Cruise control and gas mileage

[ryo]

I did a search and apologize if I missed a previous thread on the same subject, but I am on a long trip and I noticed that my gas mileage drops from about 50 mpg at 70+ without cruise control to in the mid thirties using the cruise control. Both are from times on the super slab which I have had to do too much of this trip. Has anyone else experienced this or is this a good topic for my next service visit? TIA

 

rusty

[ClearwaterBMW]

well,

i'd check into that further, because that seems unlikely.

as for 50 mpg at 70 mph +.... that's UNlikely as well

get a GPS.... even a cheap one, so that you can see your REAL speed

that R1200RT at speeds great than 70 mph will return about 42 mpg

by 85, it'll be about 30 mpg for most folks

the cruise control can't lower fuel economy, as it should really INCREASE your mpg a little

greg

[ShovelStrokeEd]

Greg,

You have a good part of that wrong.

 

50 mpg at 70+ mph is what is reported by a good many of the owners.

 

Increasing speeds to 80 or even more won't raise the fuel consumption more than 2 or 3 mpg. It is not until the speeds get well into the triple digits that a significant drop occurs.

 

In fact, a cruise control will offer a slight increase in fuel consumption over a rider who is paying attention and is smooth with the throttle. The devices are obsessed with maintaining speed and will operate the engine at large throttle openings for long periods of time while riding on the highway if their is a mild upgrade. Where an experienced rider would down shift and use much smaller throttle openings. Just for one example. I could get consistantly better fuel milage on my LT without using the cruise control as I was much more subtle in my throttle transitions and could anticipate approaching hills so as to accelerate while on the flat rather than after I had hit the hill.

 

An example would be my 1100S. It gets about 35 around town, 42 going a steady GPS 75 mph and drops to 38 at a steady GPS 100 mph. Frontal area between the S and the RT is probably about the same but the RT is much more slippery as the aerodynamically poor rider is better covered.

[eaglemike]

This last Sunday, I experimented a bit with the cruise control. Windshield up all the way makes quite a difference. Uphill makes quite a difference, as noted above. I was watching the computer (confuser) from time to time, right after fill-up, so the differences were easy to see.

 

all the best,

 

Mike

[ClearwaterBMW]

Greg,

You have a good part of that wrong.

 

50 mpg at 70+ mph is what is reported by a good many of the owners.

 

Increasing speeds to 80 or even more won't raise the fuel consumption more than 2 or 3 mpg. It is not until the speeds get well into the triple digits that a significant drop occurs.

 

In fact, a cruise control will offer a slight increase in fuel consumption over a rider who is paying attention and is smooth with the throttle. The devices are obsessed with maintaining speed and will operate the engine at large throttle openings for long periods of time while riding on the highway if their is a mild upgrade. Where an experienced rider would down shift and use much smaller throttle openings. Just for one example. I could get consistantly better fuel milage on my LT without using the cruise control as I was much more subtle in my throttle transitions and could anticipate approaching hills so as to accelerate while on the flat rather than after I had hit the hill.

 

An example would be my 1100S. It gets about 35 around town, 42 going a steady GPS 75 mph and drops to 38 at a steady GPS 100 mph. Frontal area between the S and the RT is probably about the same but the RT is much more slippery as the aerodynamically poor rider is better covered.

 

sorry, ed

i was thinking about my LT and my GS

with the LT and the screen all the way up

 

70 mph = 40 mpg

85 mph = 31 mpg

 

with the GS....

not that far off

 

i think that the RT doesn't have to reach triple digits to start dropping it's mpg

i'm talking about gps-verified mph, of course

 

no motorcycle has an advantageous coefficient of drag..... and therefore, as the speeds go up, the mpg goes WAY down in any bike on the road.... bmw's included

 

as for your thoughts about subtle throttle inputs giving better gas mileage than a cruise control... that is true as well, but i bet that on one of your patented 5,000 mile trips across the country and back that it wouldn't make a difference of 1 mpg since most of our country is fairly flat

isn't that true?

 

greg

[ClearwaterBMW]

in fact:

this has me thinking. before i go on my 2,000 mile trip on my GS next weekend

 

for folks with R1200GS's....

tell me about your experience with mileage with different gps-verified speeds, if you have the time and inclination

 

thanks in advance

greg

[ryo]

I have a GPS (Navigator II+) and am looking at real speeds (BTW, the r12rt has the most acurate speedometer I have aever had it varies between 2 adn 3 mph different than what the GPS shows at alomost all speeds above 30. The CC seems to have a 0.5 to 0.7 speed up slow down cycle which seems a liitle much to me and is continuous which my be why the gas mileage drops so much. Is this a normal amount? Quite honestly is is almost like the surging I felt on an r1150rt albeit in somewhat slower motion. I installed an electronic cc on my st1300 and it did not exhibit such a noticeable speed up slow down cycle. I guess I need to talk to my service guys unless someone has an idea. I love this bike even more after living with for over 3500 miles these past 7 days. But I do thin a new seat is in order.

 

rusty

[PaulW42]

seems to have a 0.5 to 0.7 speed up slow down cycle

Mine does the same at about 30mph but is absolutely smooth at higher speeds or at least it doesn't noticeably vary (usually around 75mph actual).

