Originally posted by Rev. Po-Jay:
It looks like I am walking the line alone! =-) I will consider myself a pioneer and leave it at that. If the little speed monitoring thing by my house is right, my speedo is off by 5mph at 60. My speedo reads 65mph at 60mph. Here is a question that someone may know.
It this an error that will remain constant, or will it be a percentage of actual speed? Will it change with different gear selected? C'mon all you brainiacs, give me input. I don't care if you are not sure, let's do some speculation. I think it will be a percentage based on the Final Drive gear so it will remain a constant percentage throughout the gearbox.




What size rim and tire are you running?

If you are running stock rim and tire then you probably have a piss poor calibrated speedo. I have already covered why the final drive should not change the speedo!
Ask yourself why the Zetec FD speedo gear is the same part number as the duratec final drive?????

Read the part in the sticky at the top of this forum about final drives on OUR type of front wheel drive transmission and why the zetec FD doesn't need calibration.
Yes I know the computer has a slot for it but it isn't necessary.
I found my own speedo with stock tires was off by 3MPH at 60MPH and that was with the duratec FD, so I have no trouble believing that you could be off by 5mph.

BTW, it should be a percentage and not a consistent 5mph.
If you are running the stock rims and tires then you can pull the lens of your instrument cluster and pull the needle off your speedo. Then while having it run a constant speed on the dyno, you can put the needle back on.

I did it on a back road believe it or not! First I calibrated my analog tachometer with the computer scan tool so that 3000 rpm on the tach was exactly 3000 on the computer. Then I calculated the speed in each gear using stock tire height at 3000 rpm with a spreadsheet. Then I cruised in 3rd gear at 3000 rpm and pushed the needle on. I had to do it about 3 times until it was accurate, but that was because I was driving!!!
Anyway, it worked great. Now I am only off by about 2mph at 85mph.

Tom

Former owner of '99 CSVT - Silver #222/2760 356/334 wHP/TQ at 10psi on pump gas! See My Mods '05 Volvo S40 Turbo 5 AWD with 6spd, Passion Red '06 Mazda5 Touring, 5spd,MTX, Black