Running 35x12.5x18 currently, but will be going to 37x12.5x18 when tires wear out

Speedo is off 3mph at low speeds to 6 mph at high speeds.

What is best method of speedo correction?I've already got a Xcal II that I use for my SLR tunes. It'd be nice if I can just use that. Especially as I'll be upsizing tires again and at tax time regearing to 4.56 gears with locker and true-trac up front

TIA

 

The best way is to adjust the tire size programming in the ABS module. The dealer can do that. I've heard that some programmers can do that but I don't think I've ever seen it really verified. Someone with AutoEnginuity can do it.

 

dang it...I searched FTE for an answer, but can't find a 100% answer

guess I'll just wait and save my $$$ for when I throw the new gears and tires on the truck. no point in spending money twice

 

I'd contact Superlift and see if they have a Truspeed unit that will work on your truck.

TruSpeed™ Speed Sensor Recalibrator · Superlift · www.superlift.com

The dealer adjusted the speedo on my dads truck when he went to 33" tires. I have 33' tires also and never adjusted it. His reads about 1-2 mph faster than actual speed and mine is spot on.(Verifyed by 2 GPS units and a roadside radar) They set them fast from the factory. The dealer told him they can only adjust for up to 35" tires. That was some years ago and on a pre-04' truck so things may have changed.

 

I'm 95% positive a Scangauge II can do it...but I've never tried it to see how well it works.

 

It only takes 5 mins to reprogram it, from what I remember on my 2000. Can't hurt to ask the dealer what the cost is, they may even do it for free.

I believe if your speedo's off, your shifts are going to be off too. I remember the shifting on my 2000 was horrible when I put the 37's on, had it reprogrammed and all was well.

 

For the money you will spend at the dealership I would just get AE. I just got AE a few weeks ago and used it to access the ABS module to make the changes on my truck. I was having the same issue due to my 35" tires. Plus you can do tons of other stuff with AE. I found the best price through Riffraff when I bought mine.

 

Absolutely the best way is to reprogram the ABS module, either at the dealership ($$$) or with AutoEnginuity (better option, very useful tool). I wouldn't spend money at the dealership or on a TruSpeed, put it towards an AE or find someone local that has one and is willing to help you out.

 

Hadn't heard of the AE thingy. I'll look it up. I hate Dealerships, so this would be right up my alley

Thx

 

I've recalibrated my ABS module with my AutoEnginuity, it's a piece of cake. Plus, to get it accurate I had to use like 33" for my 35" tires (not sure why, they were low on tread maybe). Doing it at a dealership, they would do it once and charge you and you'd probably have to pay again to redo it. AutoEnginuity is a very useful tool considering all the diagnostics it can do.

You might even check the classified section for a used one. Some people sell and buy a new one rather than pay for just a software update if they're a few years old. I'll probably be doing that in the next year or so to upgrade to their pro-line model.

 

Subscribing im upsizing to 33" tires soon and i want my speedo to be accurate as can be.

 

The other benefit of going with AE is that not only will you have access to tons of diagnostics for your truck (with the ford enhancement) but you will also be able to do the same on any other ford vehicle.

 

You do not need to correct the speedometer when you change gearing. The signal is taken off of the ring gear, which always turns 1:1 with the rear wheels.