GL1800Riders Forums banner

1 - 20 of 175 Posts

·
Administrator
Joined
·
3,713 Posts
Discussion Starter #1
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.:popcorn:

Glen
 
  • Like
Reactions: 98valk

·
Registered
Joined
·
352 Posts
Excellent write up and analysis. I was wanting a 6th gear strictly for gas mileage improvement and you are probably correct that wind resistance is the real culprit here not engine rpm.
.
.
 

·
Registered
Joined
·
335 Posts
Great write up:thumbup::thumbup:. But if I had my choice I would want a 6th gear, just for the lower RPMs..:shrug::shrug::popcorn:
 

·
Banned
Joined
·
1,911 Posts
Lot of time and effort put into that

Great job:thumbup:

should quieten down the na sayers for a while!!!

You know on reflection the only way to better (prove) this is to actually do the same test with a dyno in a wind tunnel
 

·
Registered
Joined
·
709 Posts
Gas mileage was never a consideration when I bought my Wing. However, Thank You Sir for the excellent write up. Next time, could you try on a ski speedsuit and one those crazy aero helmets to see if you can get 100 mpg? Take pictures too:cool:
 

·
Registered
Joined
·
887 Posts
Agreed

I have felt the same way for a long time..that aerodynamics plays a larger role in MPGs tha does HP vs gearing on these machines...

Now this seems to prove it...

Well done...:thumbup:
 

·
Banned
Joined
·
356 Posts
I don't think your nut's. I just think your wrong. You're test are well thought out and executed. But it's THEORY. IMO you cannot test the effect's of a taller final drive ratio. In relation to wind resistance. Unless you have the taller ratio to work with. And the exact same wind to work with. Like wind tunnel testing. Harley has already proven that a 6th gear will net better mileage at a reduced RPM. And Harley's have a barn door in the front too. With much less power to work with. My 07 Ultra,with a 6spd get's 2 to 3 mpg better across the board as my Brother's 05, with a 5spd does. Bottom line is, if you're happy with your Wing, great. But your test only prove's what happened to you. On a given day, in a particular set of circumstance's, working with what you already have.
 

·
Registered
Joined
·
601 Posts
I don't think your nut's. I just think your wrong. You're test are well thought out and executed. But it's THEORY. IMO you cannot test the effect's of a taller final drive ratio. In relation to wind resistance. Unless you have the taller ratio to work with. And the exact same wind to work with. Like wind tunnel testing. Harley has already proven that a 6th gear will net better mileage at a reduced RPM. And Harley's have a barn door in the front too. With much less power to work with. My 07 Ultra,with a 6spd get's 2 to 3 mpg better across the board as my Brother's 05, with a 5spd does. Bottom line is, if you're happy with your Wing, great. But your test only prove's what happened to you. On a given day, in a particular set of circumstance's, working with what you already have.
Making a comparison to the Ulta is kind of silly in this situation. There are no common factors between the two other than the fact they are both touring bikes.

Sure for the Harley the 6speed transmission made sense but that has absolutely 0 relevance in the GL's fuel economy discussion.
 

·
Registered
Joined
·
628 Posts
Glen,
Nice write up :yes1:

Question: were these tests made with or without
the weight of a spare key? ;)
 

·
Registered
Joined
·
87 Posts
Nice write-up and analysis... And agree mostly with your conclusions. To be honest, fuel economy isn't why I purchased the Wing, but would still like slightly lower RPMs while cruising the super slab.... It just "feels" like a more relaxing ride to me:

On my previous chain-driven bikes, I'd change the final drive ratio to lower RPMs at cruising speed.... Even swapped out the final drive on my VMAx's with Venture final drives! I'm not a speed junky or a stop-light to stop-light shooter. Have always commuted at least 35 miles hiway one way to work and complete 2 long trips (2500+ miles) per year since 1982. Granted, most of my previous the bikes had larger displacement engines so they could handle the extra torque needed at lower RPM. But on long trips, and even commuting, a lower RPM seemed to result in a more relaxed ride for me... Just stating my own personal thoughts on the subject as it relates to my riding style and experience...
:popcorn:
 

·
Registered
Joined
·
19,219 Posts
Thanks for the test. What it shows is the GL1800 gets 3 mpg better in 5th than 4th gear at speed.

I did a Mexico to Canada Iron Butt B2B in 2006 on a 2005 wing and rode 80-100mph the whole way. My mileage was 28mpg vs my regular 38mpg on typical riding at posted speeds
 

·
Registered
Joined
·
158 Posts
No Complaints with the 5 speed

Just did a little over 270 miles on Saturday to Lake Erie and back. Two up, 75-80 mph most of the way plus some around town riding at the bike fest.
37.5 mpg. I don't see a problem :shrug:
 

·
Banned
Joined
·
356 Posts
Making a comparison to the Ulta is kind of silly in this situation. There are no common factors between the two other than the fact they are both touring bikes.

Sure for the Harley the 6speed transmission made sense but that has absolutely 0 relevance in the GL's fuel economy discussion.
Not silly at all. I didn't compare the Ultra to the Wing. What I did do, oh nevermind. If you don't get it, it's just because you don't want to. You all have a great day.
 

·
Registered
Joined
·
87 Posts
Just did a little over 270 miles on Saturday to Lake Erie and back. Two up, 75-80 mph most of the way plus some around town riding at the bike fest.
37.5 mpg. I don't see a problem :shrug:
Hey Ironman!... Is that a M109R I see in your Avatar???
 

