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Uneven tire wear RV-7

J

Jettison

Member
Just noticed some uneven tire wear on the inside of my left main. I am thinking toe or camber may be the culprit?
 

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Wheel geometry is pretty much locked in with the pre-bent gear leg. Only partial remedy I do is rotate the tires (swapping tires to opposite rim periodically)
 
Previously flipped?

Looking at that tire I would say that it had already been flipped by the previous owner. I have only been flying a couple hundred hours but I have never seen an RV wear the inside of a tire out.
 
All of mine have worn on the outside first - all of them - 2 RV6’s, 2 RV4’s, 2 RV8’s. You can try to shim an RV8, but the 4’s and 6’s (+7’s & 9’s), not much you can do as far as I know. The only thing I’ve done on all of them is to rotate the tires before the tread is gone, and then replace when the tread begins to disappear. On my current RV6, my left tire is beginning to show increased wear on the outside of the left tire (110 hours, 242 landings). The right tire is wearing evenly. I’ll rotate the tires next oil change. I don’t know why one is wearing faster than the other, but I’m usually flying solo from the LEFT seat. Does it make a difference? Who knows, but tire rotation is the way I’m managing it.
 
Both my tires wear from the inside, pretty uniformly -- simply swapping left/right doesn't help. I have to pop the tire from the rim and flip it inside/outside. I do that during the annual CI. My first year had 800+ landings (lots of pattern work) and had significant differential wear.
 
I am surprised to hear some of the RVs tires wear out on the inside. Wow. Mine wore out on the outside and the inside was still like new.
 
Edit: I have had 3 RVs and they all wore on the outside and I have seen most do that on the outside.
 
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Gear

Langair can bend the gear cold but I don't know if they have a means of getting the camber and toe perfect.
 
My RV-6 had tire wear issues, some of it attributable to imperfect alignment during gear leg/mount drilling (early kit no pre-drilled). I was going through tires pretty fast, so I installed a new pre-drilled mount/legs. Much improved but still uneven wear. I decided to try the 380x150 tires on my -7, mostly for soft field operations. After 5 years and 500 hrs. The tires are wearing dead even, and plenty of tread to boot. Thinking about replacing them soon due to age.
Anybody else have wear experience with the 380's?
 
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Somebody smarter than me could pole model type and wear. My 6 wears tires.on the outside. The gear has positive camber. It makes sense that the outside contacts the runway first and would wear faster. The Bucker has even more positive camber and wears the outside as well.
 
I have experimented with tire pressures on my -6 and -7 from 25psi to 45 psi. The -6 liked 40 psi with the 500x5's, the -7 likes 35 psi with the 380 tires. The sweet spot for me is no gear shimmey and optimum tire wear. Every RV is different especially when it comes to gear shimmey, gear leg stiffeners and alignment.
 
My old RV-4 had tires like this, due to ginormously excessive toe-out. A friend drilled out the bolt holes in the gear legs and silver soldered in 4130 plugs. I filed the ends smooth, reassembled everything with a piece of angle and shims clamped to the axels to get just a touch of toe out and carefully redrilled the gear legs, being careful not to let the drill bit drift. The enlargement to final size was done with at least four drill bits, progressively larger by 1/64.” No more problems!

I’ve probably misremembered some of this, as it was 40 years ago or so…
 
Ed_Wischmeyer said:
My old RV-4 had tires like this, due to ginormously excessive toe-out. A friend drilled out the bolt holes in the gear legs and silver soldered in 4130 plugs. I filed the ends smooth, reassembled everything with a piece of angle and shims clamped to the axels to get just a touch of toe out and carefully redrilled the gear legs, being careful not to let the drill bit drift. The enlargement to final size was done with at least four drill bits, progressively larger by 1/64.” No more problems!
I’ve probably misremembered some of this, as it was 40 years ago or so…
Click to expand...

Actually for taildragger RVs, the ideal set-up is "0°" without weight on the gear.

The design of the gear is such that as soon as you put weight on the gear, it toes out slightly.
 
Mel said:
Actually for taildragger RVs, the ideal set-up is "0°" without weight on the gear.

The design of the gear is such that as soon as you put weight on the gear, it toes out slightly.
Click to expand...

Don't recall, but the toe out I had was very, very slight, done with brass shims. Maybe 0.050."
 
Positive camber will cause the tires to wear on the outside edge. The tire will wear on the part it sits on. The higher the pressure the narrower the part. Positive camber also causes the tire to want to track to the outside. To offset this tendency toe-in is required. Without the toe-in the tire is scrubbing sideways down the runway making the tire wear faster and causing sideways loading on the gear. The is something called a scrub gage that can measure . . . scrub. You can buy one on Ebay. It is called a Gunson Trakrite, not very expensive, made out of plastic. We use 'em on racecars. You roll one tire over the gadget and it tell you if you have too much or too little toe in. You can also use a piece of butcher paper. Toe in will cause the paper to bunch up. Rub you hand over the tire perpendicular to the direction travel. A scrubbing tire will create a feathered edge in the tread pattern. Your hand will move easier in one direction then the other.
 
not a -7, but a -6.9i, which means sporting an -7 engine mount/gear legs.
As one can see in the accompanying pics, a pretty even wear, which means I don't even have to flip them tires. I'll give them another few landings and kilometres, then replace. Noticeable is slightly more wear on the outer threads, most probably due to my enthusiastic driving style ;)
Those have some 500 landings, 90% on concrete, an quite a few kilometres (or whatever unit you fancy using) on them.

PS
Different story on the -8 where we flip the tires after about 200 taxi out/take-off/landings/taxi in...
 

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I’d flip those Dan. There appears to be a lot of tread left on the inside of those tires.
 
After I posted that picture, I checked the tire pressure and it was low on both sides. About 25 psi. Both tires seem to slowly leak over a few days, I will have to order some of the million dollar tubes I have heard about. I haven’t always checked tire pressure before every flight, I have just trusted my eyeballs sometimes.

With that said, it is a little tough to believe that this much uneven tire wear came from under inflated tires on a couple of occasions.
 
Are Leakguard tubes as good as Michelin Airstop? They are both ridiculously expensive, but Leakguard is about 60% of the price of the Michelin’s.
 
Camber and toe-in

Here is the solution to camber adjustments. If you have one tire wearing evenly measured the camber angle while weight is on the wheels then measure the angle on the other wheel. Make the adjust by adding the camber shims. You can buy an angle cube from harbor freight. You have to measure using the rim, not the tire (it may be obvious but some people aren’t the sharpest tool in the shed like donkey on Shrek).

https://www.harborfreight.com/digital-angle-gauge-63615.html

https://store.vansaircraft.com/catalogsearch/result/?q=Camber
 
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FireMedic_2009 said:
Here is the solution to camber adjustments. If you have one tire wearing evenly measured the camber angle while weight is on the wheels then measure the angle on the other wheel. Make the adjust by adding the camber shims. You can buy an angle cube from harbor freight. You have to measure using the rim, not the tire (it may be obvious but some people aren’t the sharpest tool in the shed like donkey on Shrek).

https://www.harborfreight.com/digital-angle-gauge-63615.html

https://store.vansaircraft.com/catalogsearch/result/?q=Camber
Click to expand...

RV4/6/7/9 gear legs are solid bent rods so no place on them to shim unfortunately - unlike RV8 & later models.
 
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