One caution, many of the lower mpg comparisons are when a car owner replaces worn tires with brand new tires. The new tires even the same exact tires will get lower mileage because they have full tread depth and a larger diameter than worn tires. Comparing worn tires to worn tires or new tires to new tires is the actual comparison that should be done to provide accurate statistics,

In summary new tires will always give less mpg than worn tires of the same brand. If the replacement tire is a different brand you might or might not see a mpg change based on comparing the diameter of the full tread new tire to the diameter of the worn tire being replaced.

The is a whole lot of misunderstanding for new tire mpg.

YMMV,
MidCow3

 

Several dumped newish tires for the CC2 because they thought they didn't like the OEMs (mostly those that got Goodyears; mine fortunately had Continentals). I changed from old to new OEM tires and saw no difference at all in MPG, but they were barely showing the wear bars when I replaced them...I did it because I could see cracks in the rubber after just 4 years of use. You will find many threads on reddit and other car forums talking about this issue with CC2.

 

Just for clarification, are you suggesting that newer tires (with the associated slightly larger diameter full tread depth tires) get worse MPG because of greater rolling resistance? Or because a slightly larger diameter tire will appear to have travelled a slightly lower distance?

 

Good point to consider. Plus, a new tire with full tread depth will always have higher rolling resistance, more squishy tread material present means more rolling resistance but safer driving conditions for the wet or slushy snow. Conversely coming from a used tire with much less tread that will offer better lower rolling resistance as it's approaching 'slick' conditions. Everywhere I look I find Michelin CC2's coming in the top of the heap for best rolling resistance when in a comparison test with other highly competitive tires. This to me is a more scientific accurate comparison when all tires are new, under ideal comparative conditions to trust results.

See time stamp at 14:58, CC2's have the lowest rolling resistance of 7.05 kg/ton:

 

Just sharing another run-flat option -- Continental CrossContact LX Sport SSR. I had the 20" Alenza runflats and found they had terrible traction -- bad hydroplaning and even poor in tight turns in dry conditions. I liked the peace of mind of runflats (not changing a flat on a busy urban highway) so did a lot of research. The CrossContact is liked by a lot of Mercedes and BMW SUV drivers so I made the switch and I have been very happy. If you don't want runflats I agree the Michelin CrossClimate 2 is a great tire, but if you want runflats I would encourage considering the Conti. It comes in an 18" size compatible with the NX as I recall, but not the 20". I decided to buy 19" wheels from TireRack and have the Cont's pre-installed on those and it has worked great. I did it after about 25K miles on the Alenzas and while it required me to spend an extra $250 per wheel I'll use them for the life of the car and I'm very happy having runflats with good traction.

 

Larger moment arm ( physics principal) requires more force (joules) The larger diameter, means a larger circumference and requires the car to provide more force for each turn of the tire. Rolling resistance is not relevant. In actuality, each turn of the tire doesn't just appear to travel a greater distance; it actually does travel a farther distance. There is no adjustment on the odometer measurement when you change tires ( it is still based on number of revolutions; very, very simple measurement) so you are correct, the measurement displays on the car will appear to have travelled a slightly lower distance.

YMMV,
MidCow3​​​​​​​

 

Yes, a larger diameter tire has a higher moment. However, it also results in the engine turning lower rpms which should offset some of the mileage loss.

If you run your tire tread down to 2/32", then you will lose 3/8" in overall diameter. Given the initial diameter is 29.1" that means the new tire is 1.3% larger in diameter compared to a worn out tire. That's not much. And from what I have read, rolling resistance is relevant. The deeper tread squirms more. There a number of people that feel the loss in mileage is purely due to the increase in rolling resistance of a tire with deeper tread depth.

I really enjoy this discussion, I've never really ever thought about lower mileage with new tires. It's always fun to get mired in the minutia.

 

A few factors impact the true realized tire rolling resistance on a car. There are SAE and ISO standard tests performed to determine this type of resistance under lab settings to provide to tire manufacturers. Tire tread depth, tire pressure, alignment of tire on car ie camber castor all will impact rolling resistance of a tire on a car.


Tire Rack has a 3 part article on rolling resistance

https://www.tirerack.com/upgrade-gar...e-fuel-economy


"During stop-and-go city driving, it's estimated that overcoming inertia is responsible for about 35% of the vehicle's resistance. Driveline friction is about 45%, air drag is about 5% and tire rolling resistance is about 15%.

Overcoming inertia no longer plays an appreciable role in the vehicle's resistance during steady speed highway driving. For those conditions it is estimated that driveline friction is about 15%; air drag is about 60% and tire rolling resistance represent about 25%.

