I just replaced my tiny 235/75/15's with some meaty 32X11.50X15's. And of course my question is..... how much is my spedo off by, and how do i fix this if i choose? Any and all help will be greatfull. Thanks well in advance!

Dave Henderson
1989 Ford F-150 SuperCab 4x4 5-spd
300-6 3.08 rears
3inch suspension lift Custom exhaust

 

The 235/75/15 tire is 29.8" tall...or basically a 30" tire. After going to a 32" tire, your speedo will read about 5mph slow at 60mph. So when your speedo reads 60, you're really going 65. At 30 though, you're really going about 33.

To fix it, you need to change the speedo drive gear at the tranny end of the speedo cable. You'll find it on top of the tailshaft of the transfercase. You'll need to count the number of teeth and the gear and get a new one from your Ford dealer. They are color coded and I believe you need one with one less tooth.

 

[font size="1" color="#FF0000"]LAST EDITED ON 21-Dec-00 AT 00:36 AM (EST)[/font][p]Just a small thing I wanted to add- the 235/75R15 tires actually are 28.8", not 30". This results in about a 10 percent difference in speed readings. Your speedo and odometer will read 10 percent slow. Check out the calcs at www.4lo.com for more help. The speedo gear will be on the top rear of the transfer case- very simple to replace. One bolt and it comes out then one clip and the gear comes off the cable- reverse the process to put it back in.

Dustin Siebert
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