Joined
·
3,713 Posts
Now that I have your attention I want to explain why I don’t think the Wing needs another gear. I’ll don my asbestos flame suit while you read this.
I see posts here telling us that the Wing needs a 6th gear to reduce RPM’s at cruise, allowing better fuel mileage and longer engine life. I read that the Wing’s torque would easily allow 70 mph cruise at 2400 rpm with 50 mpg economy and still have decent top-gear acceleration. Also, the latest edition of the Iron Butt Magazine has an article on motorcycle fuel economy. The author goes into detail about how a 40% reduction in RPM’s at cruise would net another 20% fuel economy increase. He offers some computer simulations as evidence of his claims. My only problem with this article is that computer programs have a very low frontal area and drag coefficient.
I too would like a 6th gear if I thought it would actually increase fuel economy for I really don’t mind shifting when necessary. However, I’ve long felt that our fuel economy is limited by the poor aerodynamics of the barn-door fairing we’re pushing, not by engine rpm. The bike requires the same horsepower at the rear wheel to run 70 mph whether it is in 5th gear or 6th gear. The power demand is constant.
Before you decide I’m nuts, I do realize that higher engine speeds use a little more fuel strictly because the engine itself has more frictional losses at higher speeds. In other words it takes more fuel to run an engine at 3000 rpm versus 2000 rpm even if there is no useful work performed, just due to rotating frictional losses. However, engine rpm versus fuel consumption is not a linear function when applied at speed. Frictional power losses are minor compared to the power required to push the Goldwing through the air.
I finally decided to run my own tests to determine if it is speed (read wind resistance), or RPM that has the most effect on fuel economy. Lately I’ve had the opportunity to ride my GL1800 from home at Dam B to Port Arthur and back pretty often. I decided to test my theory by making the ride one day using all five gears, and then the next ride I would make the trip without using 5th gear.
I kept a fuel log, and bought all my fuel at the same gas pump to eliminate meter errors. The direct route I normally use is mostly rural, 70 mph two-lane roads passing through a couple of caution-light communities before rolling through the towns of Silsbee, Lumberton and Beaumont. It’s about 80 miles each way with almost all cruising at 70 to 75 mph except for the small towns and the occasional Beaumont rush-hour traffic jam.
Sometimes the ride home in the evening would be longer than taking the direct route. I drove the same way at the same speeds, whether in 4th gear or in 5th gear. I admit that it is disconcerting to cruise at 75 mph while looking at a tachometer reading of 3800 rpm! I don’t feel right cruising at high rpms even though I don’t think it really hurts anything. By the way, all these runs were with my ever-present Tailwind trailer in tow.
4 Gears Data
Run #..... Miles..... Gal...... MPG..... Deviation from average
#2......... 183......... 5.24..... 34.92..... -1.93%
#4......... 161......... 4.55..... 35.38..... -0.63%
#6......... 156......... 4.15..... 37.59...... 5.56%
#8......... 165......... 4.45..... 37.08...... 4.12%
#10....... 164......... 4.71..... 34.82..... -2.22%
#12....... 173......... 4.98..... 34.74..... -2.45%
#14....... 188......... 5.29..... 35.54..... -0.20%
#16....... 195......... 5.45..... 35.78...... 0.48%
#18....... 164......... 4.61..... 35.57..... -0.10%
#20....... 162......... 4.59..... 35.29..... -0.89%
#22....... 207......... 5.81..... 35.63...... 0.05%
#23....... 183......... 5.17..... 35.40..... -0.60%
Total.. 2,101........ 59.0...... 35.61
5 Gears Data
Run # ....Miles...... Gal....... MPG........ Deviation from average
#1......... 196......... 5.35..... 36.64....... -3.20%
#3......... 165......... 4.38..... 36.67....... -0.46%
#5......... 173......... 4.55..... 38.02........ 0.47%
#7......... 165......... 4.22..... 39.10........ 3.22%
#9......... 217......... 5.65..... 38.41........ 1.49%
#11....... 204......... 5.49..... 37.16....... -1.81%
#13....... 220......... 5.95..... 36.97....... -2.30%
#15....... 222......... 5.78..... 38.32........ 1.26%
#17....... 180......... 4.84..... 37.19........ 1.73%
#19....... 180......... 4.61..... 39.05........ 3.17%
#21....... 163......... 4.26..... 38.26........ 1.10%
Total... 2,085....... 55.08.... 37.84
Total miles driven ..................4,186
Total Gallons of gas .................114.08
MPG Improvement, 5th vs. 4th ....2.23
% improvement............................ 6.28%
% RPM increase, 4th vs. 5th...... 22.89%
% RPM decrease, 5th vs. 4th..... 18.62%
As you see in the table above I got slightly better fuel mileage in 5th gear versus 4th gear. Over a total of 23 runs covering 4,186 miles burning 114 gallons of gas, I found that my 4th gear mileage averaged 35.61 mpg while my 5th gear mileage averaged 37.84 mpg. The improvement was 2.23 mpg, or 6.28%. Not much improvement when you consider that the 4th gear rpm at 70 mph is 3540 and the 5th gear rpm is 2880, a difference of 22.9%.
