Will 255/50/16's fit on 16X7" rims.

Don't do it !!!
A 7" rim is way too narrow for a 255 tire.
I've tried a similar combination & it left me with an un-driveable vehicle.
What happens is, the sidewalls contact with the rim gets squeezed, or pulled in.
Result, when you're driving donw the road, the rim wiggles around inside the tire & you will feel like a drunk belly dancer.
For 255's I would go no less than 8" rim.
The max for a 7" rim would be about 225.

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2007 C 230 Sport.

Unfortunately I already bought the tires (Michelin Pilot XGT). TireRack said that their chart indicated that they were OK. I installed them today and have noticed some pulling to the right when braking. Also the ride is a little choppy. Otherwise the car handles great and cornering is phenomenal. I "upgraded" from same tire in a 235/60/15 series and felt it important not to go down on the loan rating. I will try slightly less pressure-perhaps 32 pounds in front and 30 pounds in back to see if the ride smoothes out. The pulling to the right has me the most concerned. If I had it to do over I would get 225/60's.