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Sorry if this has been discussed before, but I searched and couldn’t find anything.
Does the coupe need XL or SL tires? Mine has the XL, but it shows the SL as an option on Tire Rack. Also, the standard SUV uses SL? Does the coupe really weigh more? I can’t find that info either.
SL vs XL is not the same as the load rating on the tire, so it's not directly related to the weight of the vehicle. The difference between SL and XL tires is that the latter can be inflated to higher pressure and has internal reinforcement. SL has a max pressure of 32 psi and XL has a max pressure of 42 psi. Although, most XL tires these days have a max pressure of around 50 psi. You find the max pressure on the sidewall of the tire. I don't know what the recommended tire pressures are for the GLE coupe, but if they are above 32 psi, then you need XL tires.
Tire pressure depends on the load. Note that there are usually at least two recommended tire pressures. Normal load and Max load. SL tires might be fine for normal load, but probably not for max load. Normal load is when you drive around mostly just by yourself and maybe another 1-2 passengers and not very much in the trunk. Max load needs to be used if you load the vehicle up with people and cargo to its gross weight. You find all this on the sticker inside of the fuel door.
To understand how this all plays together, you start with the load rating of the tire. That's the number before the speed rating letter. The load rating determines how much weight the tire can carry. This has to be greater than 1/4 of the vehicle's gross weight plus downforce, although the front tires generally have to handle more weight as most vehicles are nose heavy. The GLE doesn't produce much downforce when at speed if any, so it's mostly a function of the gross weight. However, the load rating indicates how much weight the tire can carry at max pressure, so in case of XL tires that's 50 psi. At lower pressure the weight carrying capacity of the tire is proportionally less. This is why max load pressure is higher than normal load pressure. In order for the tire to be able to carry more weight, the pressure has to be increased and that's where SL vs XL comes back in. It determines how high the pressure can be and therefore affect the maximum weight carrying capacity of the tire.
So to switch from XL to SL tires is a matter of whether the tire can achieve the necessary weight carrying capacity w/o exceeding the maximum pressure that SL allows. Not sure which SL tire you see as being available for the GLE coupe. I just looked at the 21" tires and they are all XL tires. It would very much surprise me if there was an SL tire that can cope with the weight of either the SUV or the Coupe. Both of these weigh around 5000 lbs. Even my 4000 lbs C63S Coupe uses XL tires, because the max load recommended pressure as something like 44 psi. Way higher than SL's allowed maximum pressure, but my car also produces downforce at speed, so the total weight carrying capacity has to be higher. I haven't really seen SL tires on anything that weighs close to 4000 lbs or higher.
Last edited by superswiss; 08-11-2024 at 07:18 PM.
That was the most informative response. Thank you so very much. The 22” option on Tire Rack show both an XL and SL option. Not that Tire Rack is the authority on any of this. I was just confused. Thank you again.
Not sure what's going on there. That might be a typo in their database. I do see the 22" P Zero TireRack lists is supposedly SL, but if you look at the specs, its max pressure is 51 psi.
Last edited by superswiss; 08-11-2024 at 07:47 PM.
08-11-2024, 04:51 PM
