I would really like to know, from those of you who have 26 inch GoodYear tires on your planes, what you consider to be the safest low pressure that you can have in your tires. Obviously, the gross weight of the airplane is a factor, so please include this in your reply. Also, assume that heavy breaking is applied. (If there was no breaking, the question would be moot.) Anyone who has had one of these tires slip on the rim to tear out the valve stem might be able to give the best information, since whatever the pressure was at that time was too low. Low tire pressure is desirable to handle rough terrain, but what is the limit to still be safe and not turn the tire on the rim?
I have them on my Pacer, as well as a borer prop, and I don't want to experience the flat tire event. Thanks!
Charles

I have them on my 180 & experimented down to 8 psi with no problems. I was flying with full fuel, myself & little baggage so maybe around 1800-2000 lbs. I applied slip marks to the wheel & tire. I landed on pavement & applied heavy braking until the airplane was stopped and had one slip maybe 1/16'' of an inch. I don't keep them that low because its hard to move the bird around. I keep mine between 12 psi to 15 psi.

Dave

I've run those tires on Huskys and a couple Cessna 185s. I have never had one slip, but I've always run the pressure between 12 and 20 psi.

Frankly, no matter HOW low in pressure you run these tires, you're not going to improve their performance much in terms of their being able to roll over rocks, etc. These tires are heavily built. Thick sidewalls, thick tread, and hence stiff. So, even though you run low pressure, the tire itself can't flex enough to really make a huge difference.

This is why the old Goodyear Airwheels and the current manufacture Alaska Bushwheels utilize a tubeless design, with VERY flexible sidewalls and tread. The Goodyear 26 inch tires were designed for the Goodyear Blimp, which uses these tires as a tubeless installation, with very different wheels than are used on fixed wing aircraft.

I think you'll find that running tire pressure on these tires much below 12 psi is pointless, from a performance standpoint, and you increase the risk of slippage.

There are a couple things you can do to help prevent slippage, including lightly abrading the wheel where the tire contacts it, and the tire where it meets the wheel, and applying some rubber cement to both prior to assembly. And, applying slippage marks is essential on any tube type tire if you're going to run relatively low pressure.

The Goodyear tires are a great tire, and will wear like iron. But they just aren't going to be as flexible as a Bush Wheel.

Heavy braking isn't the only potential cause of tire slippage. Touchdown on pavement exerts a HUGE initial stress on the tire/wheel assembly as well. Braking can certainly be problematic though.

If you're going to run your tires at a lower than "normal" pressure, you should include a tire pressure check in your pre-flight regime. At relatively low pressures, just a small change in pressure can cause slippage. Changes in temperature can easily cause this, if you're running 12 psi or so, and go from warm hangar to -20 or so as an example. Don't forget that tires lose pressure over time from air moving through the rubber. And, with the heavy sidewall Goodyears, it's really hard to determine pressure by looking at them.

MTV

[quote="]....Don't forget that tires lose pressure over time from air moving through the rubber. ....[/quote]

I bought "leak-guard" tubes last time around and have had vitually no pressure loss over time, either on the t/w or the mains. That's something new...... and they're no more expensive than regular tubes.

Eric

MTV seemed to hit everything I have learned through researching. If you want more, just search for "26 goodyears" over at the supercub.org site. I have gathered that the rolling resistance seems to go way up when run at low pressures on the goodyears so if you are going for STOL, well maybe not the L part, this may not be advantageous. But, with less pressure, the abuse to the airframe etc. should be lower when landing on gravel bars etc., although MTV makes the point that the stiff sidewalls.......

MTV is right - they are stiff. I ran 800's before and I think all the GY really gets you is the larger diameter for rolling better over rough ground - not really rocks. I have been running mine since Oct. last year, and they have made a big difference in landing on the rough cow pastures around my families ranch. I got beat up with 800's, but these smooth out the squirrel-holed, bumpy ground 10x better than 800's

I don't think their is much difference in rolling resistence compared to my 800's at low pressure though.

I also can confirm what MTV says that as you go down in pressure from 10psi or so, they really don't get any "softer"

I, however, have also converted to a tubeless installation. Not sure if this can be done on clevelands (I have Matco's on my Rans S7S). Have had no leaking issues, saves me 5lbs/tire, and if I do have some slippage, I won't shear a stem.

One of the reasons I went with the GY (OK, price was the biggest, but its related to this one), was that keep my plane at a typical airport w/ tarmac runway. So I just thought, from what I had heard, I would just chew up a set of ABW's. Well, I haven't landed on the runway yet. Just in the dirt/grass between runway and taxiway. No biggy at our airport, and even if you have a towered airport, you might be able to get them to OK you to do it. So that takes a lot of my fear of lots of landings that could cause slippage due to the spin-up upon wheel touchdown.

Still, to answer the orginal question - MTV has it right - running them >10lbs will not sacrifice any "performance" and be safe.

Thanks guys! That's exactly the information that I needed.
Charles

Don't forget that tires lose pressure over time from air moving through the rubber

This is one reason tire stores are using Nitrogen rather than straight air to inflate tires.

The N2 molecule is much larger than the O2 molecule and does not pass through the small gaps as well. There is also the issue of N2 not reacting as much w/ the rubber and not "aging" the tube as quickly.

I must have woken up at some time in Chem 101.

TD

Maybe a way to lighten them up is by putting He-3 in them. That's a smaller molecule than O2, so maybe N2 is the safest.

I've never run Nitrogen in tires, cause most of the places I've gone there is none available. One of these days I'll have to give it a try. It's becoming a common thing with automotive tires.

It won't change the difference in pressures associated with temperature changes, though, and unless you keep a supply of nitrogen handy, you'll "pollute" your tires with air. Maybe we need a bicycle pump that'll separate the O molecules from the N molecules in the air. Then, we could use the O2 molecules in our oxygen systems...

Sorry, slow day here, with "brisk" conditions. KCKN 252235Z AUTO 35027G35KT 1/4SM SN VV002 M14/M16 A2971 RMK AO2

Thankfully, it's calmed down a bit in the last hour or two.

MTV

Nitrogen was orginally used in racing do to it's low water content we now use argon as it is just a bit better. We now even pull a vacuum on the tire first and then fill them with argon. All of this expense because the officals won't let us run bleeders.....

For the technically inclined, here's a pdf explaining the difference between nitrogen and oxygen in tires:

http://www.narleychoppers.com/Nitrogen.pdf

Seems like if you refill the tires each time they get low, over time the nitrogen content will increase, since the oxygen permeates faster. Someone with more time on their hands than me could calculate what the limiting equilibrium concentration would be.

tom

I run 4-ply 800x6s on my Rans S7S. I used to run very low tire pressures, say 8 -9 psi. Did this for about 200 hours or so and many, many landings. Then I got a flat. Upon breaking the tire down and examining the tube I found a circumferential wear pattern and circumferential breaks in the tube rubber. One of the breaks was deep enough to leak air and give a flat tire.

I needed to turn the tire on the other side of the plane around to correct an unequal wear pattern and noticed the same wear pattern on the tube. No leaks, but breaks in the rubber.

Ordered new tubes from Aircraft Spruce and called McCreary Tire (now Speicalty Tire) in Indiana, PA. Talked to an engineer who was VERY helpful and diagnosed the problem as too low tire pressure. He suggested 23 lbs less perhaps 20% cause the plane is light. I'm running 16 lbs now and hope the problem is solved.

Hope this has been helpful.

Steve

I used to run 8psi in the GY's on my Champ. They still beat you up pretty good on rocky landings.

Just like everyone else, I cant say enough good things about going to 29" BW Airstreaks. Night and day.