Mirrors removed and bar end mirrors installed

I just joined here 20 mins ago and wanted to know whether anyone has removed their mirrors and what differences were noticed.

I actually like bar end mirrors and have had them on several bikes.

My mileage has increased dramatically per the trip computer which seems to be within a few percentage points

versus fill up and mileage calculation.

The following is my mileage over approximately 10 mile runs using cruise control and 87 octane on Interstate 93 in NH which is fairly

hilly. NO side cases, NO top case, NO stock mirrors, WITH 3" round bar end mirrors, stock windshield about 1/2 up (wind just around

shoulders) 1/4 tank of fuel, 5'11, 190 lbs, full face helmet with shield closed, 80 F, 50% humidity , light winds.

60 mph...........60 mpg (US)

70...................54 mpg

80...................48 mpg

Riding at an indicated 85-95 mph was getting around 44 mpg.

All these numbers are approximately 20% over what I saw with stock mirrors and a 45 L Givi top case which seemed to be almost

totally out of the wind stream.

I had been averaging mid to low 40s in mixed riding without side cases and sometimes with top case.

I will see what my average is over the next full tank of fuel.

I never removed the mirrors on the FJR. I had bar-end mirrors on two bikes in the past for a short time. I prefer the factory, which requires less eye movement than mirrors on the bar-ends. The only reason I would remove factory mirrors is for the track, and if it was an FJR I took to the track I would just tape them up and fold them in. However it would not surprise me that you are getting better fuel mileage without the factory mirrors and top case.

In the summer here in Central Oregon I average 50MPG with the FJR with the mixed riding I do (and the OEM mirrors on ). 60+ with my Prius.

But I live in an area where there are no Interstates, so out-of-town cruise speeds are 50-60 MPH. Side bags are sometimes off, sometimes on, but the top case is always mounted. I've not gone to any real rigor to figure out what affects drag significantly.

All three of my vehicles (FJR, Prius, Tacoma) get right around 10-12% better mileage in summer than winter AND I get better mileage here routinely driving 3000-4000 ft. above sea level as opposed to zero-ish in years past with the same vehicles. Pretty similar driving conditions otherwise, as Interstate highways just haven't accounted for much of my driving in this century.

I do fairly often ride with the side bags off. Even when empty I feel I can tell the weight difference. But sometimes I need them to carry this and that. I do have the sense they add nontrivial drag, but have no objective data to confirm or refute this.

Agreed with summer riding/driving vs. winter. Much of it has to do with the "winter blend' fuel which "they" say will only decrease mileage by a few percentage,

but I have always found that it was closer to the 10% you cite. I expected maybe a 5% increase in mileage with the stock mirrors removed, but it is clearly

significantly more than that. The high speed efficiency of this bike is impressive.

Actually there is an additional factor known as Density Altitude to pilots that's applicable to winter vs. summer mileage. At an altitude of 3000 ft MSL the "normal" temperature is 47 degrees. Here our average wintertime temperature is more like 40 degrees. In summer, 80 degrees is more typical, though we've seen lots of 90+ degree highs this summer. (FWIW, Density Altitude at my 3250 ft elevation home airport in the heat of day has surpassed 6000 ft. numerous times this summer.)

The difference in air density between 40 degrees and 80 degrees at 3000 ft. is about a 7 percent reduction. So air drag is lower by 7% at any given speed. The typical temperature variation I dealt with at sea level in years past had a similar seasonal differential.

The difference in air density between sea level at 40 deg and 3000 ft. at the same temperature is about 10%. That jives with the improvement I've seen in mileage for all three of my vehicles in similar temperatures since moving from Puget Sound 3 years ago.

Yes, I am very familiar with DA. In fact, I JUST got a text from a very good friend who is working on his CFI.

My 20 year old son is an Instrument rated Commercial pilot. I have been flying a lot in these little planes.

At those higher speeds (bikes) almost all the resistance is aero drag. Not sure how the DA and the higher O2 levels

factor in. One reason I included the temperature and humidity was because I was thinking about DA. I should have included the actual

elevation which was around 1000 above sea level.

RichDoyle said:

Actually there is an additional factor known as Density Altitude to pilots that's applicable to winter vs. summer mileage. At an altitude of 3000 ft MSL the "normal" temperature is 47 degrees. Here our average wintertime temperature is more like 40 degrees. In summer, 80 degrees is more typical, though we've seen lots of 90+ degree highs this summer. (FWIW, Density Altitude at my 3250 ft elevation home airport in the heat of day has surpassed 6000 ft. numerous times this summer.)
The difference in air density between 40 degrees and 80 degrees at 3000 ft. is about a 7 percent reduction. So air drag is lower by 7% at any given speed. The typical temperature variation I dealt with at sea level in years past had a similar seasonal differential.

