What max size of tires I can buy on W124 200D,1991 year?

That depends, are we talking about max size for stock wheels or max size that will fit under the chassis without major mods? 205/60/15 is about as much as I'd stick on an OEM 15x6.5 wheel, maybe 215/60/15 tops. The chassis itself will only go for 225/50/16 or 225/45/17 if we are getting new wheels and tires.

Hope this helps...Lee

A 205/65-15 will fit no problem, but as it's slightly taller it will throw off your speedometer a percent or two. Good luck!

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Not to mention the 205/65/15 will also act as taller gearing, hence hinder acceleration. 205/60/15 was OEM Sportline size. 205/60/15 will not change your speedo/odo any significant amount. 215/60/15 is actually slightly taller than stock but not enough to make a significant difference. To really nail down specifics you may want to visit Tirerack. They have a ultra-complete database regarding Benz fittment. My recommendations are 205/60/15 for keeping the OEM wheels, 225/50/16 for getting wheels and tires.

Happy Motoring...Lee