Skid Plates and Resonated Noise

I, along with many here, have installed alloy skid plates and noticed an increase in engine noise reflected off the plates. Some have complained about it and others have lived with it and hardly ever noticed or cared. My personal experience has been mixed. For short rides, I don't pay it much attention. But I find that on longer rides it seems to just sort of irritates me. The sort of sound that after awhile just creeps into to your subliminal mind.

So I thought I'd post on what I was trying and see how it works.

The culprit: Mine just happens to be a Flatlands. But this is no way limited to this brand.


The solution: Spray in rubberized Truck Bed Liner.


Applied:


Reinstalled:



The idea is to dampen the resonated sound coming off the back of the plate. Hopefully this product will do the trick. I don't care whether the sound of rocks hitting the plate is dampened at all. Just some of the droning coming from the engine.

Unfortunately we got a lot of snow this week and I cant really test it on the road yet. And running the bike in a closed shop with the door open for ventilation didn't reveal much. And I may not be able to tell or hear a difference. But if it changes the impact on the longer rides where it just grinds on the last remaing working nerve I have. I'll be happy. Sound is such a wierd thing. You can modify the frequency of a sound just a little.....And the percieved inpact to the brain be immense.
I'll get it out and report back as soon as possible.

Not to steal your thread, but the picture leads to a comment...

I have a different bash plate, but it is the same in that I can't help but notice how that water hose is exposed, and just begging to be ripped off (which has been documented here at least once already, I believe). I sure do wish the manufacturers had brought a bit of a wing out at the top on the right side to mask that hose from oncoming harm...

That said, I do look forward to your results and it is a pity we couldn't get accurate before and after noise measurements (although subjective is good too). The noise of the bike doesn't bother me after a lifetime of riding two smoke X'ers with screaming pipes. But I LIKE quiet, and if there is more quiet to be had for a reasonable cost, I'm all for it.

I bet the buddy pegs are for the grandkids?

dc4stroke wrote:

The noise doesn't bother me.

Hey, you might want to get that coolant leak checked out!!! Probably just need to tighten the hose clamp a little.

Of course a scientific evaluation would have been nice. But would lab testing really relate to real world in this test. You see, I'm not so sure that it is the volume, or frequency of the sound that offends me. That said, I simply wish to search for a solution to a problem in which the question may not be fully understood. I ride a 96 cubic inch air cooled V twin which makes all kinds of mechanical noise. The pipes are louder than the WR. But not loud by Harley standards. I also ride a 650cc V twin sport bike. But there is something in the reflected sound of the WR that bothers me. I did not have this prior to adding the skid plate. So the idea is to simply modify/dampen the soundboard and make observations.
I agree...... the hose is exposed. Where did I stick that scrap piece of plate? We may have to add that ourselves.

Yes......................................... the buddy pegs are for the grandkids.

And yes the hose clamp needed tightning.......thanks.

I tried a few things to dampen the resonance, I have settled on something like or is "Dynamat" which they use to sound proof car stereo installs. I went to a local car stereo shop and bought this stuff, it is a plyable tar like material sandwiched between foil (or vise a versa). It has an adhesive on it to stick to what ever you apply it to. It will not totally stop all of the resonance but seemed to be the best thing I found. I believe the resonance is mainly from the material of the skid plates, roll them around the ground, hit it with a hammer or just cringe when you bounce it off of a rock, it is like an amplifier.

First I just inserted some plastic parts here and there between the frame and the plate. It worked but the small platic parts sometine got loose and fell down. Now I use Zip & seal and strip. It's a silicone like sealer that is easy to remove by hand but that stays put even under vibration. You just have not to tighten the plate tight . Then the stuff dries and gets solid between the plate and the frame.

Took the WRR out and rode 50 or so miles. Asphalt since the the trails are nothing short of a mud bog around here right now.
And yes the sound was dampened. You could not percieve it while standing next to the bike and it running. However while running down the road it was very noticable. Am I satisfied with the results? Yes, to a point. As I think it can be improved upon even more. The next step will be to find another coating with a higher rubber content to spray on. This will be sandwiched under another harder coating of the bed liner material. Therefore giving you a three layer coating.

The ride today consisted of a fairly mixed ride of city streets, back country two lanes, and about 10 miles on the interstate. I was wearing a motocross type helmet to make the sound easier to percieve. Perhaps tommorow I'll try it with a dualsport type helmet. And make note of the sound level with the face shield closed.

