pgjonker.co.za

[By Johnie Jonker]

[Published in Leisure Wheels, May 2010]

As is the trend with many current SUVs, my car comes with a space saver spare wheel. Not very useful off the beaten track, but more so the pity for the UK buyer, where the spare wheel is an option and the car comes standard with only a can of Tyreweld.

In addition to the requirement for a full size spare wheel for off-road excursions, being stored inside the car underneath the boot floor is not optimal. Other than taking up valuable packing space, the prospect of having to change a tyre when fully packed for the holiday, necessitating emptying the boot of all luggage in possibly inclement weather, called for an alternative solution requiring some lateral thinking.

Option A:         Stand the spare wheel upright in the boot, after removing the false floor panel.

Objection A:    The image shows that the parcel shelf would not drop back fully, even when deflating the tyre, re-inflating when required. Alternatively, one could leave the parcel shelf at home or make a spare wheel sized cut-out at one end, but this would be akin to “farming”.

Vertical option

Option B:         Do the practical thing and mount the full size spare wheel on two roof bars.

Objection B:    Already being equipped with one artificial lumbar disk implant and not wanting another, the concept of manoeuvring a >20kg spare wheel above my head and onto the roof bars, trying not to drop it through the glass roof, was a rather daunting idea.

Option C:         Tie the spare wheel down onto a Thule EasyBase luggage rack clamped to the hitch.

Objection C:    For off-road use the departure angle is severely restricted by the above units due to the load surface extending far beyond (600 mm) the rear of the vehicle.

Option D:         Some cycle racks are designed to clamp to SUV rear door mounted spare wheels. Surely, an inverse design should be possible where the spare wheel is clamped to a cycle rack?

Objection D:    None, whatsoever.

The cycle rack selected for the purpose turned out to be optimal in a very important aspect – allowing a low mounting position of the spare wheel. This results in it being closely tucked in behind the boot door, maintaining the centre of gravity very close to the attachment point. It makes for a light construction, and reduces the stress on the gooseneck, although the latter advantage may be purely academic considering the low overall mass of the “clip-on” (< 30kg, including the wheel). And there is also no rearward obscuration.

Modifications to the standard rack included: 

• Newly designed clamping feet which allows the rack to hinge back so the boot can be opened – the standard unit did not allow for this.
• The clamping force to the hitch was increased above that of the standard unit in order to compensate for the higher acceleration forces anticipated when going off-road.
• All hinge pins were replaced by stainless steel bolts and locknuts.
• A mounting plate which interfaces the wheel to the rack while still allowing the scissor action to clamp/release it from the hitch, was designed and manufactured.
• A locking mechanism was devised which allows keyless fold-down but prevents removal from the hitch without unlocking.
• An illuminated number plate mounted on a custom light-board was added.
• Lockable nuts attach both the wheel and lightboard to the rack, preventing unauthorised removal.

An early concept image showed that with the space saver spare wheel one bicycle could also be accommodated. This would be the configuration for the non-off-roader travelling in civilised surroundings requiring more boot space.

Concept conceived

This gain is substantial – the boot size increased by 130 litres by removing the foam insert and false floor. This is an improvement of 54% above the standard volume (as measured by CAR magazine).

As the attachment is not visible in the rear-view mirror, an extension was added to the left upright which is visible from the driver’s position between the headrests and above the soft luggage on the parcel shelf. This enabled the response of the carrier to bumps and dips to be visually monitored during the testing phase, and nowadays to check whether it still is, well, there.

The device has covered in excess of 6400 km, which makes it compliant with the maximum requirements of the American MIL-STD-810F transport vibration specification for wheeled vehicles (for the technocrats: Method 514.5, Procedure 1, Category 4 – Truck/trailer/tracked – restrained cargo).

In addition to the intended advantages in terms of accessibility of the spare wheel, the fact that a full size unit could now be carried and also the gain in boot space, this exercise had another incidental, but useful, spin-off.

During our annual December coastal trip, the kids continuously bump into friends from back home – they practically live next door but are rarely visited during the year – but now they get invited indiscriminately to accompany us wherever, and with gran in the car, four passengers on the back seat is a bit cramped.

Six seater?

Other than the fun factor – the (junior) boot occupant gets a lot of attention from other road users – it’s actually quite comfortable in the back (David was 1.78m tall at the time of taking the picture), and as the going is never far or fast, passengers don’t get time to start complaining. Then again, it may just be that the alternative is too terrible to contemplate – walking.

And the bonus is, when you get to the beach, at least one person has a chair.

Generally, that would be me, then.

JJJ