PerryB

My truck is an '05 F150 4x4. I now have 34.8" diameter tires, originally the truck was equipped with 32's. If I want to correct the speedo only, and not alter tuning, what is the most affordable way to do it. Conversely, if I wanted a full tuner, what do you guys suggest. I'm taking it in next week for re-gearing and I figured if I'm spending this much I might as well spend a little more and fix the speedo, or maybe spend a little more yet and try a tune.
From what I understand the speedo drives off a tone ring (on the ring gear) so tire diameter will affect it but gearing changes will not. Thanks.

Mod (Ret.)

Cheapest? A used, unmarried tuner. I don't think there's a plug in OBD-II device that would only do simple changes such as updating tire size.

You could pay to have it done; might be cheaper then a used tuner.

RA010223

If your new tire diameter is a size that is a factory Ford diameter you can have a Ford dealer reprogram the computer for you and that will change your speedo and your tranny shift points where they need to be for the larger tire, again it has to be a size that is offered from the factory. I was told 100$ from my dealer, have not done it because mines not off that much.

4x4Fun

If you want to "know" the difference and just drive... https://www.tacomaworld.com/tirecalc? has a handy tool... (I also use "Speedview" [GPS speedo] on my phone plus a BlueTooth ODBII sensor and use Torque [it shows truck speedo and GPS]) and deduct the couple MPH that I need for my current tires.

techrep

iTrader: (1)

Pick up a used Edge and it will correct your speedo and you can enter your new gearing ratio also..and run level 2 tune.

PerryB

Thank you. Is there any particular model to look for?
I read about someone else liking the level 2 as well. Does it work with 87 octane or require prem.? Thanks again.

tomb1269

Are you sure your speedo is off now. I have an 05 with factory 18in rims and ran factory size tires 275/65R18 (i.e. 32" tire) and the speedo always ran 4mph fast then actual. I just changed to 275/70R18 (i.e.33" tire) now my speedo is only off by 2mph faster then actual.

techrep

iTrader: (1)

87 Octane tune and the Edge you need is 15051... you can find them used for $200-$250.. just ensure they have been returned to stock level 0

GB17

I have 35's on mine tomb and my speedo is around 5mph off at 70 and about 3 or 4 off during city. My old truck was spot on until I put 33's on it.

PerryB, if i were you, I'd leave it so that if you ever get pulled over you can say that you didn't know bigger tires made you go faster
I was concerned about it in my old truck and I found the answer to it on one of these forums.. keep searching. But I think that it said all they have to do is hook it up & recalibrate it.

PerryB

My speedo isn't bad, 57 indicated is 60 actual. I checked it this morning with my Garmin, 10 satellites locked so I know it was an accurate number. I want to get it back to the safety margin it originally had. I'll probably bite the bullet and get the Edge.