85 Octane in The FJR

[HotRodZilla]

On our way to Salida for the SW-FOG, 86 octane gas became available in Espanola and 85 was available in most of Colorado. I decided to stick with 87 or higher, just to see what, if anything, would happen.

In Espanola, I had to use 88 as that was the next level up, and in CO, I used the mid-grade 87. I truthfully don't know if there was any difference or not, but with my wife and I on the bike, and me on the throttle, we averaged 45mpg. The bike ran great.

Without running the bike the same exact way in the exact same conditions, I donno if my mileage was any better, but it seems better than I have gotten in a long time. I have always just used the 86 or 85 in the higher elevations, but I'm thinking I'll stay at least 87 from now on. There were a few times I was getting average 50mpg. The average dropped as we burned home at almost 90 in the wind.

As always, and literally, YMMV. Lol.

 

[wfooshee]

Again.

At elevation, with the thinner air, 85 octane is regular gas. It behaves the same at 4500 feet, or 6000 feet, or whatever, as 87 octane does at sea level, or 1000 feet, or whatever.

It's not a lower-grade gas. With the lower air pressure (thinner air) you don't need the same octane to get the same knock resistance. Go by the grades, not the octane.

Regular gas is regular gas. The octane is adjusted for altitude.

The only reason you'd want 87 or 88 at 5000 feet is if you'd still be on that tank when you reach 1000 feet.

As for mileage increase, the thinner air results in less fuel being required for proper air/fuel ratio at any given throttle, but mostly it means less aero drag on the bike, so less power needed to move it. A given volume of air at 5000 feet elevation has almost 20% less air than the same volume at sea level. Since aero drag is exponential compared to speed, drag still goes up with speed, but nowhere near the same amount as at sea level.

 

[HotRodZilla]

I love ya Walt, but I love it when guys that live a few hundred feet above sea level attempt to educate us that live at elevation.

For reference, my driveway is 5120 feet above sea level. I understand the relation between thinner air and fuel. What's funny is that until average elevation hits around 6k or higher, 85 octane fuel is not at the pumps. At least not here, and not in the small town I grew up in that is around 5500 feet high.

Espanola is not much higher than Albuquerque, bit they have 86 octane gas, and most of Colorado has 85. Even in the lower elevations.

My mileage comparisons are valid because I'm ALWAYS at elevation. Does 8000 ft in Colorado have that much less air resistance than the 6000-10000 feet I normally ride around in here? I'm betting not.

My only point was that by sticking with 87 gas, my mileage was very good. I know that I could possibly get the same mileage with 85 gas in the same areas, but I don't remember that being the case.

Part of what gets me is that Utah has 85 gas almost everywhere and is lower than a lot of NM. Why is that? In know the gas companies here would cheap out as much as they could and go to 85 as soon as possible.

My observations prove absolutely nothing, but I gotta wonder how many here really know what they're talking about when it comes to octane and elevation.

I do know that here, I can get my front wheel maybe 4 inches off the ground if I work at it. In Laughlin and Tennessee at around 700 feet, that thing easily does wheelies that were totally accidental. The available air makes a huge difference 4400 feet lower. But it what is the effect between fuel and elevation?

 

[wfooshee]

The effect between fuel octane and elevation is knock resistance. Less air = lower absolute pressures in the compression stroke = less knocking = lower knock resistance requirement.

And do you know how far I have to go to get a few hundred feet above sea level???!!?!?

And while I've never lived at elevation, I've been there often enough. I had extended visits with family in Colorado Springs for many years, and El Paso more recently. I wouldn't call El Paso "elevation" exactly, but you have to go through some to get there.

The effect between fuel mileage and elevation is aero drag. Mileage is still hard to compare, though, because "flat" 4,000-ft riding is going to be a lot better mileage than hilly riding averaging 8,000 feet. Climbing repeatedly sucks gas and the downhill doesn't make up for it.

 

[steve'o']

Running 85 now, did a 352km (218 miles) run the other day, filled the tank at the end, and it took 19.1 liters (4.18 imperial gals). With some quick math, that equates to a hair over 52 mpg. sounds good to me, I'll take that any day.