MINI Cooper S rear diffuser w/ underpanel

[California98Civic]

Originally Posted by InsightfulRay

Well, I have two tanks under my belt after installing the airtabs. So far the average for my last 3 tanks BEFORE installing the airtabs was 48.9 mpg. My two tank average AFTER installing the airtabs is now 50.8 mpg.

That works out to an approximately 3.8% improvement. By "tank", I mean a fill. Typically I take on about 10-11 gallons whenever I fill up. Now, of course, we all know how unreliable a one tank calculation is since I'm subject like everyone else to air pockets in my tank, how many "click off's" past the first auto shut-off I dispense, etc. So, even though I try to control as many factors as possible when I fill up, I feel more confident with a larger data set like several tanks worth before I break out the champagne thinking I've improved my fuel economy.

At this point, I'm somewhat more confident in saying that the airtabs do improve FE. I've previously reported in this thread how they are definitely keeping my rear window and hatch cleaner. However, I'd like to get 5 tanks worth of experience before I'm really convinced. It is suggestive that the 3.8% improvement I'm showing so far is about what the company quotes on their website.

Someone may suggest I take them off and continue the experiment by gathering an additional data set sans Airtabs. I'm not planning that because peeling off each airtab, even though it can be done (I had to trash a couple because I made mistakes during the installation), does ruin your chances of getting it back on. The adhesive tends to peel the backing off of the airtab body, so it's kind of a "once it's on, it's on" kind of a deal.

As far as the driving techniques, I do mild hypermiling. Tires are at 45 psi, gentle acceleration, glide whenever I can, anticipate traffic flow to avoid using my brakes, combine errands so as to avoid short trips, stay at 55 mph in far right lane on freeway, avoid the A/C. I don't draft trucks or turn off the ignition (FAS) though.

You're making me wonder anew about airtabs and a rear defuser. I am trying something a little bit inspired by this to test the raised trunk lid prototype I just made. But I'm not sure of the "whole tank" method. It seems like there are too many variables remaining unaccounted for if I average over a tankful for days, such as how many seconds with one or another coasting technique, average weather temps, average draw on the battery from breaking or headlights, humidity... My thought is to limit myself to six freeway miles on my regular commute and record separate data for each day. The time of day being the same daily will help control for weather conditions. A controlled route limits breaking and acceleration variability. I'll do no hypermiling. If I drive this strip over 10 days on my way to work, I'll have some good averages. Do you have a scangauge? I use the Ultra Gauge, and I have been amazed at how it has changed my perspective on the regularity of my fairly disciplined driving technique.

[khafra]

Originally Posted by InsightfulRay

Well, I have two tanks under my belt after installing the airtabs. So far the average for my last 3 tanks BEFORE installing the airtabs was 48.9 mpg. My two tank average AFTER installing the airtabs is now 50.8 mpg.

That works out to an approximately 3.8% improvement. By "tank", I mean a fill. Typically I take on about 10-11 gallons whenever I fill up. Now, of course, we all know how unreliable a one tank calculation is since I'm subject like everyone else to air pockets in my tank, how many "click off's" past the first auto shut-off I dispense, etc. So, even though I try to control as many factors as possible when I fill up, I feel more confident with a larger data set like several tanks worth before I break out the champagne thinking I've improved my fuel economy.

At this point, I'm somewhat more confident in saying that the airtabs do improve FE. I've previously reported in this thread how they are definitely keeping my rear window and hatch cleaner. However, I'd like to get 5 tanks worth of experience before I'm really convinced. It is suggestive that the 3.8% improvement I'm showing so far is about what the company quotes on their website.

Someone may suggest I take them off and continue the experiment by gathering an additional data set sans Airtabs. I'm not planning that because peeling off each airtab, even though it can be done (I had to trash a couple because I made mistakes during the installation), does ruin your chances of getting it back on. The adhesive tends to peel the backing off of the airtab body, so it's kind of a "once it's on, it's on" kind of a deal.

As far as the driving techniques, I do mild hypermiling. Tires are at 45 psi, gentle acceleration, glide whenever I can, anticipate traffic flow to avoid using my brakes, combine errands so as to avoid short trips, stay at 55 mph in far right lane on freeway, avoid the A/C. I don't draft trucks or turn off the ignition (FAS) though.

Thanks! Could we have the individual numbers for each of the three pre-tab tanks, as well as the post-tab tanks, so we can get a confidence interval? They're more useful than just the averages, that way.

