jetjoe

Did all of that. Using Forscan I made the corrections and also checked the odometer and speedometer several times. Both using the highway markers and timing the speedometer. Also, verified with GPS. It's accurate within one mile per one hundred. (Yes I have lots of time on my hands) In addition to the wheel change, I also have installed the 8" Sync with nav and rear camera, hill assist, the complete climate control with everything working except the obvious items not installed in my basic 150. Made the harnesses myself to aircraft standards. Changed out the speedo with the help of Livinitup. Not much work on my part. He and TexasFording are great go to folks for this. But I have become quite comfortable with Forscan myself.

Just a note about the DTE. Compared to older vintage Fords, this one is amazingly accurate. If it starts out at 500 miles to empty, you can plan on getting just that. I don't understand just what is changed with the DTE tow setting as I'm sure the calculation is based on MPG history. I guess the software folks have zoned this in pretty close. When towing the first sill up is not accurate at all but the second is very close.The fuel level transmitters must have become much more sensitive over the years.

Back to the original question. I really believe going too large with the tires has a major impact on what you can expect with towing. Correcting the speedo for factory offered wheel sizes is quite easy as the proper correction is readily available. But I see some guys with wheels that appear to have come from a front end loader dragging a ten foot trailer and a Bobcat. In this case, all bets are off in my opinion. With my subtle swap a very noticeable change occurred. Going too large has to put substantial additional load on the driveline and effect the handling characteristics. But, then again, I can't say I've seen a lot of these trucks laying beside the highway. Either I'm overstating or these guys are very skillful drivers! Maybe we need a thread "Who wrecked my truck after installing my lift kit"?

jbuddah1

Thanks for the simple explanation. Let's assume this scenario if you will.

I upgrade my wheels and tires and experience a 5% decrease in revs/mile. If I don't change my gearing, how much power/torque will I lose?

Ultimately, I'm tring to understand how my new revs/mile are going to impact my towing capacity. How many lbs of capacity can I exepct to lose from my wheel/tire change?

henfield

Your engine will not produce less or more power as a result of the new wheel and tire combo. That doesn't change.

However your effective gearing will change if you go for a larger or smaller overall diameter tire.

EG: Stock diff ration 3.31. If your new tire has a ten percent overall increase in height, that will be like changing the rear differential to 2.979. If you go smaller overall diameter by ten percent, thats like going to 3.641 final drive ratio.

Which is why, if people want to go taller on tires they opt for a "lower" (Numerically higher) differential ratio. to compensate.

What this doesn't do is account for the effect of heavier wheels and tires on braking etc.

mass-hole

I didn't find that it affected towing for me all that much. I went from 275/55R20's to 275/60R20's and now I am on 315/70R17's. My truck is 2014 Ecoboost with 3.73's. Yes, it has to grunt a little bit more to turn the bigger tires due to the change in effective gear ratio, but it can still do it without much issue. I actually liked going to the 315/70's because the truck turns a little lower RPM's and 5th gear is about perfect. Before, 5th was a little to high and 6th was too low.

mass-hole

The forward force your tire applies to the pavement in a given gear will be reduced by 5% due to the increase in the tires size. You can compensate for this simply by dropping down one transmission gear. Chances are the engine had enough overhead to overcome the 5% increase anyways, and it just means you will have to downshift a little earlier on hills than you might have before.

My tire size increased by almost 8% and I didnt find it that detrimental as my Ecoboost had plenty of spare torque to keep the larger tires moving and keep that forward force high enough. The main difference for me was that, where I might have been able to jump up to 6th gear in some low load situations(flat ground, no head wind or a tailwind) with the stock tires, I now pretty much just keep it in 5th gear and dont even bother with 6th. The larger tires dropped my RPM's in 5th to about 2100 at 70mph so it works well anyways.

jbuddah1

Ok so then i can assume it won't reduce my towing capacity? It will however force the truck to work a bit harder whn towing, right? Which would also negatively impaat fuel economy.

jbuddah1

This would be important to me if I were to tow all the time. I'm only considerig wheel change impact when i tow my travel trailer - a few times a year. I'm at the max end of the trucks towing capability now, so reducing it's abilty to tow in any capacity is something I want to understand.

mass-hole

Usually, with a modern half ton, power(or lack there of) is not the limiting factor in towing performance. Most of these trucks have more than enough power to tow their max weight ratings and not worry to much. Its going to be cooling, stability and available payload that you run into first.

What gear ratios does your truck have? And what year and engine?

jbuddah1

2020, 5.3l, 3.23

Boomerweps

Old thread.
Bonus for the OP, he was getting a 2WD, so it’s not that complicated to change rear axle ratios.