complicated question since ride comfort is subjective.

big fat sidewall tires can give a nice smooth ride since they absord bumps in road better then lo-profile.

Spongy "boat-like" is comfy and more related to springs and shocks - think 70's caddy - Land yachts if you have bad back that is what you want.

 

For maximum COMFORT in your 231 SL Class, here are my (3) recommendations, and while these recommendations apply to both ABC and NON-ABC models, you'll find them particularly beneficial and effective on Non-ABC-equipped 231's which are far more commonly seen and owned.:

1 - Use 18-inch Wheels/Tires for both front and rear, instead of 19" and/or 20" wheels and tires. There is actually a 17" MB-approved wheel option as well, but I don't recommend going with a wheel quite that small for cosmetic reasons, and besides the only 17: wheel that is 'approved by MB' is quite ugly. .

2 - Choose Non-Run Flat Tires such as the 'Ultra High Performance' Michelin Pilot A/S 3+ (W or Y speed rated). You'll note that treadwear ratings on Ultra High Performance A/S Tires are much higher than with 'Max Performance Summer Tires', so expect the benefit of a longer tread life as well as additional comfort by choosing the recommended tire type. 18" Wheels and Tires will be more resistant to road damage due to having more sidewall, than the larger 19" or 20" wheel and tire options.

All of the 18-inch wheels currently 'Approved by Mecedes-Benz' for use on the 231 SL Class can be found in the link I added below.

http://www.alloywheelsdirect.net/mer.../all/price_asc

3 - Finally, be sure to keep the 231's Suspension Setting in 'Comfort Mode', even when selecting the "Sport Setting' for the transmission, (The E/S/M Selector Button) is the transmission setting, whereas the Comfort/Sport Button is the Suspension Setting. The latter button will cause a much rougher ride when a 'Sport' Suspension Setting has been selected.

 

Comfort is a very subjective evaluation, depends a lot on your personal tolerance and the quality of your local roads, and does obviously come with performance (handling & weight) drawbacks. For maximum comfort, the more sidewall profile the better (and conversely, the smaller the wheel), but attempting to quantify the percentage comfort gained against the percentage handling lost is extremely difficult. There is a wonderful video by a professional tyre reviewer that evaluates 3 different wheel sizes with identical tyres on the same car but what he may feel is desirable may differ to your opinion. He also has a good video on the Michelin Pilot Sport 4, 4S and Cup 2 if you wish to see what effect tyre sidewall stiffness has on handling.

 

OK, I appreciate all the comments, but I guess I should try and clarify what I am asking.

I've always known that smaller wheel diameter and more sidewall depth almost always gives a more compliant ride. On my 2013 SL550, without ABC, I had 18" wheels with the Michelin A/S 3+ Y rated tires. The ride was good & quiet, but not nearly as great as the ride in my previous 2004 SL500 R230, which, of course, had ABC as standard equipment. It was pretty much JUST due to the ride quality of the non-ABC 2013 that I sold it last year.

So, I've ordered a new 2019 SL450 with ABC, which is coming in May. The dealer has agreed to swap the 19" wheels & tires for 18's, which is most likely the way I will go. BUT, the idea of doing something crazy like swapping out the stock brakes for the CCB, which would then require at least 19" wheels--if not the GORGEOUS AMG SL65 19"/20" staggered wheels, is VERY enticing, IF the ride quality won't get shot to hell. Anyway, it got me wondering, and again, here is the question, phrased differently:

How much of the harsher ride quality of the AMG 19"/20" staggered wheels, shod with appropriate tires, will be mitigated by the substantial reduction in unsprung weight?

