Thinking of purchasing a new 2016 or 2017 F150 4x4. I'd like to add a mild lift with larger tires. My big concern is not with MPH speedo being off, but more so with the transmission shift points.

The larger tires will be either 34" or 35".

So...how is everyone adjusting for the larger size of tires? Will the dealer recalibrate ECM for new rotations per mile? Aftermarket solution?

I do not want to add a tuner to the truck.


Thanks.

biz

 

I just bought a 2016 and added a 4" Rough Country lift with 35" tires. I do have a tuner but did not notice much of a power drop at all with the Ecoboost engine. the 5.0 does not have the same level of torque as the eb so you may notice it a little more but to be honest, i love my truck now. I bought a calibrator to recalculate the speedo. Shift points are not anything you will notice.

 

The dealer can not adjust for tire size anymore. Hypertech sells a device that is just for making a tire size adjustment, but at $225, it's more than half the price of a tuner.

 

Hypertech is what I bought as well. $230 I think

 

Did adjusting for tire size put it back to near stock in drive ability? Particularly the transmission shift points.

 

Yes. I didn't notice any difference in the shift points.

 

tire size is not part of the shift point calculation. neither is MPH. only RPM, throttle position, and load matter.

 

RPM is affected when larger tires roll fewer times per mile. Therefore the other factors you mention are affected as well.

 

So, today I bought the Hypertech Speedometer Corrector. I measured the rolling diameter of my tire on a level surface and divided by pi to get the overall loaded diameter. It came out to 33.28. The Toyo Open Country AT II Extreme 295/70R18 is spec'd on the website as 34.3" tall unloaded.

I connected the unit and it is very easy to use. Nearly self explanatory. I entered the closest option of 33.25" and then went for a test drive loop of about 12 miles. Using a GPS, I found that the speedometer reading on the truck to run about 2-3 MPH too fast in the 50-60 MPH range. That is inline with what the reading was for the factory tire size of 276/65R18. Ford speedometers have always read fast in my experience (I don't know if that carries over to the odometer though).

Interestingly enough, my fuel economy reading on the dash display tended to read within 5% of where it was with the stock tires. Not satisfied with close enough, I went back to my start point (my driveway) and recalibrated for a 33" even tire size. I ran the same test loop again and noted that the speedometer was absolutely correct. The fuel mileage dropped from 20.2 to 19.4. My average speed was roughly 45-50 MPH.

I am about to take a road trip to New Mexico and I will use the longer distance to gauge how the odometer reads. If the odometer is slow, I'll set it back to 33.25" and accept that the speedometer reads a little fast.

The truck now shifts as it did before, with less lugging on hills and quicker throttle response while rolling. I considered a tuner, but for now this fixes the problem and brings the truck back to near factory drive ability.

 

right, as they should be. people kept asking about a speedo recalibration affecting shift points, but your transmission shift points should never be artificially adjusted to shift at a specific MPH.

 

Nice reported info. Looking forward to the long trip data...


biz

 

Thanks for the Info! I'll definitely be purchasing a Hypertech when the time comes.


biz

 

Just wanted to add...that if you go with a tuner like SCT...I found this useful.

Apparently, if you have a SCT X4...a new update is available that will recalibrate for tire size.

2015-2016 F150 Tire Correction Update - 5 Star Tuning

Just wanted to share this info.


biz

 

I have the SCT X4 and yes, it does to tire size calibration.

 

Are you all saying that it's not possible to calibrate the stock speedometer without some kind of tuner? That seems absurd to me.