You see "skid plate foam" or whatever for sale from Moose and whatnot. Supposedly, the idea is to eliminate places for mud to build up; it looks like an open cell foam in the pics I have seen. It might have the desired effect of damping down reflected noise.

Skid plate foam ? Ahem... No. Metal has to be isolated from metal.

IOW: The plate has to be isolated from the frame and the fasteners from the plate.

Undercoating or bedliner (essentially the same stuff) will eventually wear through.

You might try slicing some tubing, maybe ty-wraping it to the frame and then find some rubber grommets to line the holes in the plate (may need to drill the holes bigger), and then use a shoulder bolt to bolt it in (otherwise you'll only get a false pre-load torque on the bolt to frame interface).

Esthetically I'd use the bedliner spray-on on the outside too. Personally, I hate the look of brushed aluminum.

X-Racer wrote:

Esthetically I'd use the bedliner spray-on on the outside too. Personally, I hate the look of brushed aluminum.

What is not to like about brushed aluminum?

There's always plastic...

WR250R - skidplate <-- linky

njbill wrote:

What is not to like about brushed aluminum?

Off-topic, but... Nothing.... IF that is what you like/prefer.

I think it looks unfinished. ....which is why people paint it, anodize it (etc.).

I like unfinished!

I'm unfinished.
All of my bikes are unfinished. No matter how much money I throw at them.

On top Chenal Mtn, Pinnacle Mtn in the background. West of Little Rock, AR.Out testing the mods to the skidplate.
I can't see the coating wearing off. I did this to the bed of my truck in 2002. And it's still going strong.

I went to my local bicycle shop and asked if I could have a few used innertubes. They were happy to give them away.
I then did a little nip tuck and wrapped them on the lower frame rails where the skid plate would be mounted and touching the frame.
I just used Zip Ties on the tubes and they are very secure. I have done alot of very rough off roading and I ride almost everyday on the street and
I hear no harmonics whatsoever. Works great....easy to install in just a few minutes....no mess...highly recommend this solution to unwanted noise:)

I had the same noise problem and tried lots of stuff. Finally I decided the skid plate was too close to the frame in the back so I started cutting small pieces off until there was more clearance... actually plenty of clearance. Noise went away. Actually I drove some wooden wedges into the gap to see if was the metal vibrating in resonance with the engine and hitting the frame, twas so then I changed the plate length for more clearance.

When I first mounted my plate I did a couple of things. First I cut the corners on the back side so it wouldn't contact the frame (flatland). Then I mounted some thick rubber strips to the plate where it would contact the bike's frame. So, it has about 1/8" of rubber running the length of the frame and plate. It is loud!

I just took it out for a thousand miles and it about drove me crazy. The sound will change as I ride. Sometimes just easing off the throttle a little will make it go away- or lessen it substantially. So, I'm thinking it is some kind of harmonic transfer. I may try more material between the frame and the plate before I apply some of the moose foam Jager mentioned. It is way louder than the exhaust and very annoying. Even makes it hard to hear how the engine is revving.

If anyone has had the problem and then solved it I would love to hear how. Thanks!

Ok I went back in a gave dampening another try. I used those thick spongy gromets that are used for passing wiring through something (they have a groove cut in them). I used contact cement to get them attached to the plate (for ease of mounting). I put the plate on and tightened the bolts just enough so that the plate does not touch the frame. I can push on it and it gives a just a little. I took a ride and the noise is almost completely gone. It is now tolerable- in fact hardly noticable. I suspect lining the plate with spongy foam (hoping it holds up t the heat from the engine) would eliminate it entirely. Now I just need to go back and use some lock tite. SO MUCH BETTER! Now I can actually hear the OEM exhaust. I am a happy camper.

I just mounted a Flatland and went for a quick zip tonight. The first thing I noticed was the amplified engine noise so I jumped on the forum and low and behold...so my question to dc4stroke is - Does the liner material work? Are you satisfied? or to is the TimdorWR solution of using bike tubes the better answer?

Thanks,

JP

My bash plate is as noisy as a dryer full of coins, but hey, it's a dirt bike. I am either giving it so much revs you don't notice the sound or if I am cruising around on it for the day on the dirt, I am wearing my ear plugs.