Tubed Tundra Tire Slip Marks

Just completing some test flying on a 26" tubed tundra tire installation. I wanted to find out what pressure and conditions would make them slip on the wheel, so I painted slip marks across the tire and wheel. After running them low pressure, and really working them on pavement, I got one to slip about 1/4". Interestingly, the slip marks were the only indication the tire had started to moved, the valve stem showed no signs of tipping or moving.

I would highly recommend that anyone running large tubed tires at low pressures paint on slip marks. If a tire starts to move on the wheel, you have a good chance of catching it before it shears the valve stem.

Mark,

I presume you are talking about the Goodyear blimp tires here, since they are the only tube type "tundra tire" around.

I don't run these things lower than 15 to 18 pounds pressure, since it is really easy to slip from 15 to 10 with temp change, a slow leak, etc. Problem is that most of us don't check the pressures regularly, and they can vary quite a lot, especially at low pressures.

Start out at 7 pounds, and it is very easy to wind up at 3 and these things will not only slip a little, but shear the valve stem right off.

What pressures were you running?

Mike V

SuperCub MD said:

Just completing some test flying on a 26" tubed tundra tire installation. I wanted to find out what pressure and conditions would make them slip on the wheel, so I painted slip marks across the tire and wheel. After running them low pressure, and really working them on pavement, I got one to slip about 1/4". Interestingly, the slip marks were the only indication the tire had started to moved, the valve stem showed no signs of tipping or moving.

Click to expand...

Heck Mark that's easy to explain. since you are probably running 8.50 X 6 tubes in them, you probably aren't blowing the tubes up enough to touch the tires so they can spin all they want.

26 inch tires with tubes

I have been running the same set of 26 inch Goodyears with the same original tubes since 1995. Bought a spare tube in 1995 that still sits on the workbench. I run the tires at low psi, low enough that they have a real good slump look on the floor, but high enough that the rubber doesn't "trumble" or flutter under heavy braking. Harder than that and the shocks of uneven ground get through to the airframe. I'm guessing that I start with 5 or 6 psi and refill when the airplane is hard to push by hand - 3 or 4 psi. Jambing a knee into the top of the tire and getting a visual on how much depression is made is how I guage the inflation for both keeping the tires equal and keeping them at an acceptable pressure. When topping the tires off, if I can't drive my knee a good inch or inch and a half into the tire then there is too much air.

For some unknown reason, the stems have never ripped off. I recall ripping off stems happening a lot when as a kid with underinflated bicycle tubes. Low pressure would rip the stems off fast - usually from steadily applied pedaling torque as opposed to intermittent braking.

The 26 inch tires walk a bit from the painted marks and then stop. If the valve stem is twisted until it angles too far, I will jack the plane up on that side, set the brakes, and let all the air out with a knee depressing the top of the tire. Kicking the tire will unseat the bead, and with a lot of wrestling the tire can be rotated back until the stem is straight.

But I don't try to keep the stems perfectly straight. Why bother? The tubes have lasted this long for some strange reason. Has anyone out there ripped a stem with this set up?

Bob Breeden

Don't want to start a big pressure debate here....They were a little under 7, close to six when one moved. (Yes, that is more than enough to blow the tubes up to size in the tires.)

The point was that most installations of the Blimp tires don't have slip marks painted on them. I think if you have the marks and watch them, you stand a good chance of catching one that is starting to creep before you end up with a sheared stem, no matter what pressure you run.

The one I found creeping with the slip marks would definately have sheared the stem if I had continued operating at the same pressure and conditions.

I have sheared the stems off on my J3 with stock tires on several ocassions when I let the pressure get too low. The wheels had serations where the tire bead seats that had all but worn away since 1938. I re-cut the serations and that seemed to solve the problem. I wonder making the bead seating area of the wheel a little bit rough would help on the SC with big tubed tires.

26 inch tires with tubes

Mark,

Yeah, paint marks are wise, and I use them. For some reason, I found that the tires slipped more when new than now. I did abrade both the tire and the rim of the wheel. I tried glues, but they were more like lubricants. So now it is just an abraded and dry rubber and wheel combination. I am thinking that the reason they slip less now is that the sidewalls are more supple and less hard and less likely to transmit a shock to the tire/wheel interface on spinup or during braking. That is just a hunch, though, and with your wisdom you may find a different cause and effect scenario over time. Some people have tried screws, like the drag racers do, but I haven't felt the need.

These tires definitely perform better with less air from a shock and floatation standpoint. And then at too low a pressure I can feel a pronounced longer takeoff roll. So I have found a happy medium in pressure. I don't know the actual number in PSI, though.

Would like to play and master 31's sometime in real rough (but safe) stuff, but have seen their failings too - as in reduced crosswind braking and control. And cruise speed and climb count. I landed off airports in new places twice today and these 26 inch tires were perfect. Of course, every environment has a special call.

