So you wanna put big tires on your 2.7 powered truck

Guessing you've got a 1st gen and/or 2wd truck?
245/75r16 were OEM size for my particular truck.

 

What size are your current 215 tires (the full number on the sidewall)? That number is just the width in mm, not the height. Going from a 215 to a 245 is 30mm wider and depending on the aspect ratio (assuming 70 for this example) you're height difference will be 70% of 30 mm which would be 21 mm which is less than an inch. Divide that in half since half the difference is above the axle and half below and you're looking at less than .5" taller. If you're currently running 15" wheels and plan to go to 17" then that adds more height and cost.

If your stock tires are 215/70/15 and you go to 245/75/16 then you're gaining around 3.6" of height, but again you need to cut that in half to measure the lift so around 1.8" above stock height.

 

Stock tires are 215/70/15 - think what I am going to do it add a 2" lift to the front and go with 245/70/17s. Read about the black box mod as well

 

Do you know what 17" wheels you plan on getting?

 

looking at

$217 moto metal MO970 17X9 6X135/5.5 G-GRY BLK LP -12MM - MO97079067412N

moto metal MO970 as well as Cragar Wheels but also open to suggestions if you have them

 

I don't know what wheels are available for the 5 lug trucks so I can't be of help.

 

Here is my experience with 2017 2.7 AT.

Previous owner put on 33x10s, heavy bumpers, overland racks, lift. I think he wasn't happy about how the truck ran and sold it with low mileage for a lot less than it would have been worth without the 5 grand in aftermarket upgrades he did (it is not the red truck in my profile - that's my old truck)

The truck ran in 4th and 3rd gear, a only little bit of 5th (1st Overdrive) in hilly country on the freeway (75, max 80mph). Pulling a hill at freeway hill was wide open throttle in 3rd gear at over 5K rpm to maintain 75 MPH. It got like 11 MPG. The larger diameter tires the previous owner installed created a mechanical disadvantage in addition to forcing the engine to run in a lower rpm range for any given gear where it has less torque - a problem in a heavy truck with a small motor. Because driving it on the freeway totally sucked, there could be no road trips with this truck.

I sat down with the Grim Jeeper gear calculator http://www.grimmjeeper.com/gears.html and made a plan I though was straight forward. I'm going to tell you about it, because there were a couple of surprises I didn't count on.

My truck had 3.90 gears from Toyota. I know a lot of people say they have 4.30 gears, but at least in 2017, according to what I oberved it was 3.90 in my AT truck. Doing the speed with a gps and calculating from the RPM I confirmed 3.90s. I changed to 4.88 because it would move the rpm range up somewhat providing a bit more torque while providing a mechanical advantage that is better than stock (around 4.30 would have balanced the larger diamater of the tires and for the engine putting it back to stock rpm ranges). The freeway plan was 4 for hills, 5 and 6 overdrive for crusing at 75/85. 4 and 5 are much closer together than 3 and 4 are, so the previous 5500 rpm hill climbs would be 4500 rpm at worst because the transmission would shift into a more suitable gear for the engine's torque. Totally counter intuitive to put 4.88 in to lower RPM on the freeway, but a six speed AT with two overdrive gears isn't a 1980's classic.

The computer shifts the transmission, not the engine. It is based on sensing the throttle position and speed. So one thing jumps right out - a truck with big tires has a messed up speedometer. The transmission things it is going slower than it is. In order to get into or stay in those higher over drive gears, you have to be going so fast for a given throttle position. If your speedometer is consistenly reading 10mph low at freeway speeds, then you are not getting into or staying in those gears. Since you really are going that fast, you have to increase throttle when your drive at higher speeds to overcome wind resistance. Say hello to driving around with 4.88's and 4th gear with a truck that drives like it can pull a trailer full of bricks, but your ECU thinks your going slower and won't let the transmission shift into the ideal overdrive gears at normal highway speeds. I found I got better MPG if I drive the truck 80+ than 65-75.