[vkash1208]

Hey there, I also own a MINI mine is a 2005 MINI Cooper S 6-speed. I'm looking into doing the same diffuser mod that you did hoping it comes out as good looking as yours.

Do you have any advice on how to do it that may make it easier for me? I read over the thread a couple times and it seems pretty simple.

[InsightfulRay]

Originally Posted by vkash1208

Hey there, I also own a MINI mine is a 2005 MINI Cooper S 6-speed. I'm looking into doing the same diffuser mod that you did hoping it comes out as good looking as yours.

Do you have any advice on how to do it that may make it easier for me? I read over the thread a couple times and it seems pretty simple.

Done a couple of more tanks but much more city driving so MPG's are down. When installing the Airtabs, I'd recommend NOT placing them into the plastic positioning strips (i.e. template) as a set of 3. I found that mispositioning a set of 3 tabs means you have to peel off all 3 and try again. Ugh! Easier to apply a strip of masking tape to the car roof (or wherever) and mark where each tab goes then apply one at a time. Just my 2 cents

[Arragonis]

Are we happy these actually work, as in make a measurable beyond the under 3% margin of error ? Derek would like to know.

[InsightfulRay]

Originally Posted by Arragonis

Are we happy these actually work, as in make a measurable beyond the under 3% margin of error ? Derek would like to know.

Personally, I'd like to accumulate more data. I'm in process of doing so. Will continue to report same as it accrues.

The nature of this mod (i.e. aggressive adhesive on each plastic tab) makes it difficult to do the A-B-A method of testing. One could apply it to a plastic film or something like that that might be more easily affixed then taken off, however, I'm not willing to do that with mine. Any other takers?

[khafra]

Originally Posted by InsightfulRay

Personally, I'd like to accumulate more data. I'm in process of doing so. Will continue to report same as it accrues.

The nature of this mod (i.e. aggressive adhesive on each plastic tab) makes it difficult to do the A-B-A method of testing. One could apply it to a plastic film or something like that that might be more easily affixed then taken off, however, I'm not willing to do that with mine. Any other takers?

A-B-A testing is completely unnecessary. There's various statistical tests that you can apply to your data to find out how credible it is. But if you don't want to do the math, just:

1. Get enough data points in the non-tabbed position that you can fit a bell-curve to them--at least 5, maybe more if they don't cluster nicely at first.

2. Tab up and do the same.

3. Put the two bell curves up on the same graph. The less overlap, the better.

4. If you don't want to do the graphing, just put the raw data points (not overall averages) up here; I or someone else will be happy to do the math.

[InsightfulRay]

Originally Posted by khafra

A-B-A testing is completely unnecessary. There's various statistical tests that you can apply to your data to find out how credible it is. But if you don't want to do the math, just:

1. Get enough data points in the non-tabbed position that you can fit a bell-curve to them--at least 5, maybe more if they don't cluster nicely at first.

2. Tab up and do the same.

3. Put the two bell curves up on the same graph. The less overlap, the better.

4. If you don't want to do the graphing, just put the raw data points (not overall averages) up here; I or someone else will be happy to do the math.

For the math-challenged among us, by "data point" do you mean "#gals consumed for miles driven". Second, your point #2 mentions "tab up". As I stated, those suckers are on to stay and I'm not about to peel them off and put them on again. I can supply 3 tanks of consumption stats prior to installation of tabs. I assume that's what you want?

Ray

[khafra]

Yes, if the miles driven and gas consumed for three tanks prior to tab installation is all you have, that'll help--but we might not be able to get a good confidence level in the results. The more post-tab data, the better; as that will help to narrow that part down.

Y'know, I really should be recording all my fill-ups, since I'll probably try aero mods sooner or later and the TDI doesn't need refills very often.

[InsightfulRay]

Originally Posted by khafra

Yes, if the miles driven and gas consumed for three tanks prior to tab installation is all you have, that'll help--but we might not be able to get a good confidence level in the results. The more post-tab data, the better; as that will help to narrow that part down.

Y'know, I really should be recording all my fill-ups, since I'll probably try aero mods sooner or later and the TDI doesn't need refills very often.

Got it. I'll dig around and post that data later today. I used to have a '96 Passat TDI. Very nice car. Even had propane injection system added to it just for kicks. Love the newer TDI's.