VW ID3 aerodynamics

[Vekke]

The values in the results are average from start highest and lowest values on the points said on the video. You can see from the results that they are getting closer to each other meaning that they are evening out the differences in values. That comes from the +-1km/h travel car has during the route. Same goes for diesel cars on that route. I have sometimes used 3 times longer distance if the results did not show enough difference on the short run. Like with torsion value testing finding the actual optimal value for each engine.

I am agree more cycles would bring more accuracy, but on the other hand I think the lines follow each other really nicely on the two runs I did with the 2,3 bars at the end of tests on 4.4.2021. Same goes for the graph Julian made. I tried to test 3 times 2,5 bars on next morning, but there was too much wind. That why I did not attach also those results to same picture. You can see those results in the video if you like to take a look of those also. If you sum the a+b error in final results 37,6vs37,7 is 0,26%. Tell me if my calculation method has error?

Thats why I have many measurement points along the route.

I would like to see where the 10% differences are in any of the results because I really cannot see them.

[JulianEdgar]

Originally Posted by Vekke

The values in the results are average from start highest and lowest values on the points said on the video. You can see from the results that they are getting closer to each other meaning that they are evening out the differences in values. That comes from the +-1km/h travel car has during the route. Same goes for diesel cars on that route. I have sometimes used 3 times longer distance if the results did not show enough difference on the short run. Like with torsion value testing finding the actual optimal value for each engine.

I am agree more cycles would bring more accuracy, but on the other hand I think the lines follow each other really nicely on the two runs I did with the 2,3 bars at the end of tests on 4.4.2021. I tried to test 3 times 2,5 bars on next morning, but there was too much wind. That why I did not attach also those results to same picture. You can see those results in the video if you like to take a look of those also. If you sum the a+b error in final results 37,6vs37,7 is 0,26%. Tell me if my calculation method has error?

Thats why I have many measurement points along the route.

I would like to see where the 10% differences are in any of the results because I really cannot see them.

I don't know if it is a language difficulty, but I can't really understand what you've written. (Or if I have understood it correctly, it looks like a terrible test methodology. Why on earth would you want to introduce other variables when you're trying to test just one?)

Perhaps if you just describe your testing methodology? That is, how you actually go about doing your tests? ie step by step.

[Vekke]

a+b measurement from 4.4.2021 chart. Lines should not cross each other. I used 100 km/h test speed in these tests. There is too much variation to say for sure which is the best pressure for lowest rolling resistance. Next rolling resistane tests will be done at 60 km/h speed. Maybe will get more reliable data at that speed. Although some measurements are exactly same already with this speed.

Problem is head and tailwinds in the test. They play bigger role at higher speeds. +10 km/h headwind means 2500w more resistance at 100 km/h. Around 60 km/h you can have almost have +20 km/h headwind to have same impact to results. What I don`T know at the moment how the car is programmed to drive and how the tire pressures effect the cars ecu program.

Test method:
Drive car warm (takes 20 km on current weather in my ID3 (warm is looked from idle fuel consumption rolling in neutral at 100km/h speed. Idle consumption is around 2,5 kwh. When that is reached the results has been reliable on the course.
- Set cruise to 103 km/h
- Zero on trip on start
- Fill measurement points on the route from AVG consumption display (highest or lowest values on the route in most cases)
- In the end fill data from end. 5,5km long test.

Make a U turn and repeat to Finish which is same as start to other direction.
Calculate a+b take 4% speedo error into account when comparing to old results.

In general more data points give you more reliability. If you can see data jumping for some reason you can redo that test. If you just take the end figures you are blind what has happened during the test.

I have previously tested my cars even on 400km test drives, but its not good for testing. Weather and other road conditions play much bigger role to results and just one tractor from side road can ruin whole day tests.

[JulianEdgar]

Originally Posted by Vekke

Test method:
Drive car warm (takes 20 km on current weather in my ID3 (warm is looked from idle fuel consumption rolling in neutral at 100km/h speed. Idle consumption is around 2,5 kwh. When that is reached the results has been reliable on the course.
- Set cruise to 103 km/h
- Zero on trip on start
- Fill measurement points on the route from AVG consumption display (highest or lowest values on the route in most cases)
- In the end fill data from end. 5,5km long test.

