-   Introductions (
-   -   Hello! New member from Switzerland (

ptitviet 12-04-2019 04:18 AM

Hello! New member from Switzerland
Hi everyone,

I'm a french guy living in the mountains of Switzerland.

After having had cheap vehicles (Peugeot 306 HDi mainly) as a student, I have enjoyed myself with a series of "sporty vehicles" including a Citroen Xsara VTS 167, a Mazda RX-8 PZ and a Renault Megane 3 RS.

I have always driven my vehicles with fuel economy in mind, discovering even pulse and glide practise with my RS (allowing some tanks to average 6.5l/100km 39mpg us which is nice I think for a 265bhp vehicle).

But shortly I have seen on Youtube conferences of JM Jancovici, a french engineer specialised and global warming and energy supply questions, which made me feel like I was wasting valuable fuel away.

So I have sold the Megane and just bought a '15 Skoda Octavia 3 Greenline Combi which is I think quite a nice fuel optimised car thanks to aerodynamics tweaks, reasonably sized tyres, a small engine coupled with a very long 6speed gearbox.

So I'm not gonna do huge modifications like some of you, but I hope to discover ways to optimise my driving further, and marginally improve the vehicle without changing too much of it.

As a land surveyor, I will try to share my science of measurements in order to quantify my fuel economy improvements.

Happy to share with you, so far I am on the first tank of diesel and my odb tells me it averages 4.3l/100km (58 mpg us) which is not bad for 0C, winter tyres, lots of 120km/h or mountain driving.

On the long run, I'd be happy if I could go in average under 4l/100km, without driving too slowly.

oil pan 4 12-04-2019 04:58 AM

Being a land surveyor probably not an ideal job to have an EV.
And nearly 60 obsolete miles to US gallons at freezing is really a good start. Diesels tend to not like the cold.

I don't believe a reasonably affordable car, with a diesel engine and a manual 6 speed has ever been sold in the US.

ptitviet 12-04-2019 05:19 AM

Hi oil pan 4!

Tbh, the Octavia is my personal vehicle we have company fwds for the job.
What do you mean by obsolete?

A diesel is especially good in my situation because I (electro-)bike to the work, and grocery is just at the corner of the street. I don't use the car on a daily basis. And when I take it, it is usually for long distances to visit family in France.

Yeah I know US market s*** for fuel economy, but it makes it funnier to hypermile I guess!

oil pan 4 12-04-2019 07:39 AM

The US environmental protection agency some times called the ethanol production agency declared war on nitrogen oxide emissions in the late 1960s or early 1970s because a hand full of places, probably around 0.1% of the lower 48 land area had smog problems because they bet on infinite exponential growth.
And that killed the diesel small vehicle market here in the US about the time it started and killed off lean lean burn gasoline engines by the 1990s.

ptitviet 12-05-2019 12:40 PM

1 Attachment(s)
Yeah ok the obsolete refers to the diesel technology. The main topic for diesel is for me the choice between CO2/global warming and particles/Nitrogen pollution.

So I have done a big research and worked my math, and have done a nice Excel to calculate my aerodynamics and rolling resistance, and afterwards calculate a theoretical stabilized speed fuel efficiency. This could help me in the future to estimate the gains in fuel efficiency related to some mods.

First was the aerodynamics. They are made of 2 parts :
- Cd (Cx in France) : can be found for my car on the web : 0.27
- S : front surface. Could not find it. I first used a rough formula :
Width * Height * 0.85 = 2.486m2
As I was not happy with this value, I digitized in Autocad the owners manual dimension page and I got a much accurate value : 2.196m2

So in the end, the estimated S.Cd value is : 0.593m2

Second : roll resistance. 2 variables, difficult to measure I had to guess :
- 0.007 for my 195 65 15 inflated to eco pressure (2.6bar front 2.7 back), please tell me if it is wrong (Conti Winter TS860)
- weight : 1280kg on the datasheet, should be pretty accurate since I have few equipment on this car