·
Registered
Joined
·
125 Posts
Glen I concur

Glen, well written write up and I for one am glad that Mother Honda has not (and hopefully won't) added a 6th gear. The RPM in 5th gear at cruising speeds (i.e. 70-80mph) is already pretty darn low. Having a degree in Aerospace Engineering from the Naval Academy, I have to agree that DRAG is the major driver on our GW's mpg. There will always be some folks that poke holes at one's approach to an experiement such as yours, but it seems to me that you maintained your controls and kept your variables to a minimum.

I personally think most GW riders are way too conservative in their shifting because of the very wide and forgiving powerband the bike has. Many folks lug around in 5th gear at 50 and 55 mph when the bike is begging to be in fourth gear (with a signficant improvement to throttle response/acceleration which could save your bacon in a pinch). We are spoiled I think with our very wide powerband. I think this would only be made worse with a 6th gear as folks would REALLY lug around in 6th gear because the bike responds fairly well in those upper gears.

I found your analysis informative and sound. It may be true that the only real way to PROVE what you're saying is to a: have a wind tunnel and b: have a bike with a 6th gear for comparative purposes.

With all the differences of opinion with the new 2012, I was pleased with what Honda DIDN'T change, namely, an exceptional power plant and gearing setup with a low center of gravity (giving us that sporty performance so many of us love). I would hate for them to add a 6th gear that MIGHT marginally improve my mpg while changing the ergonomics/CG of the bike.

Nice job.

Matt
 

·
Registered
Joined
·
4,091 Posts
I believe that Honda went with 5 gears for a much simple reason. A sixth gear would have required a longer block. This means a longer frame, along with more weight in the block, frame. If they then tried to keep the overall length the same, the swing arm would have to be shorter.... hmmm; less travel, smaller tire... or they could have designed all the gears to be thinner... hmmm, that doesn't sound good either... as it is, there were a number of compromises made. The cooling system was marginal up to 06 and may still be. Lots of folks complained about the banging their knees...
 

·
Registered
Joined
·
2,731 Posts
I don't think your nut's. I just think your wrong. You're test are well thought out and executed. But it's THEORY. IMO you cannot test the effect's of a taller final drive ratio. In relation to wind resistance. Unless you have the taller ratio to work with. And the exact same wind to work with. Like wind tunnel testing. Harley has already proven that a 6th gear will net better mileage at a reduced RPM. And Harley's have a barn door in the front too. With much less power to work with. My 07 Ultra,with a 6spd get's 2 to 3 mpg better across the board as my Brother's 05, with a 5spd does. Bottom line is, if you're happy with your Wing, great. But your test only prove's what happened to you. On a given day, in a particular set of circumstance's, working with what you already have.
Your tests of two bikes with different gearing only produced a change of 2-3 mpg, just as his 'unscientific study' seemed to suggest. Your scenario also included two different riders(different wrist on the throttle), which introduces a much bigger variable. Interesting writeup. I agree with your statement about needing true scientific studies, but I don't see any major flaws in his testing other than environmental factors such as wind, temp, etc(as you mentioned). Based on his tests I tend to agree that a 6th gear may not afford as much mpg improvement as some may think. It would mostly lower the RPM's and perhaps increase the life of an engine that will already last 100's of thousands of miles.
 

·
Registered
Joined
·
16,972 Posts
That is an odd way to go about it and I am not totally sure the method is a valid to prove the given point (maybe it is, but I do agree with your conclusion. I did some similar 'sperimenting several years ago, also maybe not so valid. No statistics, just took notice of fuel use under two conditions: First with stock tires and then with 70 rear "Valk" tire. The speedo error with the stock tire on my '02 was nearly +10% (indicated 70 MPH was actual 6 MPH); that similar error with the 70 rear tire was only +1.5%. Thus, the effective gear ratio change with the 70 rear was about 8.5%; pretty much what is wished for by folks waxing poetic over a 6th gear (second over-drive). There was no discernible saving on fuel, I could see no difference at all, I got 40 MPG day in and day out either way, plus or minus a couple depending upon riding style. Comparing top-end speeds was different: with OE tire the top speed in 5th gear was 3 to 4 MPH faster than with the 70 rear (stock bike otherwise). My crude analysis suggests the GL1800 uses the power band more efficiently with the stock gearing than it would with a next step up in over drive. However, some folks, Larry M. included as I recall, indicate a desire for a 6th gear based upon percieved comfort or some desire to have the Wing cruise at a given speed with less RPMs. That is, the present situation is seen as a bit too busy or annoying. I can say that the gearing offered by the 70 rear was very relaxing and asthetically comfortable. I don't ride ofter in triple digits very often anyway as there are few legal or even sane venues for doing so here abouts. The off the line drag race starts are not as good with the higher effective ratio and I reckon it would not pull stumps as well either, but the more negative aspect was some loss of "grunt" in powering out of curves when carving the twisty stuff -- that loss would NOT be present in a scenerio where a taller gear was added rather than all gears made taller.

prs
 

·
Registered
Joined
·
1,654 Posts
This argument has raged forever.

I doubt this will stop it, but it's nice to see some actual empirical facts brought to the table.
 
1 - 20 of 175 Posts
Top