IMHO this proves that the difference in rpm has relatively little to do with fuel economy. It is mostly the speed, or wind resistance, that determines the amount of fuel used. It requires a certain amount of horsepower to push a Goldwing through the air at 70 mph whether the Goldwing is running in 4th gear, 5th gear, or a new 6th gear. Think about it. A reduction of 22.9% rpm going from 4th gear to 5th gear netted a fuel economy increase of only 6.2%. How much more, if any, improvement would a true overdrive 6th gear with another 10% rpm drop yield? I’m betting the improvement would be negligible.
Here’s another way to look at it. In 4th gear at 3,540 rpm the Wing is going 70 mph and gets almost 36 mpg. If I shift into 5th gear and hold at 3,540 rpm the Wing will be going 86 mph. During a recent BBG when riding at that speed in far West Texas my mileage fell to 29 to 30 mpg. It’s the speed that has the major effect on fuel economy, not the rpm.
It has long been my gut feeling that Honda engineers equipped their GL1800 Flagship with a 5 speed transmission because they knew that a 6 speed wasn’t needed. 5th gear is already tall enough that the engine can’t hit redline because of the wind resistance. If it had a taller 6th gear we would just bog down the engine with no noticeable increase in fuel economy. I’m betting that a taller 6th gear would yield at most one mpg fuel economy improvement at the expense of losing our present top gear acceleration.
Now, if you want a 6th gear for bragging rights, or because you like downshifting to pass, that’s another story. Just don’t expect a fuel economy increase unless Honda does some major streamlining work.
This is what I found. YMMV.
opcorn:
Glen
I see posts here telling us that the Wing needs a 6th gear to reduce RPM’s at cruise, allowing better fuel mileage and longer engine life. I read that the Wing’s torque would easily allow 70 mph cruise at 2400 rpm with 50 mpg economy and still have decent top-gear acceleration. Also, the latest edition of the Iron Butt Magazine has an article on motorcycle fuel economy. The author goes into detail about how a 40% reduction in RPM’s at cruise would net another 20% fuel economy increase. He offers some computer simulations as evidence of his claims. My only problem with this article is that computer programs have a very low frontal area and drag coefficient.
I too would like a 6th gear if I thought it would actually increase fuel economy for I really don’t mind shifting when necessary. However, I’ve long felt that our fuel economy is limited by the poor aerodynamics of the barn-door fairing we’re pushing, not by engine rpm. The bike requires the same horsepower at the rear wheel to run 70 mph whether it is in 5th gear or 6th gear. The power demand is constant.
Before you decide I’m nuts, I do realize that higher engine speeds use a little more fuel strictly because the engine itself has more frictional losses at higher speeds. In other words it takes more fuel to run an engine at 3000 rpm versus 2000 rpm even if there is no useful work performed, just due to rotating frictional losses. However, engine rpm versus fuel consumption is not a linear function when applied at speed. Frictional power losses are minor compared to the power required to push the Goldwing through the air.
I finally decided to run my own tests to determine if it is speed (read wind resistance), or RPM that has the most effect on fuel economy. Lately I’ve had the opportunity to ride my GL1800 from home at Dam B to Port Arthur and back pretty often. I decided to test my theory by making the ride one day using all five gears, and then the next ride I would make the trip without using 5th gear.
I kept a fuel log, and bought all my fuel at the same gas pump to eliminate meter errors. The direct route I normally use is mostly rural, 70 mph two-lane roads passing through a couple of caution-light communities before rolling through the towns of Silsbee, Lumberton and Beaumont. It’s about 80 miles each way with almost all cruising at 70 to 75 mph except for the small towns and the occasional Beaumont rush-hour traffic jam.
