Stone chips - mudspats calculations.

[BruceT]

I've used a little high school physics to do some calculations on whether mud spats will stop the stone damage to the leading edge of the rear wheel arch in the door aperture. Forgive me if this looks a little over the top, but my purpose is to work out if mud spats could stop stones kicked up by the front wheels from striking the rear of the car.

My basic assumption is that in order to stop the stones the mud spats must be close enough to the ground to block their path - i.e the stones can't just fly under the mud spats and still hit the wheel arch.

Dimensions assumed (measured):
Stones leave ground after being run over by front wheel, when at a point when wheel is 15mm above the ground.
Distance to strike point: 1800mm = 1.8metres.
Height of strike point = 280mm + = 0.28 metres +
Distance to mud spat = 250 mm = 0.25 metres.

The question is: How high is the stone at the mudspat if it is on a trajectory to hit the rear wheel arch?

The following calculations have been rounded.
First calculation: assume car speed 100 km/h ~ 28 m/s
Assume stone goes straight up (an down) and it's the car' forward motion that causes the strike. Time to hit car = 1.8m/(28m/s) = 0.065 sec
Vertical speed of stone when leaving ground = 4.6 m/s
Vertical speed of stone at time of strike = 4.0 m/s
(Such a stone will reach a maximum height of 1.1 metres before falling back down - it is a potential window breaker for an oncoming vehicle.)

Time to reach mudspat = 0.25m/(28m/s) = 0.009 sec
Height above ground at mudspat = 0.041 m = 41 mm = 4.1 cm.

When I repeated the calculation assuming the car speed was 72 km/h = 15 m/sec, I got a height of the stone at the mudspat of 0.047 metres = 4.7 cm.

Assuming a direct path with no effect of gravity (worst case) = 0.28*(0.25/1.8) = 0.039m = 3.9 cm.

CONCLUSIONS:
1) Mudspats must reach to within 4 cm of the ground (and be wide enough of course) to stop stone strikes on the lowest point of the rear wheel arch in the rear door aperture.
2) The stone trajectory is quite "flat". Over such a short time gravity does not slow its vertical speed by much.

I don't think the standard mudspats go this close to the ground. They may still stop strikes on the body work closer to the front wheels, but they won't work for this problem.

[greenfoam]

That's alot of calculations well done. I find it's quite a large problem following newer cars that don't run mudflaps. I'm forever getting hit with stones thrown by overtaking cars, even had a few smack the window of the Fiesta (no big damage yet). But after reading your sums I'm sure it's given more than it's recieved

[BruceT]

Originally Posted by BruceT

When I repeated the calculation assuming the car speed was 72 km/h = 15 m/sec, I got a height of the stone at the mudspat of 0.047 metres = 4.7 cm.

Sorry, that second calculation should be at 54 km/h, which is 15 metres/sec. Everything else remains the same.

[BruceT]

StormyKnight, RapidTyphoon and Greenfoam,

These are the stone damage calculations. I've rechecked them and pretty much stand by them. Mudspats need to extend to within about 4 cm of the ground to stop stones kicked up at speed above about 60 km/h from hitting the leading edge of the wheel arch where it is exposed by the recessed door aperture.

As it is the speed of the car that does the damage I suspect most of the chipping occurs above 60 km/h. At 100 km/h the car will travel 1.8 metres - the distance from the front wheel to the rear wheel arch in only 65 milliseconds. In that time gravity will have little effect, so if you want to check if the mudspats will work, get a piece of string. Wedge one end of the string under the front wheel. Hold the other end up at the base of the rear door near the wheel arch. If you have mudspats, does the string go under them? If not you can imagine how close to the ground the mudspats need to be.

[BruceT]

One more point, I did ask at Artarmon Ford, whether they would recommend front mudspats to stop the kind of stone damage. They said they had not heard of the stone damage problem : , but that mudspats would make no difference as the stones would just fly under them.

[StormyKnight]

Out of curiousity, I will photograph & measure my mudspats, all in the name of science. I will try & get a perpendicular side on photo....

[south21]

I have the mudspats on my 3 door cl and no stone chips. Have done 38,000 ks

[StormyKnight]

I found this "information" re the topic, it may be of assistance to others....

http://www.facebook.com/topic.php?ui...510&topic=9260

A response via forum user "Ford Fiesta" is as follows...

A small number of new Ford Fiesta 5-door customers have contacted Ford of Europe as they are concerned about paint chipping that has occurred around the lower edge of the rear door aperture on their particular car. We are aware that a small number of cars are affected, although this issue may have been caused by particular driving conditions or terrain. We do have a remedial action in place which requires the affected area to be painted and a specially designed protection foil placed over the new paint which will avoid further damage in the future. This foil is being fitted to new vehicles as part of the production process from August 2009. We would ask any customer experiencing this concern to contact their local Ford dealer or national Ford Customer Relationship Centre (CRC) or to discuss their particular case. The dealer can then arrange for remedial work to take place.

