Motoring Discussion > Car wash while driving through rain Green Issues
Thread Author: movilogo Replies: 9
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New Mon 13 Jul 15 13:31 
 Car wash while driving through rain - movilogo
I observed that when I drive at motorway @ 50-60 MPH in moderate rain, the car looks surprisingly clean afterwards!

Wheels are still dirty and but everything else is clean enough to touch by hand and having no residue of dirt in hands.

Even for hatchbacks, I noticed rear hatch becomes clean too.
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New Mon 13 Jul 15 13:39 
 Car wash while driving through rain - WillDeBeest
Yesterday's repeated heavy showers certainly got the accumulated dust off both our cars without going anywhere. Probably washed a lot of crap off the roads too, and with no salt at this time of year, that might account for Movi's clean-car observation; even the water thrown up by the wheels was (comparatively) clean.
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New Mon 13 Jul 15 13:50 
 Car wash while driving through rain - movilogo
High speed water hitting stationary car is same as high speed car hitting stationary water (assuming rain is falling nearly vertically, so its horizontal velocity component is almost zero).

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New Mon 13 Jul 15 14:01 
 Car wash while driving through rain - Cliff Pope
That may be true on the bodywork, but it's always puzzled me why the encrusted dirt underneath a car is always in ridges. Why doesn't water flung off a rotating wheel inside a wheel arch simply blast all dirt off - why does it stick?
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New Mon 13 Jul 15 22:49 
 Car wash while driving through rain - bathtub tom
>> That may be true on the bodywork, but it's always puzzled me why the encrusted
>> dirt underneath a car is always in ridges. Why doesn't water flung off a rotating
>> wheel inside a wheel arch simply blast all dirt off - why does it stick?

Good question, I'd like to know too.
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New Mon 13 Jul 15 23:20 
 Car wash while driving through rain - Armel Coussine
>> always puzzled me why the encrusted dirt underneath a car is always in ridges. Why doesn't water flung off a rotating wheel inside a wheel arch simply blast all dirt off - why does it stick?

It sticks because very fine mud is sticky. And the pattern inside the wheel arch, quite often with longitudinal grooves, is produced by the tyre tread pattern basically.

Sometimes the underside further back in the middle of the car will start to display sort of crosswise striations in the layers of adhering filth. I assume they are the product of air eddies on muddy roads at habitual cruising speeds.

Proper streaming wet roads are quite rare. We get a lot more muddy half-and-half.
Last edited by: Armel Coussine on Mon 13 Jul 15 at 23:23
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New Mon 13 Jul 15 18:07 
 Car wash while driving through rain - Bill Payer
>> Even for hatchbacks, I noticed rear hatch becomes clean too.
>>

Hmm...really? Can't say I've ever experienced that.

I did get my car blast-washed while waiting to collect someone from Manchester Airport a week yesterday - wave after wave of absolutely ferocious rain was coming across the airfield and hitting the car for about 20mins. Didn't dare get out.
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New Wed 15 Jul 15 12:54 
 Car wash while driving through rain - TheManWithNoName
I'm looking forward to my annual trip up the A1, (Essex to Lake District) and hope it rains en route. The car gets its yearly bath. Even the alloys are cleaner!
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New Sat 18 Jul 15 18:36 
 Car wash while driving through rain - Oldgit
>> I'm looking forward to my annual trip up the A1, (Essex to Lake District) and
>> hope it rains en route. The car gets its yearly bath. Even the alloys are
>> cleaner!
>>

Christ! I hope that a car neglected like that, makes it to the lakes. Try driving into Ullswater and give it a deep down clean.
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New Sat 18 Jul 15 21:20 
 Car wash while driving through rain - Armel Coussine
The windscreen may stay fairly clean if the road isn't too busy, but the back of the car and its number plate get thickly coated with dirty road spray in that permanent eddy behind the car. There's an effective rear window wash/wipe for when things get a bit opaque.

I like deciphering the road dirt patterns on cars and watching their rooster tails when they are lamming past on the road. It's all information.
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