The International Cessna^® 170 Association

I would imagine that the wheel has a heavy spot that corresponds with the flat spot. The wheel would generally stop turning after TO with that heavy spot down,so naturally it is the first spot to touch down upon landing. Not much rubber on a tailwheel,so after a relatively few spin-ups to 45 or so mph presto: a flat spot.
TW tires are cheap,though,at $25 or less it's no big deal to replace every year or so as required. I usually buy stuff like that at Aircraft Spruce,or Chief.

Eric

Thought I would light this line off again. I was flying CAP Cadets a couple of weeks ago when my tailwheel went flat during taxi. I shut down and pushed the aircraft off the taxiway to keep from damaging the wheel. A mechanic came out to help and found that the tube had become pinched and abraded near the tire bead area. I elected to have a new tire put on since the old one was rather old, along with a new tube. When the mechanic announced the repair was complete, he also mentioned he inflated the tailwheel tire to 65 psi. 65 psi ! I questioned him and he said that the normal tire pressure for that tire is 65 psi and that 34 psi was much too low for a small tire such as a tailwheel tire. He said that 34 psi was probably the reason for my tire going flat as it allowed the tire to flex too much and catch the tube in the bead area.

I have to admit that his argument sounds good, and I have left 65 psi in the tire. The tailwheel steering has improved a great deal and is much more responsive.

Just as an aside....
Tires frequently have tire pressures molded into their sidewalls. What one might not think about is: That tire pressure is related to the tire's maximum weight carrying capacity. A tire might be noted to carry 485 lbs at 70 p.s.i. This would not mean that 70 psi is the correct pressure for the specific installation the tire is in...only that IF it was carrying 485 lbs then the pressure should be 70 psi. Such high pressure is incorrect for 150 lbs because it wears the tire excessively.
The Cessna 170 manual recommends 34 psi.

Just reading the Cessna service letter from 1950, which recomended 30 psi for the 140 and 170 with the scott 3200 tailwheel with a 8 inch p-numatic tire. I start out with 34 ish and end up with 30 after a few months. anything over 35psi I get the hippitty hops when I 3 point ( someday I'll tell the story how I wore out a brand new tailwheel tie on one landing), as for my mains 22-23 psi seems to be the sweet spot for the Michellins on MY airplane.

65 psi sounds more like the pressure folks would run
in a C-180 (for the tailwheel). There is more weight
on the tailwheel in a 180 than a 170. Tailwheel weight
(generally speaking) on a 170 should be around 100 lbs
(mine is 95 lbs). I think a max of around 40psi for the
170 tailweel tire is a good rule of thumb, and adjust for
conditions / intended use.

I guess there is a range that works and within that is personal preference.I use 45lbs and try not to let it go below 35. I'm usually loaded near gross on my return trip from town. My mains (the better of the two Goodyear) like around 30. It gets squirrly aove 32lbs and at 24 or so it's hard to push when loaded. Like George said you need to match your load to the pressures. Flying the tw low on pressure is the worst thing, it can tear the stem from the tube. Lesson learned long ago. What's really amazing is the last tube I bought seems to hold air for a month or more not days or weeks like I've been used to for 30 years.

Anecdotally I've been told that many inner tubes these days are made in China and they are porous compared to the "good ol' days".

What I've heard (dunno of it's true or not) is that
aircraft inner tubes are made of pure (?) rubber, and
that this is "naturally" porous... The air moleculres
are sufficiently small in size, that they will escape the
inner tube over time. Nitrogen molecules are larger
(???... been a long time since high-school science
class....) and as such, will leak to a lesser extent.

I just check all 3 tire pressures once a month or so, and
top them off as necessary.

Bela

I've heard the same for many years. It's just strange that this TW tube just doesn't leak down. I wonder if it's been made from modern materials. I'm not curious enough to take it apart and look for mfg markings or even dig up my invoice on it though. It's now about two years old.

A little ugly going from Stuart to Red Bluff on Thursday. Got to Payson yesterday so now the plane can dry out!

I use 52 psi pressure in the Scott 3200 tailwheel and it works very well for me.

You gone south for the winter already, Dave? Hope you didn't let this little jag of rainy weather run ya off.
I've been up to Stuart a couple times this summer, but never did bump into you. Sorry to have missed you, guess I shoulda made more of an effort. Oh well, see ya next year I guess.

Eric

glad this topic resurfaced. I fill my tailwheel to 65psi and try not to let it get below 45. Haven't had a problem since. I think every problem I've seen w/a tailwheel tire or tube was caused or aggravated by low pressure. Not sure I see the disadvantage to running higher pressure - a rougher ride?

I operate off-airport a lot and the consequences of a failure aren't fun. I run my 8.50 mains at 18psi and rarely land on pavement so YMMV.

One dissadvantage will be that the center tread will wear faster than the outer tread.

For what it's worth, ...Scott published a graph/chart giving the allowable tire deflection VS static load on the tire VS tire pressure. It may also be found on page 5-26 of the SRAM (Service Related Articles Manual) published by the Association. For wts up to 300 lbs, maximum tire deflection of .45", tire pressure is 35 psi (approx). (When they say "deflection" they are talking about tread-deflection,....how deflected the bottom of the tire is out-of-round when static load is applied such as when sitting on the ramp. They are not talking about side-wall deflection. The point being that for aircraft tailwheel use, the maximum deflection is .45". They show that specification being reached at 35 psi @ 300 lbs. The purpose of the graph appears to be a recommendation of tire pressure vs static load in order to not exceed the limitation of tire deflection, and not necessarily a max limitation of tire pressure.)
The 65 psi tire pressure for maximum allowable tire deflection is not for aircraft tailwheel use. According to the chart that pressure VS wt VS static load is specified for Industrial use, which has a lesser deflection limit of .30". Evidently this same wheel is used for industrial purposes.) - George (the self-appointed pressure-meister.)

Really good info George.

Eric, yeah I did leave in that mess about a week ago. VERY large rain showers but little convective activity. Had to go through CA again. Didn't get over 1800' until southern OR but RON'd in sunny Red Bluff again. Drove the van back up to tow our RV on a trip around the perimeter of the lower US. Back on Island this weekend to shut down. Well, see ya next year.