Make a U turn and repeat to Finish which is same as start to other direction.
Calculate a+b take 4% speedo error into account when comparing to old results.

So you drive at 103 km/h for just over 3 minutes, then turn around and drive back the other way at 103 km/h for the same length of time?

And from just those two runs you expect to get accurate energy consumption data for the car in that configuration?!

To be blunt, that's just ridiculous.

The number of cumulative average readings you take during the 3 minutes is irrelevant - it does nothing to improve accuracy. (I'd assumed each of those readings was for a full run!)

I am not sure what else to say: nearly everything I can think of (except having the car warmed-up) is as wrong as it could be in this approach:

- Vastly too short a distance over which to measure an average with the accuracy you're after.
- No measuring of baseline scatter (ie variations with the car in one configuration).
- Deliberately, it seems, introducing extra variables (changing load with hills).
- Recording of data that does nothing to improve accuracy (the interim cumulative averages).

I am irresistibly drawn to reflecting on the testing of EM's Jim Michler, who I quote in my big aero book. The testing of different configurations of his truck took place over 4,000km (winter) and 5,600km (summer). Now that had credibility!

[freebeard]

[04-03-2021] --I have had the car now soon 4 days.

Maybe you missed this part? That's either 2021-03-04 or 2021-04-03, depending....

[JulianEdgar]

Originally Posted by freebeard

Maybe you missed this part? That's either 2021-03-04 or 2021-04-03, depending....

I saw that. It makes it worse, not better.

To say, "So far I have got ~6% better FE" based on that testing methodology, over that period, is simply rubbish.

And that's not even covering the absurdity of statements like: "Front suspension arm covers 0,6%" [improvement].

It pisses me of when people post absolute garbage measurements because it's simply misleading. It's exactly like "My cold air intake gave me a 25.6 per cent increase in engine power", as measured on the road.

It's even more annoying because the results from modifying a Volkswagen ID3 could be really fascinating - ground-breaking, even.

[JulianEdgar]

So I have been thinking about Vekke's (wrong) way of making measurements.

If I have it correct, in short he drives for 5.5km in one direction, then 5.5km in the other direction, car warmed up and on cruise control.

He takes readings from the car's average fuel (energy) consumption display at points along each direction. It appears these readings are taken at about 800 metre intervals.

These readings get numerically closer together (ie have less variation) as he proceeds in each direction, so he thinks the reading is becoming more accurate.

So let's look at a parallel. We're measuring maximum daytime temperatures in a room, over a week. In degrees C, the temperatures are:

M - 23
T - 24
W - 21
T - 25
F - 18
S - 19
S - 23

Now let's show the average at each point:

T - Ave 23.5
W - Ave 22.7
T - Ave 23.3
F - Ave 21.5
S - Ave - 21.1
S - Ave - 21.9

As with any averaging, the the trend in the cumulative average is less variation as the number of items in the data set increases.

But this data tells us nothing about the accuracy of the thermometer, or of other aspects that might be impacting measured temperature. For example, maybe on Thursday a cat slept on the thermometer!

So it's not the number of interim, cumulative averaging measurements which is important, it's - as has been said here many times - the distance over which the average is taken. (eg if we measured max room temps over 2 months, Thursday's cat wouldn't even be noticeable in the average.)

And, for anyone who has ever tested fuel economy, two runs in opposite directions of only 5.5km isn't going to be very accurate - at least, not when tiny changes are trying to be measured.

[IRONICK]

Originally Posted by Vekke

Here are the pictures of mods:Bigger Front tire deflectors 0,5%

The front wheels are already treated by the manufacturer, now such large deflectors are no longer used.

[Vekke]

Here is the current setup explained. Also forgot to mentioned that the air curtains are fake in the front.

https://www.youtube.com/watch?v=iePbSCjmspg

[IRONICK]

You're wrong when you say there is no deflector there, that 'thing' you caught your deflector on, that's exactly what it does. Okay, you could buy Audi A3 deflectors, they are much taller and have a better effect.