i was crusing down the highway at 75 one day and look over and im passing a civic whos speedo said 80 so i had my girlfriend follow me in her 08 Mazda 3 stock. while i was crusing at 75 i called her up and had her pace me. she said her speedo said around 80. but whenever i pass those speed checkers that the cops set up it said that my speed was correct. but that was going 35. i have put 18" rims so could that be the problem and it cannot be detected going at low speeds?
2009 WH GXP #129/1829 - 224/236 612 cam, Maggie 2300, 3" pulley, 60# injectors, BAP, Kook's Shorties, Dynotech DS, SLP LM2, CNC heads, 3.70 rear, DSS level 4 axles, Yank 3200, Snow kit, Upcoming mods: HSV Fenders, Lonnies fuel system, ID850's, Forged LS3, HSV center stack, Mav Man carbon, OTTP HX, Kooks LT's, Kooks/Corsa exhaust, full BMR suspension, Camaro 3.27, DSS Level 5 axles, Full 8-rib setup 09 PBM G8 GT 08 LR G8 GT 99 Satin Black Trans am