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Tire wear pattern


John Vance

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I just replaced my 400-6 main tires after 255 landings. They wore more heavily on the outside (see photo), and I wondered if this could be caused by too much toe-in.  I plan to make a stab at measuring the existing geometry sometime soon. Yes, I may have cut it a little close, but at least there's no cord showing. 

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I too have the small tires, and was plagued for years with terrible tire wear, also on the outside.  It was bad enough that I needed new tires every 40 hours or so.

I tried every conventional fix, after I maxed out the Matco washer adjustments, they suggested I needed custom shims.  I measured everything with a home built measuring rig, and found I needed something like 3 degrees of camber change and 3 degrees of toe out ON BOTH SIDES. 

That's a huge amount, and I was worried I got it wrong.  I  engaged a CNC machinist to make shims that are tapered in two axes.  They fixed things to perfection. I have had the same tires now for 200 hours and tire wear is just now starting to show at all.

I hate to say it but you probably need something similar.

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Thanks Andy - it sounds like a change is definitely worth pursuing. I didn't know whether this is normal for the small tires or not.  It would be nice to get a few years out of a set - these lasted less than 2. 

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John, do you have Matco wheels and brakes?  If not, that is the first step.  They have some caster/camber adjustment in them, whereas the factory Marc setup has none.  

It sounds like your wear is not as bad as mine was, I was changing tires three times a year.  There might be enough adjustment in the Matcos to fix your problem.  Roger Lee said he'd never seen a CT that needed more adjustment than the Matco parts provide...I guess I was just "lucky".

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2 hours ago, FlyingMonkey said:

John, do you have Matco wheels and brakes?  If not, that is the first step.  They have some caster/camber adjustment in them, whereas the factory Marc setup has none.  

It sounds like your wear is not as bad as mine was, I was changing tires three times a year.  There might be enough adjustment in the Matcos to fix your problem.  Roger Lee said he'd never seen a CT that needed more adjustment than the Matco parts provide...I guess I was just "lucky".

The alignment problem with the CTSW's was caused by improper manufacture and installation of the landing gear knuckle. If not properly installed it will have more camber and toe. It can be adjusted, but the process is not as simple as adding washers to the axle adapter like with the Matco wheel installation. If you have the Marc wheels there are 3 was to deal with alignment. One requires paint removal, welding , and repainting. The second requires machine work for special bushings, and machine work on the knuckle and gear leg. The third is installing Matco wheels and brakes.

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You may not make them perfect without  complete gear leg work. You aren't that far off right now. I would put two washers in between the flanges on the bottom two bolts. The washers come in thin and normal thickness. Use the thicker ones. I do this to every CT that gets Matco's. FD has too camber and doesn't allow for a flatter stance. You can check this with a 2' long square measuring stick. Take the wheel pant off and set the square on the flat hangar concrete ground with the other end up the side of the tire. Make sure you pulled the aircraft forward about 10' first and not have pushed it backwards. It will change the stance.

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18 hours ago, procharger said:

I would leave it alone not bad at all.

Since he's got Matco wheels and they are pretty easy to shim, I'd say he should try to shim out the issue.  If that doesn't entirely eliminate the problem, I'd tend to agree with you.  Once you get to the shim limit on the Matcos, you get into some pretty serious corrective issues, and his wear will probably be tolerable at that point.  Landing on grass when you can instead of pavement will slow the wear down too.

In my case, even with the wheels shimmed two washers (the max) on both sides, I was still changing tires twice a year, three times if I flew a lot.  The small tires are not expensive, so it was more the hassle of having to swap them out so often than the expense, to me.  The plus is I got the operation down to a science, and I can change those damn tires quick as hell now!  :)  

 

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