mpg????

[painterman67]

OK took a ride this weekend to help my cuzin get his bike back together and hang out. On my way there the first tank of gas I ran out at 65-70 mph and got 43 mpg. The second tank was ran out at 75-80 mph and I got 33 mpg. On the way home today I ran 70 mph all the way home and got 40 mpg. Is it normal for a first gen to get such varying mpg and espcially such a drastic change when over 75 mph.

 

 

 

it all seems to be pulling fine with plenty of power all the way through the gears. Just been wandering as I have niticed varying changes in fuel economy but this is the first time I ve been able to get a hold on the mph to mpg issue.

 

 

 

Tahnks for all and any answers.

 

David

[Yammer Dan]

I do a little better than that.

[Dave77459]

Is it normal for a first gen to get such varying mpg and espcially such a drastic change when over 75 mph.

 

Drag increases with the square of velocity. In other words, a little bit of added speed adds a lot of drag. The power needed to push through the air increases with the cube of velocity. Once you hit the sweet spot, a little speed increase has an huge increase in power used.

 

According to the May 2009 issue of Motorcycle Cruiser, under 50mph around 5% of resistance is due to drag. By "highway speeds" (65?), 60% of a vehicle's energy is used to overcome drag. A motorcycle with a fairing and large windscreen has a particular problem with drag at highway speeds.

 

In short, your experience of a dramatic decrease in mpg is typical and expected.

 

Dave

[painterman67]

thanks dave. I was wandering if that was the case. I just keep hearing peaple talikng about much better mpg's and was hopeing somethign I could do to cange it.

 

 

 

David

[raceman62race]

I know you have a 1st gen but my 2nd gen MPG falls off quite a bit over 70 MPG

[Dave77459]

thanks dave. I was wandering if that was the case. I just keep hearing peaple talikng about much better mpg's and was hopeing somethign I could do to cange it.

 

 

 

David

 

Hey, I'm with you. I have an RSTD and get your worst-case mileage as my typical. My bike has that huge windscreen, and I know I could get much better mileage if I went slower. I like to ride fast, because that's how traffic moves around here, and I have a lead wrist too.

 

As far as whether your mileage is good, I dunno. If you can ride with another bike, so that you get the same gas and ride the same conditions, you'd have something to compare against.

 

Dave

[silverdeer0454]

I have been watching my gas milage very close over the past few weeks because I am putting the MotorKote in the oil this week. With two up and 70 on the highway I have been getting 42 MPG. Last week I was in a hurry to get somewhere and I averaged 78 MPH according to my GPS. On that trip with one up I got 38 MPG. I would not have thought a small increase in overall speed would make that much of a difference, but it seems like it does.

[Monty]

All I know is...I put gas in the bike.....then I twist and ride...then I put gas in again...I don't really measure how much I'm gettin'....I just ride...that's what it's really all about.

[craigatcsi]

On our recent cross country trip, I was stopping for gas every 100 to 120 miles. But I was running FAST when possible - to cover distance. I knew my mileage would suffer, and it did.

If I had it to do over again, I might think about dropping my speed to keep the mileage up and enjoy more of the scenery.

With Gas stops & traffic, I always figure 60 miles in an hour, even when running 75mph. I always seem to come out pretty close to guessing my arrival time correctly. That being said, running 75 mph instead of 70, isn't really saving THAT much time. But is does affect my mpg.

Just something to think about.

craigr

[ArcsSparks]

All I know is...I put gas in the bike.....then I twist and ride...then I put gas in again...I don't really measure how much I'm gettin'....I just ride...that's what it's really all about.

I'm with you monty, who cares about motorcyle gas milage? It's about the ride, if it got 1 mpg and the ride was good I'd be happy.

[Dano]

I would have to differ with some of the thinking here. Just got back from the MI M&E. 386 miles each way. In dry conditions with wind, I was getting same mileage (2 up with bags full) no difference of the speed. But it does seem that about 80 mph, air is flowing smoother over the bike, as buffeting decreases from 78 on up. Nav notices it too. Of course this is in free air, no traffic in front or beside. I'm running a K&N air filter with the Mac mufflers I just put on last week.

Wonder if the shape of the airfoil (fairing) has a lot to do with this? After all, the U-71 and the Blackbird were designed this way!

[BradT]

I check gas mileage often and it does not matter what you ride, MPG varies alot, as there is so many factors that affect your MPG. Wind, weight, how hard or often you roll on the throttle, temp, road conditions, air pressure, etc....

 

Wiith a small tank the avg MPG, can change even with a small amount of fuel added. Need to average your mileage over many tanks to get an accurate measure.

 

BRad

[edger]

I know you have a 1st gen but my 2nd gen MPG falls off quite a bit over 70 MPG

 

 

Exact same thing here. Up to 65 or so I can get about 42mpg. If I try to run 75 it drops off to about 36 and if there is a bit of a headwind it'll drop even further. I like to run about 65 anyhow so that works for me.

[LilBeaver]

Drag increases with the square of velocity. In other words, a little bit of added speed adds a lot of drag. The power needed to push through the air increases with the cube of velocity. Once you hit the sweet spot, a little speed increase has an huge increase in power used.

