Does it wobble all the time at all speeds?
As said, a larger, heavier wheel and tyre will exert more resistance on the road and hence your TCA bushes will be more strained. What TCA bushes are you using? What condition are they in? You said yourself, with the thinner tyres on, the wobble "was almost completely gone".
So... your wobble problem predates your modification. How are your TCA bushes?
I don't mean to be rude my man, but not having heard of this problem is like moving from a 500ml bottle of water to a 750ml bottle of water and then getting annoyed that nobody told you the 750ml bottle would be heavier. Fatter wheels offer more resistance, they tramline.. anf MK2 Escorts and Capris (and probably more Fords from the period) have always been touchy when balancing. I have never heard a satisfactory explanation why.
The information about worn TCA bushes affecting handling and wheel wobble IS out there! How are your TCA bushes? Did I ask that already?
Bet that's your problem, as someone said in like the third reply you received. Worn or poor quality inner bushes. Get some HD rubber inners and see how it is.
Problem is though dude, all the bushes are fine, most of them are new or were replaced within the last year. My mechanic has checked all this already you see, and it all checks out.
Sorry if i sounded snippy before, its not personal towards anyone, i am just beyond stressed out and fed up with this problem. These new wheels and tyres were supposed to be a positive thing, a gift from someone who has passed and its seemingly turned into a curse and i just feel like if this was a known problem with putting these sorts of wheels onto a Capri then there should have been some warnings somewhere...that said however:
An interesting development: Yesterday when i was on the phone to Martin we were discussing this problem, and he asked me what PSI was in the tyres, i told him that they were at around 34/35, and he said thats way too much for 205 tyres. He checked his book and said that a 2.8i with pepperpot rims and 205 tyres should be at 28psi. The fact that my car isnt a 2.8 or had pepperpots made no difference he said, so i deflated the tyres down to 28psi all round.
I didnt think it would make any difference (though i have been thinking the tyres were over inflated from day one. I didnt pump them up, the garage who mounted them did) but thought it was worth a shot anyway, what harm can it do?
Well, i took the car for a run down a short stretch of motorway today, got it up to the speed where the wobble usually occurs and.....its barely there!
Seriously, the intensity of the wobble has been reduced by around 85%! Its still slightly there but its minimal, and i can easily drive through it to around 69mph where it vanishes completely!
Before it would come on at 55 and be so severe you'd think the steering wheel was gonna come off, and you couldn't drive through it and it would always be there in some form or another past 55!
So ive come to the conclusion that, a combination of over inflated tyres, my slightly worn bearing (its not making a noise, but my mechanic can detect some play) and i reckon that knackered strut top mount are all contributing to the same problem, and the wider wheels and bigger tyres are just exacerbating it.
Like you say the wider and heavier wheels are just making an already existing problem worse, and deflating the tyres to the correct pressures has helped alleviate it a bit.
Worst case scenario: If once i get the bearing and strut top replaced and the wobble is still there in its present form, i can at least live with it the way it is now. If it is indeed just an incompatibility issue like you say, it has at least been minimised to a degree where its acceptable.
I am beyond happy with Martin for his suggestion, and relieved.