Will a 27.75 diameter fit a roadster? What modifications could be done to allow this?

 

12" wheel spacers.
3" lift kit.
Roll out the fenders.

Or put the tire you have in mind in your wheel well/arch.

 

Seriously, a stock wheel and tire is around a 25.5 inch diameter. What would be necessary to allow a 27.75 tire wheel combo. the wheel is a 21 in Giovanna Drama wheel size: 21x8.5 . What will be necessary?

 

There is a nut on the front suspension mounts I think - this will probably need to be ground down - there is a pic on the forum somewhere.
I have stock rims, but went with the next size up sidewall ratio - on full lock my front tires sometimes rub the inner plastic fenderwell.
Rear tires are OK so far.
I have a slightly smoother ride due to a taller sidewall.
The offset spacing of the wheel will be your biggest problem, what's the offset on the new rims compared to the old rims?
You may have a bone-shaking ride with tires that have a sidewall like an elastic/rubber bands (or whatever they are called in this country).
Try and 'dry-fit' the wheel & tire combo to see if there are any obvious errors (like not fitting in the wheel arch/limitingsteering.

 

Just looked up those wheels on google. not a bad set of wheels!! Same basis as the stock as far as being a flat rim, just 5 spokes instead of 7. especially if you getting at great deal on them. i would go for it.

 

Stock rear is 26" and stock front is 25.1". Any size increase more than 3% (about 3/4 of an inch) may cause problems with the stability control even if you found a solution (and went through all the headache) to increase suspension travel and wheel well spacing to fit it. Speedometer would be of significantly overstated at highway speeds, gearing would effectively be taller, and any appreciable increase in unsprung weight would adversely affect performance. It may look nice when parked but the tires will rub on any type of uneven pavement, and cause more headaches than its worth. Plus you'd have to keep a pretty consistent stagger size differential between the rears and the front, and trying to increase the fronts that much would be an even bigger headache and at best would prematurely wear the cars front end.

 

I have 285/35/19's on back, they are 26.9" in diameter and when the car is jacked up to put them on the tire is just a hair away from the lower front of the rear fender well.