Clubjazz - Honda Jazz & HR-V Forums
Honda Jazz Forums => Honda Jazz Mk4 2020 - => Topic started by: crosstarhonda on March 04, 2025, 05:29:50 PM
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My Jazz never got this MPG The HRV is 10 months old.
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However, those incredibly good MPG readings are measured over short distances, 5.8 miles and 2.6 miles. If the 5.8 mile drive is mostly downhill, it is possible to get great MPG temporarily.
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My new Jazz claimed 80mpg for a journey of about 25 miles with the start 50m higher than the end. Wind can also make a big difference to the mpg.
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I have a Crosstar and a HRV and the Crosstar always has better mpg. :D
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However, those incredibly good MPG readings are measured over short distances, 5.8 miles and 2.6 miles. If the 5.8 mile drive is mostly downhill, it is possible to get great MPG temporarily.
My Jazz was showing 87mpg on a return journey over 4 miles today but I’ve seen well over 90 before, however it’s the average over a tankful that really shows the economy, so now the weather has improved I will probably get my usual 60 to 70 actual mpg. ;D ;D
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The brochure (and tests) show the Jazz is the most economical, with the Crosstar slightly behind.. and the HRV further back.
I have averaged 66mpg through winter, and now I have turned the heater off due to more clement weather, I expect to see it back into the 70s.
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I don't bother about MPG
The Jazz is far better than my old 9G Civic so I just set the climate at 22°C in Winter and 19°C in Summer both Auto and let it do its thing
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Some comparative long-term data:
My 2020 Crosstar averaged 70.5mpg (based on fuel into tank) over 9,467 miles.
My 2022 HR-V averaged 62.4mpg (based on fuel into tank) over 8,704 miles.
It's no surprise that the HR-V is less economical on fuel. It's a bigger and heavier vehicle and the big radiator grille can't help the drag factor. I felt that the 1.5 litre engine has to work a bit harder in the HR-V although this is partly offset by the HV battery having (from memory) 25% higher capacity.
I hope my 2025 Jazz will be slightly more economical than the Crosstar based on Honda's WLTP test data and my feeling that the Crosstar's roof rails added drag.
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Its not just the extra size and weight. The crosstars roof bars add extra drag but also its extra ground clearance allows more air to pass under the car where its less aerodynamic. Low front air dams make a big difference.
I recently saw on TV that the WW2 spitfire fighter was 22 mph faster with flush bodywork rivets rather than domed ones. . And amusingly they tested this by using the same prototype plane with flush rivets then gluing a split pea to every rivet to simulate domed rivets. ;D
The following photo may interest some. It shows the airflow turbulance on my Mk4 caused by the rear door shut ,the join for the rear bumper and if you look at the door handle closely. No panel has been cleaned . the eagle eyed may also notice the car is on my winter wheels, which may not be quite as aerodynamic either.
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Nice photo, I've noticed similar effects in certain areas on my mk3 and indeed other cars. Aerodynamics is a fascinating subject, things are sometimes counter intuitive or at least surprising.
The main reason the fuel economy of motorcycles is poor is because the drag coefficient is usually a bit worse than the proverbial barn door. My mk3 Jazz can return better economy than most of my bikes. The only bike which betters the Jazz noticeably is my Honda NC700 , which famously used the combustion chamber of the mk2 Jazz, same bore and stroke, same con-rods and bearings etc., 670cc is half the 1340cc car engine.
Look at a motorbike and all the forward facing surfaces give drag, so open wheels for example have both the front of the tyre and also the rim at the back of the wheel giving drag. An upright rider is all head arms chest with gaps causing turbulence and drag,
humans have a dreadful aerodynamic design.
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Interesting photo, LV. I have often noticed similar dirt spots at that same location on my Crosstar after a 100 mile motorway drive. It has been puzzling me what might cause it, but aerodynamics sounds like a logical explanation.
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I cant quite figure it out. My guess is the dirty air stream is being deflected down by the door handle then sucked abruptly into the door shut line. Maybe some sort of vacuum effect is generated. But probably not good for wind resistance . The Jazz is a bit boxy anyway.
Maybe I will study the effects further. But Mrs LV will only see it as a pathetic excuse for not washing the car ;)
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I think it is a combination of wind (lower pressure near the door handle) and water and dirt around the rear door (area in between the inner rubber seal and outer part). Water and wind cause the dirt to move to the lowest pressure area where water evaporates and dirt is left behind.
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Interesting photo, LV. I have often noticed similar dirt spots at that same location on my Crosstar after a 100 mile motorway drive. It has been puzzling me what might cause it, but aerodynamics sounds like a logical explanation.
ahem, the dirt deposit actually is caused by pollution (in clean air you wouldn't be able to see the consequences of turbulence so obviously). I've noticed the same thing during longer travels with lots of Diesel cars and lorries on the road.
sorry about getting off topic even more (again):
Does anyone happen to know the drag coefficient of a modern Jazz? (this information seems to be guarded as well as the crown jewels...)
I assume it to be somewhere around 0.32 but who knows?
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I have read its 0.33 but I dont know if thats an official figure. The dirt involved is very fine so may indeed be pollutant based.And susceptible to subtle effects of pressure etc. My Neighbours Toyota is currently very dirty with what I would describe as 'farm yard' dirt. Spray patterns etc are what you would expect.
Those of you who take pride in cleaning your car are missing out on so much scientific intrigue ;D
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On the pollutants, I wear a yellow hi-vis jacket on the motorbike and the upper arms get ingrained black dirt which is almost certainly a combination of diesel particulates and rubber tyre dust. You can't clean it off. The most worrying aspect is that I'm breathing that stuff in.
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... You can't clean it off.
The most worrying aspect is that I'm breathing that stuff in.
Yes, this residue of soot(?) is quite persistant and withstands "normal" washing procedures.
As dumb as it may sound: Have you considered wearing a face mask? - We probably all have some of them left over from the pandemic; why not put them to good use. :D
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Jazz
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Sorry, yes I think you need to drive further, say 20 miles in UK to get a representative average. I can get anything on short drives like those between 30mpg and 100+mpg :)