Stock 4.56 gear w/ 31's. Should I go to 32's?

Maybe Im beating a dead horse but I am new to this tire/gear world. Currently running 265-70r16 on a 4cyl 4x4. From what I've read my current setup has higher power but lower fuel efficiency at highway speeds. Would a tire size bump to 32" improve that fuel efficiency? I live in a city during the winter and countryside come summer so lots of hills and longer road time and would like to extend gas usage over 6 months.

Thinking 265-70r16 in the winter for city driving and 265-75r16 in summer?

Maybe its not worth it! Let me know your thoughts if Im wasting time.

 

That’s a 0.3 inch difference in diameter, if anything my 3rz 4wd I had was a pig and boggy with 33s

 

With 4.56s I’d probably give it a try. I’m on 255/75/17, aka. 32, with 4.30 gears and it feels pretty good.

whether it improves fuel efficiency- maybe? Hard to tell.

 

@RoscoeTT I assume your truck has an automatic transmission?

Comparing diff ratios between autos and manuals isn't apples to apples. The auto has a higher overdrive ratio than the manual. The auto is an A340 with a 0.71:1 overdrive. The manual for the 3RZ is a W59 with an 0.85:1 overdrive. The manual for a 5VZ is an R150 with an 0.84:1 overdrive.

The common factory diff ratios for 4x4 trucks are 4.10:1, 4.30:1, and 4.56:1. Generally speaking, 4-cylinder auto trucks were equipped with a lower ratio than their manual counterparts to compensate for the higher overdrive ratio and for the relative inefficiency of the auto. That's why @0xDEADBEEF has 4.30 gears while you have 4.56 for an otherwise similar truck. That said, the compensation isn't perfect. With the same size tire your engine will spin a few hundred RPM faster than his at 70mph.

What sort of gas mileage are you getting now? If you're close to 20mpg, you're doing just fine.

 

Awesome break down. The biggest issue I have is my sweet spot is 55-65 where the truck can coast easier and doesn't need such high rpm. And thats where I can get ~ 20mpg. When I get into 65-75 I need to run higher rpms in order to keep it moving and it kills my mpg

 

Yes to the a/t question

 

That tire would be 1.1” larger. Only brings down the highway rpm by around 100 rpm. I wouldn’t bother. I also doubt it would improve mpg at all, and it will feel more sluggish. Speed hurts mpg far more than rpm.

 

So what your saying is, I should go bigger. Put some 34's on there....I kid.

 

Yeah, it's a tradeoff. My truck has a 3RZ, manual trans, and 4.10 gears. Toyota didn't switch to 4.30 for that spec until the 1999 or 2000 model year. 31"-ish tires (245/75r16).

It cruises smoothly on the interstate at 75mph, and is efficient there (22+mpg) as long as it's on level ground. 5th gear at 55mph is a slog and barely drivable here (foothills, mountains, 6500 ft above sea level).

I don't see any harm in going up a size. There's no guarantee you'll see improved fuel economy, but lots of folks run 32" tires on these trucks without issue. It's 33" where people start worrying about rubbing. Keep an eye on tire weight and tread pattern as well--both of those can affect fuel economy and highway manners.

If you change tire sizes (or gear ratios), your speedometer and odometer will be affected. A 1" might not be enough to justify re-calibrating, but it will affect your fuel economy calculations.

http://www.grimmjeeper.com/gears.html is nice for experimenting with different tire/gearing combinations. Keep in mind, though, that tire sizes aren't perfectly accurate. Variations in tread pattern, wear, inflation, etc, mean that a 31" tire is almost never actually 31" tall, and two different 31" tires aren't even likely to be the same size. It's a good tool for estimating the magnitude of change, not for calculating the exact change.

 

Again, great information. In the end, I will need new tires this summer so acquiring some quality tires at 265-75r16 will be a good direction to go. Re-gearing would be crazy at the moment. Happy with the 4.56, for now. Thanks everyone

 

Fuel economy will go down, and you speedometer will be off, and actual miles traveled will be off. So take that into consideration when figuring mpg. Running factory ratios will be the most efficient.