Main Gear Shimmy

So I have noticed a shimmy that has gotten a little worse. I checked the front tire and tension on the front wheel. The shimmy is from 35-40 MPH smooth slower and faster. Interestingly, I kept the nose off the ground my last two landings and noticed the shimmy did not go away. The shimmy is coming from the main gear. This is new for myplane so I started thinking about what caused it. I did my annual about three weeks ago and as part of the maintenance I rotated the main tires left to right as the outside of the tires were worn. Several people at my airport say this is a very common practice. The rotation of these tires is the only thing that has changed. Has anyone else experienced a main gear shimmy? Shimmy after rotating tires? Any thoughts would be appreciated.

I had similar problems resolved by balancing the tires. When you check the balance, check the tires for out of round. Some can be quite bad and could drive getting it trued up or replacement of the tire.

I have never heard of anyone balancing tires on an RV. Is it possible to do? Where would you have it done? Seems like it would not stay balanced that long due to wear etc. Wouldn't it be easier just to replace the tires than to have them balanced?

tire balance

many of us do a simple static balance via a Harbor Freight motorcycle wheel balancer for about $20. I had to get a thinner rod to do the nose wheel, but the reg tool was fine for the mains.

When I had the vib problem, had the tires balanced. One took 8 weights. They use the stick on ones on the inside of the rim.

You can statically balance good enough. For a better balance, a dynamic balance can sometimes be worked out at speed shops.
Some can also true the tires if needed.

I've experienced out-of-balance nosewheel before. Can create some pretty intense vibrations. Most wheels are less than optimally balanced when they're new and have the tire/tube installed.

Thanks for the advice. Priced the wheel balancer at harbor freight. It is $79. Decided to call Van's and just ask about main gear shimmy. Ken hit it right on the nose. When I rotated the tires, I inflated the tires with too much air. Tires were over pressurized. Took them down to 32 PSI. Problem solved.

I had quite severe shimmy on the main wheels on my RV-7A after annual.
I thought it was the through bolts in top of the legs that had came loose.
I jacked up the plane and checked for any play in the legs but there was nothing. I realized that I had filled air in the main wheels and it was at 50 psi. Lowered it to 35 psi and problem went away.

Hope this helps.

/Fredrik

Just saw you solved the problem. Note to my self - read posts more careful

/Fredrik

jtppalmer050390 said:

Thanks for the advice. Priced the wheel balancer at harbor freight. It is $79. Decided to call Van's and just ask about main gear shimmy. Ken hit it right on the nose. When I rotated the tires, I inflated the tires with too much air. Tires were over pressurized. Took them down to 32 PSI. Problem solved.

Click to expand...

This is what you were looking for, $39.95:

http://www.harborfreight.com/motorcycle-wheel-balancing-stand-98488.html

Just FWIW...I went through a lot of trial and error trying to eliminate shimmy coming from the mains. I verified it was the mains because I keep the nose wheel off on landings. My problem was that it was extremely variable with some landings with no shimmy and others with lots. I varied the tire pressure, verified they were balanced, made sure the bearings weren't binding, added wooden stiffeners to the gear legs, varied landing speeds, tried "arriving" and smooooth and there was no way of telling what would excite the shimmy. I finally simply changed tires to goodyear custom III tires and have never had another case of shimmy! Yes, they weigh more and may have a damping effect. They definitely feel more "solid" and ground handling and landings feel much better.

Thanks Sam. Didn't see that one at our local store.