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tire wear

H

Harvey rv12

Well Known Member
I was inspecting my tires & brakes during annual. My left main is very worn on the outside of the tread, while the inside is nearly untouched. Right side is similar, just not quite as extreme. What is this a sign of ?, poor alignment?, or simply a result of the built in camber of the main gear ?. has anyone tried to shim it to minimize uneven wear ?.
I am tempted to remove tire and rotate it on the rim, to get full mileage out of it. tire has 133 hrs, on it since new, and when I get home, I will count the number of landings.
What kind of tire life are you -12 owners getting ?.

Also, how do you apply lubrication to all the flight control linkage, bearings & hinges ?. I took a small 1/4" paint brush, dipped it into LPS 2 spray lube, and applied as best I could. Your thoughts ??

Thanks in advance
 
Harvey rv12 said:
I was inspecting my tires & brakes during annual. My left main is very worn on the outside of the tread, while the inside is nearly untouched. Right side is similar, just not quite as extreme. What is this a sign of ?, poor alignment?, or simply a result of the built in camber of the main gear ?. has anyone tried to shim it to minimize uneven wear ?.
I am tempted to remove tire and rotate it on the rim, to get full mileage out of it. tire has 133 hrs, on it since new, and when I get home, I will count the number of landings.
What kind of tire life are you -12 owners getting ?.
Click to expand...

That's normal, I just rotated my tires on the rims recently to use the other half of the tire. Not sure how best to measure tire life, I guess by the number of landings. I flipped mine after 140.
 
Tire wear

Very normal for the outsides of the tires to wear faster - there are several threads and postings on here related to that topic. Next question will be which brand to replace the tire with. Again, lots of opinions. Wish I had started rotating earlier to balance the wear myself.

For lube, I use the spray lube as well with the extension tube on the nozzle to help better aim/direct it to where you want it. Hold a rag behind each place that you spray to limit the over-spray mess. Lube seems to soak into the various places you are targeting.
 
After landing gear installation I found out that the left gear had a tow in of one degree.
Vans sells alignment shims in half and one degree.$ 25.00 each.
Too much tow in will increase tire wear on the outside.
 
Here is a picture I took right after I turned the tires on the rims. This was at 3 years use, about 200 hours. I haven't counted the landings.

i-gQbqk2C-L.jpg

200 hours.

Now at 350 hours and I just replaced the tires and tubes with new.

There are several threads in the forum about the tire wear. Without seeing yours it's hard to say if it is normal, but wear on the outside is typical.
 
The tires are always going to wear a little more on the outside edge due to the camber. However, you can really stretch your tire wear by taking the time to do a proper alignment of the axles. Yes, Van's sells you two different degree shims for the axles so that you can get the toe to as close to zero as possible. As I recall on mine, one axle was perfect and the other was out by about 1 degree. I shimmed it.

I used a laser straight edge to align my gear. I now have 200 hours on my first set of tires and they look like they will easily go another 100 hours, maybe 200.
 
Keep in mind that wear is not the only thing to look for in tires. My originals still had plenty of tread left at over 200 hours, but the rubber was starting to show a look of checking, after four years. Replaced all three last year at annual imspection time.
 
f1rocket said:
I used a laser straight edge to align my gear. I now have 200 hours on my first set of tires and they look like they will easily go another 100 hours, maybe 200.
Click to expand...

Randy, can you describe your laser straight edge set-up to measure toe-in. I would like to check this with a better method than the string.
 
Left vs. Right

Your question as to why your Left tire is wearing more than your Right tire may has something to do with you flying your RV-12 from the Left side with no one in the passenger seat. If that is the case and you fly alone most of the time then it's perfectly normal. However, if you have someone with you most of the time and the weight distribution is on both tires, then you may have to look at a shim for the Left side because if weight distribution is the same then both tires should be wearing at the same rate on the outside of the tread.
 
I have about 200 landings and 133 hrs, and my left front tire is completely worn on the outboard side.
Is there a tire alignment spec that call for a certain camber or toe-in-out ?.
As soon as I figure out how to use drop-box to post a photo here, I will share a pic of my 2 tires.
 
For what it's worth - my left tire is showing earlier wear than right tire. Difficult to quantify, but I think it's my flying style. I'm going to try Dresser Tire 500-5 6 PLY RETREAD "ELITE PREMIUM 2 GROOVE" at next condition inspection. I'll probably have to increase clearance for wheel pant opening.

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mwf6v5.png
 
The left tire getting more wear than the right tire, on a side by side airplane is actually quite common and not limited to just the RV-12.

