Taller Tires Don't Get You As Bad Gas Mileage As You Think?

[Spencer]

-No it wont be as good as the smaller tires but it explains the average 2-3mpg loss
-No Im not the most organized epecially when it comes to math
-Yes I realize 4runners are not calibrated to 30" tires just a number
-Yes I know this is theory is probably flawed somewhere, Im no engineer and I came up with this about 8 years ago when I was 13 so I don't expect it to be right but it always made sense to me


Just something I always thought about since I was much younger..

Say you go from a 30" tire to a 33" tire..

Thats a 3" difference.. or 10% increase that same 10% increase on your speed and your gas mileage since nobody ever gets there speedometer adjusted after.

So when people notice the usual 1-2mpg drop what are they really experienceing? Well if you have 30" tires this means your tires are rotating 672.6 times every mile

Because 30" x 3.14 = diameter or distance covered in 1 rotation which is 94" and 94/12=7.85 feet, so 7.85foot in every rotation. 1 mile divided by 7.85'. 5280/7.85=672.6

So a 33" x 3.14 =103.62"/12=8.63 5280/8.63=611.8

So a 33" tire only rotates 611.8 times every mile. Lets check and see if our 10% is still there. 672.6/611.8 = 1.1 Yes our 10% still applies

So while your odometer says you have only gone 300 "displayed "miles on the tank with your 33" wheels you have really gone 330miles. Now lets say you used to average 340 "displayed" miles with your old 30" tires. Lets do the math

310 miles / 17 gallons of gas is 20
300 "DISPLAYED" miles / 17 is 17.6
330 "actual miles" / 17 gallons of gas is 19.4

So while your calulations filling up show you have worse gas mileage with the 33" you can actually add 10% to that to show what you really have gotten.

Also when your "displayed" speed is 70 with your 10% increase your going 77 I think this is where more of the gas mileage is lost. You can slow down to "displayed" 64mph and be going 70

-No it wont be as good as the smaller tires but it explains the average 2-3mpg loss
-No Im not the most organized epecially when it comes to math
-Yes I realize 4runners are not calibrated to 30" tires just a number
-Yes I know this is theory is probably flawed somewhere, Im no engineer and I came up with this about 8 years ago when I was 13 so I don't expect it to be right but it always made sense to me

 

[ChildrenOfBodom]

A good lesson why you should always have your speedo corrected.

I like this... no this isn't facebook.

I've kinda always thought this myself. I noticed when I went from 30" to 31.7" (I think) that my mileage went up, the car went further... while at the same time I knew that the car racked miles up more accurately. but yeah I've been at work from 10-10 today and Im tired... its midnight so I dont really know how to put it... or what I'm saying.







but I totally understand what you're saying and agree.

You've inspired me to do check now. I've always documented my miles at each fill up... I'll plug in the formula and figure out the difference to stock with my current tires, I'll probably get better mileage than I thought... that and I might be able to determine the amount of miles I really have.

intriguing.

you make a tired man cry



thank you! I was always wondering my mileage seemed too low.

 

[Spencer]

Thanks!!!

If stock was 265/70/16 thats about 30.7" tall and you went up to 31.7 thats

31.7/30.7=1.03 so a 3% increase.

17mpg would really be 17.5mpg
70mph would really be 72.1

I always thought stock was smaller though..

If stock for you was 255/75/15 then thats 30"

31.7/30= 1.05 or 5%

17mpg would be 17.85
70mpg would be 73.5

if someone went up to 35".....................
35/30=1.16 or 16%!!!!!!!!

17mpg would be 19.72
70mph would be 81.2.... Watch your speed!!!

Id say if I average 17-18 mpg now combined then I changed to 35" it would probably drop to around 14-15mpg combined. Some of thats due to the extra weight but I also believe it would be also due to people driving considerarbly faster especially on the highway. I think if you drove a little slower you would probably get a solid 15 maybe 16 and throw in that 16% increase and.. your back up to 17.4-18.5... I might be going to 35s lol

 

[ChildrenOfBodom]

Thanks!!!

If stock was 265/70/16 thats about 30.7" tall and you went up to 31.7 thats

31.7/30.7=1.03 so a 3% increase.

17mpg would really be 17.5mpg
70mph would really be 72.1

I always thought stock was smaller though..

I bought my 4Runner with 30 inch tires. When you have the 4 cylinder base model 2wd, stock is 225/75/15. I must have gotten confused, I have 265/70/16 now. I was confused with 265-75-16.

So all in all its not much of a difference maybe but noticeable.

 

[Spencer]

I bought my 4Runner with 30 inch tires. When you have the 4 cylinder base model 2wd, stock is 225/75/15. I must have gotten confused, I have 265/70/16 now. I was confused with 265-75-16.

So all in all its not much of a difference maybe but noticeable.

Oh shoot... Good excuse to go bigger though?!

