Rear Rock Guards...An Interesting Observance Today

[2gypsies1]

We had to travel in rain all day today so for lack of something to do I did a study on motorhomes traveling in the opposite direction with brush-type or solid rear rock guards and those with none.

The ones with both types of guards threw water high onto the towed vehicles. Those with no guards tossed water low at tire level of the towed vehicles.

This got me thinking that when we went to Alaska we actually saw folks removing their rock guards claiming they were throwing stones at the hoods and windshields of their towables.

We have no rock guard - just flaps behind each wheel. We didn't have any rock damage to our towed on the Alaskan trip. Interesting....

[et2]

Haven't had rocks and such on ours yet. But I do notice dirt settles on the toad. Just a thought. Maybe the flap creates a Venturi effect. Creating a low pressure or vacume on the back side of the flap picking up dirt and rocks.

Now I honestly believe the flap will save my but someday from running over something. Raising the flap might help if its close to the ground. Also perhaps drilling some larger holes or slots would help break the vacume effect.

Just a thought.

[chuckftboy]

I never had stone chips with or without flaps and have towed plenty of miles both ways. What I do know, when I get to my destination, my towed and the rear of the A is much cleaner with the flap. Mine hangs 4" above the road.

[JC2]

Diplomat Don wrote:
The photo posted of the 4 piece mud flap is a bad example to use in a decision to have a mud flap or not. The one in the photo is waaaaay to low and it's obvious they drove on a nasty (probably Alaskan) road for a long time.

My mud flap is more than 5" off of the ground at ride height. It came that way and doesn't throw anything onto my toad. Someone taking one off for weight savings is silly. They're mostly on DP's and they won't change your mpg or give you increased CCW of any consequence.

This will get me flamed, but most of the people I've talked to removed their mud flaps because they were constantly damaging them or had destroyed them by not paying attention.

No flame here as I agree with what you say. I've found that our rear flap has always been mounted 4-6 inches from the ground and I don't remember any damage occuring on our toad.:)

[DSDP_Don]

The photo posted of the 4 piece mud flap is a bad example to use in a decision to have a mud flap or not. The one in the photo is waaaaay to low and it's obvious they drove on a nasty (probably Alaskan) road for a long time.

My mud flap is more than 5" off of the ground at ride height. It came that way and doesn't throw anything onto my toad. Someone taking one off for weight savings is silly. They're mostly on DP's and they won't change your mpg or give you increased CCW of any consequence.

This will get me flamed, but most of the people I've talked to removed their mud flaps because they were constantly damaging them or had destroyed them by not paying attention.

[rgatijnet1]

dons2346 wrote:

gbopp wrote:
That's a very interesting observation. I'll have to watch next time I'm driving in the rain.
I wonder if anyone has a 'scientific' explanation why this happens?

Not very "scientific" but an explanation. With the flap mounted where it almost touches the ground, it sets up a shock wave in front of it and that will actually pick up rocks, dirt, etc. and get it bouncing on the ground. The junk will bounce out from under the coach and go no telling where, usually on the toad.

From those of us that do not have a mud flap, we know that rocks are also thrown up by the duals, long before they would be affected by a mud flap. The difference seems to be that they are not thrown up quite so high as they are with a mud flap. Since the duals do throw up rocks, I'm not sure that the mud flap being up a little higher, or being all in one piece, instead of four pieces as in the picture, would make much difference. No mud flap at all seems to work the best for most people. Rocks are still thrown but they seem to stay low and do less damage.

[dons2346]

gbopp wrote:
That's a very interesting observation. I'll have to watch next time I'm driving in the rain.
I wonder if anyone has a 'scientific' explanation why this happens?

Not very "scientific" but an explanation. With the flap mounted where it almost touches the ground, it sets up a shock wave in front of it and that will actually pick up rocks, dirt, etc. and get it bouncing on the ground. The junk will bounce out from under the coach and go no telling where, usually on the toad.

[Bruce_Brown]

Sully2 wrote:

2gypsies wrote:
RE: the above pictures....that's exactly what we saw in Alaska. We never had one pebble on our hood/windshield without the rock guard.

Its because its mounted TOO LOW and drags on the road at times..therebye kicking up the rocks. If it never hit the rocks / gravel....it would never toss it backwards... Its not going to hit gravel if its UP HIGHER....willl it?:S

Plus thats not a solid piece, it's basically 4 tire flaps mounted together. Make it one soild piece across the back, not 4 individual pieces, and see what happens.

[topflite51]

Sully2 wrote:


Its because its mounted TOO LOW and drags on the road at times..therebye kicking up the rocks. If it never hit the rocks / gravel....it would never toss it backwards... Its not going to hit gravel if its UP HIGHER....willl it?:S

Exactly. Most that I have seen are mounted too low. I have had MH's drive by me when I am out walking in a campground/rvpark that are dragging their rock guards that are throwing up so many rocks that it is dangerous.

[Sully2]

2gypsies wrote:
RE: the above pictures....that's exactly what we saw in Alaska. We never had one pebble on our hood/windshield without the rock guard.

Its because its mounted TOO LOW and drags on the road at times..therebye kicking up the rocks. If it never hit the rocks / gravel....it would never toss it backwards... Its not going to hit gravel if its UP HIGHER....willl it?:S

[Fiesta]

I took mine off... for 2 other reasons.
40-50 lbs. and what a aerodynamic drag! MPG and carrying capacity now up.

[PastorCharlie]

On one 6,000 miles trip coast to coast with rear rock shield there was debris one Jeep...

On another 8,000 mile trip coast to coast with only truck flaps behind rear tires no debris on Jeep...

[Blaster_Man]

I've got an OEM rock guard that works great and I would not tow a toad without it.

[J-Rooster]

rvten wrote:
Yep plain old truck type mud flaps work the best.

X-2

[moparmaga2]

Had same issue as the picture posted in previous thread with our Safari rockguard throwing rocks at our towed Jeep. The Safari Rockguard also threw many stones into our rear radiator/ fan area where the fan threw them into the radiator, causing us to spend 2 weeks in the Yukon waiting for a new one.

Took off rockguard, threw in trash.

Result:

Not one pebble on Jeep. Not even one tiny ding to radiator all the way back the the lower 48.

If you are planning to drive to Alaska, you have been warned. Take the rockguards off and throw them away.