It's all about compromise - a study on front bumper design?

[bobo333]

Hey guys,

So my aerodynamics testing didnt go as well as planned, turns out the "long straight flat road" I used wasnt as straight or flat as i thought, and i didnt have the time or fuel to do it in both directions so the data was pretty meaningless. I also left my 10mm socket at home so i couldnt pull the front bumper off to get a rough guesstimation of its aerodynamic affect. I did however notice a pretty big difference since removing the factory under tray, so im keen to get started on its replacement as soon as possible

https://youtu.be/DAh3JHt4jbo

[MeteorGray]

Bobo, are you using Julian's idea of using a "throttle stop" to determine the comparative aerodynamic effects?

It seems doing so would show a lot within a few miles of testing.

Edit: I just noticed your attachment video and found that you are not using a throttle stop. If I were you, I'd try using one in order to see what the changes being made do to the speed of the car on a few miles of the same stretch of road, with-and-without the bumper / undertray or whatever you're trying to test. This would show if your speed changes and how much it changes, which has implications on the aerodynamic effects and, of course, fuel mileage.

[California98Civic]

The throttle stop does not seem to work on the hybrids.

[bobo333]

Originally Posted by MeteorGray

Bobo, are you using Julian's idea of using a "throttle stop" to determine the comparative aerodynamic effects?

It seems doing so would show a lot within a few miles of testing.

As California98Civic mentioned the throttle stop technique doesn't work on hybrids, nor cars with electronic throttles. The position of the pedal or throttle plate has little to do with the actual power being produced thanks to all of the computers adjusting everything to what it thinks you want.

The method I used in the video would be improved by using cruise control and driving both ways on the same stretch of road but I didn't have the time or fuel to turn around at that point and my cruise control is currently broken.

Im now back at home and locked in quarantine (again) so I decided to pull the car apart today for some measuring and playing with CAD (cardboard aided design). First step, pull the factory bumper and the last few bits of extraneous plastic.


After some messing around I've figured that I can actually have the best of both worlds with some trickery, and make a steel or aluminium reinforced off road bumper that still fits the factory plastic bumper on top.


Yes I do need more lights... The Livids are absolutely amazing on the highway, but on tight offroad tracks and twisty hills roads they are much too focussed


Next step is to replace the broken plastic undertray, and continue a flat floor all the way to the back of the rear carrier.

[MeteorGray]

My Mazda3 is run via computers and related electronic drive-by-wire throttle control, and even so I use a mechanical throttle stop to maintain consistent speed under consistent conditions.

With the WOT mechanically set via the accelerator-to-floorboard gap as determined by the throttle stop, I can maintain a selected speed on the highway that varies only due to variations in the grade of the road and the wind direction and velocity at any given time. This is to be expected, since the throttle only delivers power according to the throttle setting of the throttle stop. The computer drive-by-wire setup does not try to compensate for these variations in road grade and wind, since to do so would mean it would independently deliver variations in power that the driver isn't commanding via the throttle; that would be what a computer-driven cruise control does in order to maintain a commanded speed. My car doesn't have cruise control.

So, I guess I'm not understanding how a mechanical throttle stop doesn't work for testing changes in the aerodynamics of modern computer controlled cars with drive-by-wire throttles.

Unless, of course, hybrids truly are different. I don't have a hybrid.

[Piotrsko]

Because the computer controls the throttle NOT the pedal. It's a request system, you ask for 3% power from the gas pedal, and you get what you get from the car, say 1% to 5%.

In theory, on my F250, I can get 100% rated hp at idle to prevent stalling. Handy teaching my kids how to drive a manual. On the Golf, no such system which is a PITA.

[bobo333]

I havnt actually tried throttle stop testing in this car, but my common sense tells me that with the computer controlling the engine power dependant on load, temperature, speed, pedal position, battery charge level, hybrid motor assistance etc etc I can't imagine it working well at all.

[aerohead]

Originally Posted by bobo333

Many of you may have seen my new Off-Road Prius build that's in the works (if not there's a link in my signature).

One major component I would like to upgrade is the front bumper. Obviously the factory bumper is fairly good for aero and can be improved with a simple grille block and (more) flat floorpan, however it does not give the best approach angle for off road abuse nor is it strong enough for highway animal strikes.

This is where my study begins, how much compromise do I need to have to get my perfect bumper? Where are big advantages available in one area that detracts least from the other area?

The end product will most likely end up somewhere in the vast range between this:


And this:


And here's the car in its current guise:


Grill block and flat floor can both be combined with a metal bash plate which will likely extend all the way from the factory numberplate position all the way to the tail end of the diffuser, but other than that I'm open to front shape suggestions.

' The main contributions to the drag force originate from the rear part of the body.' Hucho.

[Tahoe_Hybrid]

Originally Posted by cRiPpLe_rOoStEr

I would also take it with a grain of salt, even though recently I got lurking about the fitment of a Prius-ish powerplant into some serious off-roader.

prius powerplant in my tahoe much more reliable ? can it even make enough power to move 3 tons?

[freebeard]

.

..even though recently I got lurking about the fitment of a Prius-ish powerplant into some serious off-roader.

Some, not one specific example.

https://en.wikipedia.org/wiki/Jeep#/..._Jeep_1943.jpg