Will an increase in the gear ratio (i.e 3.55 to 3.73) correct the change in the speedometer caused by going to a larger set of tires (i.e 255/70/16 to 265/75/16)? Or, do you have to have the speedometer and odometer reset regardless?

Thanks.

 

crain,
You're actually right on the money with your new tire size and changing to 3.73's. Those gears would exactly make up for your tire change. In 'seat of the pants' terms, it would pull/accelerate just like it did new. I'm guessing you noticed some lack of power when you put the new tires on. I read in another thread that you have a '98 model, right? If so, you can still correct the speedo just by changing a 'speedo gear' at the tranny. I've also got a '98, and I plan on putting 4.10's in it, so I'll have to do the same thing, only using a 23-tooth gear. With 255/70R16's, you should have had a 20-tooth gear, and you'll want to go to a 21-tooth if you don't want to change your rear end gearing to 3.73, and this will correct your speedometer. Let me know if you run into any snags. Happy New Year!

 

fordman3,


Thanks...yours has been the best advice yet. Actually, I haven't changed the tires yet. I am trying to get educated on what I need to do before I do it. I like my 98. I brought it used with 40K miles...great truck. The fit and finish of the F-150 is amazing. I don't know why others are buying Toyotas and Nissans.

I am looking to add a 3" body lift (once I can find someone to do it) and 285/75/16s tire. That should give me 32 inches for a much bolder look. I believe 285/75/16s will fit on the factory rim. If not, I need more money. With the 32s, I will have to go at least 4.10 on the gears.

Thanks for the help.

 

Hey,
I have 3.73's with 305 70 16 and they fit on no problem. The tires bow out a little bit but it looks great. The power did get a little sluggish, but not enough to worry me, espically since I dont tow.


https://www.f150online.com/galleries...=1467&anum=231

 

FordMan3, where did you find a 23 tooth speedo gear? I checked with a Ford parts dealer and they said the highest they have is a 21 tooth. I have a '97 F150 w/3.55. Original tires where 235/70r16 and I went to a 265/75r16. I was stopped by a cop saying I was going 78 mph when I had the cruise set at 70 mph.

 

Actually, you need a smaller gear. You should get a 19 tooth gear. I did the same tire change from a 235/70/16 to a 265/75/16 with a 3.55 gear.

Stock VSS gear was a 20 tooth. The 19 tooth one brought my speedo and odo back to normal.

 

Thanks. I pulled mine first and found it to be a 21, so I decided to go with a 19. I haven't put it in yet.

 

WhiteStallion,
Actually I haven't found a 23-tooth gear yet! I bet I've posted ten requests for where some people got theirs, and so far nothing. I do keep getting told there is one, though. I'll keep looking.

MitchF150,
You got me on that one. I got my logic backward. If you're increasing your tire diameter, you're essentially raising your gear ratio (3.55 to 3.08, for example). To get back his original torque, 'crain' would have to put at least 3.73's in to make up for the tire change. If he didn't want to do that, and just correct his speedo, he would have to put in a smaller VSS gear, not bigger like I said. I guess I'm always in the 'gear-it-down' mode of thinking. I can't wait to put my 4.10's in, and I bet I've been hauling them around for over 6 months.

If anybody can tell me where I can get a 23-tooth gear, PLEASE let me know. I've gotta have one before I install the 4.10's, and I just can't wait much longer. Thanks!

 

I have 1997 F150 Supercab with a 4.2L V6 manual tansmission. OEM tires are 235/70/16. I just replaced old tires which were 245/75/16 with 265/70/16. I am know my speedometer is off and I can replace the speedo gear to compensate.

What options in transmissions came with the V6? I did not find the gear ratio on driver side door edge, but I'll check again.

Can I change my gear ratio to correct my speedometer also and if so what additional benefits would I get with this.

Thanks