Smaller tires installed, same to worse mileage?

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6

6lug

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Dec 23, 2005
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163
1998 LC
192,000 miles
99.9% stock
Daily drive of 80 miles, 90% interstate.

When I bought it, it had 285/75R16 Goodyear Duratracs. Getting 12-13 mpg at at about 2200 RPM, calculated properly for tire size. 74 mph. I knew going in it wouldn't be great mileage, but decided with all of my interstate travel I would go to smaller tires to increase my mileage.

Put one tank of the same driving conditions on brand new 265/75R16 BFG AT's. 2300 RPM, 74 mph. 12.8 mpg. These tires are way narrower, an inch or so shorter, and my mileage hasn't changed one bit.

Am I overlooking something?

I am considering going to 255/85's to get my RPM back down since most of my time on road is interstate. I've also seen some good threads for tuning it up. But I am at a loss that I am getting less than 13 mpg with a stock rig on small tires. Any insight is appreciated.

I'm figured this thread might be a different as most people are looking to upsize tires, but I downsized and it didn't help a bit.

Thanks.
 
taller narrower tires inflated to max would/should in theory give you better mileage based on less resistance and effectively producing a taller final gear ratio... shorter tires would have the reverse effect...

what you/we have is HUGE as in Bernie Sanders HUuuuuGE surface area with our trucks... even with the stock ground clearance you might as well count the whole underside of this truck as really bad surface area that has zero positive aerodynamic features... toss in the roof rack and 6000lbs of truck you might as well take the award for worst MPG if they had never manufactured the HUMMER...

once moving on level ground... this truck should burn about 4x as much fuel @ 60mph as it does at 30mph

remove the rear seats carry nothing extra, over inflate your tires... take off and drive slow stop & start as little as you can and maybe just maybe... you could average 16-17mpg...

or suck it up enjoy driving like you want, carry what you might need... and get 12.9... that is what I do...
 
fwiw, I went from a 265 Michelin to the 315 AT KO2 and noticed an increase in mileage. While I'm no engineer, my best guess is that there is a giant difference in the tire size mileage impact depending on stop/start driving vs highway.

From a stop, it makes sense that rolling resistance, unsprung weight, gear ratio, etc will mean smaller tires are more efficient.
Once the truck is rolling though, it seems logical that since larger tires mean lower rpms at the same speed, that would be more efficient.

I noticed a significant mileage improvement when I took an exclusively highway trip from DFW to South Dakota.

In fairness, pre trip I hamfisted my way through a full 90k service, timing belt, spark plugs, oil change, air filter, etc. So that could have had a significant positive impact on mileage.
 
Nobody should be down sizing tire diameter to get better mpg at highway speeds.

Smaller tires will give you more torque, better acceleration and better braking... but not better mpg on a flat freeway.
 
Skinny pedal usage and cruising speed overwhelm most all other factors. Keep acceleration under 2100 RPM'S and top cruising speed around that range as well, and you'll get "decent" (for a land cruiser) mileage. Anything else and you're stuck under 13, or worse. I put highway treads on for a 7000 mile cross country trip (with heavy tundra steelies) and noticed no improvement over the 295 Nitto's that were on there. Acceleration and top speed FTW, but it sucks the fun out of driving a LC. I only get around 8 when off road in low range, too. Same with towing. Same with dropping it off a cliff...
 
I would focus less on the size of the tire, and more on the type of tire. Specifically, you want a highway focused tire, and avoid the high profile lugs of an AT tire.

For highway use, I would also discourage you from running too narrow a tire, as you will be sacrificing handling qualities necessary for a large heavy rig at speed.

Also, if you just drop your speed by a few mph, you'll find considerably more efficiency as aero drag goes up exponentially with speed.
 
I would first check to see how accurate your speedometer is. Download one of the free apps that uses GPS to track your speed, and compare the two. If its off you may want to look into getting a yellowbox to correct it. Once its corrected, at least you know you have accurate MPG being displayed
 
OP I think it is just a fact of life when it comes to driving a LC considering it is a full time 4wd with a V8 and the aerodynamics of a barn. I have a regular drive on weekends that is about 300 miles with 60 of that being on the interstate and I get atrocious mileage (~12.5 mpg) then but as soon as I am on the highways (through the mountains I might add) averaging about 65 mph I can manage about 17 mpg for the remaining 240 miles all while turning 33" tires.

