Yesterday I got my plane stuck on some sand. Which got me thinking about tire pressure. I have a Taylorcraft with 8.50s currently I have them aired up pretty firm which I know doesn't help rough/ and soft. How low can I go before having to worry about spinning tires on wheels. Any numbers on pressure that seam to be a sweet spot?

Depends on how good your brakes are. Oh, you said Taylorcraft, never mind, ha ha, T Craft brake joke! I tried 15 lbs. with better then Shinn brakes, in my S-7, and had "issues." I also had ripped valve stems in my tailwheel by going too low, go figure. I'd say 20 lbs. and go easy on the brakes, shouldn't be hard!

I ain't worried about the tailwheel. I can lift it out of the soft stuff. Mains it takes a bit more. I'll try 20 and see how it goes. Would really like 26s but not sure how my brakes would like them. If I keep the brakes adjusted they aren't horrible.

I ran 18lbs in the 800s I had on my Luscombe. Never had a problem.

8.50's on the Maule and running 16 to 18; no problems. I do some significant braking too. I suspect that the longer a tire has been stuck to the rim the harder it would be to break it loose during braking (...think years here). If you dismount your tires with any regularity for whatever reason then they could be loose enough to spin.

I believe that one of the keys to running relatively low tire pressures is regularly CHECKING those pressures. For a variety of reasons, many tires will lose pressure over time.

So, I suspect that sometimes when a tire slips at an otherwise reasonable pressure, that tire in fact may have leaked a bit. Airplane tires in general are tough to judge pressure by looking at them. Carry and regularly use a sensitive pressure gauge. I use a digital gauge, calibrated for low pressure, very accurate.

I see planes with hubcaps on wheels, running tube type tires and low pressure, and I assume they rarely check pressures.

Same goes for tailwheels. I’ve pre flighted a 185 and checked tailwheel pressure, which just barely registered, an invitation to roll the tire off the rim, and possibly destroy the rim.

On a T Craft, I would think you should be able to run 16 to 18 psi on 8:50 tires, IF you check pressures regularly.

And, remember, the less pressure you run, the closer to the edge you are, so the more you need to think about temperature changes.

MTV

I have Desser 8.50’s on my C180 and run them frequently at 12psi and never over 18. I do some heavy braking on pavement and, so far, no issues.

I have Desser 8.50s on my 140 (GW 1,450 lbs) and have run them down to 10 psi with no slippage under heavy breaking. Draw/paint a line from the tire to the rim so that if they start to slip a little over time you will see it. That being said I usually run them about 12 psi for normal operations.

Tire pressure is one of those damned if you do, damned if you don't propositions. Too soft, and the airplane is harder to move on pavement, and even in the short distances associated with take off and landing, excessive heat build up can occur. The possibility of tube damage as already discussed is there, too. Too hard, and the airplane is harder to move on soft stuff like sand, and the tires are more vulnerable to impact damage from rocks.

I'm glad to hear from those with experience on minimum pressures. Those happen to be about the lowest I've gone, but in my case, it's more because I've not aired my tires recently. I aired them up yesterday, and found that before I did, the mains were both at about 18 and the nose at 15. Since I run mostly on pavement, I brought them up to 30 and 28, which is slightly higher than book by about 2 psi.

Cary

I run 18 psi with 8.50x6.00 tires on a C-180H. I would guess 12-15 would be plenty of pressure for a Taylorcraft.

I have run 15psi in the 850's on my C180, but 20 makes it easier to push in / out of the hangar.
I used to run 15psi in my C150TD's 850's.
Put index marks on the wheel & tire, but never had any slippage issues.
Might help to pump it up pretty high initially to firmly seat the bead.
If you talc up the tube, don't get any on the bead.

My hangar neighbor was messing with his BBW recently, he runs his with the 400x4 "glider tire".
Interestingly, I kinda recall that the ABW instructions said to lube the bead so it would seat properly.
I think the mains would have more of a tendency to slip on the bead, but no reason why the t/w wouldn't do the same thing.

Desser 8.50's at around 9.5-10 psi seems to be my sweet spot at 1100-1200 lb gross in the Champ. Mark the tires/rims and check pressure often as has been said.

hotrod180 wrote:I have run 15psi in the 850's on my C180, but 20 makes it easier to push in / out of the hangar.
I used to run 15psi in my C150TD's 850's.
Put index marks on the wheel & tire, but never had any slippage issues.
Might help to pump it up pretty high initially to firmly seat the bead.
If you talc up the tube, don't get any on the bead.

My hangar neighbor was messing with his BBW recently, he runs his with the 400x4 "glider tire".
Interestingly, I kinda recall that the ABW instructions said to lube the bead so it would seat properly.
I think the mains would have more of a tendency to slip on the bead, but no reason why the t/w wouldn't do the same thing.

It's pretty much impossible to seat the ribbed 4.00 TW without the use of talc. Theres a reason for the lube instruction...

I have run as low as 8 PSI in my Goodyear 26" tires on the 170 fully loaded.
It sure helps in sand and over larger rocks.
I also have paint marks on tire and rim to watch for slippage and so far so good.
I am very careful to be light on the brakes or use them sparingly when at low pressures.

It does definitely take more effort to move the plane around by hand at the low pressure.

I usually run 10 - 12 PSI for the summer depending on if I will be on a beach or rocks.
I find it is much gentler on the airframe when in rough stuff and isn't that why you are putting bigger tires on anyways?
I have an electronic tire pressure gauge that seems to be accurate.

One time I went in to a white sand beach (very dry soft sand) with my wife camping and we basically sunk the plane while taxiing and decided to camp right there.
The next day I tried quite a few things to get out of there...
I shoveled about 4" deep strips down to firmer sand in front of each tire 50' out and the plane would go maybe 10' past the shovel tracks before losing momentum.
I ended up going down to about 7psi with 100' shovel tracks and it scooted right out of there.
Lowering tire pressure can be your friend

Sounds like I should try 10 and see how I like it. Probably will fly today so I might have some test results to report.

Ps anyone have some 26 inch tires I could barrow to do some testing? I don't want to throw 1500 bucks out on bigger tires and find my brakes won't hold them.

What brakes do you have on the T-craft? I had single puck Clevelands from a Cessna 172 on my 1650 gross wt Champ and they were fine with both 26 in.Goodyears and 26 Bushwheels. I usually flew at about 1500 lbs in the Champ and was able to lock the brakes with the 26 inch tires. With 29 in. Bush wheels, not quite. When I had the 26 Goodyears, I ran 10-11 lbs of air because I was afraid of slipping the tire on the rim. That pressure was fine except on rocks and rough ground, but for that surface you want Bushwheels anyway.

I have shinn brakes.... they work for 8.50s fine

Hair less then 10 psi smoothed things out considerably. Found a pretty nice gravel bar this morning.

I ran 15 PSI with larger tires (more turning moment) and a heavier aircraft (more braking required), and I never had a problem. They are starting to get good and soft at 15. I tried going lower, as low as 12 PSI, but I observed very occasional movement around the rim. This was with Goodyear "26s" (really 23") tires, so only just a little larger than an 8.50.

I'm glad this thread came up. I am still getting used to my Desser 8.50 x 6 tires on my Citabria. They are bouncy as a basketball and I wanted to drop the pressure but when I checked they were 15psi and I didn't know how low I could get.

I'm going to try 12 and see if I can feel a difference.

I was initially worried my single puck brakes wouldn't hold it for a run up (read something here I think) but they hold fine, and I can squeal them just slowing for a turn off so they're more than up to the task.