At What Speeds to Aero Mods Take Effect?

[95metro]

Originally Posted by Matt Timion

For around the town driving the height/aerodynamics really don't matter too much.

I have read statements similar to Matt's a number of times and it has me wondering at what point aero mods do matter.

As a vehicle travels it is pushing air. At low speeds the air flows easily around the vehicle, but as the vehicle's speed increases the air in front of it begins to compress and becomes a "wall" that must be push through...at least this is my understanding of things.

Obviously every vehicle is different thus similar aero mods will have different affects at different speeds, but is there a way of determining what that speed might be for a particular vehicle. Obviously CdA would come into an equation here.

[Matt Timion]

Originally Posted by 95metro

I have read statements similar to Matt's a number of times and it has me wondering at what point aero mods do matter.

As a vehicle travels it is pushing air. At low speeds the air flows easily around the vehicle, but as the vehicle's speed increases the air in front of it begins to compress and becomes a "wall" that must be push through...at least this is my understanding of things.

Obviously every vehicle is different thus similar aero mods will have different affects at different speeds, but is there a way of determining what that speed might be for a particular vehicle. Obviously CdA would come into an equation here.

Someone posted a graph here a while back. I believe that aerodynamics took effect somewhere over 40mph, but I'm totally guessing. I remember seeing that for "around the town" driving rolling resistance was the only issue.

[krousdb]

http://www.gassavers.org/showthread....highlight=tool

Ben was hosting it but the linky is brokey. I still have it.

[SVOboy]

It's on darin's site now isn't it?

[Matt Timion]

Originally Posted by SVOboy

It's on darin's site now isn't it?

Yes, but I remember someone posting an actual graph. I think it was actually you SVOBoy. Am I just making this up?

[SVOboy]

I posted a graph of my speed vs mpg, but I didn't make any mention of aero mods or anything like that.

[95metro]

Thanks guys - that's a good thread. To think, I've spent tons of time surfing MetroMpg.com and I've never come across that chart page...oh well.

[kickflipjr]

I have heard that at 35mph The engine is working more for wind resistance then tire resistance.

[95metro]

According to the chart: http://metrompg.com/tool-aero-rr.htm my car matches what you have heard kickflipjr.

I am assuming that some vehicles would be lower and some higher.

So, in the 70 km/h (45 mph) zones that I travel often I would see some marginal benefit from aero mods even in town.

[zpiloto]

Originally Posted by 95metro

According to the chart: http://metrompg.com/tool-aero-rr.htm my car matches what you have heard kickflipjr.

I am assuming that some vehicles would be lower and some higher.

So, in the 70 km/h (45 mph) zones that I travel often I would see some marginal benefit from aero mods even in town.

Don't overlook the effects of surface winds.

[95metro]

That's true, I was overlooking that. A stiff headwind could produce the same effect as a higher speed...thanks!

[zpiloto]

Originally Posted by 95metro

That's true, I was overlooking that. A stiff headwind could produce the same effect as a higher speed...thanks!

Even stiff crosswinds getting under the car will mess up the FE. I've noticed a lot more stability in crosswinds since installing the side fairings.

[thisisntjared]

Originally Posted by kickflipjr

I have heard that at 35mph The engine is working more for wind resistance then tire resistance.

that depends on the setup. all my mods are for aero and none are for rolling resistance. i have a feeling that the cross over for my car is much higher. the same is probably true for the aerodynamic sports cars with really fat tires.

[The Toecutter]

Aerodynamic drag begins to become the dominant force to overcome on most cars between 30 mph and 40 mph.

For around town stop and go driving, liberal use of properly-executed aeromods might only improve fuel economy 1-5%. In highway driving, the effect is more profound, around 15-40%. Of course, it all depends on the car.

[Mighty Mira]

I'd suggest taking a look at the link I suggested earlier in another thread. It's an excellent site that allows you to see what the power requirements will be at the wheels for a particular bodyshape, weight and set of tyres. After that it's up to the efficiency of the engine to produce that power.

Here are two graphs I made for a hypothetical camry sized car, keeping the same set of tyres on it. I suggest having a play, alternately setting the different coefficients to zero to see the raw effect of the other on the power required at the wheels.