The difference in air density between sea level at 40 deg and 3000 ft. at the same temperature is about 10%. That jives with the improvement I've seen in mileage for all three of my vehicles in similar temperatures since moving from Puget Sound 3 years ago.

Click to expand...

Density altitude also affects the Stoichiometric Air/Fuel Ratio. As the Air Density increases, a given volume of air weighs more, there is more oxygen in the air thus more fuel is required to maintain the correct Air Fuel Ratio to maintain power. Not as critical in Gasoline powered engines as it is in Ethanol or methanol-fueled engines. When I was racing Sprint Cars we monitored Air density and adjusted jetting in the Fuel Injection before every race to achieve the best power, always staying a little bit rich to preclude a catastrophic and expensive event.

I removed the factory mirrors and put on bar end mirrors. I like bar end mirrors and have used them on many bikes, the unobstructed view is vital (for me).

In the end I put the factory mirrors back on and run both sets. I just like the look of the stock mirrors and have them adjusted to cover the outside lanes nearer to me.

That's what I was referring to when I asked about the interrelationship between the higher O2 content of the denser air (allowing for more fuel and power)

but the denser air requires more energy to push through it. At highway speeds does not the increased O2 level outweigh the "heavier" air that has to

be parted?

At least with bikes we don't have the issue of lift to account for.

So, everything being considered, what conditions would allow for the best fuel efficiency with motorcycles?

I can certainly see where the side cases could make a fair difference. Even the Givi box, which may appear to be out of the direct wind stream, will make a difference in the bike's aerodynamics. Many FJR owners have noted that with the top box and no passenger, there is a significant forward "push" from "dirty" air. Also affected by windscreen position.

I would be very surprised if the stock mirrors made a significant proportion of the 20% difference in mileage although I'm sure they are a factor.

Very difficult to do a proper riding control - a few degrees temperature difference or slight changes in wind. (We assume identical route in the same direction and digital control over speed.)

Edit to add:

Aerodynamic resistance becomes a much greater factor at higher speeds. It would not have a more-or-less linear effect (i.e.20%) at 60 and 80 mph.

Wind resistance (drag) is one factor that affects fuel economy. To make a 20% difference in fuel consumption, the mirrors would have to represent a much higher proportion of the overall wind resistance (50% or more?). Looking at the front of the bike, this isn't possible IMHO.

BILI said:

That's what I was referring to when I asked about the interrelationship between the higher O2 content of the denser air (allowing for more fuel and power)
but the denser air requires more energy to push through it. At highway speeds does not the increased O2 level outweigh the "heavier" air that has to

be parted?

At least with bikes we don't have the issue of lift to account for.

So, everything being considered, what conditions would allow for the best fuel efficiency with motorcycles?

Click to expand...

It's easy to confuse 2 issues here. Without turbocharging your MAX power available dies off with increased density altitude. But this rarely affects cars, motorcycles, etc. where you rarely use/need this. It does affect us light plane drivers big time, where you almost always use wide open throttle on takeoff and for at least several minutes after. The increased availability of O2 is rarely useful on surface vehicles. So yes, you'll get better acceleration at lower elevation but at a given reasonable street/cruise speed it's no factor.

But there is another factor. Current, modern fuel-injected ground vehicles have feedback that adjusts pretty well to preserve the desirable fuel-air mixture as the O2 availability varies. Without some sort of automated feedback you've got a very narrow range of optimal performance. More primitive fuel-injected systems (such as my fuel-injected airplane) require that I manage this myself, manually leaning as the altitude increases. The basic feedback available to me is Exhaust Gas Temperature. Older carbureted systems are even more primitive where you'd wind up changing jets and whatnot to deal with this.

On my Gen 1 i removed the stock mirrors and i installed the Gen 2 mirrors with the Yamaha knuckle visors on.

On the first trip after that i noticed that the fuel consumption increased approximately 10+%.

The largest frontal surface increased the fuel consumption for sure!

So when you remove the mirrors the fuel consumption will be decreased i believe..I don't know if will be at 20% but around there..

Interesting bed time reading. Aside from expressing a lot of technical info on wind drag and air density what is your desired result? If you want maximum MPG ride with no bags, top case and lower the windscreen. I have a 2014ES with 35,000 miles on the clock. Most of my riding is long distance tours and I ride with bags and soft tail bag. I have FZ1 mirrors. My average MPG is 48.3. I am fortunate enough to afford the cost of fuel so tinkering with mirrors to increase MPG never entered my mind.