I 'm using Merc E300. One of the trye is always fallen and i decided to change it. But i discovered that the tryres bears 205 /60 R I5 but a friend adviced me to change it to 205/65 R15 for better performance. When i went to buy it a dealer insisted that i should use 195/60 RI5 to him its bigger and has good balance. I'm confused now. Is there any trye gurus pls help.

195/60 R15 is smaller in width by 1" than the stock(205/60R15). May be the tyre dealer is only trying to market the one he has to you. For better balancing and handling performance, you may use 215/55 R15 on wheel diameter 6.5" - 7.0" J. You may go to www.1010tires.com to get more info on tyre recommendation for car brands.
Cheers!

If you go out of the factory recommended tyre size, it will throw off the car speedometer. It won't read the correct speed you will be doing. Also, your mpg may suffer too.

Ikenna

215/55 R15 won't do any harm to the car. It's still within the recommended +/-3percent limit for tyre and wheel change. The diameter difference for 215/55 R15 compared to the stock tyres is +1.5percent while the speedometer difference is +1.530percent. Which is just 0.9miles per 60miles faster compared to the stock 205/60 R15. As per MPG, it won't cost any noticeable difference. The choice is yours

Simply check you car's manual for the right tire size for your car. It's highly dangerous to use the wrong tire size. Don't kill yourself o.

Did you say that tire is always losing pressure? There could be a nail in it, or the valve may be bad. Why not take it to a standard tire service shop and have it checked out? It may save you some money cos they'll usually be able to fix it (if it's not beyond repair).

But I find it rather disappointing when literate guys like you get confused by illiterate spare part sellers who know next to nothing judging by the kind of dumb advice they give you. Google it man!