So I am doing some bedtime reading last, the K100 Rider's Handbook (oh the K pox!) and was looking at the specs.

The naked does 56.5mpg @ 90kph. The RS does 65.7mpg @ 90kph & Rt 64.5.

The final drive ratio is naked 2.91:1. The RS 2.81:1 and RT 2.91:1.

# of teeth naked 32/11. Rs 31/11 and RT 32/11.

Weight (full tank), naked 239kg. RS 253kg and Rt 263kg.

So my question is, does the RS get better fuel economy because of of aerodynamics of the fairing? Or is it something to do with that missing tooth? It is carrying 14kg more!

I have just swapped my RS's handlebars from RS to RT, so with the more upright position and more drag will my fuel economy drop?

I would expect the naked to do better than that. The wind resistance and fairing factor barely comes into the equasion at 90kph and will make minimal difference but the final drive ratio does make a noticeable difference to a K.
My wifes K75 went from about 59mpg to 67 mpg by changing the ratio from 3.2 to 2.91. I have a 2.75 to put into my K1100LT which has a 2.91 and expect to get a good improvement. I did hear of a guy who put a 2.56 ratio from a R1200c into a K1100RS and got a really big improvement.

Rick G wrote:I would expect the naked to do better than that. The wind resistance and fairing factor barely comes into the equasion at 90kph and will make minimal difference but the final drive ratio does make a noticeable difference to a K.
My wifes K75 went from about 59mpg to 67 mpg by changing the ratio from 3.2 to 2.91. I have a 2.75 to put into my K1100LT which has a 2.91 and expect to get a good improvement. I did hear of a guy who put a 2.56 ratio from a R1200c into a K1100RS and got a really big improvement.

Any drop in power Rick?

Yeah there will be but as with the K75 you don't really notice it after a few miles. Occasionally you need to kick it back to overtake but not very often. It was well worth doing.

My bike is K100RT with no fairings at all. It consumption was last autumn something like 5,8l / 100km. It did not change much depending style of driving, but I did give old Goblin some action I admit. Bike has renewed (and a bit improved) engine and standard final drive (1986 model).

According to google this 5,8l / 100km is something like 40mpg - So I guess that the weight is not that important, but fairings and aerodynamics are.

Edit: Do you really get these bricks to go under 4l / 100km?? Over 600km (or 375 miles) without refuelling?

http://www.aqua-calc.com/convert/fuel-consumption/mile-per-gallon-to-liter-per-100-kilometer

Find this thread interesting as I have just removed the fairing from my RT. (Fighting the urge to put it back at the moment as its 1C and snowing outside.)
I can feel the loss of that 24kg in the handling and performance when riding the bike but too early to say if the fuel consumption is much different.
I think we need to bear in mind when comparing fuel figures that US gallons are smaller than UK gallons.
Which type of gallon do you generally use in Australia?
Had considered using the higher geared RS diff but someone else had said the difference was negligible. Rick's comments are making me think again.

Aust uses or at least used to use the imperial gallon but now it's the litre as do all except for US who use their special version of a gallon (where that came from I don't know).
In Aust we are restricted to 100kph which will return much better figures than places where the limit is 130kph or 80mph.
Despite the restrictions I have at times cruised at 130 -140kph for considerable distances and the drop off is astounding. At least 10mpg less.

Rick G wrote:Aust uses or at least used to use the imperial gallon but now it's the litre as do all except for US who use their special version of a gallon (where that came from I don't know).
In Aust we are restricted to 100kph which will return much better figures than places where the limit is 130kph or 80mph.
Despite the restrictions I have at times cruised at 130 -140kph for considerable distances and the drop off is astounding. At least 10mpg less.

Dead right Rick.

The Riders Handbook states 4.3 l/100klm (65.7mpg) @ 90km/h (56mph) and goes to 5.7 l/100klm (49.6mpg) @ 120km/h (75mph).

Nearly 25% increase in fuel consumption!

I actually tested this out on my previous LT. I was on a 2600klm road trip and you need something to occupy your mind. The figures were within 2% of what is stated in the hand book. Bloody efficient those Germans! I also did a stretch at 140kph and the tank just about imploded the fuel was leaving it so fast!

