I've been curious about this for some time.

According to government data found at fueleconomy.gov, "gas mileage usually decreases rapidly at speeds above 60 mph. As a rule of thumb, you can assume that each 5 mph you drive over 60 mph is like paying an additional $0.20 per gallon for gas. Observing the speed limit is also safer."

Now, this obviously is meant for cars. Does anyone have any thoughts or knowledge about the diminishing results of driving above the average on our bikes?

Without having taken any formal measurements since I started considering this, I felt that i gained some extra miles cruising steadily at 80 mph on the highway over a 100 mile trek versus at 65 mph under what I felt, in hindsight, were similar conditions with a full face on and a very low angled windshield. (reduced drag)

Any ideas?

Sure, I'm a curious one.

 

I've noticed that I get worse mileage going slow. As long as i'm at a steady highway speed with my big V10 truck or the street bob I always get better doin 65mph plus. I think the governement is just trying to slow us down again. I doubt they have done any tests that prove this.

 

It is different for every vehicle, you can find charts online for motorcycles, I'm too lazy to find them for you, but there is a terminal velocity, at which point the drag you create requires exponentially more power to drive you forward. For many cars (especially older ones) this occurs between 50 and 60mph, not for most sports cars, or aerodynamic fuel efficient cars... If I recall correctly, even the worst of the motorcycles doesn't hit this point until above 70... most are in the 80s or 90s, the sports bikes with fairings cut through the air, and it doesn't occur 'till well above 100mph... That’s why a Big V-Twin making twice the hp of a small, yet well geared 600cc sports bike, will still never catch it on the top-end… As the speed increases, that little aerodynamic sports bike needs less and less power to keep on going. That’s also why you probably don’t have the power to hit your rev limiter in topgear…

 

I just rode back from Leesburg yesterday, 100 miles averaging 75mph.
I was suprised at how little gas I used.
Only about 2.5 gallons.
I use a lot more gas starting and stopping in the city on my way to work.

 

There was an article on CNN.com a few weeks ago reporting out the research behind the numbers. In the study they found that for typical cars the extra force required to drive them against air resistance was such that, after adjusting for current prices, every 10 mph over 65 cost something like 57 cents/gallon.

As Herr Monk notes, the numbers don't hold for "slippery" cars or bikes, though the principal is sound. I know from personal measurement that running my bike at 80 for a few hours yeilds much better mileage than a few hours in the 50 mph twisties. (Though to be fair, twisties require a lot of acceleration/deceleration that converts fuel into heat rather than motion.)

Edit: Here's the link --
http://money.cnn.com/2008/03/26/auto...n=money_latest

Clearly my memory of the article isn't precise, but was close.

 

I tend to get better mpg between 75 and 85 than I do at 65 and 75. This is based on speeds done on long trips with little town driving.

 

sweetness... i appreciate the responses. I'm going to get some numbers down for my own informal calculations the next time I make my biweekly 100 mile trek.... I'll see about accounting for as many variables as possible. I think the major one would be accelerating at a high rate!

 

My '06 Street Bob always seems to get better gas mileage (50mpg) on highways than interstates. We're typically cruising at 60mph on the smaller highways vs 70mph on the interstates - or about 5mph over for both.