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Old 04-06-2009, 06:10 PM
lluciani's Avatar
lluciani lluciani is offline
Join Date: Jun 2005
Location: Tomball, TX
Posts: 66
Default Tire Wear - Too Much Toe In?

I was hoping someone could help me reduce my tire bill. The outsides of my tires wear out after only about 40 hours. I don't think I am dragging the brakes and I keep the tires at around 30 PSI. Could it be that I have too much toe in?

It is not easy for me to check the alignment the way Vans says to since this means jacking up the whole plane to take the weight off the main gear. With the plane level it would seem that it wouldn't make any difference. The landing gear bows outward with weight but with the same alignment, right?

Luis Luciani
RV8, 140 hours
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Old 04-06-2009, 06:19 PM
Kyle Boatright Kyle Boatright is offline
Join Date: Aug 2005
Location: Atlanta, GA
Posts: 3,186

Most RV's are that way. What happens is that the wheels are cambered in at the bottom under lightly loaded conditions. If you fly at gross more often, they will wear more evenly, because the geometry of the gear changes as weight is added.

Most of us just reverse the tire on the wheel about 1/2 way through the tire's life. That allows you to use up all the tread on each side of the tire..
Kyle Boatright
Atlanta, GA
2001 RV-6 N46KB
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Old 04-06-2009, 06:32 PM
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Bill Wightman Bill Wightman is offline
Join Date: Aug 2005
Location: OKC, OK
Posts: 687

FWIW, my RV4 would go 100 hours or more on a good set of Flight Customs with 1/2 degree of toe-in on each wheel.

Allan Tolle gave me the scoop on how to set toe-in. He recommended 1/2 degree toe-in with the plane sitting on its tail, with no passengers.

Then, with the plane rolling under load the rolling resistance of the gear would bring it back into alignment. I did just as Allan suggested, and my tire wear was really good.

This was on an RV4 - so this data point won't translate to how to set the 8's gear since they're so different in terms of deflection characteristics under load. However, since the great majority of time spent rolling on pavement will be in the three-point attitude, I suggest you take a good look at how your gear sets up in that attitude. And that's easy to do. Sounds like you have too much toe in if wearing out tires in only 40 hours...
“The important thing in aeroplanes is that they shall be speedy.”
- Baron Manfred von Richthofen

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Old 04-06-2009, 07:04 PM
scsmith scsmith is online now
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Location: Ashland, OR
Posts: 1,809
Default What I found:

On my RV-8, I shimmed to within 0.1 - 0.2 degrees with the fuselage level, and I found that I then have about 1/2 -3/4 degree of toe-in in 3-pt attitude.

this was done with the fuselage+engine weight, wings and tails off.

I measured by clamping 30" sticks to the tires and measuring at the front and back of the sticks. Some people suggest you should use a pair of metal plates with grease in between under each tire. The contact patch is so small with just the fuselage weight that I can't imagine having any torsional pre-load from the tire-ground contact.

Should know in about a month how they roll.
Steve Smith
Aeronautical Engineer
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Old 04-06-2009, 10:30 PM
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Ironflight Ironflight is offline
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Join Date: Jan 2005
Location: Dayton, NV
Posts: 11,602

Hi Luis,

40 hours to wear the outside is pretty low - I get about 150 when using Desser Retreads. I forget what came with the kit, but I seem to remember them wearing out very, very fast. I am not sure how tire pressure affects wear, but I am using about 38 psi - 30 seems quite low to me, and could be making your tire to wheel pants clearances a bit on the tight side as well (compresion during touchdown). I have never tried adjusting the toe-in or camber, as the airplane handles just fine, and I didn't want to mess that up. If you like your handling, the simplest thing to try is higher tire pressure and a different tire compound.