I personally have the tires I want and use the bad high speed gas mileage as an excuse to travel the routes that may take a few minutes more but give way better mpgs and much better scenery.
 
a_traut_man said:
OP I think it is just a fact of life when it comes to driving a LC considering it is a full time 4wd with a V8 and the aerodynamics of a barn. I have a regular drive on weekends that is about 300 miles with 60 of that being on the interstate and I get atrocious mileage (~12.5 mpg) then but as soon as I am on the highways (through the mountains I might add) averaging about 65 mph I can manage about 17 mpg for the remaining 240 miles all while turning 33" tires.

I personally have the tires I want and use the bad high speed gas mileage as an excuse to travel the routes that may take a few minutes more but give way better mpgs and much better scenery.
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12.5mpg is really low even for our vehicles. I have a 2004 on 33" and I still get around 15 when doing 75 on long trips. The extra gear in the 2003+ should be getting you more than that.
 
All speeds / mileages are verified from a GPS, not the speedo / odo. Miles per tank are corrected for tire size.

Hell, Discount Tire is giving me the option of removing these, and installing some new 255/85s for the difference in price. Basically crediting me for the price I paid for the 265's. Im tempted to try the offer, although they will have to be BFG MT's...I really like the quietness of the AT's....


BTW, thanks all for the responses. I agree and just dont understand how its so bad when basically stock (only removed running boards and have the 265/75's). I cleaned the throttle body last night, PCV valve, checked a plug, reset computer, etc. Everything looks pretty good regarding that.

I do only have a 4 speed, but some of you guys are getting way better mileage with bigger rigs and I'm wondering what the deuce is going on...
 
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I don't think you will notice much if any difference, it's not worth the hassle. lighter right foot will make the most difference, no air con etc. What you might gain by having 10mm less tread you gain by going MT anyway.
 
Its not about the right foot on the interstate. I leave it on cruise the whole time, 74 MPH. No significant hills to speak of. And i dont care about the width...its the height. 31" back to a 33"
 
6lug said:
Its not about the right foot on the interstate. I leave it on cruise the whole time, 74 MPH. No significant hills to speak of. And i dont care about the width...its the height. 31" back to a 33"
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74 MPH is the problem, and frankly, people lie about their gas mileage all the time... Bump it down to 65 (if you can without getting run over or shot) next time and see what you get. 60 even more better...
 
That's part of the problem. I get passed like I'm standing still at 74. It's a fairly trafficy open highway with not a lot of cops so people roll hard. I'm not trying to make excuses. Just wondering if in this rare instance, going with a larger diameter tire would have actually helped more than sizing down to reduce rolling mass, vehicle height, tire width, aggressive tread, etc. I appreciate all the responses.
 
6lug said:
Its not about the right foot on the interstate. I leave it on cruise the whole time, 74 MPH. No significant hills to speak of. And i dont care about the width...its the height. 31" back to a 33"
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You need to calibrate speedo for accurate mpg when changing tire diameters. You have already proved to yourself that changing tire diameter didn't effect MPG, you have already run 33".
 
As I posted above, GPS confirmed speed and mileage, calculated for change in tire size.

But yes, 13 mpg either way. 255/85 should be taller than 285/75 tho. I'm just grasping at straws. If ima have crappy mileage, might as well have some cooler tires and lower highway RPM....

I would be thrilled with 300 miles per tank, but right now max I've gotten is like 270
 
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You might want to put a scanner on your vehicle and check the Fuel Trims.
This might reveal that you need to clean your MAF sensor.
 
Julian Stead said:
You need to calibrate speedo for accurate mpg when changing tire diameters. You have already proved to yourself that changing tire diameter didn't effect MPG, you have already run 33".
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I have 295/75/16 Nitto's on both a 5-speed and 4-speed cruiser. 74 mph @ 2200 RPM doesn't sound right. Pretty sure mine is higher, even with the 33"+ tires. Most 285's run small.
6lug said:
That's part of the problem. I get passed like I'm standing still at 74. It's a fairly trafficy open highway with not a lot of cops so people roll hard. I'm not trying to make excuses. Just wondering if in this rare instance, going with a larger diameter tire would have actually helped more than sizing down to reduce rolling mass, vehicle height, tire width, aggressive tread, etc. I appreciate all the responses.
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I hear ya on the traffic, but at >70 mph, you can kiss anything over 13-14 MPG goodbye. Toyota could only manage 15 on the old, cheatin' EPA test for the window sticker, you know, the constant 55 mph, no AC, special tune version of the test...
 
I'm going to bet the $341 I'd have to pay to install the 255's isn't going to be worth the "possible" marginal increase in mileage it may provide. And the smaller tires will be less wear and tear on hard parts. So whatever. And ill slow it down a bit I guess.

As far as RPM vs speed, I was dead on 2200 RPM at GPS indicated 74 mph with the 285's.
 
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