Some pictures can be found here of the area of concern...

http://www.complaintsboard.com/compl...4.html#c305764

[dannyhilton]

Well they are called 'mud spats' not 'stone chip preventing spats.' Just my two cents worth...

[blownba]

Your forgetting the fact that most stones that are thrown by the wheels are actually getting caught in the tyre grooves and then let loose when the centrifical force overcomes the friction the tyre grabbing them is creating.
I actually think that most stones will actually fly off the wheel at a much higher height than what you are calculating.
The reason why I think this is when you run slicks and they are cold the stones that are thrown up are alot less (observed by less stone noise under the car) But when you come in on hot slicks (they are like glue for gravel and rocks) the noise starts up again.
Also when I used to run wets or grooved tyres the noise is would be far more noticeable again..
This is a race car so it probably a little different from the real world.
I have to run over gravel and dirty car park before getting onto the track.

[BruceT]

Originally Posted by south21

I have the mudspats on my 3 door cl and no stone chips. Have done 38,000 ks

The side skirts on the 3 door prevent this sort of damage.

[dannyhilton]

He has a CL Fiesta 3-Door, it doesn't have the side skirts like my Zetec.

[StormyKnight]

Originally Posted by RapidTyphoon

He has a CL Fiesta 3-Door, it doesn't have the side skirts like my Zetec.

Yes thats right the only car with the side skirts is the 3 door zertec...It should be the only one without damage....

The damage occurs at the interface of the rear opening of the rear door on the 5 doors. Because if a stone manages to hit that point, it is like hitting it square on rather than skimming off. It appears as though this section of the vehicle sits out further than the door, so any rock will hit it because it is sticking out.

Its possible that if the wheel is slightly turned out, a stone from the outside half of the tyre will impact on the vehicle as the centre line of the tyre intersects with the car.

[StormyKnight]

Some photos from our new Aug 2009 5 Door Zetec showing the stone chip protection & mudspat size.



Front 'Mudspats' on 5 door Zetec





Factory Modification Tape showing the extent that is covered





Closeup of the tape showings its construction...

NOTE that the tape is virtually invisble to the naked eye, I had to look twice to see it, but the camera flash shows the tape edges very well!

[dannyhilton]

Thanks fir the photos mate. The local Ford dealer here seems to have older stock, bit their only Zetec has front mud spats and the protector. Perhaps this is standard equiptment now, the front mud spats anyway?

[Fi.ES.TA]

http://www.fordforums.com.au/attachm...id=56994&stc=1

[BruceT]

[QUOTE=StormyKnight]Some photos from our new Aug 2009 5 Door Zetec showing the stone chip protection & mudspat size.



Front 'Mudspats' on 5 door Zetec
QUOTE]

Interesting Stormy Knight,
You also appear to have Hankook tyres rather than Continentals. That helps to explain the discount you got.

[Zetec-4-Me]

Originally Posted by RapidTyphoon

Thanks fir the photos mate. The local Ford dealer here seems to have older stock, bit their only Zetec has front mud spats and the protector. Perhaps this is standard equiptment now, the front mud spats anyway?

Not sure if the mudspats are standard now as my Zetec arrived in Brissie on the same boat/day as Stormy's and it doesn't have them. Mine is also an August built Fiesta (once again like Stormy's) so it should be the same. I will have to have a close look in the daylight tomorrow to see if the tape/protection is there!

[StormyKnight]

Yeah still not sure if "they were standard" i.e. already fitted OR my dealer was being pro-active. In addition he initially said that he would fit all 4, but when we turned up for the car, he said that they can only go on the front. Sounds more like to me that the car didn't come with them, they are aware of the stone chip issue & they wanted to be one step ahead....even though the mudspats where effectely free & my Zetec is an Aug build which is the cut in month for the modification.

[BruceT]

StormyKnight, I completely forgot to thank you for posting the pics.

It is clear Australia (and you) is/are now receiving the Fiestas with the "specially designed protection foil placed over the new paint which will avoid further damage in the future."
See the letter from Reha Alev here:
http://www.complaintsboard.com/compl...t=datea&page=2

Also see photos of the protective strip here:
http://i854.photobucket.com/albums/a...909_095101.jpg
http://i854.photobucket.com/albums/a...70909_0951.jpg

So the good news (for you) is that stone chips in this region should not be such a problem - with or without the mud spats.

After doing some dirt road driving I do have a smalll paint chip (<1 mm) in exactly the region described - no where near as bad as examples shown on the complaints site:
http://www.complaintsboard.com/compl...4.html#c351423

The leading edge of the rear arches is also where pieces of grit tend to stick after driving on dirt after rain.

[greenfoam]

I still haven't asked the local deal to fix the chipped paint but once they have stock of the new cars it will make the conversation much easier I think

[StormyKnight]

When it is done, you will have to make sure that the paint job is properly repaired, before the "New Tape" goes on.....otherwise corrosion will be your next problem....