18" wheels will drop my MPG?

Hello,

I have a 2011 Jetta TDI with stock 16" alloys. I would like to change it to an OEM VW 18" and keep my 16" wheels for a winter set.
I am curious if the 18"s will impact my MPG, because I do like my commute with 43 MPG. (mostly city some hwy)
I hope you guys have some info on that subject.
Thanks

deszka said:

Hello,

I have a 2011 Jetta TDI with stock 16" alloys. I would like to change it to an OEM VW 18" and keep my 16" wheels for a winter set.
I am curious if the 18"s will impact my MPG, because I do like my commute with 43 MPG. (mostly city some hwy)
I hope you guys have some info on that subject.
Thanks

Click to expand...

All depends on the outer diameter or the tire.Larger tire will increase mpg and decrease acceleration performance while a smaller tire will do the opposite.

Here is a long example:

say your 16in wheel has a 19in diameter tire. the circumfrence is about 59.5 inches. where as a 18 in wheel say has a 20.5in tire and a 64.5 in circumfrence. This means for ever revolution of the tire the 18in one travels 5 (about 8%) inches further. This means that at the same engine rpm you will get more distance out of a larger tire, thus better mpg.

Think about pedaling a kids tricycle versus a mountain bike. You can accelerate faster with the small tire but you can travel much faster and with less energy on the larger mountain bike.

Yep. Some people report as much as a 3-4 MPG drop going to 18" Wheels are typically heavier, tires are heavier, and the weight is concentrated at the tread. If you do a lot of stop and go driving the FE loss will be more significant, less so with steady state cruising where the wheel/tire is up to speed and you're not slowing or accelerating lot.

Expect a 10% drop in fuel economy or more, depending on what type of tires you put on those 18" wheels.

18" vs 16"

Thanks for your posts guys.
I was thinking about going from 205-55/16 to 215-45/18, but i don't like the potential 5-10% MPG loss. I think I will stick with the 16"s and just lower it with H&R springs to enhence cornering and visual appeal.

pdt165 said:

All depends on the outer diameter or the tire.Larger tire will increase mpg and decrease acceleration performance while a smaller tire will do the opposite.

Here is a long example:

say your 16in wheel has a 19in diameter tire. the circumfrence is about 59.5 inches. where as a 18 in wheel say has a 20.5in tire and a 64.5 in circumfrence. This means for ever revolution of the tire the 18in one travels 5 (about 8%) inches further. This means that at the same engine rpm you will get more distance out of a larger tire, thus better mpg.

Think about pedaling a kids tricycle versus a mountain bike. You can accelerate faster with the small tire but you can travel much faster and with less energy on the larger mountain bike.

Click to expand...

i'm not sure if this is correct man. i used to think the exact same thing. i was then told it was all wrong. i still don't fully comprehend it but that's what they say.

i thought it's just the overall diameter that matters. the so called 'pros' said it's the diameter of the rim that makes a bigger difference than the overall diameter. if someone can explain it to me in english, i'd like to hear it too.

Deszka - how are you getting 43 city?

In Seattle I can only get 34 if I am lucky.

Does your commute have little stoplights and cruise around 35-45? I am constantly going up a hill here and I am sure that is killing it. Sometimes I get 25 mpg. All the stop and go, lights and hills.

On my 2010 going from 16s to 18's (205/55/16 to 225/45/18) The wheels are actually lighter than stock. I lost about 12% fuel economy across the board. Greater rotational inertia and a wider tire are definitely the cause.

Small price to pay for way better handling and the look, IMO.

Wider tire = bigger contact patch = more rolling resistance = lower MPG

deucelee said:

i'm not sure if this is correct man. i used to think the exact same thing. i was then told it was all wrong. i still don't fully comprehend it but that's what they say.

i thought it's just the overall diameter that matters. the so called 'pros' said it's the diameter of the rim that makes a bigger difference than the overall diameter. if someone can explain it to me in english, i'd like to hear it too.

Click to expand...

Its all about torque.

More of the weight is concentrated on the outer edge of the wheel/tire combo with larger diameter wheels. Fix yourself up some basic wheel/axle combo you can spin by hand, you'll find its much easier to spin a "wheel" with the weight towards the center of the rotation than out towards the end.

The 18"s will probably be wider as well, increasing the weight even further as well as adding friction from the larger contact patch.

Also don't forget, rubber compounds change from tire to tire. Most tires that are going to be sold with those 18" rims will be high performance or above. They all swear to more "grip" which is a function of two things: Contact surface area with the road (due in part to tire size and tread pattern) and the overall friction coefficient between the specific rubber compound and the road.

Yes the bigger size gets you further per rotation, but your motor has to work harder to get it/keep it rolling.

Ok, granted my explanation doesnt take into account moment of inertia, rolling resistance etc..... Go with what experience proves.

I went from the stock 16s with 205/55R16 tires to an 18-inch TSW/Goodyear combination with an 18X8-inch wheel and 225/40R18 tire and the new tire and wheel actually weighs 0.75-pounds LESS than the stock 16-inch wheel and tire!!!

I haven't ran through a full tank yet to check mileage, but I also lowered it at the same time with Eibach springs so I am guessing that it will be a wash with the increase in MPG from lowering (reduced aero drag) and a decrease from larger contact patch. But I can confirm that it handles and looks MUCH better!!!

The TSW wheel is their Rotary Forged Interlagos and the tire is the Goodyear Eagle GT. I was hoping weight would only go up by a pound or to and was VERY pleasantly surprised that it dropped by the 0.75-pounds!!!

mileage down for sure. cooler look. lousier ride. stickin with my 16's....

I think mine still rides great! Yes it is firmer than it was but in a performance minded way not a harsh, go-kart kind of way!

deszka said:

Hello,

I have a 2011 Jetta TDI with stock 16" alloys. I would like to change it to an OEM VW 18" and keep my 16" wheels for a winter set.
I am curious if the 18"s will impact my MPG, because I do like my commute with 43 MPG. (mostly city some hwy)
I hope you guys have some info on that subject.
Thanks

Click to expand...

The test result on the link below may be helpful.

http://www.caranddriver.com/features/effects-of-upsized-wheels-and-tires-tested

I checked the mileage on a 180 or so mile trip yesterday and I got 48.3 MPG hand calculated topping off at same pump before and after trip. So in my case the MPG is the same or better but I made several mods at once including lowering the car with Eibach springs, new wheels and tires 225/40R18 Goodyear Eagle GTs, dieselgeek.com skidplate and aFe intake install. I have generally been getting between 45-47 so I have a slight improvement!

AND I think the car looks much beter and handles much better with the new combo!!!

I went from standard 15" wheels to 18" 225x40 and then back to 15" again and theres that many variables when driving if you average your mpg out over time you don't really notice any drop

unfortunately yes... expect around 10 % (5mpg) The wheels are heavier, and the rolling resistance higher... alas (18s do look WAY better!)