32" Tires/ MPG loss and gear hunting

So I just lifted my truck about 2-2.5" and put 32.1" BFG 255/75/17 C rated KO2s on there with some SCS Blaze10s. I was previously running a 31.6" 265/75/16 load E tire on stock TRD wheels. My new wheel/tire setup is both narrower and lighter than the last setup.

My tires are only 1/2" bigger than the last size, but I noticed on my drive home that the truck is absolutely struggling to get out of 4th (maybe 5th?) gear at higher speeds on the highway. I was getting about 19-21 mpg including on the highway doing 75-80 mph before the lift and tires. Now the truck wants to stay up in the 3-4k rpm range in the lower gears and it is killing my mpg. I can tell that it's not the lift/extra drag - I am positive the MPG loss is due to the gear ratio which seems to have tipped the scales going from a 31.6" tire to a 32" tire.

Anyone else experience this? Will the adaptive transmission "learn" with the new tire size over time and adjust at all to get me down out of the high rpms at highway cruising speeds? Would a tune help? Or am I f----d?

If all you have to say is that I should drive 60, save it lol. That doesn't answer the question.

 

Pretty normal unfortunately. Heavier wheel and tire combo in addition to the size is enough to cause the trans to act up.

 

The tires are lighter and narrower and only 1/2" taller than the previous tires. That's why I'm so confused.

 

I believe the adaptive learning will resolve this in a couple drives. Keep us posted.

 

God I hope so.

 

Gears definitely help. I'm on 285/75/16 KO2s with 5.29s and it probably gave me an increase of 2mpg city and 3mpg highway. Oddly enough the stuff in-between seems worse but that's the nature of ratios. I may get a tune at some point..

Most of what you are experiencing is probably just the speedo/odo being off due to the fewer revolutions per unit of distance. You need to either do a manual calculation and see how far you would actually be going to see correct mpg OR get a speedo corrector.

You can see the % easily by using the Tacomaworld tire calculator

 

Nope. I am 100% certain that the truck is staying at lower gears for longer under the same circumstances with the larger tires. I did adjust mileage for the difference from stock and I still am seeing a 5 mpg loss with the 32s compared with my previous 31.6" tire size. It makes no sense.

 

Not sure how much your ko2's weigh, but i have 285 70 17 load range c ko2 that weigh 53lbs each, i also have 17-8.5 blaze 10 which weigh 21lbs or so each which is around 74lbs per wheel/tire. A stock OR wheel and tire together is 61lb (i weighed mine) 13 lbs each tire doesn't sound like a big difference, but its more than just static weight. the rotational weight of that extra 13lbs is more than the 13 static lbs of weight that the truck needs to push and get going. Bigger tires are always gonna make the engine and trans work harder and affect your mpg. Look into ott tune, it will definitely help with the gear hunting and give you more power

 

"I just lifted my truck and added more weight and rotational circumferance and it's not performing as stock anymore, wat do?"

 

Going bigger would affect mpg and gear hunting. Might need a bit of time for the ECU learning to change over. However, might want to look into getting a tune.

 

Gears will help.
It will never shift and drive like stock.
Every bit larger increases drag and reduces fuel consumption. These trucks are “programmed” and geared for fuel mileage.

Consult with a tuner…..or change gears

 

A few things.

Your new tires are only 1/2" taller than your previous tires were when they were new. But I'm assuming your previous tires were worn out when you bought the current tires. Tires with 40,000+ miles on them that are near the end of their useful life will be about 1" shorter than when they were new because most of the tread is gone. In reality you moved to a tire 1 1/2", maybe 2" taller than what you took off.

That's about 5% taller, and that means both your odometer and speedometer are now reading about 5% lower than previously. You're driving faster and farther than you think. That will throw off your on-board computations as well as hand calculations if not compensated for.

I don't believe for a second you were actually getting 19-21 mpg running 75-80 mph with a tire that was already 1" taller than stock. Tacoma's from the factory are often inaccurate, and the onboard calculations are usually optimistic. I'd only trust hand calculated MPG, and only after compensating for larger tires.

