i have a 97 EK hb with a civic Si speedo in it. tires are 205/50/15s

why does my speedo show me a speed of 70mph when i'm actually travelling at 60mph (according to gps). the difference in speed is approx a constant +10mph.

and for some reason my trip + odometer suddenly got an attitude and stopped working after i put in a full tank of gas and reset the tripmeter.

i have read and calculated that the increase in tire diameter from stock 185/65/14 to my current setup will only affect about 1.4% or so of my speed. (about 1mph on normal speeds)

VSS problem? or is it just possible to recalibrate the speedo to make up for the 10mph gain? i don't know how it was before.. i just got the car and found out that the speedo was funny cuz i was going too slow on normal roads. haha.

thanks for the help guys

 

at 60mph you are really doing about 59mph......... at 35mph you are doing 34.4 mph........ i would take it to a speedo shop and see if they can fix it... that would be my first stop

 

but with comparison with the GPS, i'm constantly doing +10mph across the speedo. is that supposed to be happening? or is the speedo in need of some sort of recalibration?

 

Silly question, but the possibility is there... have you had the needles off?

If not it sounds like either your speedo is going bad, there is a loose connection somewhere, or your VSS is going bad.

NOTE: loose connection could be anywhere, screws on the rear of the cluster, in the VSS plug or anywhere in between.

 

Yup, it's a mechanical problem of some sort. The difference in tire sizes cannot account for that large discrepancy.

 

hmm i just got the car and it came with the civic si cluster in it installed. the previous owner said that he used to take it out and fiddle around with it but it's never done this to him before..

will check the connections on the VSS and the back of the cluster and see what's up. hmm, but is there a way to CALIBRATE the speedo? i don't think so right?

 

about the only way to set the speedo needle without expensive equipment is to do this...
pull cluster, remove clear plastic cover, pull speedo needle off.
Reinstall cluster without clear cover.
Drive car beside or behind another car on the highway at a known speed (cruise helps a lot), reinstall needle pointing at that speed as you drive that speed.