Can you also confirm the wheel-rim widths and wheel-offsets, associated with the various wheels and the rear wheel-arch's inboard & outboard clearances, with the various wheel and tyre combinations!?!
Even with a 185/55 R15 tyre on a 5½J x 15 inch alloy wheel, with a nominally 31 mm wheel-offset, there doesn't seem to be much rear wheel-arch, outboard clearance, on my 1974 Triumph Toledo 1300 "HL".
I don't think this is really the place for this question to have been asked, surely "Dolomite Related" is more appropriate,
anyhow the MGF steel wheels are 14x5.5J. Offhand I don't know the offset but will try measuring it tomorrow.
What I can confirm is that these wheels with 185/65 tyres give clearance on a Sprint (and in fact fill the arches better than Sprint alloys).
http://www.mgf.ultimatemg.com/group2/su ... he_mgf.htm
Such a question had been posted in the following thread, but so far there has been no response:
Board index » The Triumph Dolomite Club » Dolomite-related [Start here!] » MGF WHEELS
I am not trying to fill the wheel arches, but ensure appropriate clearances between the wheel & tyre assembly and the adjacent wheel-arches & suspension components, under all conceivable driving conditions. Using 185/65 R15 tyres, is predicted to give the overall effective engine gearing I seek, whilst also employing 65-Series tyres for minimum rolling resistance, as well as good overall handing and ride comfort.
I've got no measurements to speak of, but having fitted and run MGF 6x15s for some time, with a variety of tyre sizes I can say this:-
On the front they fit fine and work with either 185/55 or 195/50s. No interference detected under any conditions, even with the suspension lowered beyond the realms of reason (this was not deliberate, at one point in time when my new springs were bedding in and settling, I let it get VERY low before resetting my ride height adjustable shox)
The rear is a different matter, I tried the car initially on 205/50s and these interfered rather badly with the outer arch, even at stock ride height or a bit over, though they missed the inner arch by the narrowest of margins. I have now settled on 195/50s. These still interfere with a standard arch a bit under extreme cornering conditions. Rather than go any narrower on rear tyres, I gave up at this point and turned up the rear arch lips. Several folk have asked why I didn't try the 185/55s that I had available on the rear. The simple answer is that it never occurred to me to try! And now trying is pointless because I have turned up the lips and all is well!
Being a more performance oriented soul, I have not and would not even consider a 185/65 fitment as it permits too much sidewall roll for safe high speed cornering. For your application though, I don't see why it wouldn't work, profile has no significant effect on width. If it will work with 185/55s on the rear,, which others have reported it will (just) then it SHOULD be OK on 185/65s.
However, I would suggest that a 185/65/15 has a noticeably bigger rolling radius than a 155/80/13 (Standard Toledo size) or for that matter a 175/70/13 which is standard Sprint size. Which will probably upset your speedometer and odometer readings.