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California98Civic · 10-18-2011, 01:40 PM

I have long noticed that my speedometer is about 2.5 MPH too fast, relative to roadside police radar readouts and more recently against my Ultra Gauge. I just stumbled across a possible explanation--though I am not sure. Using this calculator I estimated the difference in my car's stock wheel/tire combo with a 5th Gen Civic's stock wheel/tire combo. The difference in MPH readings is about 2.279 lower with my 14" wheels as opposed to the previous gen's smaller 13" wheels. I know the transmissions often just bolt onto one another, and I have learned that most gearing is about the same 5th/6th gen, but the final driven gear is often taller on the 5th gen cars. Did I figure this correctly?

10-18-2011, 01:40 PM	#1 (permalink)
California98Civic Cyborg ECU Join Date: Mar 2011 Location: Coastal Southern California Posts: 6,299 Black and Green - '98 Honda Civic DX Coupe Team Honda 90 day: 66.42 mpg (US) Black and Red - '00 Nashbar Custom built eBike 90 day: 3671.43 mpg (US) Thanks: 2,373 Thanked 2,172 Times in 1,469 Posts	Interesting Civic tech quirk I have long noticed that my speedometer is about 2.5 MPH too fast, relative to roadside police radar readouts and more recently against my Ultra Gauge. I just stumbled across a possible explanation--though I am not sure. Using this calculator I estimated the difference in my car's stock wheel/tire combo with a 5th Gen Civic's stock wheel/tire combo. The difference in MPH readings is about 2.279 lower with my 14" wheels as opposed to the previous gen's smaller 13" wheels. I know the transmissions often just bolt onto one another, and I have learned that most gearing is about the same 5th/6th gen, but the final driven gear is often taller on the 5th gen cars. Did I figure this correctly? __________________ See my car's mod & maintenance thread and my electric bicycle's thread for ongoing projects. I will rebuild Black and Green over decades as parts die, until it becomes a different car of roughly the same shape and color. My minimum fuel economy goal is 55 mpg while averaging posted speed limits. I generally top 60 mpg. See also my Honda manual transmission specs thread. Last edited by California98Civic; 10-19-2011 at 08:32 PM..