speedo calibration for larger tires and gear swap

[allgravey20]

I just did a 2"front/3" rear lift adding 33"x10.5" tires and a gear swap (3:73 to 4:10). By calculations the tire size makes my speedo off 5 mph at 30 and 8 mph at 55. My question is what does the gear swap do to that? I drove it to work this morning and it felt like i was going slower and i was getting passed by others. So i was wandering if the gear swap put me closer to where i need to be.

 

[1997XLTRollover]

Your speedo is actually probably pretty close. On my 96 when I went from stock 235/75/15 to a 32x11.50x15 with 4.10's my speedo was exactly what it used to be as if nothing changed. I never did put the 4.10's in so it's off but I changed my speedo gear so it's more accurate.


EDIT: Here you can use this chart. I'm assuming your factory tires are 30's since your truck is an 01. And based on this chart my assumption that your pretty damn close is accurate.

http://i41.photobucket.com/albums/e256/OnlyInMyXJ22/Random stuff/gear_ratio_chart.gif

 

[allgravey20]

Thanks, and yes it looks like i am close. Do you know what those numbers on the chart actually mean?

 

[Rockwood]

Your speedo is actually probably pretty close. On my 96 when I went from stock 235/75/15 to a 32x11.50x15 with 4.10's my speedo was exactly what it used to be as if nothing changed. I never did put the 4.10's in so it's off but I changed my speedo gear so it's more accurate.


EDIT: Here you can use this chart. I'm assuming your factory tires are 30's since your truck is an 01. And based on this chart my assumption that your pretty damn close is accurate.

http://i41.photobucket.com/albums/e256/OnlyInMyXJ22/Random stuff/gear_ratio_chart.gif

That's a little confusing XLT, so you said you went from 235s to 32s with 410s but didn't change to 410s? Did your rig come with 410s or need 410s for the tire swap?

 

[1997XLTRollover]

That's a little confusing XLT, so you said you went from 235s to 32s with 410s but didn't change to 410s? Did your rig come with 410s or need 410s for the tire swap?

haha sorry. What I meant was my original plan was to jump to 32's and also swap to 4.10's. I made the jump to 32's but decided to not put 4.10's in. My truck came factory with 3.73's. After seeing how the truck drove with 3.73's I really saw no need for 4.10's, so decided to just change my speedo gear to correct my speedo.

 

[1997XLTRollover]

Thanks, and yes it looks like i am close. Do you know what those numbers on the chart actually mean?

It's the RPM. I don't know what transmission gearing it was calculated for but as long as your start and end number are close you're good to go.

 

[2TimingTom]

On my '97, after I did gears and tires, I had to swap out my speedometer gear on the transfercase. It's a small plastic gear (each different tooth count has a different color) that costs about $20.

Not sure how the speedo is done on your 2001.

 

[gmanpaint]

For 98+ yrs, the speedo is re-calibrated by a OBD programming tool.

There is no geared VSS in the 4wd T-case, it uses the rear ABS sensor and tone ring.

Any local Ford stealership can do it.

 

[allgravey20]

Thanks guys. I was going to stop by the dealership and get a speedo gear today after work, i guess thats a saved trip!

 

[intelisevil]

For 98+ yrs, the speedo is re-calibrated by a OBD programming tool.

There is no geared VSS in the 4wd T-case, it uses the rear ABS sensor and tone ring.

Any local Ford stealership can do it.

My local dealer "Can't do that, we have to send it out. It'll be about $300". I love their Parts department, they've helped me track down all sorts of odd parts. The Dis-Service department is out to lunch . . .

So I bought the piece of service equipment (that my local dealer probably has sitting around collecting dust) and fixed it myself! eBay to the rescue.

The good thing about the way our 98+ work, the tone ring is bolted to the ring gear. If we only change gearing we don't have to recalibrate. On the other hand, when we change tire size we have to play with the computer.

Good Luck,