Wheel size change: Can I really improve FE?

[bikemaniac]

Hi,

Can I reduce my fuel consumption by mounting smaller wheels? I've been reading so much on this subject but don't get any definitive answers, so I will try my luck here.

Setup:

1) 2015 Volkswagen Polo 1.4 TDI with the CUSA engine. Right now the car has 15 inch rims and Michelin Primacy (185/60R15) tires are mounted but they are worn.

2) I need a new setup with new All Season tires and I am willing to make the investment in new rims if necessary.

3) The most important feature is fuel economy, handling and grip is secondary.

4) I will mainly be driving highway and not city.

5) The car can (legally) be fitted with the following tire sizes:

a) 175/70R14
b) 185/60R15
c) 215/40R17
d) 215/45R16

6) As I understand, special low rolling resistance compounds are mainly offered for bigger wheels, but again, smaller wheels have the "classical" benefits without the special compounds.

Main question:

Will I get a fuel economy benefit by purchasing 14 inch rims and mounting the smaller tires? Will the 215 tires give me a bigger benefit due to the special compounds? Can anyone estimate the benefit in % - or maybe with a test?

Lucas

[Gasoline Fumes]

I would choose the most efficient tire available to you in either 175/70R14 or 185/60R15. I'm assuming the tire you pick will make more difference than the wheel size. 175/70R14 will likely be lighter, but it won't be that important on the highway. How important is comfort? 175/70R14 will probably give you a smoother ride.

[bikemaniac]

Originally Posted by Gasoline Fumes

How important is comfort?

Not important

[Gasoline Fumes]

These are apparently really good.

185/60R15 88V Michelin CR.CLIM. 2

Wet grip: B
Fuel efficiency: B
External noise: 69dB

[Gasoline Fumes]

My favorite tire channel:
https://www.youtube.com/@tyrereviews
He mostly reviews tires sold in Europe.

[Ecky]

There are a lot of variables at play. Some things I can say:

-In new vehicles with multiple wheel size options (e.g. 17", 18", 19"), I can think of zero examples where the larger wheel doesn't get worse fuel economy than the smaller option(s). However, the smaller wheels may also be shipping with tires that are more economy focused.
-Narrower tires are meaningfully more aerodynamic.
-Smaller wheels are almost always lighter, and the part of the wheel that causes aerodynamic turbulence is smaller.
-Smaller wheels are tires are generally cheaper, though you may never fully recoup the cost of the wheels in fuel savings.
-Tire selection is generally worse in smaller sizes. I still find adequate choice in 14 but it's dwindling.
-You'll want to make sure your 14" option will clear your brakes.

I almost always downsize when given the option.

[19bonestock88]

Originally Posted by Ecky

There are a lot of variables at play. Some things I can say:

-In new vehicles with multiple wheel size options (e.g. 17", 18", 19"), I can think of zero examples where the larger wheel doesn't get worse fuel economy than the smaller option(s). However, the smaller wheels may also be shipping with tires that are more economy focused.
-Narrower tires are meaningfully more aerodynamic.
-Smaller wheels are almost always lighter, and the part of the wheel that causes aerodynamic turbulence is smaller.
-Smaller wheels are tires are generally cheaper, though you may never fully recoup the cost of the wheels in fuel savings.
-Tire selection is generally worse in smaller sizes. I still find adequate choice in 14 but it's dwindling.
-You'll want to make sure your 14" option will clear your brakes.

I almost always downsize when given the option.

He beat me to it. It’s worth mentioning that between your smallest and biggest wheel sizes there is 40mm worth of tire on each side of the car and that’s significant from an aero standpoint. Were it I doing it, I’d probably stick with a 15 and maybe try and fit an aero disc to the wheel.

[Piwoslaw]

In general, as mentioned above, smaller tire should weigh less, which makes more of a difference in stop & go city driving. Less unsprung mass also improves comfort.
Smaller wheel will also give you better acceleration.

On the other hand, a larger overall wheel radius/diameter (not just the rim) lowers your engine's rpms, so can lower fuel consumption when cruising on the highway.

Originally Posted by bikemaniac

5) The car can (legally) be fitted with the following tire sizes:

a) 175/70R14
b) 185/60R15
c) 215/40R17
d) 215/45R16

What about 175/65R15?
Or maybe even 165/80R14?
I put 185/65R15 for winter on my previous Peugeot 307, even though the smallest should be 195/65R15. On the P308 I have 195/65R15 for both seasons, only because it was difficult to find 185s with low RR.

Also check the tire's rated max pressure. Most have 51psi, but some have 44psi (as I found out only after purchasing). I pump my tires to their max pressure, but never more. Some prefer 10% below max.

[bikemaniac]

Thanks for all your replies :-)

[CapriRacer]

Originally Posted by bikemaniac

Thanks for all your replies :-)

Did you notice you didn't get a definitive answer to your question?

That's because tire size doesn't play much of a role in fuel economy - except to say that a larger diameter tire changes the car's final gearing.

What plays the largest role is the tire itself. As a general rule, OE tires give the best fuel economy. That's because car manufacturers specify extremely low rolling resistance tires - and they get that by having the tire manufacturers sacrifice treadwear and/or traction, especially wet traction.

But OE tires generally go out of production after the year/make/model car goes out of production. That's because very few folks are more interested in fuel economy than treadwear and traction.

So your next best bet is tires that advertise low rolling resistance. Those aren't as low as OE tires, but are generally better than other tires with the same treadwear and traction. That's because those are made with a tread rubber compound superficially designed to do that. That also generally means a bit more cost. Cheap tires aren't have that.

HOWEVER, if we consider the total cost involved, changing wheels is expensive, so that isn't the best way to go about this.

Most likely the least expensive option is to stay with the original tire size and select tires with the best combination of fuel economy and treadwear.