So I'm looking at upgrading to a bigger tire, and was wondering what kind of power loss I can expect with a 34'-35' tire with the 3.31 gear ratio. I have heard from some people that there is hardly no power loss, and from others that there is significant losses. Anyone have any real world experience with a bigger tire combined with this gear ratio? I'm thinking about going with a 295/70/18 tire size.

 

3.31 here on my 4wd SCrew. I went up to a 275/65/20 (roughly 34.1") in March and have not noticed a significant power loss. Tires weigh about 57lbs each which is roughly 16lbs per tire heavier than stock. The power is still there, but the one thing I have noticed is the truck is not as responsive/snappy from a dead stop. It's not major enough to really complain about.

I will add that I am tuned and calibrated for the tire size. Keeps the transmission from hunting and the tune gave me almost all of my lost mileage back.

 

Running 275x60x20 Toyo's (33x11) and only one inch taller then the stockers. I can tell a slight difference in performance but not bad. I think it dropped the final gearing down in the 3.20 range by going up an inch. I'd limit my tire height to a 285x60x20 (33.5) but thats just my thinking!

 

I run a 4" lift with 305/65R18 KO2's which is 33.6" x 12.

87 P/T 5* tune.

I still find I have tons of power for towing and driving. Not a rocket off the line but no slouch either. I didn't really notice much of a diff going from stock size no tune to 33.6" tires tuned.

Never driven a 3.73 geared truck so I don't know what I'm missing lol.

 

Thanks for the replies guys! I think I will go for a tune first before upgrading to bigger tires.

 

That's a good process. I hate going back to the stock tune on my truck for service. The increase in diameter definitely makes the transmission a little wacky. If for nothing else, the tune is worth its weight in gold just to re-calibrate the truck.

 

I put 34.2" tires on a 3.5 ecoboost with 3.55s and was severely disappointed in the performance. Stock tune though, which didn't help. I was so unhappy that I sold the tires a week later and bought 275/60/20 and took a beating on the others.

 

In my personal opinion, upsizing tires without a re-calibration is like playing a full round of golf with just a putter and no other clubs. Sure it'll work, but your results aren't going to be as pleasurable.

Get it calibrated via a conservative tune and call it a day.

 

There have been multiple threads on this topic. Here are links to them.

https://www.f150forum.com/f38/ecoboo...-tires-317635/
https://www.f150forum.com/f38/ecoboo...egrets-190277/

I myself put on some 285/65/18 (32.6" x 11.2") BFG AT KO2's on my truck. There was a definite drop in off-the-line acceleration. I think the biggest problem is that they are E-range tires. I put an MPT tune in the truck at the same time as the tires, so I can't speak to the tires with the stock gear and tune. I can say that I am very happy with my tune.

I will be replacing my wheels and tires with Raptor wheels and tires. I will run the 3.31 gears and tune for the time being, but I plan to eventually replace with 4.10 gears.

 

3.31 gears, 34x10.50r17 ko2's on mine. They are D load so that helps with weight. It was between them (56lbs/each) or toyo Mt's (70lbs/each) which I have ran many sets of on past trucks.
I'm very happy I went with the slightly narrower and way less heavy tire.
For me the off the line power loss was very minimal, sometimes still break the tires loose.

I also run 5 star and mpt tunes which makes it so I can spin the tires from a stop pretty much anytime I want now.