I am absolutely sick of this. I had to return to stock for a dealership visit and re-uploaded my circumference of 2556mm apparently is way off.. I have 33x12.5/20" Toyo M/Ts. That is the posted size on the tire. I hate that there is not a metric size which would make this loads easier. Most say they are the same as 305/55/20s but that is not enough for me. I am trying to get my mileage and speed/rpm spot on.

The tires have almost 50k miles on them, because of the low treads, and the vehicle weight, they measure a total height of 31.80" I would say, just shy of 32"s. The 12.5 is still on, and the rolling distance test with tape came up to 99.15/16"s. Just one cm from 100"s. The book says to multiply the inches in the rolled distance to 25.4, which gives me 2540mm.

Now, I go down the road and get to 70mph, i'm turning 1890 - 1905rpms. Way off, stock tune it does 2000rpm at 70mph. Before hand of returning to stock it usually was 1960rpm @ 70. What I don't understand is why with the correct math, why is it not correct in the gauge cluster??

I found an online calculator that told me 33x12.5/20 = 318/52/20. I did the steps in the book to figure that out and came up with 2634mm. 94mm higher than what the math gave me. The rpms were about the same at 70mph! If anything maybe a little lower even, by 20rpms. What gives? I made sure it is set at 3.73 ratio and have only adjusted shift points and idle rpm upped 50 just for a little idle sound.

There is just no way a 2007 5.4L 4wd with the 4r75e and 3.73s can turn that low of rpms at 70mph, I feel like I am not at the full speed of 70mph and am adding more miles than I am actually putting on! Any advice?

 

Do you have access to a GPS? GPS will give you TRUE mph.

Just keep tweaking the tire size input on the tuner until mph matches the GPS's mph.

 

There is an even easier way than that.

Enter a TS of 2000.
Clear both the truck and GPS trip meters
Drive 20 miles
Use this equation:

GPS miles/Truck milesx2000= new TS

 

I do not own, or have access to a GPS.

 

No smartphone, Darren? I thought all you young pups had smartphones.

Has this just started happening or have you had this problem since you got the new truck?

Edit: Never mind. I see now that it just happened since returning from your trip to the dealer.

It probably doesn't matter now, but did you try to 'load previous settings' when reloading your tune(s)?

 

No problem. Since you have access to the internet the next easiest and accurate option is to go to google maps or mapquest and plot your exact route from home to work (or work to home) and get the exact mileage. 1/10 of a mile will be plenty accurate but it needs to be at least 10 miles from start to stop. Use that number instead of the GPS mileage.

 

^ ^ Longshot is smart.

 

If you don't have a smartphone, don't you have friends or relatives?

I have an Android, and I have a free app that gives me a speed readout.

 

It's like everyone is supposed to have one of those things now. I refuse to buy them because of the fragile, tiny screens and lack of buttons...and watching college students literally walk into trees, benches, buildings, cars, bicycles, etc. because they were trying so hard to read size 3 font. People's IQs also drop instantly with them because they don't need to think thanks to the phrase "there's an app for that."

 

I honestly dont know what i would do without my Android, I have everything on it from Google maps to First Aid. Heck, it even keeps my up to date on my sprts teams when im out here in the oil field. Life is alot easier.

 

I would just use what you find online and tweak it. I remember i found mine online and it was like 5mph off so i just changed it a few times and mine is about 1mph off now

 

I have a Droid Bionic smartphone I just don't pay the GPS/ navigation fee. Is there another way to get a GPS with speed readout?

 

download Ulysse Speedometer in the play store.

 

I also use the ulysse speedometer free app and it works great for me.

 

Thanks guys. I was able to snag up my friend's GPS unit and am thankful for it, and I DL'd this Ulysse app on my phone, both have verified they work well and after about 4 re-tune uploads and adjustments I got my speedo correct. Turns out that 2510mm is my tires size. I knew the rpm was too low for 70mph. Thanks for the handy app!