowing the rack to fold back to the position illustrated in the original post article. With a bit of practise, it is a one-handed - left - operation. Pushing it back requires two hands, though. When folded down, the hatch swings by easily with space to spare.

Team_v, the angle to which the spare wheel folds back, is determined by the length of a slot machined in the clamping feet, and has been made to measure for the Tiguan. On a VW Caddy towbar, due to the rear door being much taller than that of the Tiguan, it does not fold back far enough to allow the door to swing by. However, it would be a simple process to extend the slot - you need a milling machine, and it will take longer to clamp the part in the vice and put the cutter in the collet than it would take to do the job - so that it would be suitable for ANY car. In the lowered position it can also be swung side-ways, giving wider access when loading, although I've never had the need to do this for holiday packing.

And you are right, without the extra space under the floor, there is just no way all the luggage would go in. Mainly because my sons and I can stick to the rule of ONE bag per person, but SWAMBO is still learning how not to pack for 4 seasons .

I'll take/post some side-views to illustrate both explanations above.

[jcubed]

Boot Access

Hi Guys,

Herewith the explanation as to how the gadget works around town.

Lever Up, shows the tensioning arm in unlatched position. Folding Down is about halfway to the endstop. Your elbow is pressed against the indicator (black) rod stabilizing the rack laterally, feeding it lower in a controlled manner, as otherwise gravity is rather abrupt.

;

Hatch Clearance shows the closest the lip of the hatch gets to the rack. So in hindsight, the slot could have been shorter. Swung Out shows maximum access. Yes, it swings both ways ...

;

Hope this clears up the questions.

[team_v]

It sure does clear up the questions i was having.
I didn't realise it folded down/swung out.

Definitely worth looking into if anyone is going off-road or wants a full sized spare/bigger boot space.

Might need to look at a protective casing for the tyre though as i know if i had it like that, the local thugs would probably end up slashing it or letting the tyre down as they would have easy access.




Thanks for sharing the pictures with us.

[jcubed]

Any interest in a Spare Wheel Carrier?

Hi All,

I have looked into a number of options as to the possibility of making the Spare Wheel Carrier available in Australia. One option that was eliminated straight away, was making it here (South Africa) and shipping it, as the transport cost would kill it.

All the parts, with the exception of the wheel plate, could be either purchased off the shelf or machined by someone with access to a lathe and milling machine. I therefore enquired locally what the manufacture of the plate would cost - this has to be laser cut - but regardless, the shipping for this part only, would still be in excess of $100.

Plan C, was to get a quote from a Melbourne-based company to do the laser cutting, thereby limiting shipping to inland parcel post cost, and this resulted in the plate itself costing similar to what only shipping from here would be. However, to get them at this price, I need to order a minimum quantity of 5.

The Australian end of the manufacturing and assembly would be managed by Transporter (Adelaide), and he has already reserved one of the plates for his own use. I need an indication from other readers whether they would be interested in such a device, bearing in mind that the application is not limited to a Tiguan, but will fit ANY vehicle towbar. The different standards in number of car wheel bolts, diameter and PCD, as well as the fold-back distance for your particular rear door, will be adapted to order by Transporter.

I don't want your money yet, but purely an indication of the interest in the device. For now, I need 4 more takers. This intent will then be used by Transporter to source and price the remainder of the bought-out items and machining cost and to derive a selling price from this. This will then be communicated back to you via the forum and could either be reasonably priced or we all come to the conclusion that it is not practical.

I know of no other comparable device world-wide, so Transporter would have to use his common sense and knowledge of the Australian market to guide him here. But as he is in the motor industry, he should have a good idea.

One of the concepts is to market the device as a kit to the mechanically minded - a giant USEFUL Meccano set - and also as fully built up (by Transporter) for the less practical.

I am awaiting your response with anticipation.

Regards

Johnie

[jcubed]

A Grand Day Out - at the Test Facility

Hi softroaders and engineering types,

As I will shortly be driving a vehicle with a full size spare wheel, I have been thinking of different applications for my spare wheel carrier, e.g. carrying two jerry cans.

Although the present format has travelled more than 10000 km safely, two jerry cans are somewhat heavier than a spare wheel, to the tune of 50kg vs 30kg. One way to determine whether the rack would stay on the hitch with the extra mass - or rather the moment caused by it - is to execute a "pull test" to see at what point the clamp starts slipping.

An ex-colleague of mine who manages such a facility was kind enough to help me out earlier this afternoon. By way of pictures, I thought that some readers may be interested in the results.

First off, the spare wheel was removed to allow the strap to be attached to the wheel plate so that the pulling force would be applied from where the wheel centre would be. It is important to pull from a known point, as the distance from here to the centre of the ball - the ARM - is crucial in order to calculate the moment at which the clamp friction is overcome. This moment is used in additional calculations to determine what mass of any number of items, e.g. jerry can, larger wheel, etc can be accommodated safely. In this case the ARM length was 350 mm.



Next, the other end of the sling was attached to a load cell. The load cell measures what force is exerted on it as the sling is tensioned, this information being fed to a PC. The other end of the load cell is clamped to the floor, which has threaded inserts arranged in a square grid.



The complete section looks like this, with the PC in the background.



The load cell is attached to a hydraulic ram, which can be extended or contracted. The complete setup is shown next, with the hydraulic pump on the right, with the pipes feeding the load cell.



Here is what the computer read-out looks like - pardon the sky-light reflection:



And the final spread-sheet result:



The test was repeated 3 times, with virtually identical results everytime. The graph is interpreted as follows. The point where the clamp begins to slip, is where the graph levels off. This is at around 0.72 kN.

Multiplying this value: 720N by the ARM (0.35m), gives a torque of 256 Nm. Compared with the max engine torque of a 1.4 TSi engine (240Nm), you could therefor use this coupling between the engine and transmission without it slipping.

To now calculate what mass could be carried, Nm has to be converted to kg by dividing by g, which gives 26 kgm. A typical jerry can is 200mm deep with the centre of gravity halfway between the front and back, i.e. at 100mm. This is the distance of the CG BEHIND the wheel plate, which is directly above the hitch, and in this example constitutes the ARM.

Divide 26 by 0.1m = 260kg can be supported THAT FAR BEHIND THE BALL CENTRE. Closer more, further back less, in the ratio of the arm.

This however is the static loading, and on the threshold of grip. As soon as the car starts moving, the friction will be overcome, and the clamp slip.

However, if a sensible mass of say 60kg is supported, this will give a safety factor of 4.3, or in different terms - the attachment can withstand an acceleration of 4.3g. This is a ball-park figure for the manoevring load applicable to light helicopters.

So yes, the cycle rack could carry two jerry cans.