Why are bike manufacturers struggling with MPG?

The car world has made some big strides in Diesel technology, but things are not clear cut.

My 1983 1.3 litre petrol Ford Escort used to get 35 - 40 mpg.
My Wifes last Fiesta, 1.4 petrol used to get 35 - 40 mpg.

In 20 years, comparing broadly similar sized cars, any fuel economy gains have been lost to increased mass and other factors. Emmissions technolgy and NVH refinements sap potential power and fuel economy.

Modern Diesels are now producing 90HP per litre, while delivering 50 MPG plus fuel economy, which is excellent, but going back a few years, my Mondeo idi Diesel used to get close to 60. My colleagues old NA Escort Diesel could get 70 on a good day. OK, it was not nearly as refined, powerful etc, but my point is that progess in fuel economy terms is not as good as everyone assumes.

People think its improved because a lot of people have moved from petrol to diesel vehicles over the past 10 years.

I think the steps taken by BMW and Honda, to try to deliver high economy bikes are interesting. I am really interested in seeing what they come up with in the next generation. I reckon we will soon start seeing Diesel engines introduced by a mainstream manufacturer. I think only BMW or Honda have the balls to to this.

Talk about comparing apples & oranges!

There are a few fundamental factors which have yet to be mentioned, which will go a fair way to helping motorcycle manufacturers avoid losing face from an mpg perspective;

-Thermal efficiency- the pursuit of power has led to more cylinders, shorter strokes, higher redline rpm & the accompanying friction loses. All have a negative impact on thermal efficiency. Unfortunately, shorter strokes invariably means less torque/rpm, so the gearing is normally adjusted to keep the motor spinning higher than a car would. Cars' relatively long strokes & large cc (for a bike) engine means more bang per buck & can operate at lower revs minimising the heat/energy losses per mile

Volumetric efficiency- Turbo charged cars (mostly diesels nowadays) have a huge advantage here & can fill their cylinders with a greater air than the engine would accommodate at atmospheric pressure. Motorcycle manufacturers have to play the game of adjusting cam timing (duration, lift & overlap), throttle bodies & back pressure to ensure the gases enter & leave the engine as quickly as possible over a much broader rpm range than with cars

I dont want to get bogged down in detail, but suffice to say, to increase the mpg of bike there are a couple of of options if the rev range is kept narrow;
-small cc, single cylinder screamer
-Larger cc, multi-cylinder plodder
-forced induction, any cc
None of these will be fast, but before you write off motorcycles as thirsty beasts for their weight, just think about what mpg you could expect from a car with comparable performance to a motorcycle? A Fireblade will beat a Ferrari Enzo to 60mph & also spank it on mpg.

Put a car engine in a bike & you'll get a tank that's a pig to ride & runs out of breath too soon, but great mpg, but this brief has already been filled by scooters

Hi Oliebloke

You've posed 2 questions.

I believe that the answer to the second question is that they're not struggling because they're not really trying. At the moment they've no need to, certainly not in westernised countries. Mpg has, in recent times not been a prime consideration for most potential buyers. Motorcycling has become mainly a leisure pursuit has it not, with excitement and pleasure the primary objective. Even those using their bike for daily transport have probably bought it with a view to extracting some enjoyment out of the journey (except in winter!)

That perpective may be undergoing a general change, with people's emphasis moving back more towards fun and for some buyers, outright frugality. The motorcycle (and scooter) has always had congestion busting characteristics, for obvious reasons, but people used to look to the motorcycle as a cheaper option to using the car. Good mpg being high on the list, as well as purchase and maintenance costs, relative to buying a car. Maybe there's the beginnings of a general move back to those qualities. If so, we'll see just how economical a bike can be.

Looking at the new Honda nc700 it's difficult for me to see any progress in 35+ years of riding. Pretty much the same power and weight as my cb550k3 but 150cc more. More storage space, granted. Better (kinder) emissions.

Bearing in mind adilmon's comments, maybe the optimum is something akin to a modern xbr500. Opened out to 600 cc. Didn't Phil Irving say that 600cc is the optimum for a single?

Regarding Oliebloke's first question.

Doing something along the lines of what he proposes would be possible I reckon. Giving your bike a Jekyll and hyde personality to suit the requirement's. It would need mechanical complexities like variable valve timing, variable valve lift, exhaust "exup" "valves, variable inlet trumpets, (variable stroke?)etc.

At the end of the day the best device is on top of our shoulders. Read Kevin's article on knocking just 10mph off your speed.

