My Green Skoda Fabia (VW Polo) R3 CRTDI - finally smashed the 3L / 80MPG barrier

[GreenTDI]

Originally Posted by ptitviet

Wow!!! Congrats it is awesome I am a bit jealous as I cannot for the moment go much under 4l/100km and my instantenuous fuel consumption at 62mph (real speed, so about 105 at the gauge) is more about 4l/100km. But it is true I haven't used all your tricks now and I live in the mountain. Even with much care, it can't be helped that a lot of gasoline be wasted downhill in brake dust and heat. Do you know the official SCd figure for your car? Mine is 0.60m2, and at 80km/h my engine revs at 1300rpm, which is fine but couldn't be lower.

I might try overinflating the tyres but I will only do that on long trips.

First of all, nothing to be jealous about! You have a bigger and heavier car, and your engine has one more cylinder. These cars can't be compared properly.
Secondly, my speed is 100 km/h on the meter (so 96 km/h or 60 mph real) Consumption increases exponentially with speed, even a few km/h less will do the trick.

I wonder if your engine is running under too much load in highest gear, could it be that your 6th gear is too long for 100 km/h? Especially on hilly roads. Try 5th gear for a while. (at lower gear you will also have to brake less downhill). My experience with the 3-cylinder TDI is that it loves to make a little bit more revolutions, without consuming more. I 've noticed that the 'sweet spot' for constant speed is between 1500 and 1900 rpm = I never use highest gear below 80 km/h. But then again, it's a smaller engine.

What do you mean with SCd - frontal area or Cw value? That last one is 0.32 stock, but maybe I'll have it down to 0.30 with modifications.

[California98Civic]

Keep trying ptitviet! Summer is coming...

[ptitviet]

Hello! Yeah I am trying more and more and hopefully there is a possibility of improvement through longer trips throug hotter air

SCd I mean the product of frontal area and Cw factor. For instance, on my car the front area is 2.2m2 and Cd is 0.27. Which gives a result of 0.593m2. I got through coastdown testing a value of 0.606, which is 2% of official value so I am happy with my protocol. And coastdown testing told me that folded passenger mirror made my SCd down by 0.02m2.

When I receive my new grille block I will do a new coastdown testing to try and see the actual difference.

[GreenTDI]

Originally Posted by ptitviet

Hello! Yeah I am trying more and more and hopefully there is a possibility of improvement through longer trips throug hotter air

SCd I mean the product of frontal area and Cw factor. For instance, on my car the front area is 2.2m2 and Cd is 0.27. Which gives a result of 0.593m2. I got through coastdown testing a value of 0.606, which is 2% of official value so I am happy with my protocol. And coastdown testing told me that folded passenger mirror made my SCd down by 0.02m2.

When I receive my new grille block I will do a new coastdown testing to try and see the actual difference.

So my SCd is 0.643m². It seems you're car has a much better Cd too - a longer car usually scores better and you have the optimized Greenline model. I bet you still can make a lot of progress! Keep me updated!

[GreenTDI]

Some pic's of my last modifications. Simple mods, but with great effect.

- closed the rims with some strong tape
- removed 112 pounds of junk out of the car.

Those are standard 15" alloy rims with 195/55 tires. They will be replaced with narrow tires when they are worn out (next year). Preferably in combination with a light forged rim from Audi and a closed hubcap.
Now the tire: it could be 165/70, 175/65 or a 185/60. But is narrow always better? Assuming you could go faster trough corners with wider tires = less braking and accelerating?

[California98Civic]

There is a long-running debate about whether narrower tires are better. There are several, sometimes conflicting factors. A narrower contact patch can ironically have higher rolling resistance, but also have better aerodynamics for being part of it thinner tire in the air flow. And then the weight and the chemical composition of the tire matter. Is that wider tire also a low rolling resistance tire? What is the overall weight of the wider tire versus the thinner tire? Because if a heavier tire out further toward the outer diameter of the overall wheel, it has a higher rotating mass effect. Lots to think about.

[COcyclist]

https://ecomodder.com/forum/attachme...2&d=1589535320

I did the same to my car. It is crazy how much the VW seat backs weigh. It has enough structure to hold the middle passenger seat belt with the other seat back folded. I can carry my bicycle inside instead of out in the airflow.

[GreenTDI]

Originally Posted by California98Civic

What is the overall weight of the wider tire versus the thinner tire? Because if a heavier tire out further toward the outer diameter of the overall wheel, it has a higher rotating mass effect. Lots to think about.

It's a pity that the weight of a tire is never mentioned as a specification.
The almost worn out tires that the car is now driving on, has already lost a lot of thread and therefore weight. Also tires have the least rolling resistance at the end of their life (but also less grip which I sometimes notice).

Anyway, the new tires must have a bigger diameter to change the gearing a bit. That's another aspect of tires.
Current 195/55 let the car go 62 (real) mph at 2000 rpm.
Taller 175/70 for example, would increase it with 5% (~65 mph) at same engine speed.

So yes, a lot to think about!

[GreenTDI]

@ Cocyclist:

A great space saving without the seats! And when you think about it, they are rarely used. Though, perhaps more often as the kids grow up and get hobbies or little friends where they want to play

[California98Civic]

Originally Posted by GreenTDI

It's a pity that the weight of a tire is never mentioned as a specification.
The almost worn out tires that the car is now driving on, has already lost a lot of thread and therefore weight. Also tires have the least rolling resistance at the end of their life (but also less grip which I sometimes notice).

Anyway, the new tires must have a bigger diameter to change the gearing a bit. That's another aspect of tires.
Current 195/55 let the car go 62 (real) mph at 2000 rpm.
Taller 175/70 for example, would increase it with 5% (~65 mph) at same engine speed.

So yes, a lot to think about!

Right. Bigger diameter, taller gearing, but also the weight is further from the hub so a hit from rotating mass. You can get tire weights at tirerack.com