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      11-25-2018, 06:54 PM   #7

Drives: 2018 M3
Join Date: Jun 2012
Location: Long Island, NY

iTrader: (0)

437M Winter Tires / General Questions

Please see this document from toyo tires explaining load index.


In general, the load index of the tire refers to amount of weight that the tire will support at a given tire pressure. If you look at the chart on page 29 you can see that changing the tire pressure changes the amount of load the tire can handle.

I did a quick search on Tirerack for winter tires in sizes that will fit the rear 437s. They mostly have a load index of 96-100. It is not necessary to chose a tire with the exact same load rating. In general they're all pretty close and you can easily adjust the tire pressure to compensate. Keep in mind that people run all sorts of different tire pressures without any regard for the changes to the load. This should give you some indication as to the relative leeway engineered into load specs required by the car and tire manufacturers, as well most of us never get close to approaching the maximum carrying capacity of the car. I've not seen this topic discussed too often and it is likely the last thing that any of us look at when buying tires. Tirerack wouldn't offer tires that posed a risk to the vehicle because they didn't support the load.

Regarding the size, the 255 will fit however it will be "stretched" just a little bit. This means that the bead of the tire won't be 90degrees to the bead seat of the wheel and therefore the sidewall will angle in slightly. Some installers may shy away from putting on any stretched tires as there are some risks to stretching tires, though usually it's only dangerous in extreme cases. You can call around and ask or check with the dealer to see if they will do it. The other option is to go with a 265 or stock 275. Tirerack has the LM-32 in both of those sizes. I run these tires and they work great. Put 255s in front and 265s in the rear, 100lbs of sandbag in the trunk and you can pretty much go through anything your front bumper will clear (and then some).

When it comes to all-seasons, they will not work well in any snow more than a dusting and even then not well. All it will take is one unplowed or icy hill and you'll regret it. I've been to Pittsburgh and Have seen some of those hills. I myself would be nervous one those hills and only all-seasons. Any real snow and I would be taking the bus or staying home. Stick with switching to a full winter tire when the cold weather comes.