 

My guess is harsher ride due to less sidewall..

unsprung wieght on ride quality is very minimal if noticeable at all... more likelay a plecabo effect..
do this.
DRive it with the 19s when you get it and change out week later to 18s with more sidewall.... you should be a bit happier

 

I have never driven a R231 SL with 18" wheels, so I cannot directly speak about their ride quality. I can however speak about the difference between 19" and 20" at the rear of the car. The 20" forged rear option is for a wholly larger wheel diameter, keeping the exact same proportion of tyre sidewall as the 19". I drive my car daily and frankly believe that there was no change to ride comfort at all. I believe there are others on this forum (Wolfman?) who have swapped to the19/20" forged wheels as well who could perhaps offer their opinion. The change to the unsprung weight doesn't affect ride quality as much as it completely changes the car's responsiveness and handling. No SL is a SLS or a SLR, nor should a SL attempt to behave like one, but even a minor loss in unsprung weight completely changes how a car behaves. The best description of how I felt about my car afterwards was that is was much more nimble and awake than sleepy.

Have you driven a R231 SL on 19" with the current ABC suspension? If not, I would strongly recommend you do so, as the difference between springs and ABC in terms of ride comfort is dramatic. If you find that to be tolerable, from my experience there is no noticable decrease in comfort between that and the 19/20".

 

Not really possible to answer such questions without actually road testing your new ABC-equipped 231 with the precise wheel/tire specs you mentioned and whatever suspension settings you might choose for the test..

I think 19":is risky enough, and with a 20" wheel/tire option you are 'just asking for' less ride comfort and more susceptibility to road damage form potholes and the like.

Only you can determine just how much risk of road damage you can handle, and just how much comfort you are willing to sacrafice or the sake of very expensive 'show car size' wheels.

If your 231 is going to be used as a 'daily driver' then I suggest you err on the side of practicality when it comes to the wheels and tires. A rough riding 231 will annoy you long after you have gotten past 'the wow factor' of a 20" wheel/tire option.

 

 

Finding a 2017 or later SL550 with ABC to test drive is virtually impossible. Finding an SL450 with ABC to test drive IS impossible. I believe that it would almost be easier to find a used, late model SL63 or SL65 with the 19's/20/s wheels & CCB to test drive. I guess if I can deal with the ride quality in either of those, I should be very happy with the same wheels & brakes on my much softer sprung 450. At any rate, I will give the car a good shakeout when it arrives, driving a bit on the 19's and see how I like it. Then I'll decide what to do going forward. Thanks for all your fine advice and information.

 

My SL will be kept in the garage most of the time, pretty much only coming out for drives up and down Pacific Coast Highway, with the top down, on perfect, sunny days, here in South Orange County, CA. No pot holes, no rain, no snow and I have an S560 sedan for my daily driver. As for "show car" wheels, the wheels I am talking about are original equipment on the recently departed SL65 and available on recent SL63 models. Other than the feature of being staggered front to back, they are IMO, pretty tame looking, but I have always loved them, so they would be a consideration. Having greater stopping power and no brake dust, along with what I perceive to be the very good looks of the CCB rotors and calipers pushes me in that direction as well. It's just a fun thing to consider doing.

 

I don't have any experience with 18" wheels on the R231 but had the R230 with 18" & 19" wheels. We have forged wheels on the SL and E63s which also has Carbon Ceramics. SL has ABC which I love (a much discussed topic on this forum).

In terms of comfort, you will NOT gain anything. Simply get All season tires on either 18" or 19" wheels and set the car to Curve mode. This will given you by far the most comfortable ride.
Lower unsprung weight improves handling and the agility of the car. The car will feel much lighter on its feet which is good since the SL is heavy to begin with and the V8 is a bit front heavy. This is a great benefit when coupled with performance tires.

For a blend of capability, performance, handling and looks, I love the 19"/20" forged wheels with Michelin PS4s tires. All-season tires are good on the S-Class but the SL should sport better rubber

 

Your feedback is spot on in regards to the lower unsprung weight. The car with 19/20" wheels and performance tires is extremely comfortable to me but then I also drive in sport plus mode and the car is lowered a bit via a lowering module.
I currently drive the SL with stock 19" wheels and Pirelli Sottozero snow tires (by design snow tires are softer tires); the car feels like a different car. It feels heavier and a bit more work to drive.