Paul F. Dye
Editor in Chief - KITPLANES Magazine
RV-8 - N188PD - "Valkyrie"
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Old 04-07-2009, 05:16 AM
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f1rocket f1rocket is offline
Join Date: Jan 2005
Location: Martinsville, IN
Posts: 2,283

If you really want to fix your tire wear problem, you need to re-align your gear. First, a little background. The Rocket guys have been messing with this problem for some time because the heavier weight of the IO-540 makes minor gear alignment issues more acute. Also, our gear legs tend to flex a little more so having the proper alignment is really critical to having a good ground handling machine, and as a result, getting good tire wear. Here's what we've learned:

Your goal is to have ZERO toe with the airplane in the three-point configuration with it fully loaded with your normal flying weight. To get this, you have to put some grease plates under your tires and add weight to simulate fuel, pilot, etc.

Since your gear sockets are already drilled, you can either try some axle shims or you can re-drill your sockets to your gear legs. I'm not sure on your particular model of RV how the axles are attached but if you try for zero toe in this configuration, you will not only fix your tire wear problem, but improve your ground handling and gear leg shake.

If you can't get it to zero, having a little toe OUT is preferable to toe IN. For the Rocket guys, toe in is BAD!!.

I know there are lots of opinions around regarding whether you want toe in or toe out. Well, most of that talk is based upon hangar flying. I've persoanlly flown my Rocket with different toe configurations and I speak from experience, at least from a Rocket perspective. As always, YMMV.
Randy Pflanzer
Martinsville, IN (II87)
Paid through 2043!
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Old 04-07-2009, 11:11 AM
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lluciani lluciani is offline
Join Date: Jun 2005
Location: Tomball, TX
Posts: 66
Default Thanks

Folks, I really appreciate these suggestions.

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Old 04-08-2009, 03:18 PM
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Danny King Danny King is offline
Join Date: Dec 2004
Location: Southlake, Texas
Posts: 566
Default Been there and done that!

In the first hundred hours, I wore the outside half off both my original tires smooth. At the first conditional inspection, I replaced the tires. When the wheels were off, I removed the axels and installed a one degree shim on both sides to take the toe-in out. The next set of tires lasted three years.

I could also tell the toe-in was there in how the Doll behaved on a wheel landings. When either tire touched down first, the aircraft would attempt to turn away from that side until the other tire touched and then it would balance out and track strait as the outsides of the tires were being scuffed off.

Buy two one degree shims and remove the toe-in, and you will be fine. Trust me!
Danny King
Beautiful Doll 80434 TT 1565 hours
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Old 04-08-2009, 05:29 PM
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rocketbob rocketbob is offline
Join Date: Jun 2006
Location: 8I3
Posts: 2,923

All you need to do is buy shims from Robby Grove, and set your alignment for zero toe, zero camber with full fuel. Its a lot easier to do on the RV-8 than it is on the Rocket. I have a friend with over 300+ hours on a set of tires on his F1 and I helped him set the alignment.

To set the toe, clamp two four foot angles to the brake disc's, parallel to the floor. Drop a plumb line from the CL of the firewall and another one at the tailwheel, and pull a string underneath both points. Measure from the front and back of the angles to each other and also make sure they are even with the center line.
Bob Japundza CFI A&PIA
N55BC RV-6 borrowed, flying
N678X F1 Rocket, under const.
N244BJ RV-6 "victim of SNF tornado" 1200+ hrs, rebuilding
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Not a thing I own is stock.

Last edited by rocketbob : 04-08-2009 at 05:36 PM.
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Old 04-09-2009, 06:47 AM
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Ed_Wischmeyer Ed_Wischmeyer is offline
Join Date: May 2005
Location: Savannah, GA
Posts: 656
Default Toe OUT, not toe in

It's really counter-intuitive but on an airplane, you really want a small amount of toe OUT, not toe in like you'd have on a car. Somebody else will have a better explanation, but the reason is that if the plane is banked on the ground, toe in works against you for recovery. There was an article about this in Sport Aviation many moons ago.

When I bought my RV-4, the spec for toe out, measured across one axle, was 0 to .050". The builder had gotten a little enthusiastic, though, and had put in nearly 5/16" of toe out. After I fixed that, and it was an epic project, the RV-4 was so much easier to land... and the tires didn't need to be rotated in / out every 15 hours...
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