Rick G wrote:Aust uses or at least used to use the imperial gallon but now it's the litre as do all except for US who use their special version of a gallon (where that came from I don't know).

apparently in the old days ships would deliver supplies to the American colonies and one of these consumables was rum in "one gallon" kegs....but yet again it was thought that the sailors would withdraw a specific amount from each drum prior to delivery so then the Americans had much smaller gallons....

Klompy the grey brick wrote:

Rick G wrote:Aust uses or at least used to use the imperial gallon but now it's the litre as do all except for US who use their special version of a gallon (where that came from I don't know).

apparently in the old days ships would deliver supplies to the American colonies and one of these consumables was rum in "one gallon" kegs....but yet again it was thought that the sailors would withdraw a specific amount from each drum prior to delivery so then the Americans had much smaller gallons....

Wow Klompy, your memory goes way back

ooohaaahhh Jim lad it were true....( splicing the main brace it were ) a tot for everyone, the colonials will never notice...hic, hic

until they start getting really crappy miles per gallon figures...

Klompy the grey brick wrote:

Rick G wrote:Aust uses or at least used to use the imperial gallon but now it's the litre as do all except for US who use their special version of a gallon (where that came from I don't know).

apparently in the old days ships would deliver supplies to the American colonies and one of these consumables was rum in "one gallon" kegs....but yet again it was thought that the sailors would withdraw a specific amount from each drum prior to delivery so then the Americans had much smaller gallons....

Now I am getting confused. I went into local Total Wine & More over here in the US and I was able to buy my "Duty Free" Rum in cc measurement bottles. Nice and easy for a dumb ass like me. 3 x .75 litres means I am under the 2.25 litre limit upon return to the colony. I bought three bottles for the price of one at duty free prices at the airport.

Dave.

how times have changed...and it is time you updated your ownership list...Darth Tackler and his Matt Black K75RT....

We in Finland have (summer) speed limits outside cities and towns etc. ranging from 60km/h to 120km/h. I usually drive those little roads with lots of curves, and not much cops. They range from 60 to 80, but I admit that I don't always drive excactly like the sign says...

Tenox wrote:. . . I usually drive those little roads with lots of curves, and not much cops. ...

+1
That's were the fun is!

I once learned the rum 'evaporated' through the wooden casks.....

I have never seen better than 45 mpg out of any K100, and with the ethanol content of the fuel we are served today, my mileage is in the mid to high 30's, occasionally nudging 40 mpg if I exercise maximum adult restraint. A good old fashioned desert road hoon can drop the mileage down to 30 even.

We have 4 different fuels here (+ diesel of course)
RE85 (with 85% ethanol)
95E10 (with 10% ethanol)
98E5 (with 5%) I mainly use this, it is bit more expensive though.
Vpower = 99E5

Last one is sold only in few stations (Shell) and is the most expensive normal fuel in Finland.

Gas - buy the way - costs about 1,6 - 1,8 euros / litre here.. So it is little less than 40e for a full tank to K. (~50 US $)

Hi there, what I've measured is 18.95km/l @115 km/h and 13.63km/l@140km/h.
Best regards
JAP

I thought my K75 was good at 19.5kpl but when I changed the F/D to an rt's 2.91:1 I got 21.5kpl thats just going to work and back around 48k's each way back in them days. biggest difference though was in letting out the clutch we moved further faster in 1st than on the old F/D of 3.2:1 and quickly became obvious when doing a toyrun all that clutch in clutch out wasn't needed so much on the old F/D, cant imagine what the boys in motorcycle mags would have written about our bikes if they all came with a 3.2:1 f/d in 1983 they would certainly have got up and boogied in the stoplight stomp. The Mason's keep it at 7ooorpm would be easy with that F/D.

I'm certain its mostly gearing.

When I exchanged the K100RS 16v paralever rear end for a K100RT Monolover rear, my sidecar went from getting 17km/l at 100-110kmh to 14km/l. I changed from an obnoxiously loud leaky 4-1 exhaust for a standard K100 exhaust at the same time.

Al