The speedometer reading does not come from the transmission, and it does not have a little $20 gear that is easy to change. You have to instal a circuit with a microprocessor that applies a new ratio to the electronic pulses that come from rotation sensors on the wheels. The speedometer corrector isn't hard to instal, it's just expensive and I'm still pissed about spending that much money on it. It did help to an extent, and around town and suburban two lane highways the truck became a real pleasure to drive. My trips to and from work went from 15-17 MPG to 19 to 21 MPG.

On the freeway, especially long trips with mild hills / mountains (Arizona/New Mexico), sixth gear was still something hard to find and freeway mileage was about 16-18 (which is better than the 11). The 4.88 gears has the engine running at a somewhat higher RPM than stock which means more torque. The 2.7 had pleanty to give and could hold an overdrive gear relatively efficiently if you give it a bit of gas, but the transmission still wanted to shift when throttle position increased. The ECU was still programmed to operate with a 2.7 engine that was lower into its torque curve (running at a lower RPM) and assumes it can't hold the over drive gears without lugging if you have to put some petal into it to take a hill. It is programmed to shift out of the gear when the throttle position increased past a certain point.

In full disclosure, because someone is going to point it out. I really didn't want a 2.7 with an AT, but a used low mileage MT at the right price coudn't be found, and I'm simply not going to the dealer and paying for the premimum.

OVTune has a version of VFTuner for the 2.7L. The 2.7 version is pretty basic, it doesn't have the gear lock feature or all the maps they have for the 3.5 (yet). But it will let you adjust the shfit points and that is what I did. With VFTuner I can program throttle position and speed for each shift. I lowered the speeds for the downshift and raised the throttle angle. Finally, the 4, 5 and 6 plan for the freeway is realized. I'm still gathering data on the mileage but so far I do better than 20 in mild hilly freeway travel. I'll probably do better tweaking the torque converter locking.

The bottom line is this: Always remember the computer runs the truck, and any mechanical change you make needs to be reflected in the ECU's programming, and the sensors that provide information to the ECU. If the ECU is running blind, or with bad information/assumptions you won't have a good result. Program the ECU to match the reconfiguration you did to the truck, and things are more likely to work like you expect.

If you were like me and don't know jack about programming the ECU, then you got more to learn.

 

Great analysis, David. I hope other people appreciate what you've shared as much as I do. Interesting you discovered that your vehicle has 3.9 gearing--contrary to what most say. I have the manual transmission 2.7L from 2016 and I do not believe that it has 3.9 gears, again contrary to common opinion. I suspect that it has 4.3 gearing like the other manual transmission models of the third generation, but I don't know how to check that. What's the easiest way to derive the gearing from speed and RPM, as you did?

I'm curious about the ECU's relationship to the engine with a manual transmission. Obviously the computer is not deciding when to shift, but I imagine it still makes a lot of decisions about how to run the engine given certain conditions and demands. I'm curious if regearing my truck would require reprogramming the ECU with a different set of givens so that it isn't working with invariable mechanical conditions that are no longer valid.

Thoughts?

 

You can't expect a MT v6 and 2.7 to have the same gear ratio. I do know, for fact, that 3rd gen V6 MTs are 4.30 gear. One of my wheeling buddy's had one and ran 35s on it, somehow lol!
I'm geared to 4.88 with my 2.7 and MT, running 35s. It's kinda like stock (4.10) and 33" KM2s, but slightly better and waaaaaaay cooler. 4.88 and the 255/85 KM2s was too much gear in 5th on the interstate, imo, it needed a 6th.

 

Seems to me that anyone with an auto behind the 2.7 needs geared from factory (before you ask, no, Toyota won't put better gears in there for ya ) or a tune is an absolute must.