A lot of pilots tend to touch down very slightly left wing low when they are looking out the left front corner in the landing flair. That means the left tire touches just a bit before the right. Add to the equation a little bit of yaw misalignment and a bit of extra speed that is fairing common with the average pilot crowd and you have a formula for faster wear on the left tire.

That still doesn't mean that a particular airplane might not have an alignment problem, but it isn't an automatic indicator that it does.
 
Tire is slightly larger in both diameter and width. Also the profile is more "square" than "round".
 
Harvey rv12 said:
Scott;
Are you aware of an alignment specification for the RV-12 ?, ie any camber or toe in-out ?.
Click to expand...

The camber is intended to be set by the tolerances of the bends on the gear legs.

There is a specification and tolerance for toe (the important one) in the landing gear section of the KAI, along with instructions how to measure and adjust it.
 
Tony_T said:
Randy, can you describe your laser straight edge set-up to measure toe-in. I would like to check this with a better method than the string.
Click to expand...

First, I level the airplane side-to-side and back-to-back. I then shoot a centerline on the floor that aligns with the center of the firewall and the tailwheel. I mark this line on the floor with string and tape it down. Then I use a straightedge along the wheel hub and align the laser with the edge of the straightedge. I mark this on the floor as well. Do this for both sides. Now you can measure the distance between the centerline and the wheel edge line to determine the amount of toe. A little math and you can calculate the degrees. I shoot for as close to zero and I can get.
 
I will layout the geometry on my hangar floor and do an all wheel alignment, just like Les Schwab.
I got TinyPic to work. Will post my first pics this weekend.
 
I have the same extensive wear issue on the outside of the L tire. The right main tire looks like the day I installed it. I flipped the L tire at 125hrs, and then replaced it at 250hrs since it had worn the outside edge again. A couple people in these forums attributed the L outer wear largely to the torque effect on takeoff. They said if I applied a bit of R aileron on takeoffs, I would not have the problem. (Unfortunately I seldom remember to apply said aileron bias on takeoff!)
I tend to believe I have a toe-in issue that contributes to the problem in a big way. i need to check the toe as mentioned above.
 
jv3n1k.jpg


This is after 133hrs and about 200 landings.
Seems like rapid wear but I Will reverse the tire on the rim and get some more life out of it. Hey, my first meaningful photo post!!.
 
Mine are significantly worse at 97 hours. How can you tell the difference between "toe in" verses the normal "gear flex" condition in spring gear suspension?
 
Matco Wheel Taper Shims

Hey guys, I thought you might benefit from this, since IIRC the RV-12 uses Matco wheels & brakes as well. I have a 2007 Flight Design CTSW that has had *terrible* tire wear issues. Here is a copy of an e-mail I posted to the CT forums about it:

--------------

As some of you know, I have been struggling with excessive tire wear since I bought my CTSW three years ago. The wear has always been greatest on the outside of the tire tread on both wheels, the left slightly worse than the right. The problem is bad enough that I go through 2-3 sets of main tires annually. In contrast my nose wheel tire is the original factory tire and looks fine with 430 hours on it.

I upgraded to Matco wheels and brakes to try to solve this problem. However, experimentation and measurement (at least to the best of my ability) show that I have both excessive negative camber (tops of wheels farther out than the bottom of the wheels) AND excessive toe-in, which combined explain the outside wear pattern. Whoever set my gear up originally must have done it on a Monday morning following a "fun" weekend... :D

The Matco standard shimming procedure using washers won't work for my airplane, because I can't shim both directions to the degree I want to within the Matco limit of two washers per bolt station. I tried adjusting only camber to the limits, and that helped some. The camber in that config was just about neutral but the tire wear is still way too high. I needed way to make large adjustments in *both* camber and toe-in.

I sent an e-mail to Matco to ask about this, and they immediately replied with "you need taper shim plates". A little back and forth with Matco showed that if you use a plate that fills the gap between the axle halves, there is no limit on how much you can shim, because there is no "air gap" as with washers, and the axle halves are fully supported. They said you can put a taper shim of the correct angle in there for each axis, stacked together, and that should do it.

I talked to my A&P, who does a lot of Diamond maintenance for the local flight school, and he had shims for the Diamond wheels. They were a perfect fit for the Matco wheels, with the exception that they use AN4 bolts instead of AN3 bolts like the CT so the holes were bigger. The other problem is they Diamond shims come in 1° and 2° adjustments. My measurements showed that I need 4° of camber adjustment and 3° of toe out. That would be a LOT of stacked shim plates...and they cost $65 a pair. Hmmm...

