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John Vance

Tire wear pattern

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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. 

IMG_0011.JPG

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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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Hi John,

Those tires don't look that bad. If you have Matco's then just a washer shim may take care of that. If you have the Marc wheels then Matco's will take care of that.

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Thanks, guys. Luckily, I do have the Matco equipment.  I'm going to take a few measurements, then give Matco a call.  This would be a good time to make some tweaks, while the new tires are still fresh. 

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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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Ok, thanks Roger. Do you normally use two thick washers on each bolt, or just one each?  

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Depends on how far out the camber is. It may be one thicker washer on each bottom bolt in between the flanges or two. Two is the max allowable. Your tires don't look that bad so I would just use one and keep an eye on them.

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1 hour ago, Ed Cesnalis said:

Don't think of tread left as money wasted, you really don't have to wear off every last bit of it to get your moneys worth.

Well said.

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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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