Speedo question with new rims

ok im just curious as to wether im going faster or slower now. old rims where 275/40/17, and i just got some 275/40/18's. like will my odometer rack up the km/s or will they go up slower.
TIA

Indicated speed should be about 6% less than actual speed.

My calculator says you went from a 25.66" tire to a 26.66" tire, and the speedo would read 3.9% less than actual speed, and you will be adding only 962kM to the odometer for each 1,000kM you drive.

These number can vary slightly, depending on the exact measurements for the specific tires you chose.... not all manufacturers show identical dimensions for a given size tire.

thank you very much good sirs :)