[The Ninjalectual]

I have a set of 245/75 Michelin LTX M/S tires that are rated up to 80 psi. I've been running them at 60 psi and getting 21 mpg on the highway, which I thought was pretty good. The other day I aired them down to 45 psi while doing some offroading, and on the drive home my mileage went UP to 25 mpg on the highway! Huh??? I was expecting to take a hit on mileage until I stopped to add more air, but instead I got this huge improvement, into a range I didn't think the Tundra could even reach. In the week since, my in town mileage has gone from 17 mpg to 20 mpg.

Can anybody explain this? I'm not complaining, but it doesn't seem to make sense, and I would like to understand.

 

[pirates712]

60 PSI is a LOT of pressure for tires on these trucks. Usually you go by the pressure listed in the door jamb or in the manual, NOT by the maximum pressure on the tires.

Not completely sure why you saw such an improvement though.

 

[The Ninjalectual]

Why would you go by the door jamb rather than the actual tire? The tire is the thing holding the air pressure, I would think you should go by that.

But this does beg the question: would I see even more improvement if I dropped to 35 psi? I will experiment and report back.

 

[2003bajatundra4x4ac]

funny thing happened last weekend in baja. i was averaging around 14 mpg on the 250 mile drive down on pavement. i saw 16.57 mpg on a 285 mile round trip on the dirt, i.e. 5-35 mph with the average being 20mph. all with the same air pressure.

WTF?

 

[DevinSixtySeven]

Correct air pressure depends on the load on the tire, and the tire construction.

Search for "chalk test".

-Sean

 

[Erki]

is this an instant reading for mpg or a number calculated by distance and consumption. If its an instant reading maybe the tire diameter changed and the computer not knowing that...?

 

[G-TEK]

Can anybody explain this?

When you were off roading you hit a gnarly bump and whacked your dome on the steering wheel then read the gauges wrong.

Just my guess.

 

[The Ninjalectual]

is this an instant reading for mpg or a number calculated by distance and consumption. If its an instant reading maybe the tire diameter changed and the computer not knowing that...?

Calculated by distance and consumption, measured after burning at least half a tank, generally more.

 

[The Ninjalectual]

funny thing happened last weekend in baja. i was averaging around 14 mpg on the 250 mile drive down on pavement. i saw 16.57 mpg on a 285 mile round trip on the dirt, i.e. 5-35 mph with the average being 20mph. all with the same air pressure.

WTF?

Perhaps you have a tendency toward a lead foot on the pavement, but you are much more cautious with the gas pedal on dirt?

 

[kerryman71]

Why would you go by the door jamb rather than the actual tire? The tire is the thing holding the air pressure, I would think you should go by that.

But this does beg the question: would I see even more improvement if I dropped to 35 psi? I will experiment and report back.

I think the door jamb is a recommendation from the auto manufacturer for the most comfortable ride taking into consideration the vehicle the tires are on. I don't go by it as it's recommended 26 psi for the fronts. I have mine at 30 on the fronts and 32 on the rears. I also have a different size tire than yours.



John

 

[cleanb13]

45 psi when off road? That must have been a real sh*tty ride. I lower mine down to 15-20 psi. The idea is to have the tires take the brunt of the bumps, at 45 psi (which is 5 psi more than I use on the street) there is alot of stress on the truck and suspension. Next time you go offroad, lower the psi to 20 and feel how much of a difference it makes.

 

[Chudlles]

If you look at the load rateing on a tire (10ply), it will give you 2 load rateing. eg. 122/125. That is at different pressures. Unless you want your truck to ride like a tank, never max the pressure on any tire, unless your hauling a heavy load. My 10 ply tires on my 2000 areset at 40psi all around, and thinking of going to 35psi. You could run them at 26/29 and still be fine with a 10 ply tire. I wouldn't recommend it as the tires may wear a bit funny. I do work at a tire shop and most cars get 32-35 psi, and trucks with a 4 ply tire get 34-35 psi. then for 3/4 and 1 ton trucks we set the pressures to the pla card on the door jamb. Then there's the vehicles with TPMS, Don't get me started with those. (I think a woman invented them)

 

[mdboyd]

25 MPG in a DC? Was there a vehicle behind you pushing the truck?

 

[zcd]

I have a set of 245/75 Michelin LTX M/S tires that are rated up to 80 psi. I've been running them at 60 psi and getting 21 mpg on the highway, which I thought was pretty good. The other day I aired them down to 45 psi while doing some offroading, and on the drive home my mileage went UP to 25 mpg on the highway! Huh??? I was expecting to take a hit on mileage until I stopped to add more air, but instead I got this huge improvement, into a range I didn't think the Tundra could even reach. In the week since, my in town mileage has gone from 17 mpg to 20 mpg.