 

Paul

[ShovelStrokeEd]

Sounds to me like your cruise control is defective or the actuator is in need of adjustment. Even the one on my LT didn't hunt appreciably. It was a little slow to react to a hill and would drop 1 mph or so before adding throttle but other than that was dead smooth.

 

Sounds like a trip to the dealer and a bit of warranty work is in order.

[smiller]

In fact, a cruise control will offer a slight increase in fuel consumption over a rider who is paying attention and is smooth with the throttle.

 

I think that is probably quite correct. In fact I read about an interesting test a short while ago where an individual drove his car on a loop course (steady-state, no starts/stops) at a steady 40 mph in two modes... using cruise control, and maintaining his speed as precisely as possible by manual control of the throttle. The results were that manual control actually yielded somewhat better mileage than cruise control. Apparently a human being can beat the rather simple cruise control units found on most vehicles in maintaining a consistent throttle (under these test conditions), and I don't find that surprising at all.

 

Of course this is like the old 'I can beat ABS under perfect conditions' saw. You probably can, and you may find that you can beat cruise control under perfect conditions as well, but obviously those don't represent any kind of real-world driving environment so the results are more of an intellectual exercise than anything else. For instance, the tester noted that it would never be practical for a driver to keep the level of concentration required to beat the cruise control up for very long and that in the real world an imperfect cruise control was probably more efficient than a perfect human, and that also makes sense. Still, there has to be a crossover point somewhere, and perhaps an attentive rider might indeed beat the computer for one stretch or another, or maybe even overall (especially if there are hills as a human will manage speeds in that environment much better than a cruise control.)

 

Regarding your problem, if you are really seeing a 10+ mpg drop when using the cruise control then... get it fixed because something is wrong.

[STUFF2C]

My .02

I live in Fl so take that into account if you wish but these #’s are combined states. I have yet to see below 42mpg average on a tank. I use Garmin GPS #’s to calculate mpg most of the time. On the Hwy cruising at 80mph GPS indicated with the windshield around halfway up, I have averaged just about 50 mpg, add the city and it drops around 5 mpg. My GPS and speedo have a 3mph discrepancy (it was 2 with a new tire). 6k miles on it so far. This CC thing is going to cost me $$$ I'm sure, because I do 80 all the time now.

[smiller]

On the Hwy cruising at 80mph GPS indicated with the windshield around halfway up, I have averaged just about 50 mpg

 

Please don't take this wrong, but... 50 mpg at 80 mph..???

[ShovelStrokeEd]

Seth,

I have heard other R12RT owners reporting this as well. I still find it hard to credit when the best my 1100S will do, with my careful throttle hand, is around 42 at that same speed. There just isn't that much difference in the aerodynamics unless I'm really missing something. Nor is there any real difference in the power output between an 1100S and a 1200RT. Given that those two factors are nearly equal, it should take the same HP to drive the thing at 80 mph. Give the new final drive a few minor points for lower friction and I just can't see the cause.

 

The only other thing left is engine efficency and I also find a 25% increase in efficiency hard to swallow, even with variable secondary spark timing, dual O2 sensors and whatever other voodoo they have come up with.

 

Of course, our oilhead motors were really optimized for emissions rather than performance and it just might be that the new motor has moved the compromise more into the performance direction.

 

I am puzzled.

[ClearwaterBMW]

On the Hwy cruising at 80mph GPS indicated with the windshield around halfway up, I have averaged just about 50 mpg

 

more power to you... but there must be some kind of Star Trek type of IMPULSE POWER at work !

 

so weird that my LT is so opposite as i mentioned above

yes, the LT is a 2002

yes, the LT is heavier

yes, maybe the LT is LESS slippery to the wind

but, i'm getting almost 18 mpg LESS at that speed (of course, the shield is all the way up)

 

hmmmmmm

greg

[PaulW42]

Overall my RT is averaging just over 54mpg (so about 45mpg per US gal)and is by far the most economical bike I've owned. I don't know what it is like at a constant 80mph (limited opportunity/desire over here!)but I would not be surprised to see over 60mp imperial gallon. By comparison my 1200GS averaged 48 mpg (40mpg US) and my 1150 approx. 40mpg (34 US). And the RT is getting better all the time.

 

Paul

[ClearwaterBMW]

very useful info

thanks for your input

greg

[STUFF2C]

I had a 1200GS and averaged around 42 mpg over 22k miles. What BMW has done with the RT I have no clue, but it is what it is. Lucky Me!

The milage does suffer when I run with the sport bike crowd. Their expressions are priceless when they see the "Electric Marshmallow" tucked in tight on their A$$.

 

I don't feel so alone or feel the need to go back and check my numbers when these posts are all over the place.

 

You'll be glad to know your mileage will actually go up as the miles go up. Well, that's how my RT has been. The mileage (47mpg) I have gotten recently has been all commuting and running around town. Lot's of stop and go traffic. On the highway it does even better. Closer to 50mpg if I keep it under 85mph. BTW if you're headed to the BMWRAlly in Tennessee perhaps I'll see you there. Texas plates, big trunk, no radio, and blue springs on the shocks (Wilbers). Finally, I don't know if you meant you owned a FJR1300 or were considering one, but I have already fed one to my RT in the Ozarks. He didn't stay with me through the first turn. Neither did the K1200RS rider who was with him. Yeah, I love my RT too.