255/75/15-265/70/16 thats only 2%

 

[ChildrenOfBodom]

someone like haddix though, with 35s... or 240m3srt wants 37s...

a big difference there!

 

[Spencer]

someone like haddix though, with 35s... or 240m3srt wants 37s...

a big difference there!

yep like 20% now one more thing to consider however long you actually ra the larger tires on your 4runner the more your mileage will be off. EExtreme but if you ran 37" from day 1 at 150k you really went 180,000 miles

 

[glenyoshida]

You are spot on. Speed kills your gas mileage. Air resistance is nominal when you are slow but is a whopper at high speeds. Take the Bugatti Veyron for example. It’s capable of a top speed of 253mph.

A Geo Metro has a 1 liter 55 hp engine and can easily reach 50 mph. By reasonable logic it makes sense then that to reach 250 mph you would only need a 275 hp engine but in reality the massive amount of drag demands the Veyron have an 8 liter 1001hp to reach it’s top speed.

My 2001 SR5 came stock with a 28.3” tire. Now I run a 32.8” tire so my difference is 16%. I also carry a lot more weight in tools, gear, have a 4.5” total lift, a roof rack, etc. If take all those things into account my gas mileage is virtually the same.

I would be willing to put money down that you are right about people driving faster. And also that people won’t do the basic math to figure out what their true mpg is. Most people (except really old people lol) can’t bear to drive under what their speedometer matches as the posted speed. Sure you can do the math and try and remembering that when going 70 mph you really need to keep your speedo at 16% lower but it’s too much brain damage and it’s a mind screw even if people to take the time. I would be willing to bet a $100 that none of my friends (or myself) can keep their speedos at or under the posted speed limit for a week. In fact even if I gave them 5mph over the speed limit I bet they still couldn’t do it. It’s just too hard to discipline the need for speed. lol

 

[LINY4Runner]

I would say that most of the MPG loss of using bigger tires is attributed not to the height of the tire, but the width (more drag), and mostly the weight.

My stock wheel/tire combo weighed around 55-60 lbs
My 285/70's on the 17" Sequioa wheels are between 80-90lbs

times 4

that's around 130lbs EXTRA of rotating mass. that's where your MPGs suffer.
add to this that the 5VZ engine is underpowered to begin with...

I have been tracking my gas mileage using the Gas Cubby app on my iPhone, which if you're not familiar with, calculates your MPG to a tenth of a mile. Bone stock (225/75/15) she averaged 19.8. After the 31x10.5 she averaged 15.9 (with the ACTUAL distance used rather than the odometer). Now with the 285/70, my average is 13.1 (again, with the actual distance taken into account)

But I do agree...using the odometer to calculate gas mileage will result in 2-3mpg less than your actual value.

just my .02


But like I've hear alot of people say, if you're worried about your gas mileage, you bought the wrong vehicle.

I just got an 88 Camry about a month ago. So far been averaging 28-32 mpg and the car has already paid 10% of itself off in gas savings over my 4Runner. If you're worried about your gas mileage, do what I did.

(that did kinda sound pretty ****-ish of me, but I meant nothing by it...just my 2 cents, as I said)

 

[p nut]

Good thoughts, but you cannot defy physics. Bigger tires usually mean more weight, especially further away from the center. It WILL take more power to turn, which means more gas. Width doesn't matter as much (to an extent). For instance, I went from 265/70/16's to 235/85/16's and noticed a 1-2MPG drop. It is better than when I had 265/75/16's (2-3MPG drop), but it still DROPPED. Simply, it will take more power to turn those tires. (And BTW, the miles driven were all calibrated accordingly.) You can change the gearing to compensate, but you will still see a drop in MPG.

 

[JohnsD90]

I would say that most of the MPG loss of using bigger tires is attributed not to the height of the tire, but the width (more drag), and mostly the weight.

My stock wheel/tire combo weighed around 55-60 lbs
My 285/70's on the 17" Sequioa wheels are between 80-90lbs

times 4

that's around 130lbs EXTRA of rotating mass. that's where your MPGs suffer.
add to this that the 5VZ engine is underpowered to begin with...

I have been tracking my gas mileage using the Gas Cubby app on my iPhone, which if you're not familiar with, calculates your MPG to a tenth of a mile. Bone stock (225/75/15) she averaged 19.8. After the 31x10.5 she averaged 15.9 (with the ACTUAL distance used rather than the odometer). Now with the 285/70, my average is 13.1 (again, with the actual distance taken into account)

But I do agree...using the odometer to calculate gas mileage will result in 2-3mpg less than your actual value.

just my .02


But like I've hear alot of people say, if you're worried about your gas mileage, you bought the wrong vehicle.

I just got an 88 Camry about a month ago. So far been averaging 28-32 mpg and the car has already paid 10% of itself off in gas savings over my 4Runner. If you're worried about your gas mileage, do what I did.