 

 

This is probably the most straight forward explanation that I can find on the effect of unsprung weight and the relationship to ride comfort; as noted above, tire aspect ratios, wheel diameters, and suspension type also come into play when making these evaluations:

The unsprung mass of a wheel offers a trade-off between a wheel's bump-following ability and its vibration isolation. Bumps and surface imperfections in the road cause tire compression, inducing a force on the unsprung mass. The unsprung mass then reacts to this force with movement of its own. The motion amplitude for short bumps is inversely proportional to the weight. A lighter wheel which readily rebounds from road bumps will have more grip and more constant grip when tracking over an imperfect road. For this reason, lighter wheels are sought especially for high-performance applications. However, the lighter wheel will soak up less vibration. The irregularities of the road surface will transfer to the cabin through the suspension and hence ride quality and road noise are worse. For longer bumps that the wheels follow, greater unsprung mass causes more energy to be absorbed by the wheels and makes the ride worse.

Pneumatic or elastic tires help by restoring some spring to the (otherwise) unsprung mass, but the damping possible from tire flexibility is limited by considerations of fuel economy and overheating. The shock absorbers, if any, also damp the spring motion and must be less stiff than would optimally damp the wheel bounce. So the wheels still vibrate after each bump before coming to rest. On dirt roads and on some softly paved roads, the induced motion generates small bumps, known as corrugations, washboarding or "corduroy" because they resemble smaller versions of the bumps in roads made of logs. These cause sustained wheel bounce in subsequent axles, enlarging the bumps.

High unsprung mass also exacerbates wheel control issues under hard acceleration or braking. If the vehicle does not have adequate wheel location in the vertical plane (such as a rear-wheel drive car with Hotchkiss drive, a live axle supported by simple leaf springs), vertical forces exerted by acceleration or hard braking combined with high unsprung mass can lead to severe wheel hop, compromising traction and steering control.

A beneficial effect of unsprung mass is that high frequency road irregularities, such as the gravel in an asphalt or concrete road surface, are isolated from the body more completely because the tires and springs act as separate filter stages, with the unsprung mass tending to uncouple them. Likewise, sound and vibration isolation is improved (at the expense of handling), in production automobiles, by the use of rubber bushings between the frame and suspension, by any flexibility in the frame or body work, and by the flexibility of the seats.

Hope that helps!

 

Sure. It's horrible outside now but here are a couple nice weather pics

 

Sensational looking car, thanks for the photos. Now I'm second guessing my color combo--again!

 

I had a 2004 R32 VW that came with 18x7 cast wheels. I replaced those wheels with identically-sized forged BBS wheels that were 6lbs lighter (each). The first time I drove the car with the BBS wheels on it, I had gone less than half of a block down the bumpy road by my house when I realized how much better the ride quality was over those bumps that I was used to with the standard cast wheels. In fact, the improvement in ride quality was the main difference that I noticed. The suspension (especially the shocks) just has an easier time dealing with less un-sprung weight.

 

I'm sorry if I'm misunderstanding you, but are you under the impression that those larger wheels will weigh less than the standard smaller ones? Why would this be true? Unless the AMGs are forged and unusually light, there's not much chance of them being any meaningful amount lighter than your stock 19s...

 

 

Are the rear suspension springs of the 2015 and 2016 SL550 identical? HR lists lowering springs only for SL550 up to 2015, nothing for 2016, 2017 or 2018. I bought the HR springs for the SL550, but I am not sure they will fit my 2016 car. Anyone can help?

 

'15 and '16 should be identical...


I do stand corrected. I left the CC brakes out altogether. Though the added cost would be heinous, that big a difference in unsprung weight would definitely be noticeable...assuming you could test drive both setups in an A/B comparison.