5th Gen Dirty Butt Disorder..... Who can explain this?

[Bobby12many]

super silly post... hoping someone far smarter than myself can shed some light on this dirty-butt phenomena.

Just recently returned from a trip to NE Iowa, which consisted of 5-15 miles a day of wintery dirt roads. I soon noticed how quickly the back of the 4R gets completely covered un dirt/road-grime, esp compared to most other vehicles.

Considering how flat, boxy and vertical the rear hatch is, I can understand how filthy it gets. One only needs to open the rear window at speed to see how there is a "pressure pocket" formed back there which allows stuff to just "swirl" back towards the vehicle....

Now, what I cant figure out is the perfect line of delineation from the lift-gate to the rear quarter panel. How can the D-pillar be nearly spotless? The rear liftgate curves a bit towards the sides, which makes me think it cant just be attributed to surface-angle changes alone. Likewise, the rear bumper seems to "hold onto" road grime on the side of the vehicle far more than the 1/4 panel.

Is this due to the 1/4 panel, liftgate and bumper all being from discrete materials (al, steel, plastic?)

 

[Whippersnapper02]

All SUVs have an air vortex behind them as they drive that makes the rear dirty. Some more than others. Pickups have it in the bed.

 

[Bobby12many]

All SUVs have an air vortex behind them as they drive that makes the rear dirty. Some more than others. Pickups have it in the bed.

That I get - but look at how clean the d-pillar is vs the hatch..... is the gap between panels creating an " air shield" preventing any dirt from getting on it?

I have no idea why this intrigues me so much lol the wife asked if I "cleaned that part" of the truck when I pointed it out

 

[Whippersnapper02]

That I get - but look at how clean the d-pillar is vs the hatch..... is the gap between panels creating an " air shield" preventing any dirt from getting on it?

I have no idea why this intrigues me so much lol the wife asked if I "cleaned that part" of the truck when I pointed it out

I think the only way to see why is to run it in a wind tunnel or tape tufts to the exterior to observe airflow as you drive.

 

[Ripper238]

Its the Iowa dirt, it has a fondness for rear ends. :biggrin1:


The air vortex is the cause for so much on the back, but the clear lines where the dirt does not sit is likely due to how the wind bends around the vehicle and some of the cracks forcing air flow out of them preventing the dirt from sticking. That back hatch can catch the air and create turbulence in any of the cracks connected to it.

Just my thoughts.

 

[Toffees]

I think the only way to see why is to run it in a wind tunnel or tape tufts to the exterior to observe airflow as you drive.

I suspect it's the spoiler which makes it more noticeable on the 4R

 

[Bobby12many]

Its the Iowa dirt, it has a fondness for rear ends. :biggrin1:

Just my thoughts.

LOL

That makes logical sense to me..... I wonder how defined the lines would be the gap between the door and hatch were taped up?

this info provides zero value to any of us, and for that I thank you all for indulging me

 

[Ripper238]

LOL

That makes logical sense to me..... I wonder how defined the lines would be the gap between the door and hatch were taped up?

this info provides zero value to any of us, and for that I thank you all for indulging me

Get some painters tape and try it out. Completely seal the gap between the body and hatch.

 

[Forgetful]

That's actually pretty neat.

 

[jp.vegas]

A lot of SUVs and wagons have a spoiler with a space between it and the rear glass/hatch. This space directs air down and across the back window to help keep it clear. If you look at the 4R, we have a spoiler but there's no space allowing that airflow, so instead we get a huge low pressure area behind the truck that causes shit to stick to it.

As far as the sides go, just how the airflow moves across the vehicle.

 

[MossJenks]

I've got one word for you my boy: aerodynamics.

 

[chrisridebike8]

is the truck ceramic coated? maybe they forgot the coat the hatch. I've literally seen lines like that between coated and uncoated surfaces, even if they were on the same panel

 

[Bobby12many]

is the truck ceramic coated? maybe they forgot the coat the hatch. I've literally seen lines like that between coated and uncoated surfaces, even if they were on the same panel

lightbulb!

Yep.... it was one of those "upcharge" bs ceramic coatings from the dealer as well (fought it, long story, tied it to their commitment to financing, etc blah blah blah)


That actually makes a ton of sense as to the lack of any dirt on the body vs the hatch. Great call

After my next good wash I may have to expiriment with some painters tape to test these theories....

 

[Bobby12many]

A lot of SUVs and wagons have a spoiler with a space between it and the rear glass/hatch. This space directs air down and across the back window to help keep it clear. If you look at the 4R, we have a spoiler but there's no space allowing that airflow, so instead we get a huge low pressure area behind the truck that causes shit to stick to it.

As far as the sides go, just how the airflow moves across the vehicle.

Super interesting....


Is there such thing as a spoiler-less 5th gen?

I wonder how introducing more vortices into the flow of the air over the spoiler would change anything positively? Lie an Evo-style "vortex generator" strip on top of the spoiler....

 

[johnnygraphic]

lightbulb!

Yep.... it was one of those "upcharge" bs ceramic coatings from the dealer as well (fought it, long story, tied it to their commitment to financing, etc blah blah blah)


That actually makes a ton of sense as to the lack of any dirt on the body vs the hatch. Great call

After my next good wash I may have to expiriment with some painters tape to test these theories....

You could also buy some ceramic detailers spray and hit the whole vehicle on your next wash and see if it makes any difference. Heck, you could do only half of the back hatch too.


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[97BlackAckCL]

Am I the only one who thought having a Dirty Butt Disorder sounds like a personal hygiene problem?

 

[skag1T]

I installed airtabs in the hoopes it MIGHT help with this dirty butt.

Still have to go on a dusty road, but the theory behind them is interesting.


Airtab | Aerodynamic Fuel Savers | How Airtabs Work

Airtab - Airtab(R) Improve Stability, Reduce Spray, Save Fuel

 

[jp.vegas]

Super interesting....


Is there such thing as a spoiler-less 5th gen?

I wonder how introducing more vortices into the flow of the air over the spoiler would change anything positively? Lie an Evo-style "vortex generator" strip on top of the spoiler....

Vortex generators may reduce drag and clean up the air passing over the spoiler, but you are literally creating a huge sucking vortex behind the truck. The only way to address that is to direct moving air downwards across the back of the truck effectively disrupting that low pressure area.

Removing the spoiler will have zero effect, you literally need some sort of air scoop sticking up into the flow coming off the back of the roof and directing air straight down breaking up that vortex.

The 4th gen was the same way. Rear window was rolled down and back up for effect:

 

[GT0neX]

All vehicles that I currently own have a rear hatch design and they all tend to do this.

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[johnnygraphic]

I installed airtabs in the hoopes it MIGHT help with this dirty butt.

Still have to go on a dusty road, but the theory behind them is interesting.


Airtab | Aerodynamic Fuel Savers | How Airtabs Work

Airtab - Airtab(R) Improve Stability, Reduce Spray, Save Fuel

I’d deal with the dirty butt disorder vs that.


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