[SantaCruzer]

Is this just a bad idea? I've been searching for a while and finally found a late '21 at a pretty good price, but it's got a 3.31 ratio. My plan has been to throw on a ~4" lift and 35 x 12.5's. What can I expect from this setup? I live in a really mountainous area and often road trip over mountain passes fairly loaded, but also head into the bush here and there. Up to this point I haven't done any towing...not sure that I plan to.

 

[SantaCruzer]

Okay so I did a bit of reading and found that going with a 34" might be a bit better but will reduce the gear ratio to 3.10. More difficult pickup and faster top end speed, right? As far as speed while climbing long mountain passes, how will this ratio play out with the 10-speed and 3.0? I read that the 10-speed in 3.31 is like a 6-speed in 3.73. If I could find a truck with 3.55 I'd go for it but the 2021's seem to be few and far between.

 

[EDank]

I’ve done the larger tire and lift kit thing in the past. Sometimes it was successful sometimes not. If you are not going to do anything with your truck other than drive it unloaded and not tow anything it will work. You will need to recalibrate the speedometer. Fuel MPG’s will tank just as they do when towing. This 3 ltr engine has the torque to get you moving. It’s not going to be as quick as stock. But it will go.
That said if you plan to off road or tow or use the truck to actually carry anything more than some groceries keep your tire size closer to stock. This engine and transmission package was designed to deliver the most the way it came from the factory. It’s not like it’s Big brothers the 6.7 ltr engine. In the end it’s your truck. How you want to live with it is your choice. I’d love to do a leveling kit and a set of 315-70-18 tires on my truck. But I tow a lot. And I really enjoy getting 26-32 mpg day in and day out. I was lucky my 21 came with the 3.55 gears in the rear ends. The lower gears help towing.

 

[SantaCruzer]

I’ve done the larger tire and lift kit thing in the past. Sometimes it was successful sometimes not. If you are not going to do anything with your truck other than drive it unloaded and not tow anything it will work. You will need to recalibrate the speedometer. Fuel MPG’s will tank just as they do when towing. This 3 ltr engine has the torque to get you moving. It’s not going to be as quick as stock. But it will go.
That said if you plan to off road or tow or use the truck to actually carry anything more than some groceries keep your tire size closer to stock. This engine and transmission package was designed to deliver the most the way it came from the factory. It’s not like it’s Big brothers the 6.7 ltr engine. In the end it’s your truck. How you want to live with it is your choice. I’d love to do a leveling kit and a set of 315-70-18 tires on my truck. But I tow a lot. And I really enjoy getting 26-32 mpg day in and day out. I was lucky my 21 came with the 3.55 gears in the rear ends. The lower gears help towing.

Thanks for your input. So I should be looking for a 3.55 minimum, which with 34's would set the ratio to a 3.31. Sad because I really wanted this 3.31 truck to work out.

The road trips I'm taking will load the truck down about 1200 lbs. Its payload sticker says 1453. Apologies for simple questions because I'm just learning about all this- Obviously larger tires will decrease MPG with any gear ratio, but what is the reason that MPG decreases with a 3.31 vs a 3.55 when loaded close to max payload?

I would love something like a diesel Rubicon for the trail and these f-150's for road trips. Tough to find the right spot in between the two!

 

[EDank]

I’m not trying to steer you away from this truck. Knowing what I know about this engine/ truck package I strongly recommend it. There are many members on here towing close to the max recommended size trailers with the 3.31 gears. And the trucks preform quite well. I can’t stop smiling when I drive my truck. Great ride comfortable seats. Super fast heat in the winter. And great fuel MPG’s. This 10 speed transmission gears 8-9 and 10 are all overdrive. I tow a 25’ boat that weighs in around 7400 lbs with the trailer. Last year, keeping speeds around 65-67 mph I averaged 14.9 on my 4000 mile trip to Florida and back. The 2013 Cummins /Ram I replaced would average 13.5 on the same trip.
I’m just advising you to go with a more conservative tire size. In the end I think you will be much happier and the truck will preform better.
As for higher gears and lower mpg, it all comes down to the torque curve of the engine. You want the engine operating within its torque curve. Lug it too much and it’s as if you are always climbing a mountain. Not saying it can’t, 420 Ft lbs of torque is way better than a big block gasser .

