Author Topic: Only getting 22 mpg out of my fully loaded Honda Jazz!  (Read 1545 times)

Jamrock

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Only getting 22 mpg out of my fully loaded Honda Jazz!
« on: August 19, 2018, 09:43:43 PM »
Hello

I've just started a long drive across Europe and am shocked to see how bad my mileage is now i'm fully laden with cargo. I'm driving a Honda Jazz Mk1, which I generally find to be quite economical, although I've never really measured the mpg. I'm 2 days in to the trip and got quite a nasty shock about how quickly the fuel seems to be going down, although I know that not driving in the most eco-friendly way (I have a roof box which is fully loaded, 2 adults, 2 small children and lots of luggage in the car, have the AC on and am driving on motorways).

Have any of you ever seen mileage this low in your Jazz? Is there anything simple i can do to improve this (eg, a certain speed i should keep below)? It's too late for me to reduce my cargo now!

Lee

Rory

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Re: Only getting 22 mpg out of my fully loaded Honda Jazz!
« Reply #1 on: August 19, 2018, 10:01:29 PM »
Speed makes a massive difference as drag increases dramatically so drive as slow as is bearable.  What speed are you typically doing?

Only other obvious thing I can think of is make sure the tyre pressures are on their max.  Hopefully you did that anyway.

John Ratsey

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Re: Only getting 22 mpg out of my fully loaded Honda Jazz!
« Reply #2 on: August 19, 2018, 10:18:35 PM »
The aerodynamic drag increases with speed squared so, for example, 70 mph has 60% more drag than 55 mpg. Combined with the extra drag from the roof box this could also mean the engine working outside its most efficient range. Potter along at lorry speed even if it takes a bit longer and you might see 40 mpg.
2022 HR-V Elegance, previously 2020 Jazz Crosstar

Jamrock

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Re: Only getting 22 mpg out of my fully loaded Honda Jazz!
« Reply #3 on: August 19, 2018, 10:22:08 PM »
Thanks both

Yes, full service and two new tires before I left.

On the first day I was driving the speed limit (about 80mph) but slowed down today as I realised that wasn’t too sensible so kept below 60mph all day. Do you think that I would benefit from going slower than 60?

Jocko

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Re: Only getting 22 mpg out of my fully loaded Honda Jazz!
« Reply #4 on: August 20, 2018, 06:44:52 AM »
I found 60 mph on my Mk 1's speedometer gives me my best motorway mpg. It equates to 53-55 mph on the sat nav GPS. Mind you, that is without a top box. A top box decimates mpg, especially as speeds go up. With a car as heavily laden as yours the tyre pressures should be increased, when cold, to at least the maximum indicated on the B-Pillar sticker. Mine states 33 psi front and rear, for a loaded car, but I run 35, two up, and would go to the towing figure of 38 on the rear, if heavily laden.
80 mph, fully loaded and with a top box, would probably give me the numbers you are seeing. As John says, potter along with the lorries. I would sit in behind one (not too close as to be unsafe), and take advantage of them pushing the air aside for you. I have seen a 50% improvement in instantaneous mpg doing that.

sparky Paul

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Re: Only getting 22 mpg out of my fully loaded Honda Jazz!
« Reply #5 on: August 20, 2018, 06:32:12 PM »
I've read elsewhere that a top box kills the mpg on the Jazz, and it would make sense on most small cars. My experiences with top boxes are limited to much larger cars, where it still made a difference, but was tolerable.

As others have said, adding drag has a increasingly bigger effect as speed increases, so avoid motorway speeds at all costs. The poor little Jazz really hasn't got the guts for it - you might be better off with a small trailer with a cover, although it will increase the cost of any ferry crossings.

smilertoo

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Re: Only getting 22 mpg out of my fully loaded Honda Jazz!
« Reply #6 on: August 21, 2018, 03:53:29 PM »
The Jazz seems to basically drive like a brick if it's heavy, the difference between just me and having passengers is massive.

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