Octane rating - is it worth it?

I have several older larger vehicles - one with 85,000 miles (2002 3/4ton chevy) and one with 174,000 miles (1998 suburban 1500). Both ‘recommend’ or ‘require’ use of 87 octane fuel. Is this really necessary as these cars are older? Fuel costs are so high, it could save some cash going to a 85 octane. Thoughts?

This question has been asked literally HUNDREDS of times. Do a search and you can read about it for hours.

Save what, 10 cent a gallon? That would be only 3% savings. Maybe a dollar on every 10 gallons. You’ll spend more than that on the first fuel-related repair. Plus, the reduction in fuel mileage will really eat into it. Best to stick to what it asks for.

If 85 octane gas is for sale in your area, you live in an area that’s over a mile above sea level. At low altitudes, 87 is regular grade and they don’t sell anything lower.
The higher the altitude, the lower the octane rating your engine needs, that’s why they sell 85 instead of 87 in places like Colorado and Utah.
If the owner’s manual says use 87 but you live in a high altitude area where 85 is sold, you can most likely use 85 with no problems, just remember to switch to 87 when you visit Florida.

If “recommended” using lower octane fuel will reduce performance and mileage. Maybe it will reduce the mileage enough to pay the difference in cost, maybe not. You call.

If it says “require” then in addition to the above, you may damage the engine by not using the prescribed fuel, that is going to cost you more what you could save on fuel.

Yep. The thinner air means less air is getting compressed in the engine which results in a lower compression ratio, which means you can use lower octane gas.

Where I live, we have 87 octane but about 60 miles to the east it goes down to 85 or 85.5. I always just fill up with whatever the “regular” grade is and I’ve never any problems with it on any of my newer (post 1985) cars. If I’m out in that neck of the woods with one of my older cars, I will occasionally fill up with the 88 octane midgrade when I’m heading back to the low country.