im just wondering if putting 18's on my 98 civic would make my speedometer say i was going faster than i really was and if so how much differnce??

 

14 views... am i an idiot?? has noone ever thought of this before or what?..

 

Since I'm here, The larger the outside diameter of the TYRE from factory fit TYRE size would mean that your speedo will show LOWER than you are actually going.

If you fit 18" wheels onto a car normally fitted with 16" wheels you can simply reduce the tyre profile fitted to compensate. eg: normal size 185/70/16
new size 185/50/18
Well you get the idea!!