[Ziyang]

The mpg figures are mostly benefited from Michelin’s Energy Saver tires. Don’t go with other brands or models, otherwise your mpg would just drop.

I bought Continental PureContact LS 225/45/R18 (also claimed to have EcoPlus) with aftermarket 18” wheels. Same width, right? That week my mpg dropped by 10 even for pure city driving. Later I replaced them with 235/45R18 because the former tire only has 91 load index. Guess what? No difference between 235 and 225.

Therefore, I highly doubt if decreasing tire width by 10mm would help your mpg figures, but choosing any tire other than Michelin energy saver will 100% decrease your mpg by 10, to say the least.

The downside of high-profile tire is also vivid. I have been enjoying the much improved cornering support from both 225/45/R18 and 235/45R18 tires. They also make highway lane change a swift compared to OEM 225/50/R17 which just feels uncertain and risky. Now if you go 215 with higher profile, no doubt the handling is adversely impacted, as well as braking distance.

While Michelin Energy Saver does give fancy mpg figures, I doubt if it compromises too much for traction, and its higher price makes up some fuel saving $$ in the life time too.

 

[Ziyang]

(1) You have aftermarket wheels. How much do they weigh? My random guess is they weigh more than the stock oem 17 inch wheels which weight 27.46lbs each and are constructed to reduce drag. So, maybe your 18 inch aftermarket looks fancy and not built like oem 17" to glide through air.

They weigh 25 lb each, lighter than OEM wheels.

Are the shape of wheels really important? I wouldn't agree. Someone did experiments with Tesla aero wheels, but the results are not significant at all, and didn't support the argument that aero-designed wheels help more on higher speeds.

Besides...I already said that's city mileage, so the major difference is only tire compound.

If you want to compare highway mileage, I also have some figures for your reference. Doing 80-85 mph on mountainous highway, OEM setup gives 33-35 mpg, my 18" aftermarket setup gives 30~33 mpg. The difference is actually smaller because at higher speed drag resistance (which is mostly determined by a vehicle's overall shape in the flow, specifically the frontside projected area and the rear shape that flattens out low-pressure zone) accounts for more %.

I just swapped to another set of 18" flow-forming wheels which only weigh 20 lb each. My new wheels are also 5mm inward so it should bring less drag. But again, I see no difference vs the 25lb wheels. Therefore, I do believe that wheel shape and wheel/tire weight are just negligible factors unless you go extreme.

(4) Last but not the least, I wonder what psi you are running. I am currently running 36psi all around with stock tires. When I buy my new tires 215/55R17, I will run them at 38psi or 40psi.

I set front 35 psi and rear 33 psi for the balance between highway cruise and handling.

I honestly don't know whether running higher psi is worth it. You risk having longer brake distance in emergency situations, and your tires risk uneven worn out...

2 quarts 0W16 and 2 quarts 0W20. Someday, I MIGHT try running straight 0W16.

Since our hybrid powertrain is covered under an extremely long warranty period, I would never consider changing the oil viscosity and compromising high rpm protection. I do find it necessary to floor it at 6200 rpm from time to time.

There are options like Mobil 1 Advanced Fuel Economy full synthetic. I had good experience with it before, although I switched to Costco branded full synthetic just because it's more than 50% cheaper...

 

[Ziyang]

I'd say you could trade in your Accord hybrid for Insight hybrid lighter, smaller, with 1.5L engine.

My friend has Insight hybrid, and he easily does 55 mpg without taking any cautions.

 

[Ziyang]

I just found these links and thought I should share with you and others who may just want to have a glance. Tesla vehicles have it on their door jam to run their psi at 42psi or 45psi. That is on tires which have maximum psi of 50psi. They all say Tesla recommends this for maximum efficiency and best mpg.

You know Teslas are very high performance cars but also give great mileage. So, for the manufacturer to suggest those very high psi it means they know what they are talking about.

According to Tesla, the high psi gives best mpg and range. They are running their tires not at the maximum psi of the tire. 42psi or 45psi is lower than the max psi of 51psi, but still a high psi for someone like me who drives a Honda Accord where they recommend 33psi. I am running 36psi now and I believe it is not a high number per say. But I would love to experiment with 40psi on my next set of tires because that tire has a max psi of 51psi. This is what I plan to do to my car.

Tesla Model 3 high recommended oem psi of 42psi and 45psi...

Tesla high recommended psi across many years and models...

Thanks for the link, but I disagree with applying Tesla’s tire pressure recommendation to Accord (hybrid).

Tesla and many other EV models all have a heavy battery (>75kWh, or 1060 lb) and they must set higher psi for the tires to provide the sufficient load capacity. — A tire’s load capacity is more or less proportional to its pressure until a max value, say 35psi for non XL and 41psi for XL tires.

The high psi does not necessarily mean they are good. A lot car reviewers have commented that these long range EVs all have a ‘bouncy and firm’ ride due to the high tire pressure.

You simply cannot apply this to Accord hybrid because it isn’t that heavy, and your Honda manufacturer never recommends you inflate the tires to 41 psi. 41psi makes a Tesla’s tire have desirable contact patch on road, not an Honda Accord.

 

[Ziyang]

Do you prefer to do alignment at dealership, or any tire shop? I’m a bit curious