Highway fuel efficiency numbers observed on my Yamaha R15

Noticed a mysterious drop in fuel efficiency which went away on the return journey.

BHPian SaurAswale recently shared this with other enthusiasts.

As stated in my previous post, I did go on another ride on the same route, starting a bit earlier this time. I started at 7 am from my PG and returned at 12:30 pm, adding 241 km to the odometer. There’s nothing particularly special to report, but I have some numbers and a doubt.

During my last ride, I received great fuel economy while returning—56.7 kmpl. This time, it was different. I took a break at 40 km, and up to that point, everything was normal. However, for the next 75 km leg, the fuel economy dropped mysteriously. It was showing 38-40 kmpl at a constant 90 kmph cruise. Previously, it showed around 48, and much less than that around 95 kmph. I'm still not sure what caused this. The bike ran perfectly, didn't feel any reduction in pickup and no hesitation at higher speeds. But the drop in FE was real.

I refuelled at the same petrol pump—5.44 litres at 103.55 rs this time. The bike had run 284 km from the last refuelling. The indicated fuel economy was dropped to 50 kmpl, and the calculated FE was 52.21 kmpl. It is a great number in isolation for any bike while doing those speeds. But the last 75 km leg affected it by at least 5 kmpl.

Magically, the issue went away on the return trip. I gunned it for the first 30 km, with the average speed showing 87 kmph—15% less than the cruising speed and some short bursts above it. Even after this, the fuel economy was still a strong 45 kmpl. The bike was back in its element. That's why I love this 155cc.

After that, I settled down to 90 kmph for the remaining part of the highway. The last 25 km were full of traffic as always. Due to reduced speeds, the indicated FE jumped to 53.4 kmpl when I parked it.

Here are some more numbers I observed during the return (I'm an engineer, can't help it):

• Below 80 kmph constant speeds: 60+ kmpl
• 88-90 kmph: 52 kmpl
• 95-96 kmph: 48 kmpl
• At 100 kmph: 44 kmpl ( VVA activates at 96)
• At 105 kmph: 38 kmpl

92-96 kmph (85-88 on GMaps) feels like a sweet spot in terms of efficiency and safety while maintaining good average speeds. The engine still has a little torque left if needed.

The next ride will be on the third weekend of this month to celebrate 1 year of the purchase. Maybe to the same place- maybe somewhere else. There are also some uncertainties in my professional life for now.

With that, I'll conclude this post. Please let me know if you have any idea why the fuel economy dropped suddenly and then recovered magically after the stop. I inspected the bike after refuelling but didn't find anything abnormal.

BTW I've still not renamed it, how does Nimbus2000 sound like?? Too cliche??

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