The following is a summary of the key steps in mounting dual rear wheels to the M-06 RWD chassis - in this instance, the Lowride Pumpkin kit that I built up as a homage to the Cars movie Tow Mater.
There is a more detailed series of photos towards the end of the vehicle's build thread here on the TC forum:http://www.tamiyaclub.com/forum/index.php?/topic/75039-wbo2014-you-say-tow-mater-i-say-tamata/
The parts you will need are as follows:
1x pair/set of 1:14th Scale Tamiya Tractor/Truck dual rear wheels - pn. 56518
1 x pair of 'TG10 long' stub-axles - pn. 50808
2 x pair of suitable tyres - note the 1:14th scale truck tyres are around 83mm diameter, so I used 2 pairs of Rough Rider/Buggy Champ front tyres that are 73mm diameter, to fit inside the low-ride pumpkin arches and more closely match the diameter of the front Smoothie tyres I'd fitted to this model.
You will also need some 2mm styrene/plasticard, to extend the wheel-aches depending on your chosen body, plus glue, filler and paint.
Step 1: The stock M-chassis stub axles (TG10) are around 3mm too short for the dual wheels to fit. replacing these with the TG10 Long version (as fitted to the WR-02 chassis such as the Wild Willy 2) gives you the necessary extra thread length, while the drive flanges and pin hole etc. remain in the same position as the original length TG10 axles, and you use the original M-chassis hexes too.
Step 2: Test fitting the wheels you'll notice the inside flange of the inner wheel just touches the wishbone of the M-chassis. Fortunately, since the chosen tyres would sit better on a slightly narrower rim anyway, removing the bead flange on the inside face of the inner wheel (so that effectively the inner flange now becomes the outer flange) makes the tyre sit more square to the wheel, and gives you approximately 5mm clearance between the wheel and suspension.
note. you will also need to cut/trim/grind part of the ribs between the inner flanges away, to create a new bead seat for the tyre (see photo 4 below).
Step 3: Similarly, you will also have to narrow the outer wheels, so that the tyres sit square in the same fashion. However, in this instance, to retain the rim lip detail on the outer wheels, you cannot simply cut the outer flange off leaving the inner, rather you need to cut both flanges off (ie. cut through on the side of the ribbed centre section), and reattach this double flange to the wheel once you have removed 5mm of plastic from the centre section.
note. If you have a lathe you can probably turn the wheels down the sufficient width with a nice clean cut. Alternatively, I used a fine blade hack-saw to cut the outer flanges off, then very carefully sanded the remain wheel down using 120 grit sandpaper on a flat surface. I sanded the remaining wheel section until it was 10mm wide, then glued the original two flange section back on using superglue initially, then filling in the centre section with Araldite for greater strength - see photos 5 & 6.
Step 4: With the wheels glued, and then bolted together (the 2mm allen screws and nuts come in the wheel kit), you can mount the tyres and the wheels to the new axles, using the original wheel nuts. Now you're rolling again on your dually wheels!
The next stage is to extend the wheel-arches if necessary - which it was on my model that uses the Midnight Pumpkin Ford F100 shell.
Step 5: Cut the original wheel arch off the shell carefully - I used a Dremel cut-off wheel.
Step 6: You then need to fabricate a suitable extension to the arch - in this instance I mocked up the with using a strip of thin cardboard (cereal packet), and found I needed a strip 10mm wide to cover the new tyres, and approximately 177mm long from the bottom of each arch. I cut two strips from styrene, and used a heat gun to soften the plastic and bend them to follow the profile of the original arch.
Step 7: The extension strips are then glued in place - initially tacked using superglue, then the joints inside strengthened with Araldite.
Step 8: Once the glue has dried, I used Isopon P38 body filler to smooth any gaps in the joints, and sanded the arches ready for painting - in this instance, I used the salt technique to create a weathered rusted surface to match the rest of the car.
The result (I trust you agree) is a pair of extended arches that look like they were part of the original moulded shell?
I also feel it significantly changes the stance of the whole vehicle by having the wider/ dual-wheel rear end (if you compare the first and last photos below).
Hope that helps!
If you liked those pictures, you should see these...
Ta^Mater (2017: dually conversion)