Why would MB not put the best size tires on the car when they manufacture it? They, engineer the car, build the car, professionally test drive the car, run it in different conditions, run it in the lab for performance and efficiency, etc. They could put any tire on there that they thought was the best one available for it......I mean they are MB. They probably have some of the best engineers and test drive professionals in the whole world.

I understand about winter tires and summer tires and they have to decide on what design is the best for marketing. They might be tied to one brand or another for pricing or performance.... But I have to believe that they put the best size tires on the car when it leaves the factory. Maybe I am wrong, but it is something I don't understand.
I mean MB engineering probably decided the tire size.....MB engineering.

 

It seems that there is a bit of confusion about tire sizes and options for the SL.
First off, while Mercedes installs certain tires and brands and marks them as MO or MOE (run flats), there is no need to use those brands or stay with run flats. Anyone saying this doesn't know what they are talking about (this includes tire shops or MB dealers). Mercedes certifies its factory wheels with tire specs and as long as those tire specs are met (size, speed and load rating), you are good to go from a ride and legal perspective. Mercedes likes to think their tires are optimized from a ride quality perspective but I find that subjective at best. I have attached the official R231 tire spec/wheel list (only in German but you can use translation tools). This is a larger list than what might be available in the US.

Since the car comes only with staggered wheels which results in slightly different wheel circumferences, the cars electronic safety systems and speedometer are designed to manage it without corrections.
In Germany the maximum speed of the car can be restricted when using lower-rated tire (like snow tires).

For Dr. Manhattan: It's a common setup in sports/super cars that the rear wheels are larger in diameter than the front wheels. Wether one likes it or not, there is no way to buy many cars without this wheel setup. Porsche 911, AMG 2 door models , Ferrari, Lamborghini, even Corvettes...

In regards to slightly modifying the tire size due to availability or liking to fill out the wheel wells, that seems completely fine as long as the circumference does not change too dramatically. I would stay within the same difference of the factory spec (<3% F/R). If all 4 corners get larger tires, the concern would be a slightly wrong speed on the speedo and rubbing but that would be minimal on a single step up (i.e. 35 vs 30)

 

If you are leasing the car has to be returned with tires equivalent to those originally installed or you will be charged a sizable fee.

 

Anyone running the Michelin Pilot Sport All Season 4 tires? I keep going back to the Pilot Sport 4S but I'll be moving to NC in a couple months and might run into colder weather. Any help would be greatly appreciated.

 

According to Tire Rack, the best tires for both wet and dry roads would be #1: Continental Extreme Contact Sport ($1015.96)and #2: Michelin Pilot Super Sport ($1170.48). Both, much cheaper than the Pirrellis. To me, handling well on both wet and dry roads in Florida is way more important than wear.
Interestingly, the only one Tire Rack shows handling in snow is the Continental Extreme Contact DWS 06.

 

Vredestein's Ultrac Vorti is a superb tire, especially considering price.

 

I'm a little more concerned about when it's colder.

 

Try this:
https://www.autoguide.com/the-best-h...-you-need-them

Guide to high performance winter tires.

 

I just returned a leased, 2018 S560 sedan. It had non-RFT on it. No problem. At the same time, I took delivery of a new, 2020 S560 and part of the deal was that the dealer would swap out the RFT for my choice of conventional tires.

 

For reference, the MBFS lease return guide for tires/wheels:The following vehicle conditions will result in excess wear and use charges:

• Wheels that are cracked or bent
  
• Wheels that weren’t originally equipped with the vehicle at the time of delivery (upgraded aftermarket wheels installed by an authorized Mercedes-Benz dealership are acceptable)
  
• Rims that are bent or have breaks (regardless of size)
  
• Tires with less than 1/8” tread depth
  
• Tires that have sidewall damage (which includes plugs and cuts), bulges, or exposed cords
  
• Tires that are mismatched: Tires on each axle that are not the same size, brand, model, type and/or speed rating, and equivalent in quality and performance to the original tires
  
• Spare tire and rim (or inflation kit for those vehicles without a spare tire) that are missing or not in operable condition
  

 

No...I meant 295/30-19. That slight change from the standard 285/30-19 is just enough to more or less equalize the front and rear tire diameters.

 

Why?
SL is not 4matic. All RWD Mercedes cars use slightly smaller diameter rear tires (even though they're much wider than front).
SL450 specifically does not have traction issues, say SL63/65 has, so what is the benefit?
There's no run flat 295/30-19 tire (assuming one runs 255/35-19 run flat front).
Finally, 295/30-19 should be mounted on 10" wide rim as a minimum width for safe fitment (yes I'm aware some put them on 9.5", but I wouldn't).