 

[SantaCruzer]

Oh I still plan on finding one of these! Everything you've described is why I'm looking for one, just maybe not with 3.31 axle ratio. The '21 had peaked my interest because it's a late '21 so it has 4 years of powertrain warranty left....which I now realize could be void by adding the tire size I want anyways.

The consensus among 3.5 EB owners running 3.31 and 35's seems to be mixed. Some say it feels just fine, even for towing...some say it's a turd on the road. That's the only resource I can find to compare it to for now, but did find this interesting. The ratios of the 10 speed vs old 6 speed. The 10 speed really does make a difference, even with a ~3.1 ratio.

From this discussion

 

[navyR113]

I’ve done the larger tire and lift kit thing in the past. Sometimes it was successful sometimes not. If you are not going to do anything with your truck other than drive it unloaded and not tow anything it will work. You will need to recalibrate the speedometer. Fuel MPG’s will tank just as they do when towing. This 3 ltr engine has the torque to get you moving. It’s not going to be as quick as stock. But it will go.
That said if you plan to off road or tow or use the truck to actually carry anything more than some groceries keep your tire size closer to stock. This engine and transmission package was designed to deliver the most the way it came from the factory. It’s not like it’s Big brothers the 6.7 ltr engine. In the end it’s your truck. How you want to live with it is your choice. I’d love to do a leveling kit and a set of 315-70-18 tires on my truck. But I tow a lot. And I really enjoy getting 26-32 mpg day in and day out. I was lucky my 21 came with the 3.55 gears in the rear ends. The lower gears help towing.

Regearing your front and rear differentials would solve all the problems mentioned above and have the truck running like it's still running the stock tires (performance-wise, at any rate).

Gear Ratio Calculator

Easy to use gear ratio calculator. Use our gear ratio calculator to find the correct gear ratio to run when changing tire sizes to keep your stock gearing.

tiresize.com

 

[PeteK]

I have a 2021, totally stock, with 22,000 miles, and I really like my truck. I also like the bigger screen and additional capabilities the 2021 has.

You still haven’t said whether you will be towing anything heavy, say more than 6000 lbs. so, I’ll assume that towing heavy is not one of your requirements. The 10 speed tranny will choose the correct gear to keep the engine in its power band regardless of what wheels or load you out on it, or what you put in the bed. You also can manually select a lower gear if you think you need it, and you can select tow/haul mode which will shift the transmission at higher RPM. Therefore I would not worry about changing the wheels and tires to a larger size even with the 3.31 ratios. I would only be concerned if you want to run big tires AND tow heavy.

 

[SantaCruzer]

I have a 2021, totally stock, with 22,000 miles, and I really like my truck. I also like the bigger screen and additional capabilities the 2021 has.

You still haven’t said whether you will be towing anything heavy, say more than 6000 lbs. so, I’ll assume that towing heavy is not one of your requirements. The 10 speed tranny will choose the correct gear to keep the engine in its power band regardless of what wheels or load you out on it, or what you put in the bed. You also can manually select a lower gear if you think you need it, and you can select tow/haul mode which will shift the transmission at higher RPM. Therefore I would not worry about changing the wheels and tires to a larger size even with the 3.31 ratios. I would only be concerned if you want to run big tires AND tow heavy.

Thanks, I'm feeling okay about it now. I won't be towing, just loading gear up to ~1200 lbs for long trips. I had a chat with the service manager at my local dealership and he had no concerns either. I've bought the truck and it'll arrive in 2-3 weeks!

 

[EDank]

Congratulations on your new truck.