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Logic · 03-27-2025, 09:52 AM

While the results are likely very much car specific, here's someone that has actually done A-B-A tests as he was replacing the bumper anyway:
https://www.ek9.org/index.php?thread...26/post-158601

Bumper with holes
From A to B: 208km/h
From B to A: 208km/h

Bumper without holes
From A to B: 205km/h
From B to A: 206km/h (just barely)

Description of experiment
We drove to a parking spot next to the autobahn. There we launched. I kept accelerating untill a certain spot (next parking spot, few km's) and then we noted that top speed we got there. We turned around at the next point where we could. Then we would go flat out again from the beginning on the autobahn, only opposite direction obviously. Untill we came across the first parking spot, we then noted the top speed again.

Description of results
With the bumper with holes we got to the top speed pretty quick. With the new bumper, we were not only slower, maybe it was even more surprising how long it took to get at the top speed, compared to the bumper with holes. For example, on the B -> A run with hole-bumper we got to our top speed relatively quick and just before we got to the parking spot we had the feeling it might even get to 209, but there was a car that got in front of us. The run without hole-bumper was pretty different. It took way longer to get at 205 and only 100 meters before the parking spot where I'd let go of the gas pedal it went to 206. I have yet to download the G-Tech results, but for my feeling the bumper with holes made some difference in higher rpm's in 4th and 5th gear.

I NB that this is a low hanging, parachute shaped rear bumper without any sort of rear diffuser.
This is (still?) the case on many cars.

Looks aside, what I like about this idea is that this is one of the few aero mods that reduces weight by a tad and weight reduction is THE Eco Mod 98% of the time:

In the UDDS (urban) driving cycle: (98% of driving)
Rolling Resistance (%): 19
Aerodynamic Drag (%): 14
Inertia (%): 68

In the HWFET (highway) driving cycle: (2% of driving)
Rolling Resistance (%): 29
Aerodynamic Drag (%): 47
Inertia (%): 24

https://ecomodder.com/forum/showthread.php/inertia-vs-aero-drag-vs-rolling-resistance-urban-41665.html

03-27-2025, 09:52 AM	#81 (permalink)
Logic Master EcoModder Join Date: Aug 2022 Location: South Africa Posts: 790 Thanks: 317 Thanked 319 Times in 279 Posts	While the results are likely very much car specific, here's someone that has actually done A-B-A tests as he was replacing the bumper anyway: https://www.ek9.org/index.php?thread...26/post-158601 Bumper with holes From A to B: 208km/h From B to A: 208km/h Bumper without holes From A to B: 205km/h From B to A: 206km/h (just barely) Description of experiment We drove to a parking spot next to the autobahn. There we launched. I kept accelerating untill a certain spot (next parking spot, few km's) and then we noted that top speed we got there. We turned around at the next point where we could. Then we would go flat out again from the beginning on the autobahn, only opposite direction obviously. Untill we came across the first parking spot, we then noted the top speed again. Description of results With the bumper with holes we got to the top speed pretty quick. With the new bumper, we were not only slower, maybe it was even more surprising how long it took to get at the top speed, compared to the bumper with holes. For example, on the B -> A run with hole-bumper we got to our top speed relatively quick and just before we got to the parking spot we had the feeling it might even get to 209, but there was a car that got in front of us. The run without hole-bumper was pretty different. It took way longer to get at 205 and only 100 meters before the parking spot where I'd let go of the gas pedal it went to 206. I have yet to download the G-Tech results, but for my feeling the bumper with holes made some difference in higher rpm's in 4th and 5th gear. I NB that this is a low hanging, parachute shaped rear bumper without any sort of rear diffuser. This is (still?) the case on many cars. Looks aside, what I like about this idea is that this is one of the few aero mods that reduces weight by a tad and weight reduction is THE Eco Mod 98% of the time: In the UDDS (urban) driving cycle: (98% of driving) Rolling Resistance (%): 19 Aerodynamic Drag (%): 14 Inertia (%): 68 In the HWFET (highway) driving cycle: (2% of driving) Rolling Resistance (%): 29 Aerodynamic Drag (%): 47 Inertia (%): 24 https://ecomodder.com/forum/showthread.php/inertia-vs-aero-drag-vs-rolling-resistance-urban-41665.html