Long story short (too late, I know), a friend of a friend is a pilot and an engineer with access to commercial CNC milling and grinding equipment. He offered to make me some shims if I gave him specs. I asked him if he could makes shims tapered in two axes to minimize the thickness needed, and he said sure and sent me some CAD drawings. It looked great, so he went ahead and made them, tapered 4° in one axis and 3° in the other:

shims3_zpsclzkceus.jpg


Amazing work, he even engraved the taper on each axis! Yesterday I installed them, they fit great. The only issue is that the holes in the axles are at their very limits of play, and should probably be enlarged, but I only wanted to do that if absolutely needed. So I assembled the shims to the wheels, tightened the nuts, then took it back apart and checked the bolts. They were not bent or deformed by the side loads on them, so I think they are okay. My plan is to taxi and flight test them, then change to fresh tires. When I do that I will pull and check the hardware again, and if any stress is evident I'll ream the holes a little to relieve the shear force on them. Here they are all assembled:

shim1_zpscks6sd2j.jpg



shim2_zpsezjicaqv.jpg



Fingers crossed that this solves my issue. I fully expect that there will be some tweaking required, and possibly either new shims made or a slight grind to change the angle on the existing shim plates. Just eyeballing everything, the right wheel looks great in both camber and to-in. The left looks like it still has a *very* slight negative camber, and it might have transitioned to a very slight toe-out. But I won't know for sure until I taxi it and observe the wear pattern and how the airplane tracks. I'll use some chalk on the tread during taxi testing to see how and where it wears.

-----

Hopefully some of you RV-ers will find something useful in all that. :)
 
Last edited:
Camber is a function of weight!

Keep in mind that the camber angle changes based on the weight of the aircraft.

Since light sport aircraft are a bit on the light side by design, the gear legs flex a lot with change in aircraft weight, so the camber is usually set at a compromise angle to accommodate the expected range of operating weight.

Adjusting camber to be near zero when the aircraft is empty is not a good idea. It could make it possible for the inboard side of the wheel pants to contact the runway in a very hard landing. In a severe case it could even allow the brake disks to contact the runway.

The majority of tire wear is the result of 3 primary causes.

Wheel missalignment - Obviously should be checked if there seems to be excessive tire wear, but it is not a good idea to deviate from the manufacurers specs (there might be a good reason for them)

Wheel spin-up at touchdown - An RV-12 should have a ground speed of no more than about 35 Kts at touchdown (even less with some wind). Fast landings are common with a large percentage of the pilot population (sit at any airport and watch landings some time). If you think you have excessive tire wear (and you have confirmed proper wheel alignment), perhaps a detailed assessment of your skills/practices would be a place to look.

Heaving braking / skidding - Pretty obvious, but is slightly connected to wheel spin up wear....
I.E. if you are always landing fast in situations that then require hard braking, you have excessive tire wear from two related causes.
If you are good at landing at proper speed but like to use the first turn-of at 250 ft, extra tire (and brake) wear will be a price you have to pay while demonstrating the capabilities of the RV-12 to all your airport buddies that might be watching ;)
 
rvbuilder2002 said:
Keep in mind that the camber angle changes based on the weight of the aircraft.

Since light sport aircraft are a bit on the light side by design, the gear legs flex a lot with change in aircraft weight, so the camber is usually set at a compromise angle to accommodate the expected range of operating weight.
Click to expand...

In the case of the CTSW, the factory camber is set aggressively negative, probably with the idea that the gear will "splay" at weight and neutralize camber. However, experience over the fleet has shown that this does not happen, or at least not to a significant degree. So this can be essentially taken out of the equation on the older CTSWs like mine. The CTLS and newer have different composite gear legs (over the older aluminum) that may have more camber flex.

I can't speak to the RV-12, but in the CTSW the camber does not change significantly with weight, at least up to gross. I have had my camber set at neutral (when aircraft empty) for some time, with no effect other than improved tire wear. Hopefully the combination of corrected toe-in with the camber change will really help things.

Again, RV guys will need to make their own calculations regarding camber changes with weight.
 
True confession time: I started out trying to measure everything like the KAI said and concluded I couldn't do it with meaningful accuracy, so I thought: VANs has been right on everything else, so I'm gonna just go with what I got.

I'd rather be lucky, than good any day.
 
tomkk said:
Is toe-in measured with weight on the wheels or with the aircraft jacked up?
Click to expand...

Ideally you should measure toe with the airplane on the ground at your typical landing weight with grease plates. i used bags of salt to simulate my weight and about 15 gals of fuel.
 
With the type of gear leg the RV-12 has there is little if any change in toe alignment with leg flex.
That is why the procedure detailed in the KAI (wheels removed and no weight on the legs) works just fine.
 
Interesting. I would have thought there would be some change in toe-in as the leg flexes and the camber changes but the geometry of the leg & attachment must minimize that.
 
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