37s with stock gears

2.5 and 3rd compatibility? I don't think so.

 

A larger tire is a larger lever arm, just like a torque wrench or a breaker bar, the more leverage the less force you need. In this case the tire has more leverage so there's less force going to the ground to move the truck forward.

Secondly, even if a 37 weighs less than a 35, the weight is further out from the hub so the actual inertia and power required to spin it up is drastically higher, and unlike the lever arm effect that is proportionate to tire diameter, the moment of inertia increases much faster (think of it as an exponential increase).

So there's compounding effects. For the most part people just think about the lever arm distance, but it's not the only factor at play though it is the easiest to understand. Plus you have rolling resistance and all that other shit that is harder to calculate.

 

https://nitro-gear.com/rpm_calculator_us

65 MPH RPM in 6th gear...
Stock gears/32" tires: 1702


Stock gears/34" tires: 1602
Stock gears/35" tires: 1556
Stock gears/37" tires: 1472

5.29 gears/34" tires: 1971
5.29 gears/35" tires: 1915
5.29 gears/37" tires: 1811


I run 34" (275/65/20) tires with 5.29's and would NEVER want to go back to stock gears. Never. There is no down side. Sure, it spins another 271 RPM at 65 MPH than all stock, but it needs it. These trucks are geared too tall in stock trim.

I'm bumping up to 35" (285/75-18) tires this fall and it will still be great.

 

Yours is one of the best explanations I’ve heard.

On top of all of this, the ecu sees the higher throttle position and pulls timing while adding fuel. This causes an actual loss of power to compound all of the above.

 

Bds 7inch on 35 ko2.

 

Interesting. You would think Ford's Raptor would have higher gearing since you can get it with 37's from factory. I guess the 10 speed transmission is enough to counteract the need for that. Would be nice if our tundras had a few more gears. Thanks for the info lads.

 

Thank you for chiming in, Keith!

Isn't it just gearing though? I mean, a 14% taller tire (37) will be geared 14% higher. If you geared it 14% lower you'd compensate for that aspect. Granted the truck is geared high to start with, and a lift and big tires will increase aero drag and probably rolling resistance, so if you are going to bother, 5.29 is the way to go.

I've been favorably impressed with my MPG and truck performance with fat 35" ATs and a 2" level (no regear). I live at 7,000 ft and it's quite hilly. I've done a couple long trips between 5k and 8k ft with pretty flat 80 mph freeway, and winding mountain roads (~65/35) and averaged 17.7 mpg with no gear hunting issues. I don't know how smart the ECU is, but everything is harder (the engine is working closer to max vs at sea level), so it seems it would be more likely to pull timing and add fuel...? I wonder if Toyota modded the ECU at some point to make it work more sensibly.

 

I think you mean lower gearing, and having 10 gears vs 6 definitely helps! The F150s have higher diff ratios available too unlike the gen3 Tundra... don't know about the Raptor specifically.

 

If you have bigger than stock tires, and stock gears, and no gear hunting issues, you’re the only one without gear hunting issues.

when a slight incline comes up, it’s supposed to hold 6th gear without slowing down. (Depending on speed of course).

for anything 34 or smaller, go 4.88, bigger, go 5.29

run as small a tire as you can and your project still work for u

 

My truck has 4.30’s and I’m running 34’s and it’s nothing but downshift city going up slight inclines. Towing a trailer with three four wheelers on it and it’s useless above 4th gear unless I’m doing 70mph and then it can hold 5th but only at half throttle which just puts strain on everything. These engines need rpm to get into their power band. Don’t be afraid to let the rpm’s get up there. Won’t hurt anything. And high rpm’s don’t necessarily equate to bad mileage. You have to take engine load into consideration.

 

@dirtydeeds are you still doing re-gears these days? Im in San Clemente...

 

Yessir. In Escondido. 760-877-4234

 

Anyone have a shop in Northern California they can recommend for regearing??

 

Stellar built in Sac

 

The 4x4 Shop in Livermore did mine. They do quality work.

 

I am at 6500' and I notice I get significantly better MPG with my Lexus GX than most others claim. I am on 285/70's and seem to average around 18 whereas a lot of people cant get that stock.

I do wonder if it has something to do with the lower air density and cylinder pressures. I wonder if the ECM keeps the engine leaner knowing that its not generating as much power.

 

The Raptors have actual torque at low RPM. I run 315/70R17's on my otherwise stock 2014 F150 Ecoboost. Thats just the old 6 speed and 3.73's, which is similar ratios to a 2nd gen Tundra. Even at 6500' of elevation where I live it has zero issues. Only 7% grades doing like 55mph does it need to drop out of 6th down to 5th. If I am going faster and spinning more like 2000 rpm it will chug up the hills in 6th no problem.

Back when the original ecoboost came out they claimed 90% of peak torque from 1700 to 4000 rpm. That puts it at around 380 ft-lbs at 1700 rpm and it increases to 420 ft-lbs as you get to 2500 rpm(and really its higher than that if you are using higher octane fuel). The newer Ecoboosts, like in the Raptor, are making more than that.

The other thing though is that the Raptors factory 37's are very light. I wanna say they are under 70 lbs. The BFG KO2 315/70's I am running are from a Raptor and are only 62 lbs. My wheel tire combo was the same total weight as the 275/60R20's and stock 20" wheels they replaced.

 

The ECM certainly will lean it out to match the incoming air. I just towed from AZ, thru Utah, Nevada, and into Oregon; with a lot of it at elevation. Highway speeds at higher elevations it gets great mileage. Now the 80 MPH interstates at elevation, now I see why guys want 5.29's. That speed at sea level is no big deal, up high, it was running hard.

 

Thats not what I meant. I mean maybe it doesnt go insanely rich like it normally would at sea level, thus drinking gas, because the cylinders arnt filling as much and you effectively have a lower compression ratio. The ECM might not have to "protect" the engine as much.

But yeah, the GX struggles at elevation for sure.

 

Lower air density reduces the power it takes to go a certain speed. Air density at sea level is ~25% higher than it is at 6k ft, and aero drag is proportional to air density, so figure total HP required at 80mph is ~15+% higher at sea level. Engine efficiency goes down a little at altitude, but not as much as the benefit from reduced drag.

 

True, max power is down so it's working relatively harder, and a regear would be nice... but it seems to run fine and doesn't hunt for gears. If it did I'd just put it in S5 though, no worries.

 

Wonder what it's like to burn a tank of e85 at 6k ft elevation?

 

Probably not needed since the cylinder pressures are lower and you could hit MBT timing on a lot less than 108 octane equivalent. You could probably max timing out on E30 or E50.