my car came with 225 55 17 front and 245 40 17 rear,

time to change them ,and i find out that front should be 225 45 17.at least this the manual and all sites says.

i want to know whats the difference between 225 55 17 to 225 45 17.
any difference in the way i will feel how the car goes?

You bought the car used? It didn't come that way from the factory. That's about a 7% difference and if it were really that much the wheel speed sensors would shut off the ABS and light the ABS warning. Go here and input your own data.

http://www.1010tires.com/tiresizecalculator.asp

The rolling circumference of the front tyres is too large. You are approaching triggering the ESP.

I can't comment on the feel but your odometer isn't accurate due to the wrong tire size. I hope you didn't have them on for too long.

Check this out:

http://www.paspeedo.com/calculator.htm

The speedo operates from the rear wheels.

The Mercedes had built a special version I think in 2009 which had placed tire 235/60R17 at the front, 255/55R17 at the rear.http://paultan.org/2009/06/18/w204-c...edition-model/

Yes - but then the tranny tailshaft sensor output would be calibrated in the system to take this into account. Can be set with the STAR.