Glee Fuel economy

[shameless_frank]

A question to the other glee owners:
What speed do you find you get the best mpg whilst on the motorway?

I've tried 60-65mph which didn't do much. Tried 70  (same again) but going 80mph I'm getting 66-67mpg.......how does that work????

[Oop North John]

Drag is velocity squared, so double the speed = quadruple (thanks Greywolf       ) the drag which is why you need loads of power to get a few more mph than our bikes.

For me, 2 up with panniers cruising at a GPS 75mph gave about 60mpg. Ideal cruising speed for the engine is at max torque, which for us is way above most roads speeds limit.

[Jacko]

Yes, and sustained 95mph will deliver you 46mpg. You pays your money...

[greywolf]

Squared means double the speed is four times the drag. The best fuel economy comes at about 40mph in 6th gear. No bags and body down on the tank even helps. Bikes are very dirty aerodynamically compared to cars.

[Mitch]

60-65 gets me up to 84mpg on a run. (Did last year from West Yorkshire to North Wales).
65-70 gets me around 68 to 70mpg.
I'm 6ft 4 with givi airflow as high as it'll go and top box.
They are really frugal at 60mph, pity 60 is too slow and you spend you're time hgv, s welded to your rear.
The faster you go the more you pay. I hate motorways,  they square your tyres off.

[Jacko]

Motorways get you where you want to be more quickly, then you can start evening off the squaring with more time on the bends. They're a necessary evil.

[hookie]

Squared means double the speed is four times the drag

Yes. It's called the "inverse square law." It basically means that you need four times the power to go twice as fast or twice the power to half as fast again. This assumes all other things like drag and other frictional losses remain constant, which they tend not to. With regard to fuel consumption the efficiency (cylinder filling, combustion efficiency etc), the torque curve of the engine and the gearing all come into play as well and adjustments made to suit your all up weight and preferred cruising speed can give you the best overall figures. Just gearing the bike as high as possible will make it use more fuel and be sluggish to ride.

[greywolf]

People going to one or two teeth greater front sprockets on Wees have reported no improvement in fuel economy. The lower rpms are offset by the need to open the throttle more as less power is generated at lower rpms.

[Oop North John]

I could only envisage an reduction in the fuel consumed if a sprocket change took the engines rpm to a point that has a much better torque output.

[Andy M]

Constant speed is best in my experience. Better to go with a line of cars at 75 all the way than have to accelerate into an overtaking gap only to drop back to  65 to maintain your theoretical ideal (acceleration is another square for the benefit of our mathematicians). If the road is clear and you can just bimble along at 50 and never touch the brakes fair enough, but most of your day on a motorways isn't going to be like that.

Average speed is interesting too. Try and cruise at 60 and you'll average 40-something. Try and cruise at 90 and your average hardly changes. Add in blood pressure and you might have another inverse square relationship!

Andy

[Juvecu]

I played around with gearing the bike longer so that the revs would drop at motorway speeds. I found that there's practically no difference in fuel economy, but if you get it right the vibrations are reduced and you have a more comfortable ride. The trade off is less acceleration in the lower gears, but it's not so much as to be any kind of problem, particularly not if you're someone that spends a lot of time on motorways. I ended up going back to stock sprocket rations when my commute went down from ~185 miles per day to ~125 miles a day. I'd only go for longer gearing if I start doing some serious miles again, but even then I'd just go to a 45 on the rear instead of a 47, that was a good setup for me.

[user650]

On my Lakes trip Thurs and Friday 340 mls over all types of roads and "only" managed :-

[ziggy]

Whilst site seeing around Scotland this weekend I had 75.4 mpg showing for most of the weekend until our run home when it has dropped to 62 after the 550 mile run home.

 

[Newmp]

Just back from a tour in France. Best MPG was 77.1 pottering around the Dordogne & worst was 57.2 hammering (for us) up from Treignac to St Malo on the autoroute.

[alan29]

My highest was 84.2 after pootling around for an afternoon. My lowest was 49.7 at the end of a 250 mile journey south from Scotland along the M6 in high wind and driving rain with full luggage on. Glad to say that my bargain basement clothes didn't let a drop of wet in.