315/70r17 + stock gears + OTT tune

Regarding the 3rd Gen Tacoma Double Cab Long Bed configuration, equipped with a 3-inch lift, skid plate, rock sliders, and a tonneau cover, I can offer the following insights based on my experience with 315/70r17 tires, stock gear, and with OTT tune.

Initially, concerns regarding the need for regearing were present; however, the current setup provides sufficient power for optimal tire performance. Transitioning from 285/70r17 tires, where an average of 18.2 mpg was observed, the Ultraguage calibration for the 35s surprisingly indicates an average of 19 mpg.

This data reflects driving conditions that include both hilly highway routes and city driving.

I am interested in understanding your experiences with a similar setup.

Could you provide potential explanations for the increased fuel efficiency observed with the 35s compared to the 33s?

Your insights and experiences are highly appreciated.

 

Different tires will have different rolling resistances.
What are the specs on the new vs. old tires? (brand? model? load range?)

 

Old tires were 285/70r17 Toyo RT Trail C rated
New tires are 315/70r17 Nitto Ridgegrappler E rated

 

Interesting that the E is the one doing better...
I will say though, I have Toyos on mine now (M/T 285/75R17-E), they seem like they have the most rolling resistance of any tires I've had. There's a long very gradual downslope on a street near me and most vehicle/tire combos I've had will very gradually pick up a little bit of speed while coasting down it in neutral... These Toyos OTOH will very slowly lose speed on that same street. Given what I paid for them (and the tread getting torn up from going offroad), they've been a bit of a disappointment.

If I was to guess, Nitto has a more compliant carcass they make their tires from, so they roll easier down the pavement.

 

That's interesting feedback. I'm sure the tread patterns could mess with the rolling resistance. But going from a lighter tire to a heavier one, I thought it'd be the other way around.

 

I should also add that the 35s appear to have smoother gear changes compared to my 33s.

 

If your talking about the toyo MT that is one of the heaviest tires around.

Yoko g003 285/75r17 63

Toyo mt 285/75r17 69

What i want to know is how long has the test period been? Has the regular route changed much ? Did you change wheels with the tires? Have you always manually calculated mpg or gone off the dash/ultra gauge? I dont think this math is mathin. You can't add 14lbs of rolling mass per corner and not take a bigger hit.

Nitto ridge grappler 315/17r17 E
70


Toyo rt trail 285/70r17 c
56

 

First of all, those are 34" tires and advertised as such. (Nitto sells actual 35x11.50R17 and 35x12.50R17 under SKUs 218850 and 217020, respectively.)

The larger tire diameter has the same effect as taller gearing in highway driving - your rpms are lower at any given road speed.

I went from 32" GY Duratracs to 35" Kenda RTs and noticed no change in fuel economy. I'm in the similar situation - stock gearing with a tune (KDMax 6.0). I get 15 mpg in my normal commute (rush hour highway) and 18 mpg in longer distance highway driving.

 

.8/18.2 =0.044 is probably within statistical error of being considered equal. There are so many factors involved. You didn’t mention how long you drove or the conditions when you drove.

 

I agree with most of what you said accept for the conjecture that a more compliant tire has less rolling resistance. More flexing of the rubber does not increase efficiency. Quite the opposite. That’s why higher air pressure typically reduces rolling resistance. However, a more compliant tire filled to higher air pressure can certainly beat a less compliant tire with lower air pressure. Maybe we are saying the same thing.

This is easy to see with bicycle tires. Low rolling resistance road tires are super thin and compliant, but you need to pressurize them to about 100 psi where they become super non-compliant.

 

A heavier tire alone doesn't have a huge impact on MPG unless a lot of stop-&-go driving is involved... It's the same thing as having weight in the truck itself; once that weight is moving (spinning), it takes little energy to keep it moving.
The difference is more in how much resistance the tire has on the ground to it rolling. Tread design obviously plays into it, but so does tire construction.
If you're old enough to remember the last days when bias-ply tires were common, they almost universally sucked for both MPG as well as tread life compared to radial tires (some of the last bias tires available are made by Interco Tire (of Super Swamper fame). These are about the absolute worst tires you could possibly put on a street-driven rig, but old-tech as they are, they are still very formidable offroad).

I have 35x12.50R15 General Grabber X3 tires on my other rig, it gains speed coasting down that same street where my Toyo M/Ts lose speed. At 72lbs, they're three pounds heavier, but clearly have lower resistance to rolling.

We may be saying the same... A tire that has less resistance to flexing is "springier" (I guess you could say) it won't generate as much heat (energy loss) within the carcass as a tire that is stiffer and resists flexing more. Higher air pressure does lower the rolling resistance of ANY tire, but of course you do want an appropriate pressure that will encourage even tread wear.

 

I've heard a common feedback from other people I know that have went with heavier tires, the best theory we've all come to is that the heavier tires add inertia so once you're moving they help to keep you moving. So especially on the highway the same or better fuel economy may be observed. In strictly city driving though, fuel economy seems to be much worse.

Either way, thats always good and welcome news when a change to your vehicle increases fuel economy aha

 

True story. It’s true that rotating mass increases effective mass more, but tires are so light compared to the total mass of the truck that it isn’t as a big factor as popular culture expresses. A decent rule for thumb is that every pound of tire weight is equivalent to 2 pounds of non-rotating weight. So for example, 1 pound of extra tire weight is equivalent to 8 pounds of non-rotating weight (1 lb x 4 tires x 2). That’s 0.1% the mass of a 4600 lb 4x4 DCSB taco.

And as you said, you only lose this energy when using the brakes, so it’s more prominent during city driving.