Big tires for the 7ECA

I use 32 psi in 6:00x6 (Decathlon) and 8:00x6 (J3 instructional Cub). They last longer, and no sheared valve stems.
I use 24 psi in the stock Cubs.
 
I have 8.00x6 on mine and run the, at 20 psi on both grass and pavement.

The conventional wisdom for tubed tires is 1 psi per 100 pounds of gross weight to prevent the tires and tubes slipping inside the wheels and cutting the valve stems. In other words on a Citabria with a 1750 lb gross weight, 18 psi would be sufficient.

The other conventional wisdom on tire pressure is with full fuel and no people, inflate the tires until the outer tread ribs are just off the pavement. That seems to give very similar tire pressure results.

I run 20 psi in both the 8.00x6 tires on my 7KCAB and in the 8.50x6 tires on my PA-20. really don’t see any significant advantage with a lower pressure.
 
Watch your tread wear. If they wear on the outside, your pressure is too low.

For back country work, the lower the better. Just remember at takeoff time lower pressure = longer takeoff rolls.
 
I’ll expand on what Bob said about low tire pressure increasing ground roll.

There’s never a free lunch and pretty much everything comes with compromises. It’s always a good idea to understand what those compromises are before you make them.

A couple years ago I indicated in this thread that as was running 8.00x6 tires on my 7KCAB and that I thought I might end up with 8.50x6 Air Classics. At this point, I don’t see that happening as the 8.00x6 tires are working well. There are a few reasons why:

1) About 95% of my landings are on grass and about 75% of them are not on charted airports. around here in NC that means mostly wet and or sandy soil. There just are not many rocks around here.

2) When I lived out west, where the grass could be taller and could hide some fairly large rocks bigger tires might make more sense. However, even back there, I flew a PA-18, a couple 7GCBCs and a PA-12, all with 6.00x6 tires off airport all the time with no issues. I guess we just didn’t know any better then. But here in NC it would be extra money, extra drag (both on the ground and during the take off roll) and extra weight cutting into an already low useful load.

3) I do have 8.50x6 tires on my PA-22/20 as it’s a heavier airplane and it does benefit from a bit more contact area. It’ll probably be getting a baby bush wheel fork and tire at some point as the standard tailwheel digs in a bit on days like today where we had rain and flash flood warnings last night. It almost never lands on a hard surface runway and 8.50s however are it’s sweet spot in terms of soft fields, crustose speeds, useful load, etc.

4) One of the guys on out field uses 26” tires on his CC-11 cubs but that’s mostly because he uses them for flight training and they are very forgiving tires that make it an even more forgiving trainer. ***

5) A friend of mine lives on my home field and he’s a 30,000 hour pilot with 15,000 of that bush flying around Dillingham AK before going to Everts to fly DC-6s and now MD-82s.
- He’s not a big tire fan and feels 8.50x6 tires will get you anywhere a bush pilot is legitimately going to need to go. I’m in general agreement with that and suspect about 90% of the pilots with 26” or 31” tundra tires don’t actually need them.
- he’s also not real impressed with the instructor with the CC-11s. He’s noted students showing up with real promise making fairly good landing that need just a little tweaking in their technique and then leaving as less impressive pilots with a lot of bad habits.

Take that for what it’s worth. I’m biased as I‘ve flown quite a bit with him in both my Citabria a pacer and he’s taught me some excellent advanced bush pilot techniques in landing both aircraft in very demanding conditions.

———

Bigger tires might make sense for a pilot, or not, depending on their situation. Choose wisely.
 
Plus 1 on all that.

But - some folks simply like big tires. For them performance is not an issue - and most operations are on pavement.
I am currently flying a 160 Cub on 29" tires. I do not like the way it lands, and definitely am cautious when direct crosswinds are above 8 kts. I fly a regular J3 in up to 20 kts direct crosswinds.

I put 26" Goodyears on our instructional Cub. They were ok, but not nearly as good as the current 8:00x6 for student work. You can really feel the difference!

Again, if you just like the looks of big tires, go for it! Just be aware of serious performance hits.
 
darrell whitley said:
6 ply Air Trac, cowboy
Click to expand...
Howdy,

One thing I found about the 8:50x6 tires is it gets the nose up a bit higher, making for a slower STOL configuration close to the ground as you can have the tail touch first and mush the mains down onto the low pressure, pollow soft main tires.

Been going to the STOL Competitions (Only as an observer) and talking to the pilots, they say getting the nose up higher is the trick for them very short landings. That's why a lot of Citabria pilots are putting on the Aluminum Scout gear, Taller and lighter.

My technique is getting better but you have to admit that a 7ECA w/ 115hp is underpowered especially when hot, humid, high density altitude, loaded to gross, as so forth.

I did see a 7ECA almost identical to mine, (Many Years Ago) that had VG's, 31 tires, and Aluminum Scout gear. Nose was pointed up 10 degrees higher than stock! I would watch him come in and drag the tailwheel, back down the power till nose started to drop and add some power to soften the mains on touch down. He was quite talented.

Wish I knew who it was but he was from New Brunswick, Canada.

I wish I could make such graceful landings as I have seen him perform. Takeoff was impressive, he would add power, tail up, get speed, and rotate in ground effect flying 3 ft off the ground at that nose high attitude till speed increased. I think he also had a climb propeller, or beyond. He said he only cruised at 80kts, which would be about right.

Anyway, something to think about. Grass always looks greener on the other side of the fence. But, my grass is green enough for me so far.

Ken "COWBOY" Winiarski
Cowboys Air Ranch (84ME)
 
I think you can get the nose equally high with 6:00x6 tires, and in a Citabria (don't try it in a Decathlon) the main gear touchdown will not be as jarring as you might think.
However, if landing rollout is your goal, soft 31s will shorten that. Pump them up for takeoff, if you are really that strapped for runway length (or are competing in both landing and takeoff roll).
 
Grove has an STC for double puck brakes and tires from 6:00x6 through 26" Goodyears. We have them on one Cub, and are currently running 8:00x6 on that. We flew it for a year with 26"ers on it, but they were not really satisfactory for our operation. Not sure he got them approved for the Champ - but you can check.
 
Bob Turner said:
Grove has an STC for double puck brakes and tires from 6:00x6 through 26" Goodyears. We have them on one Cub, and are currently running 8:00x6 on that. We flew it for a year with 26"ers on it, but they were not really satisfactory for our operation. Not sure he got them approved for the Champ - but you can check.
Click to expand...

What did you find worked best?
 
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