Wide tires, gas mileage, dealer added.

I'm looking at a 2011 regular cab 4 cyl. and the dealer added different tires that stick out an inch or two. I guess it looks cool but I think it will decrease gas mileage. When I asked the salesman about this he gave me a blank look and then said it wouldn't change the gas mileage. All the other trucks on the lot have their tires nicely tucked under the fenders so I'm sure the mileage figures reflect that configuration.

Any opinions?

 

more rotational mass whether its taller and/or wider will mean that it will take you a little more throttle to accelerate up to speed...

 

Make sure the tires are actually wider and there isn't just a wheel spacer added or wheels with a different back-spacing. Can you read what tires and size they are from the side? You can search them on Tirerack.com for their actual weight and compare them to the stockies. Or you can just list them here and we'll look em up for you if you're mobile right now.

 

I lost a 1 - 2 mpg with the wider tires I put on my Tacoma. Width was the only thing I changed, overall height remained the same.

 

bigger footprint means more rolling friction means more power needed to roll means less mpg; pretty simple.

 

well, technically all this is right.... more friction = more traction = less gas milage

BUTT

I highly doubt you would notice a change in gas milage from wider tires... i would say what it comes down to, is do you like the look of the wider tires... because at least on the lots around here there is an endless number of tacos to choose your perfect one, so get the one you like, wider tires won't cause you to get a noticeably worse milage, especially with these trucks that already burn a ton of gass

 

I agree and disagree with your statement. You'll notice a change in mpg, depending on how much wider of a tire you put on. I went from stock 245/75R16 to stock 265/65R17s. Same overall height, drop in gas mileage 1-2 mpg, nothing big but noticeable. Tread pattern and load range also affect this. Higher load range (heavier tires) and more aggressive tread patterns hurt your gas mileage also. Usually when people go wider, they put on more aggressive tires.

 

I would definitely agree with the tread pattern affecting milage, but i believe that a slightly wider tire on this guy's ( I believe he said 4 cylinder ) won't affect milage to a noticeable degree. First of all, i think that he would only have spacers and not an actual rim and tire that are 1-2 inches wider, and if he did, they're probably street tires, not knobby off roaders so...

Even if it is a 1-2 mpg diff, that should not make a difference in buying a TRUCK!!! If you're buying for milage, he shouldn't be buying a truck...

I think that the truck this guy wan't should also be avalible with normal tires on it, so it should only come down to if he likes the look or not..

 

I want a truck with better gas mileage than a full size PU whick I have right now. I absolutely need a truck and a box the size of Tacoma is fine. I like the dependability of a Toyota. I can have them change out the tires in any case but I was curious what others experienced in mileage drop off.

Thanks for the things to think about. No one mentioned the aerodynamic change in the side surface of the truck--I've been reading the posts about toppers, shells, tonneau covers and tailgate removal and I would think this might be a factor.

 

That's not entirely true. Although a wide tire adds horizontal width to the contact patch, it also takes away from the front/back patch size which means the amount of tire in contact with the ground will be about the same size. The truck will only exert so much pressure per square inch on the road surface. If a tire is wider, it spreads the weight of the vehicle to the sides rather than front to back. A skinnier tire will put more weight front to back. Rolling resistance is going to be about the same for a similar tire compound. What will make a difference is the weight of the tire. More weight further out means more rotational mass and more power to turn it.

 

I'm sorry guys. I'm probably going to sound like a total prick, but I have to say it.

I think the idea of having more frictional resistance from a wider tire and thereby having a noticeable decrease in MPG is pretty naive. I'm no physics expert, but I just don't see that making such a great impact.

HOWEVER, the difference in rotational mass afforded by heavier tires and wheels could most definitely have a an impact in my eyes (especially in a vehicle with low torque).

Sorry if I've offended anyone, but I just don't see the friction issue being such a big deal. Just my thinking, I guess...

Side Note: The point made by Evil_Monkey about the actual surface area of the tire also goes decreases the likelyhood that the "Frictional Resistance" is the real culprit. Good thinking. Though not the exact same, the surface area would indeed be similar.

To the OP: You are correct that it "could" decrease your mpg by having increased wind drag; however, the points you mentioned about the tailgate and such represent MUCH larger wind blocks. I suspect the wheel-wind drag 'might' have the slightest of affects. But most likely negligible in the grand scheme.

 

My 2008 V6 DC Prerunner, TRD Off Road,

Stock wheels, stock 265/70/16, 17.5-17.9 MPG
20x9 wheels, 285-50-20 Yokohama, tires flush with fenders, 17.5-17.9 MPG
18x10 wheels, 285-60-18 Toyo AT, 2.5 inch lift, tires about 1.5 inches outside the fenders, 17.5-17.9 MPG

That is average MPG, probably 80% Interstate @ 75 MPH

 

Tire width does have impact on your mpg. If you want to check it out, do three tanks one under inflated, and one with over inflated tires.

Your mileage with over infalted tires will be better than the under inflated.

8" x 4" = 32sq inches of contact (typical tire)
9" x 4" = 36sq inches of contact. (one inch wider)

4 sq inches x 4 = 16 added square inches of contact or about a 10% increase in friction resistance.

This is without taking into account the "stickness" of the tire. The sticker a tire the worse the mileage.

 

Thats rolling resistance, much different than width.

 

I will concede the "stickness" point without any hesitation. The softer the ribber, the easier it'll become sticky from friction.

Also, the fact that an under-inflated tire will decrease MPGs. Though that could also be attributed to the fact that an under-inflated tire would drastically increase surface area. That would definitely go against Evil's point. As would the formulas that you posted, as ideally the "4" should decrease due to weight dispersion.

But, as I said before, just my thinking.

 

When you deflate, you're increasing the size of the contact patch because the tire has to spread to support the weight of the vehicle. This doesn't represent a wider tire even though the contact patch is wider.

In two equally pressurized tires, the contact patch will be the same regardless of the width. As I stated earlier, the truck exerts the same weight on the tires. With two tires of equal pressure but different widths, it's going to spread the contact patch in different directions, but it will still be the same overall size.

 

what about lo pro tires

 

the profile of the tire doesn't play into it. You start affecting your mpg's with low pros because you usually end up sticking a larger rim on the vehicle which weighs more.

The psi in the tire is roughly what the tire exerts on the road. Wider tires, same truck weight, usually have slightly lower tire pressures.