And buy a bike with fewer cylinders :)

Bdimon: you're right! In one sentence.

We want what they got. Bit of a chicken and egg thang. Until (impending?) circumstances impose a change on the status quo.

Incidentally, people are referring to Kevin as a guru. He's a guru of motor sickles. They're made of metal (ok, plastic too). That must make him a metal guru.

Ah the voices of reason - Motorcycle engineers have been ahead of car technology for some years - look at the variety of engine layouts - single , flat 6 , 4 in line, twin, flat 4, V twin , V4 two stroke ( ahh RD400) etc - very much trying to give what we want .

Take the Honda cub - pretty well the biggest selling set of 2 wheels world wide -and you can pretty well do what you want with it from its commonest use as family transport to moped racing , touring what a product .

The Western world has also been given what it wants with performance - 194 HP for a roadgoing Busa with a bulletproof engine to the fire breathing Duke Panigalle , Fireblade etc they have never stopped developing and in general with fantastic reliability ( we have been pretty lucky)

Diesel bikes have been tried but weight and power delivery never really been as efficient as petrol yet cars in the last 15 years diesel has become the everyday item - i have a 170hp Scirroco that can do 46 mpg on a tankful yet still provide me with bike type thrills ( adjustable suspension is a hoot to play with)

There has been a lot of discussion on the new Triunph Explorer with regard to tank capacity ( its only 20 litres) they have revealed this week that the feedback from the original spy shots was so negative that they were spurred ino action to redesign it in pretty quick time ( glad they did) but they have focussed everybodies questions on how far can you go on an adventure bike with 20 litres ( incidently same cap as the GS) . Several of the Triumph staff at the stand have claimed 250 miles from a tankful - this will be very intersting to see unless they have made a quantum leap in technolgy or their testriders were riding like pussies ( unlikely) i cant see it going that far ( would be good as i have put a deposit down) as its 130 odd hp 1200 cc 3 cyl !!!!

What we will see as with the Honda 700 is development for scooters and smaller cc vehicles to be more fuel efficient - cant see them touching the performance engines unless driven by emission regulation where you have to put more in to get the same out .

MPG or performance

Which do you want?

If your focus is on MPG then probably you are interested mainly on minimizing the total cost, including purchase, of getting from A to B.

Traditionally, when economy is the focus, we want the purchase price to be at most about 1/3 the cost of a small economical car.

At this purchase price point, what are your options?

A good used simple bike, with a history of reliability, up to 650 cc with low mileage may be a good option to consider.

I was thinking about a used Kawasaki KLR650. Single cylinder engine , big tank and with even some wind protection.

Pittsy, if you want to do a thrust curve graph on the NC700, I wonder how it would compare to the KLR650 at road speeds up to say about 80 MPH?

JAG

Would not we all!

How much are you willing to pay for both?

JAG

"before you write off motorcycles as thirsty beasts for their weight, just think about what mpg you could expect from a car with comparable performance to a motorcycle? A Fireblade will beat a Ferrari Enzo to 60mph & also spank it on mpg."
... good comment. And the bottom line too.

And I agree with Jag - performance 'OR' economy; the two are mutually exclusive in their purest sense. And so, like Sid, many have to compromise with a sporty turbo diesel car for instance.

Cars and bikes weight have steadily increased if anything in the last quarter of a century and even further back in time probably. Some of that can be explained away by the additional kit such as abs brakes, SatNav, interactive screens, electronic motors for seats and bigger everything to handle the performance. And of course safety aspects, car wise, in terms of: air-bags, stiffer frames and so forth. This has a direct and negative affect on all speed and handling related performance aspects.

And yet no longer are we content with 16 secs 0-60 mph on our cars. When our neighbours car does it in 7 seconds then surely 5 in our replacement car sounds all the better to us doesn't it? Well if we are growing, our cars are growing and yet we demand that our vehicles heave us quicker than ever before, then don't be surprised when your K1600GT doesn't return the economy of the XBR500 you once owned as a younger man in the eighties. Without overstating the bleeding obvious it's not rocket science in its inevitability is it?

I can think of some really frugal bikes, they're like listening to Nigel Mansell recite poetry. Is that what you really want from your motorcycle escapism from the real world? No of course not. Now stop bleating and take your metal and plastic friend out for a good thrash without worrying about it's economy or the planet for five minutes (copyright Clarkson) ;-D

Performance and economy,

So pittsy wants both.

Could you have both?

Maybe, but the cost of purchase may go up. How much are you willing to spend to have a bike with dual personalities and save a little gas?

