Speedo is off.... what can I do?

[MO-KAN SHO]

Okay, I know this is common, and actually rather minor, but at highspeeds (read 75mph) my speedo is exactly 5mph slow, so I get tickets for 80mph instead of 75 which makes a rather significant difference in the amount of the fine. jpshakeh

Is there I anything I can do to correct this? It seems I have a habit of forgetting about the little inaccuracy until the trooper tells me he got my at 5mph faster. doh

TIA...
Ben

(And if this should be in a different forum, say so... wasn't sure where the best place was.)

 

[Slo-Sho]

What is/are the size(s) of your tires?

 

[Ishodu]

I remember seeing somewhere on shotimes a procedure for adjusting the speedo. One that Josh T had written up you make adjustments to the clock spring on the speedo itself. You would get a better explanation if you find it there than I could explain it right now.

 

[SHOZ123]

Take the clear cover off the IC and pull the speedo needle off, replace it just barely so it is easy to take off again. Get a stop watch and find the interstate.

Play with the cruise until you are going 1 mile every sixty seconds as measured by the mile post and stop watch. Then put the speedo needle at 60 miles per hour.

 

[drdave]

That would solve the problem at hand. But I have noticed on both my 90 and 93, I loose about one mile for every 22.5 driven. So over the years, I have actually lost a bit of money filing my mileage expenses with my company.

 

[Ishodu]

http://www.shotimes.com/php-bin/modules.php?op=modload&name=News&file=article&mode=thread&order=0&thold=0&sid=134

 

[MO-KAN SHO]

Not sure what the tire sizes are off hand, can find out in the morning. What should they be, do you know?

Thanks for the help... if the tire sizes are right, I know how to take care of it now, which I greatly appreciate.

You guys rock. thumb

 

[sdpatt]

The original equipment manufacturer (OEM) tire was the Goodyear GT+4 in the 215/60VR16 specification. The overall tire diameter was

(215mm x .60 x 2) / 25.4mm/in + 16in = 26.16in

The 225/55-16 is a replacement that is very close to the original speedometer calibration.

A 225/60-16 tire is the largest that will (almost fit) a gives a 26.62in diameter. That results in a -1.35 mph error so the problem may be within the speedometer head.