Poor fuel mileage after new tires, a flowmaster 40 series exhaust, and a k&n air fliter?

[Jermo760]

I have a 2021 ram 1500 with the 3.6 pentastar V6 E-Torque. I put new tires on which originals were 275-65-R18
I put on 285-65-R18, a new flowmaster 40 series, and a k&n air filter( not cold air intake and cone) and my mileage is like 17.6 now from around 25. Can anyone give me some pointers on If this is causing it or what else I should maybe look into. No warranty anymore so trying to figure it out before paying dealer prices for diagnostics and such.

 

[JohnGow383]

I have a 2021 ram 1500 with the 3.6 pentastar V6 E-Torque. I put new tires on which originals were 275-65-R18
I put on 285-65-R18, a new flowmaster 40 series, and a k&n air filter( not cold air intake and cone) and my mileage is like 17.6 now from around 25. Can anyone give me some pointers on If this is causing it or what else I should maybe look into. No warranty anymore so trying to figure it out before paying dealer prices for diagnostics and such.

If you put bigger tires on then you will be going faster than what the speedo is reading. Did you re-calibrate the speedo? If you didn't then this will also mess with your mpg readout

 

[SD Rebel]

The bigger tire, even by just a little bit will have a noticeable effect on your mpg, I did the same on my F150 and lost 1.5 mpg right off the bat. But as mentioned it will effect your speedo. In this case slightly, at 71 mph, your speed will read 70 mph. Only a 1 mph difference at highway speeds based on a 275-65-18 vs 285-65-18.

Factor in a louder exhaust that you will want to push on your accelerator a bit more to hear it, and you got the right ingredients for lower mpg. How you dropped from 25 mpg to 18 mpg is likely a mixture of bigger heavier tires and more aggressive driving to hear your muffler.

Try driving exactly like you did before the mods, and retest your mpg. Your efficiency loss shouldn't be as pronounced as 7 mpg, more like 1-2 mpg based on just the tire.

 

[Jermo760]

I don't drive any differently but I have noticed that my RPM's stay higher before it shifts to the next gear. But have no slipping or any noticeable issues driving. I didn't think I would loose 7 mpg cause the change. But no the speedo was not recalibrate to my knowledge.

 

[Jermo760]

I don't drive any differently but I have noticed that my RPM's stay higher before it shifts to the next gear. But have no slipping or any noticeable issues driving. I didn't think I would loose 7 mpg cause the change. But no the speedo was not recalibrate to my knowledge.

Recalibrated **

 

[SD Rebel]

I don't drive any differently but I have noticed that my RPM's stay higher before it shifts to the next gear. But have no slipping or any noticeable issues driving. I didn't think I would loose 7 mpg cause the change. But no the speedo was not recalibrate to my knowledge.

1 mph difference on the speed calibration isn't going to make a big difference in mpg. When you do your hand calculations, you will see how much fuel you are really using, regardless of speedo calibration.

While tire size makes a difference in mpg, that small difference you made shouldn't do 7 mpg. Your muffler and air filter isn't going to do that either. The only thing it can be, besides and actual mechanical issue or fuel leak is your driving style.

As someone who has always puts on aftermarket exhaust, It's really hard not to push a little harder to hear it. Even subconsciously, you maybe driving just a bit harder to hear the extra noise added to your your truck. Reset and recheck your mpg again. If you confirm it's not your driving style, I would considering speaking with a mechanic and see if something could have happened to lower your mpg.

 

[JohnGow383]

I don't drive any differently but I have noticed that my RPM's stay higher before it shifts to the next gear. But have no slipping or any noticeable issues driving. I didn't think I would loose 7 mpg cause the change. But no the speedo was not recalibrate to my knowledge.

Also, the tires are wider, which means more resistance and therefore more fuel. If they have a more agressive tread pattern this will also affect it. In theory, the performance exhaust can give better gas milage as there is more flow and less resistance, but it does have the affect of making the driver drive more agressively which is the biggest way to reduce fuel economy. Basically, everything that is done for fun ruins mpg. But the speedo has not been calibrated so you are probably getting a lot better than what it's reading since your actual distance traveled and speed will be more irl.

