Why are Euro gears bad for fuel mileage?

[Brian Moffet]

The XZ400 gears are not the taller euro-spec but are actually shorter than US. Good for acceleration, bad for fuel mileage.

Now here's an interesting question for those people who don't know.  Why are the gears bad for fuel mileage?  At 60 mph, you're moving the same amount of air out of the way, the same amount of tire friction, the same amount of bearing friction, and yet the different gearing is bad for fuel mileage.  Why?

Brian (yes, I do know the answer, but I'm willing to bet this will be useful information for people who don't.

[kiawrench]

both my bikes have euro gears, i seem to either have to top a gear out,, or lug it ,depending on posted speeds, both are bad for mileage .

[Kenny]

  ??? Our bikes two with Euro Gears get "better Mileage" with the gears than without,I'm not sure how you guys feel you are lugging this bike but at my riding speeds I'm usually right in the power band .This bike gets its best volumetric efficiency around 6 grand.
    The other 83 has North American gears it has makes power earlier  but it also burns more fuel.   ;)
  Cheers Ken S.

[supervision]

 walt is, saying that the euro (taller) gears, are better for mileage.  It is the 400 that has short gears, even shorter than the US 550. Taller gears will generally produce better mileage, as long as you are not over geared for the task at hand, like carrying a huge load, and or big fairing, and bags, and lots of speed.

[Brian Moffet]

Yes, but why does revving higher cause fuel mileage decreases?  Or under-revving?  What is the underlying cause of the mileage difference?

[kwells]

once over the rpm for max torque the volumetric efficiency of a given engine decreases.

[supervision]

  If the throttle is not open enough, it makes for a braking affect on each intake stroke, that's why when you close the throttle, the engine has compression braking.  Diesel engines, have no throttle, and take a full amount of unrestricted air on every intake stroke, thus no compression braking.  On a gas engine the throttle needs to be open a fair amount to make for the least restriction of air thru the engine.

[Brian Moffet]

once over the rpm for max torque the volumetric efficiency of a given engine decreases.

And for those people who don't know what this means?

On a gas engine the throttle needs to be open a fair amount to make for the least restriction of air thru the engine.

So I should run as high RPM as possible to get the best fuel efficiency?

[Rick G]

My old hero , Gorden Jennings , once said , that the best mileage was to be  achieved , with a fairly small engine turning fairly fast . His point was that a large  slow turning v twin 9 or any other, large displacement, slow turning configuration) would not get nearly as good a mileage ,as a  small  single or twin that buzzed along , as  kwells and SV have explained .

I usually ride at around 6200 to 6500 rpm , the engine just floats along neither lugging or over revving.  Part of the reason for this speed  (80 mph, give or take ) is the roads here in AZ, and probably NM, TX, NV , that are sparsely populated  and head for a horizon that recedes into the distance endlessly.  65 mph seems like your crawling along.

[dieseler]

Basically for any given engine there is a peak efficiency range.  Above or below that range and you're losing fuel mileage.  Now that range will vary on the engine, load, gearing, speed, vehicle, ect ect.

[supervision]

  I was reading somewhere about the loss that comes from having a dedicated intake and exhaust stroke. If we could fire every time the piston comes to the top, like a two stroke, only no drool, then we would have something!  I think there are more gains to be invented in internal combustion, we just started computers a few years ago.

[supervision]

 In F1, they are testing transmisions with flywheels built in as brakes, then using the stored energy to launch off the corner

[Kenny]

O.K. I agree with Rick (Gordon Jennings) about 4 years ago three of us went from here(Trenton ON) to Vancouver B.C. myself on a BMW R1150rt , Dorothy on the 83 XZrk  & Zack on his 83 R100cs .Now other than the fact that both BM's broke down R1150-alternator, R100cs -clutch disindigrated,& the Vision ran flawlessly!
    The Vision was equiped similar to the R1150rt (hard bags,waterproof duffle ect.) the vision returned better fuel economy than the two beemers. ie less liters added at each fuel stop. ?fuel injection,ect vers CARBS ?
           Thoughts Ken S. 

[motoracer8]

Gentalmen,  There has been some discussion here about primary drive gear ratios, and that the Euro 550's have a higher ratio than the US models. Is is fact? Has someone counted teeth on the primary drive gears to see what they are? Also it was said that SR500's have this taller primary ratio. I have a SR500, and a TT500, Both of these machines have a 2.56 gear ratio, that is 30 teeth on the crank gear, 77 teeth on the clutch gear. My Vision, an 83, has 33/73, whitch is 2.21, that gives higher overall gearing than a SR. One of the reasons the singles have a lower primary drive ratio is to spin the gear box faster to take some of load off the gear set, as you can gear them up with a smaller drive sprocket, difficult with a Vision.

  Ken G.

[Blake]

Gentalmen,  There has been some discussion here about primary drive gear ratios, and that the Euro 550's have a higher ratio than the US models. Is is fact? Has someone counted teeth on the primary drive gears to see what they are?

Yes and Yes.  I dont remember but it drops your rpm's by about 500.  Rick G and I both got our sets from a member in Poland.

[Night Vision]

There has been some discussion here about primary drive gear ratios, and that the Euro 550's have a higher ratio than the US models. Is is fact? Has someone counted teeth on the primary drive gears to see what they are?

yes again

from XZv2's website: http://home.tiscali.nl/saniris/motor/XZgearing.htm

and home page: http://www.xz550.nl/

[Brian Moffet]

So after all of this, any one think one answer is more correct, or understandable, than any others?

Brian

[Blake]

So after all of this, any one think one answer is more correct, or understandable, than any others?

Brian

In all the common theory i learned in school:


Euro gears =better gas mileage
US gears = normal gas mileage
400 gears = worst gas mileage.



all things being equal, the lower rpm of the euro gears when going to same speed will mean better gas mileage.  As simple as i can put it, you're turning less engine revolutions per mile with the lower rpm.  less revolutions = less gas consumed.  plus, when your going 60mph you're not using all 100% of the vision's power.  Even 600hp cars only use 30-50hp at cruise. thats why you have to give it more gas to maintain speed going up a hill-more power is required to keep the bike moving.

note: there's a lot more variables to it than that, but this is the simple explanation.

[Brian Moffet]

the lower rpm of the euro gears when going to same speed will mean better gas mileage. 

So the best gas mileage will be when you're not moving?  ;D

[Blake]

So the best gas mileage will be when you're not moving?  ;D

My bike certainly gets unlimited miles per gallon when loaded on the back of the truck  ;D