(that did kinda sound pretty ****-ish of me, but I meant nothing by it...just my 2 cents, as I said)

the engnie is still turning that 3(5 or 3 or 7)" wheel, which the larger the tire height wise, the more power required to turn it.

 

[steezemcqueen]

remember that most speedometers usually read about 5% over what you are actually driving. i went from a 28" tire to a 31. now my speedometer matches my gps and those radar carts almost exactly :banana:

 

[Spencer]

Good thoughts, but you cannot defy physics. Bigger tires usually mean more weight, especially further away from the center. It WILL take more power to turn, which means more gas. Width doesn't matter as much (to an extent). For instance, I went from 265/70/16's to 235/85/16's and noticed a 1-2MPG drop. It is better than when I had 265/75/16's (2-3MPG drop), but it still DROPPED. Simply, it will take more power to turn those tires. (And BTW, the miles driven were all calibrated accordingly.) You can change the gearing to compensate, but you will still see a drop in MPG.

I never said it would get you the same or better. I understand more weight/roll resistance all I was saying was, well its in the title.. Not as bad as you think..

 

[jinxed13]

as mentioned before gearing is an issue. i unfortunately have the 3.90 gear ratio and am running bfg 285 mudders. so highway mpg isnt really an issue, its the acceleration, which i live in a city so there are a lot of stop lights and signs.

i get 250 tops a tank, thats with adding the 10%

so, yes the statement is correct in theory. however there are many more issues to consider.

someone donate me some 4.88's, and ill ***** no more.

 

[Shoke]

I would say that most of the MPG loss of using bigger tires is attributed not to the height of the tire, but the width (more drag), and mostly the weight.

The surface area of a tire does not influence its friction on the road, It remains the same regardless of its width.

Weight does play a role in the amount of friction present between 2 surfaces.

 

[Spencer]

The surface area of a tire does not influence its friction on the road, It remains the same regardless of its width.

Weight does play a role in the amount of friction present between 2 surfaces.

It's commonly thought to be more rolling resistance.. Care to share your theory as why? I know bicylists use skinner tires when doing anything other than moutainbiking let's just say road use because of less rolling resistance..

 

[Shoke]

It's commonly thought to be more rolling resistance.. Care to share your theory as why? I know bicylists use skinner tires when doing anything other than moutainbiking let's just say road use because of less rolling resistance..

Physics my friend. As pertaining to two surfaces moving against each other, surface area doesn't influence the coefficient of friction between them.
Learned it in Biomechanics a couple semesters back.

But thinking about it, maybe this only applies to two flat surfaces moving each other. I'm not sure. But heres a small explaination of why it works that way.

"Although a larger area of contact between two surfaces would create a larger source of frictional forces, it also reduces the pressure between the two surfaces for a given force holding them together. Since pressure equals force divided by the area of contact, it works out that the increase in friction generating area is exactly offset by the reduction in pressure; the resulting frictional forces, then, are dependent only on the frictional coefficient of the materials and the FORCE holding them together.

If you were to increase the force as you increased the area to keep PRESSURE the same, then increasing the area WOULD increase the frictional force between the two surfaces."

http://www.physlink.com/education/askexperts/ae140.cfm


Here at the bottom it states that if you increase the force(weight) then increasing the width would increase friction. So i suppose if you were to upgrade to a heavier tire and wheel the friction would increase as a result of the force increase. But simply increasing the surface area of the tire would not increase friction.

 

[p nut]

Good thoughts, Shoke, but you have to remember that there are other factors in this. One of which is, the sidewalls. When you look at your tire, what is touching the ground? You will notice JUST the treads (hopefully, anyway). The sidewall bulges out, and how much it bulges out depends on its stiffness. However, it does NOT add to the contact patch. You will notice as you go wider, the bulge is not as prevalent with the same given pressure. That's because it is absorbed by the bigger contact patch of the wider tires.

Why do you think race cars run WIDE tires versus tiny skinny ones if the traction were to be the same? Wider DOES mean bigger contact patch, which equals better traction.

Also, this is why I run tall, skinny tires (235/85/16), because of the better deformation for off-road purposes.

EDIT: Ok, I misread your post. I see what you're saying. However, the two factors (surface area/contact patch) are NOT direct reciprocals. There is a point where MORE contact patch does not equal better traction, though. For instance, I have run 265's on my race car, but I didn't pull any faster times than running 215/225's. I suppose that "no advantage" point is somewhere between that. But I centainly pulled better times than running 195's.

 

[Spencer]

Well wouldn't you 195s run faster since there lighter?

 

[p nut]

Well wouldn't you 195s run faster since there lighter?

Yes, less RR, BUT!! two things.

1- Cornering/turns. Not that great due to less traction.

2- Straights/acceleration. Cannot get the tires to hook up as easily.

If you go too wide, same factors apply. Need to find happy medium.