Is this necessary?

[fgutz3rd]

I s been posting alot guys because I am new to the whole lifted trucks and big tires. I was reading that when you go up in tire size you need to re do your gearing so the truck will run at it’s optimal with the new bigger tires. My 2021 F 150 Powerboost FX4 with a 3 inch lift. The stock tires were 275/65/R18 and the new tires I went with are the Nitto Recon Grapplers LT295 /70 R18 129R E1 BSW. We enjoy taking the RV out is why I went with E rated tires. I found this gear ratio calculator and this is what the results were. Is this really necessary, will my truck perform normal. I managed to get my speedometer within 1 mph under so I’m good with that. So If I do need to make the changes, can I change it using Forscan? Oh truck came with 3.73 gears. Any help would be appreciated.

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[nomarhits400]

I s been posting alot guys because I am new to the whole lifted trucks and big tires. I was reading that when you go up in tire size you need to re do your gearing so the truck will run at it’s optimal with the new bigger tires. My 2021 F 150 Powerboost FX4 with a 3 inch lift. The stock tires were 275/65/R18 and the new tires I went with are the Nitto Recon Grapplers LT295 /70 R18 129R E1 BSW. We enjoy taking the RV out is why I went with E rated tires. I found this gear ratio calculator and this is what the results were. Is this really necessary, will my truck perform normal. I managed to get my speedometer within 1 mph under so I’m good with that. So If I do need to make the changes, can I change it using Forscan? Oh truck came with 3.73 gears. Any help would be appreciated.

I am not sure why- or how- you would modify your gearing for new tires. You want to adjust for any difference in rolling circumference for multiple reasons- but unless you are going extreme I think you should be good to go once that is accomplished.

 

[JIMFOUNTAIN]

Aired up load range Es will help stability and sidewall squirm. Not sure on trailer weight but keep an eye on payload as you will run out of that capacity before you hit GCVW (check driver door placards).

With the 10 speed you will be fine... May not run in 10 or in electric as much but there are a lot of gears to work with. Enjoy!

 

[fgutz3rd]

Yeah man I changed the circumstance and it was still off by 4 mph backwards. Weird but then o kept researching and I saw this post about getting your circumference and multiplying it by .697 and it did the trick. When I set my cruise at 75 mph. The gps goes between 75 and 74. Good enough for me. A question I had was at 75 mph my rpm’s are at 1.8. Is that normal for my truck? What is the powerboost normal rpm’s at 75 at stock?

 

[fgutz3rd]

Aired up load range Es will help stability and sidewall squirm. Not sure on trailer weight but keep an eye on payload as you will run out of that capacity before you hit GCVW (check driver door placards).

With the 10 speed you will be fine... May not run in 10 or in electric as much but there are a lot of gears to work with. Enjoy!

My RV weighs 8500 pounds. I am slowly learning. I have my tires aired up to 40 psi. Should I air them up more?

 

[JIMFOUNTAIN]

40 vs 35 will help your mileage and handling. Makes for a little rougher ride and E sidewalls are generally stiffer than P metrics at a given pressure.

Since they are load range Es you need to be cautious about running them with low pressure. Their rated weight capacity is at max inflation. A P metric tire running at 40 psi (52 max) may well have more capacity than an E tire at 40 PSI (80 max). Check this out:

https://www.motortrend.com/how-to/1611-tire-tips-101-load-range-vs-weight-rating-and-more/

1. Make sure you have enough pressure to handle the load on the tires.
2. Add more air to aid stability as necessary (or just start out "higher.")
3. Don't exceed max pressure on the sidewall.

I always run higher pressure than the door placard as I drive harder than what Ford assumes. Higher pressure wears centers quicker but I offset that wear with higher cornering speeds so wear remains equal. Higher pressures will cut down wet weather handling...... But boost mileage.

 

[fgutz3rd]

So I should fill them to 80 or could 60 or 70 be okay? What did you mean by
40 vs 35?

 

[FirstFord]

I am not sure why- or how- you would modify your gearing for new tires.

You can't modify/change gearing through technology. To change gear ratios, you must physically change the ring and pinion gears in the rear axle.

 

[fgutz3rd]

Yeah I figured that. Now about what you meant by 40 vs 35? If you’re talking about the tires I installed they are 34’s I believe

 

[JIMFOUNTAIN]

So I should fill them to 80 or could 60 or 70 be okay? What did you mean by
40 vs 35?

40 psi you have in them vs the 35 on the door placard.

Do the math so that the E tires capacity match the max capacity by axle/2. That will ensure you have more than enough pressure to handle the trailer load. At 80 PSI the tires will definitely be more capable than the F150 rating. And around town unloaded you can run less pressure.

 

[fgutz3rd]

So I don’t tow my rv every weekend. Maybi ask what would you recommend I run my tires at or if you were in my shoes, what psi would you run your tires if you only towed heavy a few times a year and occasional a couple thousand every now and then with a 16 ft utility trailer

 

[JIMFOUNTAIN]

Doing the math on some P metric tires (2,535 pounds at 44 psi) that were like near original specs you get 2535 lbs * 35 psi/44 psi for a tire capacity of 2016 lbs at placard. Switching to LT E tires (3,195 pounds at 80 psi) and to match/exceed placard capacity you get 3195 psi * x psi/80 psi >= 2016. Solving for x >= 50.5 PSI.

I would consider that a minimum because sidewall flex and friction create heat.. the killer of tires. I think many of us switch to Es and then run them underinflated.... Most would not run P metrics under 35 PSI... yet we put on heavy tires and have them flexing more than the "lightweight" factory tires? Most folks me included never really thought it through....

So if the numbers on your Es are similar to above run 60.. If too much trailer wobble air on up as necessary. Air down to 50 around town unloaded.

 

[fgutz3rd]

I really appreciate the help. Thanks man. God bless you

 

[fordhouston]

honestly i personally wouldn’t worry too much if i was in position. however i would suggest to reset the transmission shifting tables to accommodate your new heavier tires.

 

[fgutz3rd]

And how do I do that? Can I do that on forscan?

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