Then I made a table with the force created by this two elements :
- rolling resistance : 87.90N at whatever speed (I know it is not totally correct but I have no way to calculate the aerodynamic lift)
- aerodynamics : 1/2*rho (took sea level with temp 20C) * V^2*S*Cd
176N at 80km/h
275N at 100km/h
397N at 120km/h

then I converted it to the equivalent engine power. Problem is (and I'd be happy to get a clue on it), very difficult to get realistic values of transmission losses. I estimated to 10% considering it is a front wheel drive (no transmission tunnel) and a manual gearbox.

Until here I think my guesses are not too wrong, as the top speed of the car is given for 204km/h, the estimated necessary power for driving 200km/h is 99.77hp, 114.70 for 210 and my car has a 110hp engine.

Then using the gearbox ratios and wheel diameter, and finding a correct bsfc curve on the web, I translated the bsfc curve on a table and using some interpolation extension I went to the estimated fuel consumption :

speed (km/h) fuel consumption (l/100km)
80 2.41
100 3.02
120 3.73

What is interesting to know is just to change the air temperature from 20C to 0C :
speed (km/h) fuel consumption (l/100km)
80 2.50
100 3.14
120 3.92

This illustrates the big importance of temperature in fuel economy.

I'm happy to share the OpenOffice sheet, if whoever wants to chek it and give me an opinion I'd be happy. To use it you need the interpolation extension. Next step will be to determine SCd and Crr experimentally in order to accurately measure the future improvements.

ptitviet 01-02-2020 06:47 AM

Hi everyone, and happy new year!

During the holidays, did some coastdown testings on a 750m long stretch road. Online DEM shows it flat (max 0.1m elevation difference).

First had to calibrate my speedometer with a GPS which showed it was 5% too optimistic.
Then coasted down two times each way from 80km/h to around 50km/h and filming the speedometer.
In order to have some comparisons, I did the same test again with the passenger mirror folded.

I think my biggest error would be in the weight estimation, otherwise I've had my air density values checked by a real engineer and corrected with local absolute pressure (QFE) and temperature.

I am getting the following values :
0.606m2 for CdA stock
0.587m2 with passenger mirror folded (which means I would save about 0.08l/100km at 120km/h (73mph))

0.0112 for tyre rolling resistance. Not that bad since they are winter tyres (Continental TS860) but the smallest size possible (195/65/15).

This seems quite good as I get only 2.3% difference between the stock experimentally determined value of 0.606m2 and the initially calculated value of 0.593m2.

Otherwise for the time being my fuel efficiency has been worse, about 5l/100km (47mpg us) but I haven't done any long trip (max 70km) and it has been mostly mountain driving to ski resorts, which can not be good with a 1300kg car.

teoman 01-04-2020 02:46 PM

Welcome to the forum.

There is a software called VCDS. You can recalibrate the speedo and a lot more with it.

Also register on (also has app) to track fuel , maintenance and other costs.

oil pan 4 01-05-2020 12:20 AM

I like diesels. I was referring to miles as being obsolete.
If you wanted to buy a set of summer tires Europe has a good roiling resistance rating system so you can get good rolling resistance tires.

ptitviet 01-05-2020 12:00 PM

Thanks for all the replies!

Yeah I am using Spritmonitor and normally it should show itself in the signature.
I will be happy to use VCDS in the future, and for now I am thinking about coding a dedicated tool for drag determination, possibly in C#, as I am not happy with the accuracy of the results made with the Excel sheets found on the web. I'll keep you updated!

teoman 01-05-2020 12:08 PM

Excell also accepts c# code nowadays.

I would make it an online tool but you would probably need

All times are GMT -4. The time now is 07:54 AM.

Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2021, vBulletin Solutions Inc.
Content Relevant URLs by vBSEO 3.5.2
All content copyright