 

I'm going to say that I don't have a 3rd Gen 2.7L MT truck and have made no observations about it (mine is an 2.7L AT). My opinion is the 4.30 gear in the MT makes sense because it is easier for the new MT driver to shift without stalling. My opinion is the 2.7 trucks are bascially the most very base model 3.5L trucks with a less expensive motor dropped in for fleet customers who are simply looking at price vs reliability (and care less about drivability). It is also my opinion that Toyota made no other changes unless they saved money, so if the 3.5 MT had 4.3 gears, and people say the 2.7 MT has 4.3 gears, I would start my obervations simply to validate that assumption. (a lot of opinion there but you asked what I thought)

If you know the specifications of the gear ratios in the transmission and you don't want to crawl under the truck you can use a GPS to fix your speed, record the RPM for speed in a particular gear and use the http://www.grimmjeeper.com/gears.html gear calculator to plug in the ratio you suspect it is and see if it validates. This is actually a more complicated technique but you may want to use it because the weather is chronically crappy or because you are researching the feasability of changing gears so you are doing all this work anyway. Use this technique to validate an suspected value, not to determine an absolute value.

It is simpler to jack your rear end, block your front wheels, put the truck in neutral and turn the drive shaft by hand and observe the tires turn. Again determine what your suspected values are and what you think you should obvervations for each of those value. In other words if you suspect 3.90, 4.30 or 4.88 then you would expect to turn the driveshaft just less than four times for the wheel to turn once, just a little more than four and a quarter times for a single revolution of the wheel, or just less than five times.

I think if you have a MT truck, the world of larger diameter tires is a whole lot easier for you because you control the transmission and how it shifts. The OVTune for the 2.7 is very basic, and right now it doesn't do much more than adjust the AT and ignition advance. Unless you have an AT, I would say it is not worth it for the 2.7 in its current state.

I wouldn't jump to the assumption you need gears. If you are considering gears, either 4.88 or 5.27, think through not only the gain but what you will loose on the highway. The AT has some really high over drive gears. I don't remember for the MT - you find out. I wouldn't do a 4.30 to 4.88, not worth it. But a 5.27 might have you running 3500 at 80 mph. Do the gear calculator and find out for your self; you may simply want to leave it alone.

 

If anybody needs to confirm gear ratio, go to the link and put in your VIN# and enter, then click on the model code, and then look under the power train link.

https://www.toyodiy.com/parts/q.html

 

That link shows my truck has a 4:30 gear, and I took out 3.90, so nothing is actually confirmed. Observe = confirm.

Information gets republished from one online source to another all the time - what actually happens on the assembly line is a lot like what happens in Vegas. The only real way to know is to make your own observation of your own truck. The simple and more complex ways of doing that have already been beat to death in this thread.

 

I’m really liking my 32” 255/75/R17s on my 2015 MT, C-Load

Just stinks I can’t hit 18MPG though, the slight mountains here in WNC mean you have to drive it a bit harder and shift more. I need to experiment with non-ethanol high test and non-ethanol 87. Both are available locally. I know the 2000 Land Cruiser loves the E-Free 93 at the QP. I get almost 14+ MPG lol...

It’s worth it to me as the wife (not even close to being a car person) loves the way it looks now! Hahaha

 

Rocking the stock 4.10 gears and can't complain. The 255/80/17s aren't bad but I'd imagine with 285s the 4 cylinder would be chugging along for sure.

 

265/70-17 Falken Wildpeak on my '15 DCSB PreRunner suck on the highway. They look great and are great offroad but thats where it ends. The size is too big for maintaining anything over 70mph without running in 3rd gear. And forget using the cruise.

 

I went from 285's to 305's and didn't notice any difference. I think the 33" height is what makes it chug along. Obviously, the heavier tires will hurt but I'm actually getting the same mpg or even a little better.

 

I always like the way your truck looked with those tires. Maybe the next set will be the size your running. Always liked the stance. Just gotta prepare with control arms and doing a CMC before a new set I'd imagine.

 

My truck has the SPC UCA's so I have them set at position C to push the wheel forward and I still get a little rub on the cab mount at full lock. I think I could grind a little of the mount and it would probably be almost no rub but it's not a big enough issue to worry about it.

 

@whatstcp I really like what you did there. 2G, regular cab, the plastic fender trim is gone. I still have my old 2G, never traded it in when I got a 3G. I'm inspired.