 

According to the May 2009 issue of Motorcycle Cruiser, under 50mph around 5% of resistance is due to drag. By "highway speeds" (65?), 60% of a vehicle's energy is used to overcome drag. A motorcycle with a fairing and large windscreen has a particular problem with drag at highway speeds.

 

In short, your experience of a dramatic decrease in mpg is typical and expected.

 

Dave

 

Actually, most importantly here is the bike (the 1st gens that is) was geared/designed for when the highways had a speed limit of 55 mph. So this will likely play a much bigger part in the drop in fuel economy than the air resistance when you go above say 60mph.

 

For a standard automobile once you are at around 88 Feet/sec (60mph) the drag force is proportional to the square of the velocity. Below that it is roughly linearly proportional to the velocity. These approximations are for a standard sedan. On a bike, the speed is actually a little bit higher that the drag force is proportional to the square of the velocity; but I have not done those calculations so I will not even estimate that number.

 

This is a topic that is discussed in most introductory Physics text books in mild detail at least. (That is, if anyone is interested anyways). I use Gioncoli's introductory text when I teach those classes, but there are many other good ones out there.

 

However the gist of what you have written is correct, I just thought I would throw this out there.

 

- Rick

[Winesap7]

If it helps any my 90 VR gets between 25-28 average in town and on the highway. As was noted my mpg really drops at highway speed. Oh, by the way mine is a trike, more weight and more surface area with the trike but as others have said I like to ride and the trike is a lot easier on old legs.

[Dave77459]

For a standard automobile once you are at around 88 Feet/sec (60mph) the drag force is proportional to the square of the velocity. Below that it is roughly linearly proportional to the velocity. These approximations are for a standard sedan. On a bike, the speed is actually a little bit higher that the drag force is proportional to the square of the velocity; but I have not done those calculations so I will not even estimate that number.

 

Rick,

 

Interesting. One thing the Motorcycle Cruiser article talks about is how sedans are designed to reduce drag via laminar flow. Cruiser motorcycles, with their upright rider, do a poor job of maintaining that flow. They say a typical motorcycle has a drag coefficient of around .6 to .7 (about the same as a bus), while a sedan is around .35.

 

I just know that my mpg drops a lot over 60mph. The best mpg I ever got was through hairpin curves in AR, where I was lucky to hit 45.

 

Dave

[Condor]

I just know that my mpg drops a lot over 60mph. The best mpg I ever got was through hairpin curves in AR, where I was lucky to hit 45.

 

Dave

 

I hit 50mpg running the twisties all day long. Using the motor and down shifting into the curves and powering out of them. Mostly running in second and third. Occasionally hitting 4th. And the mileage is not a freak, it happens every time I get into that type of riding situation. Others have report the same thing happening. Mileage will drop to 38mpg when running the slab at 4000 rpm and around 72-73mph in fifth. I don't care when it was built, or what it was designed for, wind resistance is the enemy. And when it comes to resistance I'm big enough to be considered two up all the time.

[Yammer Dan]

I have broke 50 mpg several times with "Ugly." Grindo does it a lot with that 1700 and Skid used to do it with "Brown Sugar" (1st Gen).

[jlh3rd]

took a ride last weekend, two up,.....40-50 mph ,....never in 5th gear.....42 mpg...

[LilBeaver]

Interesting. One thing the Motorcycle Cruiser article talks about is how sedans are designed to reduce drag via laminar flow. Cruiser motorcycles, with their upright rider, do a poor job of maintaining that flow. They say a typical motorcycle has a drag coefficient of around .6 to .7 (about the same as a bus), while a sedan is around .35.

 

Dave: I would believe this for a bike with no windshield or fairing. But as you have mentioned the windwhield/fairing would allow for much smoother airflow around the bike.

I'd be interested to check out that article. Maybe I'll find some time in the next week to actually go through and figure this out.

Thanks for the info though!

I found if I keep the speedo pegged at an indicated 70 (with no wind anywhere) I can get around 45-47...

 

- Rick M.

[long_black_train]

If it helps any my 90 VR gets between 25-28 average in town and on the highway. As was noted my mpg really drops at highway speed. Oh, by the way mine is a trike, more weight and more surface area with the trike but as others have said I like to ride and the trike is a lot easier on old legs.

Hello Winesap7...My fiberglass man and I are mulling an idea of making wind deflectors to mount on the front of the trike body so the wind will be deflected outward instead of a blunt face catching the wind...He has 30+ yrs with glass and seems to think it will work..and give the body a more sweeping design...I have the design drawn...now it's his turn to put it in practability with glass...Have a Good Day:rudolf:

[Sandbagger]

I am having similar issues.

When I get over 3500 RPM's gas mileage falls off drastically.

Stay at or below I will run low 40's.

Going 4000 rpms and I will get low 30's.

I'm no expert, but my theory is that Gen 1's were geared for 55 mph lifestyle.

They are awesome performing and efficiency up to 65 mph.

One guys opinion