Still Dreaming: All4 R55 MINI
flatisflat last edited by flatisflat
In this edition, we'll discover how simultaneously easy and complicated this conversion would be mechanically.
Specifically: the subframes.
Section 4. The Front Subframe
In the first part of the 2nd installment, I got into the front end dimensional differences between the 2nd gen Countryman (R60) and Clubman (R55) and reviewed how much of a part each individual frame/suspension bit was playing in that equation.
We were left with 0.8" inches needing to be taken up by either the subframe pick-up locations or the LCA length.
Well, comparing realoem.com diagrams for each, I believe we can rule out the subframe.
While it may be difficult to discern which subframe is which, I overlaid the two diagrams and there appears to only be one subframe pick-up point that changes its location in space.
The R55 pick-up point is the one further away from the subframe main 'beam'. The more I looked into this, the more sense it made. The R60 is designed with a slightly larger tunnel to better accommodate both the driveshaft and the exhaust piping. This narrower subframe plate -- and thus pick-up point -- on the R60 is a reflection of that increased tunnel width.
Separate from that, the R60 rotates its engine mount pick-up orientation 90 degrees. The other major subframe modification comes at its center.
Here you can see both the rotated mount pick-up, but also the changed 'crossover section' stampings.
These aren't the best view of what all is going on, but the gist of it is this: clearance.
While on the R55, the exhaust makes slight bends to run under that 'crossover section', the R60 All4 doesn't take that same liberty with the driveshaft, unless they were to sacrifice ground clearance / packaging:
Here you can see that the transfer case output is still relatively 'high and tight'. The R60 subframe 'crossover section' is revised in a way where the rigidity and support of that structure is shifted upward and around that cavity (more on that in a second), thus allowing for another inch or two of clearance to let the driveshaft have its direct line to the rear of the car.
Now, for that cavity:
That's where the steering rack lives. Remember, the mounting points are unchanged between the R55 and R60, and the steering racks are effectively identical between the two cars. So, they simply modified the subframe to 'wrap around' the steering rack somewhat to help create clearance for the driveshaft below, but the steering rack is located in the same 'space' on both cars.
Soooo, the rear subframes?
Again, differentiating between what is what is less important as the fact that none of the subframe mounting points are the same. None. Zero. Zilch.
This also goes for the lateral links.
The links themselves are the same between the two cars, but the mounting points for them between the two subframes change.
Referring back to that Edmunds article, the rear track width of the R60 is 3.6 inches wider than the R55: there isn't a fender flare in the world to make that look alright on my car if I tried a straight-up switch -- never mind the fact that the geometry would get screwed since the trailing arm pick-up point wouldn't move, so the angle of the trailing arm would be significantly different. I would have rear toe-in for DAAAAAAYS.
The solution? I've thought about this off-and-on for a few days now and I think the only way to go about this is to have a custom 'hybrid' subframe built. I need to be able to retain all my OEM pick-up points, but then have the middle section modified to incorporate the front differential mount and enough clearance for the diff as well.
You might say, "just get custom adjustable lateral links; that should be cheaper than a custom subframe", and you'd be right, but that alone doesn't fix the issue of all the subframe mounting points being different.
Then there's this elephant in the room....
That's the differential rear mount ...moustache bar... thing...
Between that and the differential, I'm pretty sure I'm losing my spare tire well. I have thoughts on being able to create a new mount for the spare donut in the area of the trunk under the false floor, thereby sacrificing overall trunk space but still being able to carry a spare. But that's altogether kinda small potatoes in the grand scheme.
As for the custom subframe, I figure: get a used R60 All4 and R55 rear subframe; drop them off at a fab shop / metal worker; tell them what I need and then give them plenty of time to measure twice / cut once / weld -- perhaps even before making the big donor vehicle purchase to facilitate the rest of the conversion...hhmmm....perhappity yes.
TL;DR: front subframe swap good. Rear subframe swap bad.
And that brings us to the conclusion of this installment. Thanks for stopping by, Hyphen!
pip bip last edited by