Can anybody explain this? I'm not complaining, but it doesn't seem to make sense, and I would like to understand.

Can I buy some pot from you?

 

[The Ninjalectual]

25 MPG in a DC? Was there a vehicle behind you pushing the truck?

I am not exaggerating--okay, maybe it's only 24 mpg. But I am surprised too, thus this thread. I am getting over 500 miles per tank, when it's all highway. I'm using 87 octane (which is mid-grade where I live), and I drive 65 without any cruise control (which will floor it in order to maintain 65 at all costs, whereas I let speed burn off when climbing hills, and I allow the truck to accelerate a little over the limit on the downside of hills). I used to consistently get 21 mpg highway, and the only thing that's changed is the tire pressure.

 

[mdboyd]

I am not exaggerating--okay, maybe it's only 24 mpg. But I am surprised too, thus this thread. I am getting over 500 miles per tank, when it's all highway. I'm using 87 octane (which is mid-grade where I live), and I drive 65 without any cruise control (which will floor it in order to maintain 65 at all costs, whereas I let speed burn off when climbing hills, and I allow the truck to accelerate a little over the limit on the downside of hills). I used to consistently get 21 mpg highway, and the only thing that's changed is the tire pressure.

Heh, I'm not accusing you of exaggerating Ninja, but considering the F-150 Supercrew with Ecoboost engine is only rated at ~22 MPG highway, you'll have to understand that it's sort of difficult to believe. If those numbers are real, there's a lot of us that are quite envious of you!

 

[Donskee]

Hey all,
I know this is an old post but I have some questions.
What size rims are you running? If they're 17's, it's a taller tire, and will change your rear end ratio.
What rear end ratio are you running? I just bought a used 05 DC, and got 16.8 all 70-75 on the fwy. I'd like to get 18.8 with a lower rear end ratio
Do they put ethanol in your gas in Colorado? We get 10% here in California, and I know it kills my mileage
I was running LTX MS/2 E rated on my 02 AC, at 29/32 psi. Still a bumpy ride, but I need to be able to air them to 80 when I'm hauling a load, or my camper. Stiff sidewalls make for a great secure ride. I didn't have them long enough to see how they would wear in the long run..

Thanks,
Don

 

[SuckersWalk]

Search for "chalk test".

-Sean

i'll second this

 

[Highwaylizard]

Hey all,
I know this is an old post but I have some questions.

Hey Don welcome to the forum!!! You realize as a newbie you have to post up pictures of your truck so the rest of us can drool over them. Be aware of some of the shady characters here who will ask for pics of your old lady - or worse offer you pics of your old lady.

What size rims are you running? If they're 17's, it's a taller tire, and will change your rear end ratio.

My truck came stock with 17 inch rims and 265/70/17R tires.

What rear end ratio are you running? I just bought a used 05 DC, and got 16.8 all 70-75 on the fwy. I'd like to get 18.8 with a lower rear end ratio

My truck came stock with 4:10 gears in the front and rear differentials but as a result of a screw up by the "Real Men of Genius Team" of which I am co-founder I now have 3:91 gears in the front and rear differentials. At 70 MPH I run a little under 2100 RPM.

Do they put ethanol in your gas in Colorado? We get 10% here in California, and I know it kills my mileage

Yep - ethanol here too and it just trashes the mileage.

I was running LTX MS/2 E rated on my 02 AC, at 29/32 psi. Still a bumpy ride, but I need to be able to air them to 80 when I'm hauling a load, or my camper. Stiff sidewalls make for a great secure ride. I didn't have them long enough to see how they would wear in the long run..

Thanks,
Don

 

[jmo]

In general under inflation kills your mpg because it increases the amount of rolling friction. Any chance your Tundra has a V6 in it? That would make more sense in regards to the mpg you are experiencing...