To increase the efficiency of the engine is a challenge. As you indicated, the gas engine is not very efficient. Maybe only about 20% of the energy in the gasoline actually gets to the drive wheel. Where does the other 80% go?

You probably have more HP coming out of your exhaust then what gets to the rear wheel. The cooling system is just about as bad. So if you want to have a more efficient engine you have to lessen the losses to the exhaust and cooling system, lower pumping and mechanical losses. A tall order.

If you could just lower the total losses by 5% you would have a gain to the rear wheel of 20%.

In the short term why not just go out and buy a small vacuum gauge and attach it to your intake. When you want to get good MPG, run the engine in the gear that gives the slowest RPM possible that gets a high vacuum reading at the least throttle opening.

JAG

Pittsy, I side with what you say. It should not be beyond expectation to expect significant improvements.

If we have to use cars as a comparison then I can say that even unexciting dull, utility vehicles have improved greatly in the economy aspect. I had a Vauxhall Cavalier in the late eighties that would return about mid 30's mpg with just me in it. The family SEAT bus I have today took three adults, two kids, a boat with outboard engine and all associated family crap, the fourteen hundred kilometres to the south of france this summer and returned damn near 50mpg. The performance of the new car is no worse than Vauxhall was so improvement can be had.

I think the question of performance or economy is not the whole picture as it is one of those ideas that states the option has to be either/or and that is not the case. Just beacuse say the new 700 Honda is going to be frugal does not mean that it is going to be dull as ditch water. It may not be a knicker dropper but at the same time time it does not have to be a bout of halitosis either.

The good Capn mantions (and I paraphrase) that we are no longer happy if our vehicle does 0-60 in a week and our neighbours does it in sparrow's fart time. Actually I am one of those people that don't give a monkey's what the neighbours car does. His Posrche is completely uselss when he needs to pick up a sheet of plasterboard from the DIY super store and on the drive into work every day he gets there in the same time as everyone else that is stuck behind the JCB blocking the by-pass. I do take what Cap'n is saying though and know that he is making a broader statement about basically the stupid world we live in. There is room for improvement though in a bike that delivers some fun and that does not have to be high speed related but at the same time can also return fuel consumption figures that can equal a small family car, if not better them.

I suspect a Porsche owner can pay for a plasterer, LOL! ;-D

When I lived in Blighty I had an Audi A3 2.0 TDI (140hp jobbie). It accelerated quicker than any car I'd owned before. I used to cruise to work at 90 mph for most of the journey (not a JCB in sight! ;-D), I couldn't get it to do less than 50 mpg and it would often eek out 500 miles before wanting a drink again. To top it all I only had to take it in for a variable-mileage service every 18,000 miles or so. Apart from having all the toys and a fit interior, it was everything I could wish as an ideal compromise of performance and economy, providing a great overall ownership experience.

And maybe this is what we are talking here regarding bikes? I don't know what the two-wheeled equivalent is of the Audi I owned. Maybe a Tiger 800 roadie? Quicker than most traffic in the right hands, fun, whilst frugal and cheap to live with? Maybe? Maybe not? Maybe some manufacturers are already doing this under our unobservant radar? For instance Honda claims of the CrossTourer equate to a bike that is lighter, more powerful and with better economy than the Varadero it replaces. Shame those darn tanks keep getting smaller mind!

Sometimes it actually costs more, not less, to make a engine more mpg efficient. eg, adding EGR system. Sometimes better mpg is a by-product of perfomance mods eg injectors that atomise the fuel better.

One thing is for certain is that lightweight turbo charged cars have been regulated out of existence

Ref Kei cars, yes. I used to have a Suzuki Cappuccino, which was easily derestricted (one wire cut) to release a 115mph top speed. Suzuki stopped importing because of the emmissions regs. The Smart Coupe doesn't cut it, despite the extra CC because the emissions regs strangle it. Also, crash protection regs have led to heavier cars. I don't know how new caterham 7s are allowed on the road nowadays though!

I have my own spec sheet for a nippy, fun car with great mpg & only the Cappuccino came close (desite the rubbish name)

On the 2 wheel side, I decided V-twin was a good shout because the broader spread of torque means it can be kept at lower rpm when cruising to extend the range if needed & less down-shifting required when the pace increases

The Long Way Round is freedom. A ride to Box Hill is escapism. The difference is the time and resources available to us before other aspects in our lives begin to suffer. We all know which one would make us the happiest and which one is the most accessible. They are probably different! ;-D