Let's explore a scenario where a high performance replacement radial tire has a whopping 20% increase in rolling resistance over a low rolling resistance Original Equipment standard passenger radial. To calculate the potential change in mpg resulting from using the high performance tires in place of the Original Equipment tires, we would multiply the tire's percentage of influence on the vehicle's overall resistance (15% in the city and 25% on the highway) times the high performance tires' 20% increase in rolling resistance.

If the vehicle equipped with standard Original Equipment, low rolling resistance passenger tires normally provided 25 mpg in the city and 30 mpg on the highway, installing tires with 20% greater rolling resistance would only drop fuel mileage by a calculated 3% (to 24.25 mpg) in the city and a calculated 5% (to 28.5 mpg) on the highway. While this is a measurable difference, it probably isn't much more of an influence on real world fuel economy than being stuck in rush hour traffic a couple of times a week or being stopped at every red light instead of continuing through a string of green lights.

The easiest way to reduce rolling resistance and enhance fuel economy is to make certain that the tires are properly inflated. A vehicle that requires its tires to be inflated to 35 psi (based on the vehicle's tire placard) will have an increase in rolling resistance of approximately 12.5% if the tires are allowed to become under-inflated to just 28 psi. Therefore, maintaining the vehicle manufacturer's pressure recommended for light load and heavy load conditions may almost be as important as the tires being used."

Tires and their difference in rolling resistance have very minimal impact on changes to a car's gas mileage as noted above. I don't know how anyone can say they are getting from a tire swap 5-10% in noted gas mileage changes. You would need to go to a track tire to see that sizeable type of swing.

 

New Tires Generate More Rolling Resistance Than Worn Tires

Tire Rack Rolling Resistance Pt3:

" New Tires Generate More Rolling Resistance Than Worn Tires

It's been observed that rolling resistance drops by about 20%, as a tread wears from its original molded depth to worn. While this reduction in rolling resistance over time is subtle, a switch from worn tires to a new set increase rolling resistance by a noticeable 20%. The automotive industry estimates a 10% increase in tire rolling resistance equals a 1% to 2% decrease in vehicle fuel efficiency. So, drivers should expect a 2% to 4% decrease in mpg after installing new tires.

New Tires Travel Farther per Revolution Than Worn Tires

Vehicle odometers calculate distance based on a tire's revolutions per mile. Many tires are molded with tread depths of 10/32" to 12/32". As a tire wears, it loses diameter and revolutions per mile increase. As a result, the odometer's accuracy is affected adversely.

To determine the amount of error, Tire Rack drove a 2008 BMW 328Ci on a set of new 205/55R16 tires, and later, on another set of the same tires shaved to a worn-out depth of 2/32". GPS was used to measure a 100-mile distance, traveled in dry conditions at an average speed of 70 mph. The number of miles as indicated by the odometer was then compared to the GPS receiver and highway mile markers. After 100 miles, the vehicle equipped with new 12/32" tires, registered 99.4 miles, while the vehicle equipped with tires shaved to 2/32," indicated 101 miles. As expected, test results showed that an odometer will overstate mileage by about 1.5% on a vehicle equipped with worn-out tires."

 

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Please report back any MPG change (good or bad) with the conti's

 

I just checked tirerack.com and it's saying the tire is not available for the 20" NX450h+. See attached.
[img alt="screen shot from tirerack.com
"]https://cimg9.ibsrv.net/gimg/www.clublexus.com-vbulletin/2000x1299/screenshot_2025_03_21_at_7_36_50_am_24e7c4e4f805121fcb174a67dcc50ee4e0769579.png[/img]
screen shot from tirerack.com

 

No material change in MPG with the Conti's

 

Correct, those Conti's are available in an 18" size for the NX, but their 20" sizes did not work well for the NX. I decided to purchase 19" wheels from TireRack that were compatible with the NX, as those fit a wide variety of tires (runflat and other) that work well with the NX. I figured if the Conti's were a mistake it would allow me many other options. I like the Conti's so will probably stick with them, but I'll look again in a few years to see if there are any better options.
Wheels I chose: 19x8 Enkei Performance PX-10 GUNMETAL
Tire Size I chose: 235/55R-19 Continental CrossContact LX Sport SSR
TireRack sold them as a pre-mounted package -- wheels+tires+sensors which I liked as I wanted to de-risk and since TireRack confirmed the Wheels would fit my NX and the Tires would fit the Wheels, I had them pre-mount and ship to a local tire shop who then simply put the new tire/wheel combo onto my NX. I kept the Lexus wheels rather then re-sell in case better 20" tire options are available in the future.
Wheels were $246 each, Tires $265 each, Pressure Sensors $42 each ... so total including 5% sales tax was $2355. Much more than a set of tires, but it leaves me very happy so was worth it to me. Tires are cheaper than others I looked at so over a few sets I'll make back part of the cost of the wheels anyway.

 

Thanks for that. I'm going to keep your post for future reference. My NX only has 600 mi on it so it'll be a while before I'm in the market but will be eventually.