Bob Breeden

Do you see a degradation in braking with the 26" Goodyears. I just rebuilt the calipers and mastercylinders on a Husky and went out a test flew it and it is dificult to lock one wheel to turn. Everything feels firm, no air etc. Tires were at 12 psi but have run them as low as 6psi.

Tire Radius

Steve,

Obviously any increase in tire radius will reduce the torque of the brake. I think that 26 inch tires are a good medium though, because with brake boosters on a Super Cub on landing you can brake hard enough to keep the tail up even with full aft stick and a rear passenger or baggage area weight. Secondly, there is enough brake to safely land in a 30 kt crosswind. (Texas Cavalade remember Amarillo? Like, remember the Alamo!) That downwind wheel needs mega brake and some power applied when leveling the wings after touchdown in this type of crosswind. I have seen a 31 or 33 inch tire equipped cub get a little crooked bounce going and go over on its nose in less crosswind. I like the 26's, because you can plant them and get good adhesion and control. Yes, they will skid less than a smaller tire because there is so much rubber meeting the road. A smaller tire would have more brake torque, but wouldn't be as forgiving or practical.

It is fun to lock up the brakes on the 26 inch tires when landing on soggy wet grass. It keeps the stripes off of the bottom of the wings, too.

I don't know about the brakes on a Husky, but would be concerned that if all the gear geometry is the same, then that heavy constant speed prop and 180 up front would necessitate that less brake be used to prevent noseover, especially when flying solo with those big flaps down. Maybe brake boosters can be used on a Husky?

My two cents,
Bob Breeden

I run 9 psi and have never had a slip with heavy braking.

I think 9 psi will work fine normally. The problem is that if you have a heated hangar, and the tire pressure is at 9, you roll it out and fly it at +15 degrees, by the time you land, the tire pressure is probably around 4 psi. That can be a problem with the 26 inch Goodyears.

Further, if you have a slow leak and don't pay attention, one tire can easily bleed off to 2 and you may not notice. These tires are so stiff, it's hard to notice differences in tire pressure by "squat" of the tire.

For what it's worth, just pay attention to pressures regularly if you are going to run these low pressures.

Mike V

mvivion said:

Mark,

I presume you are talking about the Goodyear blimp tires here, since they are the only tube type "tundra tire" around.

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Actually, the GAR Aero is also a tube type set up. Of course they are 29" rather than 26" if that is what you were basing the destinction on. My tires are screwed to the rim so they can't slip with slip marks on the wheels and adapters. Once I pulled a stem right off the tube because I let the pressure too low and the tube crept. With 6 psi, or over, they won't creep.

So far I have gotten 15 years of service out of the set up with only that one problem which was my own fault. Looks like it should last another 5 years.

Good topic and good suggestion Mark. The slip marks are a good idea regardless of what pressure anyone uses in large diameter tube type tires.
I'm putting them on tomorrow.

And, by the way, they're not a bad idea on smaller tires as well. Those too can turn on you and cut a valve stem. In fact, with smaller tires and heavy braking, it's quite possible to cut a valve stem.

We put slip marks on everything.

And, yeah, I wasn't talking about the Gar Aeros, which work just fine. However, as you noted, ANY tube type tire needs slip marks, since the consequences for slippage are severe, ie: cut valve stem, and flat tire. Same logic applies to the Gar Aeros as the Goodyears.

The Gar Aeros aren't restricted to the 29's, by the way. We've run 8:50X10 tires, which gives you an effective 25 inch tire, with a wide footprint. If you are using the 29's, you really need to have some rubber buffed off the stock tire, though. The Goodyear 26's are heavy and stiff, as are the 29 inch X 10's on the Gar Aeros.

Mike V

Years ago a friend of mine in Kodiak bolted his tundra tires (tubed obviously) to his wheels after shearing off valve stems on his PA-12. Anyone else ever heard of this?
Mikey

Most commonly use screws, as opposed to bolts, but yes, this is not uncommon.

Mike V

delete

Are any of these kind still available anywhere? Still in use? I have seen one cub in AK with the 35" airwheels back in '95 but haven't heard of any one using them much anymore, if I recall the owner said they were quite a bit heavier than other options at the time. If any of the ones belwo are still available, where do you get them and are their any special mounting requiremnets.

a. McCreary Tundra Tires (8.50-10)
c. McCreary Tundra Tires (29x11.0-10)
d. Schneider Racing Slicks (14.0x32.0x15)
e. Goodyear Airwheels (35x15.0-6)

The 10 inch tires are readily available from either McReary or Goodyear, from any tire retailer.

The racing slicks were stc'd by schnieder, but the tires are racing slicks made by several manufacturers. You will have to get the stc to get these approved.

The old airwheels are no longer available, though there are undoubtedly some around. Would require a field approval, though, they were never stc'd on anything, as far as I know.

Mike V