I've been promising this for a couple of months, but finally the results are in, so let's talk about fuel economy.
Motorcycle engines are performance machinery. In theory, they should benefit from running higher-octane fuel no matter what the riding environment. So is it a false economy to put cheaper, lower-grade fuel in your tank as a commuter?
• The bike: a 2008 Suzuki GSX650F with 19,000 miles on the clock.
• The rider: me - 51 year old IT Analyst and part-time Motorcycle Journalist with 16 years riding experience. Riding style best described as 'fairly smooth'; for this test I'd try to keep the bike running at about 6,000 revs.
• The roads: A couple of miles of local roads before joining the A12 (normally a busy but flowing dual-carriageway. But when it goes wrong, the tailback can be the length of my journey) for seven or eight miles then three miles to the centre of London via the East India Dock and Commercial Roads - horrendously busy, but bikes benefit from bus lane use.
If the A12 was screwed, the alternative is the A406 North Circular to the A1020 Docklands road (again normally flowing but can get horribly backed up) past the Excel home of the MCN London Motorcycle Show) before heading into London using the roads mentioned above. This is also the home of the control petrol station; Tesco Beckton. By filling up at the same petrol station the fuel quality should be broadly consistent.
For the test month I restricted my riding to commuting, at the same times each day. I decided to run the test in June, hoping the weather would be stable... at least the other controls were consistent!
The bike was filled up four times during the test period; the first octane level being the petrol added, the 'reserve' being what was in the tank from the previous top-up:
Week 1: 95-octane onto a reserve of 95-octane
Week 2: 98-octane onto a reserve of 95-octane
Week 3: 98-octane onto a reserve of 98-octane
Week 4: 95-octane onto a reserve of 98-octane
I would try to fill up at as close to the same miles on the clock as possible, to ensure a consistent mixture of fuel grade.
The assumption is there should be an improvement in economy in weeks 2 and 3, tailing off in week 4. Unless, of course, the usual mix of backed-up traffic and snarl-ups in a commuter environment, combined with not being able to open up the engine to use the performance flattened out the curve. But would any improvement balance out against the higher cost of filling the tank?
After four weeks, the following results were generated:
Week/Fuel/Pence per Litre/Miles at refill/ Fuel added/Litres per 100 miles/Cost per mile
Wk1 /95 on 95/ 131.9/ 135.7 /16.43 /12.11 /15.97
Wk2 /98 on 95/ 135.9/ 131.7 /15.93 /12.10 /16.44
Wk3 /98 on 98/ 133.9/ 133.1 /16.28 /12.23 /16.38
Wk4 /95 on 98/ 126.9/ 134.7 /16.49 /12.24 /15.54
Of course, there were price differences during the test period, so applying a control price of 4p per litre difference between 95 and 98-octane per litre, (130.9 for 95-octane, 134.9 for 98-octane), the 'Cost per Mile' gave these results
Week/Grade of Fuel/Cost per mile
Wk1/95 on 95/15.85
Wk2/98 on 95/16.32
Wk3/98 on 98/16.50
Wk4/95 on 98/16.02
This was a surprise. Running the lower-octane, cheaper fuel gave better results on the commuter run. As the ratio of higher-octane fuel in the tank increased, there is a notable increase in the "Cost per mile, which tails off when the lower-grade fuel is reintroduced.
I'd say I rack up 6,000 miles a year commuting. If I use the higher-grade fuel all the time, over the course of a year it would cost me an additional £40 per year - equivalent to roughly two refills.
It should be borne in mind that the engine in the GSX650F has essentially been around for a very long time and it is fair to say is not at the leading edge of engine technology - but this is true of a lot of commuter bikes. A bike with a more sophisticated mapping system might benefit from higher-grade fuel, but this needs further testing.
So is running lower-octane, cheaper fuel a false economy? This test suggests not. I would say the bike felt better to ride running the 'good-stuff' - whether that is worth the additional cost is down to your wallet.
With petrol prices hitting record levels and still rising, economy is becoming more important than ever. Electric bikes are making big strides, but in 2012 they are still a way off being ready to take over from conventional motorcycles. So there is a need to look at ways of improving economy. And Honda really took the bull by the horns, creating the NC700X - a parallel twin featuring effectively half a Honda Jazz car engine... and a reputed 78 miles per gallon range.
Clever move, Honda. Lots of attention has been (rightly) aimed at the NC700X - the 'X' is the one that catches the eye (so the perfect one to garner the interest). But Honda has been smart enough to take the "modular" approach and bring out two other machines based around the same engine and chassis; the Integra scooter, and the more conventionally styled NC700S. With shorter, lower handlebars and a reduced seat height, it is a fair bet this is the one that is going to appear on the commuter run.
Honda has a real winner on its hands. It is a fun bike to ride, but does the commuter stuff well. And you might want to take a photo of your local petrol station... you won't be visiting them too often in the future.