15" VS 16" Ride quality
 

Would the ride quality improve if I switch from 15"x7" too 16"x7" wheels?

It would decrease.

agreed.

Depends on what you mean by improve. I went from 15" with 205/55 to 17" with 215/40 and the ride did get a little harsher but ride control increased quite a bit especially in the turns. I guess it depends on what you are looking for. Going up 1 inch and down a few percent in profile I do not think would affect you ride adversely. Just my opinion.

Really? What about cornering and performance? My suspension is not stock any more: poly bushings, Bilsteins, bigger sway-bars. Looking for a firmer and better controlled ride.

Depending on sidewall height. The added unsprung weight makes the ride harsher. .

I assume that you plan to use a tire that would maintain the overall diameter of the 15" tire currently in use. If so, moving from a 15" to 16" would require you to use a tire with a shorter sidewall, which generally allows less sidewall flex, resulting in a tire more responsive to steering inputs. The downside is that the shorter sidewall will result in a rougher ride.

That's correct. I like the more responsive steering aspect.

16x7x20mm VS 15x7x20mm, what would be the best tire size for the 16" wheel? And what are the opinions about the rims: top is 15" and bottom pic is 16" rim?

http://i662.photobucket.com/albums/u...MultiX_out.jpg

http://i662.photobucket.com/albums/u...eminis_out.jpg

On my wagon I went from 15" to 16" with the ultra lightweight CLK wheels. From a performance standpoint, taking mass out of the rotating assy can result in significant improvements. When there is less mass, the suspension doesn't have to work as hard at keeping the rubber against the pavement.

I love the 16's on my SD.

Ride quality is still Mercedes, and cornering and road feel are better.
The combo I am running is almost exactly the weight of the 14" bundt set, so there are no effects from variations in the unsprung weight.

Have not noticed any change in fuel economy either.

I like the look of the top rims, however I think 16" s would give you better handling.

560SEC comparo
 

As you can see, ... at the same time, http://i353.photobucket.com/albums/r.../mini-0491.jpg

I've owned a stock 1990 with 15" tires,

http://i353.photobucket.com/albums/r.../mini-0341.jpg

http://i353.photobucket.com/albums/r.../mini-0221.jpg

http://i353.photobucket.com/albums/r...ade91/0031.jpg





and also a 1991 with 16" tires that are wider profile tires, and the car itself being lowered with eibach springs, and Bilstein HD shocks...

http://i353.photobucket.com/albums/r...e14d0073_m.jpg

http://i353.photobucket.com/albums/r...f362668c_m.jpg

http://i353.photobucket.com/albums/r...5cd3329b_b.jpg



and I must say, there is a very substantial difference between the two.

The stock one, with the 15''s - rides more softly and serenely, but wallows luridly when caned hard into corners.



And the modified one, has a harsher but not annoying, ride at higher speeds, and I took it once, quite briskly into a decreasing radius turn that felt pretty lurid and on the outer edge of control, until I glanced down at the speedometer and noticed the speed - I was going 90 mph!!!! My god that was amazing! :eek:

So that was the car I kept...seen here in its euro clone guise a couple of months ago. The one you saw in West Los Angeles when we met up about a year ago...

http://i353.photobucket.com/albums/r...s/photo_1a.jpg



So for your car, i'd definately go the 16" route; so long as there is no wheel well scrubbing, I think you'd be ok for that beautiful 780 coupe there should be nothing to worry about, but before you do I'd check with brickboard and sweedspeed...

If THEY give the thumbs up then yes, AND thenyou should see about shocks from Bilstein (HD or Sport- though Sport are almost impossible to get in USA I have heard and they are revalved HD's anyway I think)

and then go to the ipd catalogue and order up sway bars for your Volvo 780 if they still have them.

Your car is stunning. I have seen the AMG pentas on a Volvo; looked pretty damn good, not sure how they mounted it.

Don't overlook the difference in tires...I had a Grand Cherokee with 16 inch wheels and Goodyear Wrangler ST tires that had a really soft ride. I went to a stock 17 inch wheel with Michelin of some sort, that really firmed up the ride, minimized understeer too. When they wore out, I put Kumho Solus tires on it, and it wallowed around more on the 17 inch Kumhos than the 16 inch Goodyears, and understeered dangerously.