[Badass76]

1zhelp: I recently put new tires on my car. Orignaly the car had
P225/75R14's now it has P235/60R14's. They are a lower sidewall, wider tire. Now my speedometer is off. Could someone please tell me how far off it is? it was correct with the old tires on it, so when it said 60mph i was going 60mph. I realy like the new tires, they grip reallly nicely, cornering improved too. but the damn speedo is off.
thanks for your help
Joel:

 

[72cat]

I queried this a while ago and got quite a good lot of replies, very good replies in fact, let me see if I can find it for you.

 

[72cat]

http://www.mercurycougar.net/forums/showthread.php?s=&threadid=3980

Go to this link.

 

[Badass76]

wow that was a fast reply, i figured out my speedo is 8% too fast, wich means when it reads 60mph i'm actully goin 55.2 mph thank you very much!!!!!

 

[texrep]

Keeps you from getting those tickets from John Law... But also effects your odometer.....

just a thought


Don

 

[Badass76]

I though my odometer was rakin up miles a little to fast...... damn it! lol oh well, how much does it cost to get a speedo calibrated???

 

[Cougrrcj]

Bad,

The platic driven speedo gear, the gear that is on the transmission end of your speedo cable is only about $2.50 from most of the parts vendors. Once you determine which gear you have now, do the 8% correction factor and get the gear that's closest to what you really need.

OK, let's say you had 21 teeth on the gear you have now. 8% of that is 1.68 You'd need to get a smaller driven gear to make your speedo read faster, so you'd need one 1.68 teeth smaller. Well, obviously you have to do a bit of fudging, and say 2 teeth. You'd need a 19 tooth gear. This is still going to leave you with a slight speedo error, but you'll be closer than you are now.

 

[greggieatthebat]

Cougrrcj- When you say "vendor"... where do you find a speedo- gear vendor? Do I need a Speedo shop or will an average parts store (like NAPA) work? (I won't bother with Pep Boys)...

 

[69Kat]

Greggie, Mustangs Unlimited has them. (Page 53 in the catalog) Not very expensive. You will need to check out the driven gear on the speedo cable as there are two types and the drive gear in your transmission. once you determine what you have use this link and you can calculate which drive and driven gear to get.
http://www.classictruckshop.com/garage/shopmathgearcombo1.asp

 

[modifiedmark]

Try this guys. http://www.kellnet.com/chambers/speedo_gears.htm