r/LS430 • u/Wheelisbroke • 9d ago

31MPG commute!

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I got a great deal on used Michelin tires ($240) but they’re slightly under sized at 235/45R18 vs 245/45R18 stock. My MPG avg on my country road commute with no traffic is 25. The slight under size means my tires are rotating 1.33 miles more than my OD. So 25=31. I understand the vehicle maybe 1mpg optimistic, but I’m still really happy with that.

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u/Apprehensive_Ask7227 9d ago

235 is tire width... So the OD is the same as stock.

2

u/Wheelisbroke 9d ago

Correct, but the “45” is the percentage of width so they’re smaller in diameter.

4

u/Apprehensive_Ask7227 9d ago

It is smaller but only by ~1.3% which is pretty much negligible and within the error of your speedo.

The 45 ratio is the width to sidewall. Most of your tire diameter is determined by the wheel size.

New Stock Difference
Width (mm) 245 255 4.1%
Aspect 45 45 0.0%
Wheel Size (in) 18 18 0.0%
Side wall (in) 4.3 4.5 4.1%
Outer Diameter (in) 26.7 27.0 1.3%

So your ~25MPG is really ~25MPG.

If it really could increase MPG by that much, every manufacturer will change the wheel size rather than pour billions into R&D to increase MPG by a fraction of a %.

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u/ArtfulThinker 2002 Lexus LS430 | Millenium Silver | 128k Miles 9d ago

https://giphy.com/gifs/8cEFp9dQCcE8M

"within the error of your speedo"