RWD would be good for a further reason: wheels will not spin that easily as they do on a FWD. I am considering a 4WD with my project #3 Mini.
Any suggestions which rear axle to use?
The trick bit seems to be getting Miata hubs/brakes onto the Mini rear subframe..
In any small RWD project, Miata bits are good candidates... but they don't have the same wheel bolt pattern as a Mini: Mini is 4-on-4" (101.6 mm), early Miata is 4-on-100 mm. Close is not good enough in bolt pattern PCD (pitch circle diameter).
The wheel mismatch might not matter - a RWD Mini could end up rear-heavy (depending on battery location), and wider wheels might be used in the back, meaning that front and rear wheels wouldn't interchange anyway. As long as you can buy the same style of wheel for both ends, it would be a non-issue.
If you're really going AWD, you're looking at two Leaf motors, or using something like a RAV gearbox and differential, with a VTEC subframe up front and this in the rear:
{all wheel drive rear subframe}
It gets pricey fast.
Even for RWD (not AWD), this AWD subframe kit might be the way to go. It uses the NA/NB Miata/MX-5 rear suspension design, but with custom control arms, presumably to fit the much narrower track width of the Mini. It's easier to understand in context with this
image of a completed installation (toward the front of the car is the top of the image).
I'm surprised that there is so much room under the trunk floor of the Mini to fit this relatively tall suspension - with no installation instructions, I don't know if this requires cutting out the floor above it. In many FWD cars the fuel tank, spare tire, or muffler would sit there... is it just the muffler in a Mini, or maybe the muffler below the floor with the spare and perhaps battery to top? I know the fuel tank is not there in a Mini.
With all that room - enough for a final drive unit (differential assembly) - it would be nice to be able to place the motor and gearbox there, but that's asking a lot and seems unlikely. This AWD kit uses the stock exhaust tunnel for the propeller shaft; it would be possible to mount a motor longitudinal under the rear seat, but the tunnel would need to be enlarged and it would be much higher than the seat base... and where does all of the battery go if the motor and final drive + suspension are taking all this space in the rear seat and trunk areas?
It would be unfortunate to build a RWD Mini for better drive traction with the rear weight bias, then end up piling the front so full of battery that the car is still front-heavy. It would be the reverse of the current silliness of production EVs based on FWD platforms, which drive the front wheels but are rear-heavy due to their centred to rear-biased underfloor battery packs. Of course, RWD with even a slight front weight bias is better than the reverse, and adding passengers and cargo shifts the weight distribution rearward.
I wish they just sold this, but with drivable hubs:
{rear coil-over subframe kit}
Ready-made would be nice, but that's certainly something that can be custom-fabricated by many shops and home builders. It has an interesting feature which mounts the hub carriers with two bolts, one of which can be adjusted to control toe; the same thing could be done with an adjustment at the inboard mount of the trailing arm instead, if you don't want to accommodate their anti-sway bar system.
A common production rear suspension design for FWD cars is to combine the trailing arms into one assembly with a beam joining them at the pivot axis. The middle part of the beam has to be able to twist to accommodate the arms moving different amounts, and acts as an anti-bar. In this design toe is not normally adjustable, as it stays fixed in the as-built condition unless the assembly gets damaged. This is simple to mount (just two forward mounting pivots plus springs and shocks for the whole thing), but not trivial to design because the deliberate twisting must be accommodated.
Early Miata (NA/NB) rear hubs are hard to use with anything other than the stock hub carriers (uprights), because the bearings mount directly into the hub carrier. Modern (so, newer than an NA or NB Miata/MX-5) practice is to use a replaceable hub and bearing assembly that bolts (with four bolts) into the upright - using those makes building a suspension arm easier, as it just needs a plate with the four bolt holes in the right pattern and a big hole for the hub - even U-Haul trailers have used this approach. You need this from something driven, which can be the rear of a RWD, the rear of an AWD, or even the front of a FWD (although these assemblies are more commonly used in the rear). The current (ND) Miata/MX-5 is an example. Of course, none of them will have a 4-on-4" wheel bolt pattern.