Going to a slightly bigger tire will usually be more accurate than the factory size. My guess is that the MPG's you're getting now are off, but closer to being accurate than you were getting previously if you're basing it off the MPG readout on the dash. In reality when you THOUGHT you were doing 75-80 previously you were actually doing 70-75. Tacoma's tend to do pretty good on gas if kept under 70. Once over 70 it's like hitting a wall and fuel mileage will drop significantly. Even straight from the factory with no mods.

I think your lift had more to do with MPG loss than the tires. You have a lot more wind resistance now and that matters more at higher speeds.

Tire tread matters. I've seen lots of people go from a street tire or mildly aggressive AT tire to an aggressive off road tire and lose 3-4 mpg even though they stayed with the same size and load rating. It's the rolling resistance. More aggressive tires don't roll as easily, and that factor is usually far more important than tire diameter or weight.

I don't think re-gearing is going to be cost effective. You didn't go enough bigger to change it much. You may get back a little more performance, but probably not any better mpg's. It wouldn't pay for itself.

 

I think you nailed it Marshall.

 

I've only ever had 235/85/16 (32") on my truck, only thing I notice is it stays in a lower gear for longer than I think it should after cresting a hill. I had the dealer change tire before I took delivery so I don't have a comparable.

 

Maybe you should try an actual quote instead of this. My rotational weight has reduced and my tire diameter increased by 1/2". This should not result in a 5 mpg loss. Thanks for the help...?

 

Yes, this is similar to what I am experiencing. But it is also staying in lower gear too long at highway cruising speeds above 65-70 mph.

 

Its not because the tires are bigger, its because when you lifted the truck you exposed more of the tire to the airstream.
You lifted 2.5 inches and added 1 inch more of tire. So now your front bumper is not covering 3 inches by *tire width and that is a huge amount of flat wall the air is hitting.

My truck got terrible mpg when I lifted 2.5 and added 33s, I put the sport front valance on and my mpg went back up to 20.

 

I wish you were right. But, even when my previous 31.6" tires were almost new (I bought the truck when they had about 10k on them) and certainly close to actual diameter, I was still getting 19-21 on the highway.

Again, no. My previous 265/75/16 size was a full 1" bigger than stock (not to mention the added rotational weight of the e-rated tire). That size was already giving me a speedometer and odometer reading that were lower than reality, both of which I checked using the appropriate methods. And, I know how to check my MPG. My calculations are not based off of the dash MPG, they are real calculations based off of fill-ups and odometer readings, with the new tire diameter taken into account in the calculations.

Let me be very clear: What has happened is that my AT transmission has seemed to hit a "tipping point" at higher speeds on the highway, where it is just refusing to get out of the lower gears and wanting to cruise for much longer at 3-4k rpm. Many 3rd gen owners actually prefer this, but I didn't mind the constant, short-duration downshifts when accelerating that I was getting with the smaller tires. Because keeping the RPM lower for more time was helping with my gas mileage. Now, with RPMs higher for much longer, my mileage is getting obliterated.

I am asking 1: whether other people have had this specific experience with such a noticeable difference in the 3rd gen AT trans shift point after such a small tire change and 2: whether there are any tunes out there that could help bring the trans shift point back closer to where it was and 3: whether the adaptive trans learning system will fix this after some time.

 

Don’t waste your money on gears unless you plan to bump up to 35’s. Otherwise just get a tune. Makes a world of difference. I’m about to put 285/75/16s on and have the KDMax 10.0 tune.

 

I disagree. Not only did I go from a 265 to a 255, but this also just isn't what is happening. I tow a small, 1300 lb fiberglass travel trailer frequently and I know the difference between losing mpg due to wind resistance and added weight and what is now happening. The reason for my mpg loss is the transmission shift point with the larger diameter tires. When I am towing or hauling a lot of weight with the old tire size (which, by the way, is 1/2" smaller than the new one, not 1"), my mpgs do go down, but my trans acts the same. It gives me acceleration with short duration downshifts, only there are more of them when towing or hauling. Now, those downshifts are dragging on for way longer than needed and the truck doesn't want to come out of lower gear.