Sometimes the ride home in the evening would be longer than taking the direct route. I drove the same way at the same speeds, whether in 4th gear or in 5th gear. I admit that it is disconcerting to cruise at 75 mph while looking at a tachometer reading of 3800 rpm! I don’t feel right cruising at high rpms even though I don’t think it really hurts anything. By the way, all these runs were with my ever-present Tailwind trailer in tow.
4 Gears Data
Run #..... Miles..... Gal...... MPG..... Deviation from average
#2......... 183......... 5.24..... 34.92..... -1.93%
#4......... 161......... 4.55..... 35.38..... -0.63%
#6......... 156......... 4.15..... 37.59...... 5.56%
#8......... 165......... 4.45..... 37.08...... 4.12%
#10....... 164......... 4.71..... 34.82..... -2.22%
#12....... 173......... 4.98..... 34.74..... -2.45%
#14....... 188......... 5.29..... 35.54..... -0.20%
#16....... 195......... 5.45..... 35.78...... 0.48%
#18....... 164......... 4.61..... 35.57..... -0.10%
#20....... 162......... 4.59..... 35.29..... -0.89%
#22....... 207......... 5.81..... 35.63...... 0.05%
#23....... 183......... 5.17..... 35.40..... -0.60%
Total.. 2,101........ 59.0...... 35.61
5 Gears Data
Run # ....Miles...... Gal....... MPG........ Deviation from average
#1......... 196......... 5.35..... 36.64....... -3.20%
#3......... 165......... 4.38..... 36.67....... -0.46%
#5......... 173......... 4.55..... 38.02........ 0.47%
#7......... 165......... 4.22..... 39.10........ 3.22%
#9......... 217......... 5.65..... 38.41........ 1.49%
#11....... 204......... 5.49..... 37.16....... -1.81%
#13....... 220......... 5.95..... 36.97....... -2.30%
#15....... 222......... 5.78..... 38.32........ 1.26%
#17....... 180......... 4.84..... 37.19........ 1.73%
#19....... 180......... 4.61..... 39.05........ 3.17%
#21....... 163......... 4.26..... 38.26........ 1.10%
Total... 2,085....... 55.08.... 37.84
Total miles driven ..................4,186
Total Gallons of gas .................114.08
MPG Improvement, 5th vs. 4th ....2.23
% improvement............................ 6.28%
% RPM increase, 4th vs. 5th...... 22.89%
% RPM decrease, 5th vs. 4th..... 18.62%
As you see in the table above I got slightly better fuel mileage in 5th gear versus 4th gear. Over a total of 23 runs covering 4,186 miles burning 114 gallons of gas, I found that my 4th gear mileage averaged 35.61 mpg while my 5th gear mileage averaged 37.84 mpg. The improvement was 2.23 mpg, or 6.28%. Not much improvement when you consider that the 4th gear rpm at 70 mph is 3540 and the 5th gear rpm is 2880, a difference of 22.9%.
IMHO this proves that the difference in rpm has relatively little to do with fuel economy. It is mostly the speed, or wind resistance, that determines the amount of fuel used. It requires a certain amount of horsepower to push a Goldwing through the air at 70 mph whether the Goldwing is running in 4th gear, 5th gear, or a new 6th gear. Think about it. A reduction of 22.9% rpm going from 4th gear to 5th gear netted a fuel economy increase of only 6.2%. How much more, if any, improvement would a true overdrive 6th gear with another 10% rpm drop yield? I’m betting the improvement would be negligible.
Here’s another way to look at it. In 4th gear at 3,540 rpm the Wing is going 70 mph and gets almost 36 mpg. If I shift into 5th gear and hold at 3,540 rpm the Wing will be going 86 mph. During a recent BBG when riding at that speed in far West Texas my mileage fell to 29 to 30 mpg. It’s the speed that has the major effect on fuel economy, not the rpm.
It has long been my gut feeling that Honda engineers equipped their GL1800 Flagship with a 5 speed transmission because they knew that a 6 speed wasn’t needed. 5th gear is already tall enough that the engine can’t hit redline because of the wind resistance. If it had a taller 6th gear we would just bog down the engine with no noticeable increase in fuel economy. I’m betting that a taller 6th gear would yield at most one mpg fuel economy improvement at the expense of losing our present top gear acceleration.
Now, if you want a 6th gear for bragging rights, or because you like downshifting to pass, that’s another story. Just don’t expect a fuel economy increase unless Honda does some major streamlining work.
This is what I found. YMMV.
Glen