 

[JohnGow383]

Are you running at the correct tire pressure? The lower the pressure the worse the mpg

 

[SD Rebel]

Also, the tires are wider, which means more resistance and therefore more fuel. If they have a more agressive tread pattern this will also affect it. In theory, the performance exhaust can give better gas milage as there is more flow and less resistance, but it does have the affect of making the driver drive more agressively which is the biggest way to reduce fuel economy. Basically, everything that is done for fun ruins mpg. But the speedo has not been calibrated so you are probably getting a lot better than what it's reading since your actual distance traveled and speed will be more irl.

Great point on the tire tread pattern.

His speedo is just a little more than 1% off from stock, the 1 mph (at 70 mph) .5 mph (at 30 mph) is barely above common error, but his mpg loss is over 25%. I'm not sure he will find much improvement with a speed calibration.

 

[JohnGow383]

Great point on the tire tread pattern.

His speedo is just a little more than 1% off from stock, the 1 mph (at 70 mph) .5 mph (at 30 mph) is barely above common error, but his mpg loss is over 25%. I'm not sure he will find much improvement with a speed calibration.

I guess he's not gone up to 35s so it won't be that much then. I do think it's a combination of all these things mentioned, and the tire is probably a little heavier which also has a small impact.

 

[Dewey]

That’s a very small difference in tire size.


Also exhaust and air filter will not hurt your mpg. If anything it would be slightly better. Gotta be something else going on. That’s a real drastic mpg change.

 

[Scap]

Summer blend fuel vs winter blend fuel can change your fuel economy.

 

[JohnGow383]

That’s a very small difference in tire size.
View attachment 141539

Also exhaust and air filter will not hurt your mpg. If anything it would be slightly better. Gotta be something else going on. That’s a real drastic mpg change.

Oh I see.
Yeah when setting the tire size it's important to use the revs per mile number into 63360 to get the correct rolling circumference.
I wonder what pressure he's running them at.

 

[ferraiolo1]

If they are a heavier rated tire, aggressive tread pattern, or wrong air pressure it will make mpg drop.

Also when installing a muffler mpg does decrease because you tend to be a littler more heavy footed to hear it. And don’t notice you’re doing it.


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[Jermo760]

Oh I see.
Yeah when setting the tire size it's important to use the revs per mile number into 63360 to get the correct rolling circumference.
I wonder what pressure he's running them at.

Tires are at 40 cold psi usually runs about 45 all around. I don't do anything crazy. Don't tow much at all. It's just my daily driver.

 

[Jermo760]

If they are a heavier rated tire, aggressive tread pattern, or wrong air pressure it will make mpg drop.

Also when installing a muffler mpg does decrease because you tend to be a littler more heavy footed to hear it. And don’t notice you’re doing it.


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With everybody talking about being heavier footed to hear the exhaust I'm gonna be clear. Yes people suck at driving and there are times I have to get up and go around them or leave a lane and be at speed for traffic flow. But even when I am driving a long distance (200miles or more) and I have cruise control set I'm only getting 18 or so. And for the 3.6 V6 I know it isn't horrible but a run from Atlanta to Nashville NEVER ( even with traffic) took a full half tank. Now it's like a half tank easily.

 

[n8zcc]

I have a 2021 ram 1500 with the 3.6 pentastar V6 E-Torque. I put new tires on which originals were 275-65-R18
I put on 285-65-R18, a new flowmaster 40 series, and a k&n air filter( not cold air intake and cone) and my mileage is like 17.6 now from around 25. Can anyone give me some pointers on If this is causing it or what else I should maybe look into.

The likely loss of MPGs is the sum of all points posted plus new tires offer a resistance to roll until they are broken in, about 500 miles or so.

 

[JRW323]

Are the new tires LT? Because tire weight from standard load to LT is pretty significant.

 

[HSKR R/T]

How many miles have you driven since the change?

What is the exact tire you are running now?

Get the computer adjusted for the new tire size to get a true comparison.

 

[ferraiolo1]

With everybody talking about being heavier footed to hear the exhaust I'm gonna be clear. Yes people suck at driving and there are times I have to get up and go around them or leave a lane and be at speed for traffic flow. But even when I am driving a long distance (200miles or more) and I have cruise control set I'm only getting 18 or so. And for the 3.6 V6 I know it isn't horrible but a run from Atlanta to Nashville NEVER ( even with traffic) took a full half tank. Now it's like a half tank easily.

Why aren’t you talking about the actual tire you put on or the pressures you’re running?


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