The Cessna 120-140 Association Forum

I have 800-6 tires but my A&P doesn't know what is the max psi? There is nothing listed on the side of the tire. Do you know what PSI they should be inflated?

Those are two entirely different questions. Max pressure relates to the tire's structure whereas the correct pressure relates to the load. Since the recommended pressure for 6.00-6 tires is 16 psi I would start a little lower, say 14 psi. If your tire wear is in the center, go down and if it's on the (both) edges, go up. If it's on one edge, get an alignment!

Someone who has actually used those tires may have a different recommendation.

Max pressure will most likely be different based on ply rating, but will almost certainly be way higher than you need.
Tires I’m running on my main are actually meant to be Crop Duster tailwheel tires and are 10 ply tires, and I think max pressure is something crazy like 90 PSI or something, I run much lower of course.
Bush guys with much larger tires often use as a reference to inflate the tire until the last groove is just clear of the ground on pavement.
If your running larger tires, assumption is you want greater floatation, and that comes at lower pressures.

What size are those crop duster tailwheel tires, a64?

Ok I realized I asked the wrong question.. what I am asking is what is the normal tire pressure of 800-6 6 ply tires on a Cessna 140?

16# works fine for me on my 800's with no extenders/straight legs. If I get in a dither I put 18# in for mostly asphalt, makes me feel like I unstick a little quicker but who knows. 800's are nice on grass and the beach up here but some folks think they slow you down a little bit.

klyde sessna wrote: ↑Thu Sep 24, 2020 9:16 pm What size are those crop duster tailwheel tires, a64?

600-6
S2R-T660. All other thrush turbines use 500-5 except for the H-80 which used the “square” tailwheel tire used on the T6 Texan and many other old taildraggers.
When I bought my C-140 it came with 800-6 tires, I took them off and as it came with the pants in a box put 600’s on with the wheel pants. At the time I had a Maule M6/235 and had a set of 29x11x10’s on it with Alaska Bushwheel wheels, so the 140 with 800’s wasn’t needed.

8466 wrote: ↑Fri Sep 25, 2020 2:31 pm Ok I realized I asked the wrong question.. what I am asking is what is the normal tire pressure of 800-6 6 ply tires on a Cessna 140?

I don’t think there is a normal pressure, it will vary with aircraft weight, but assumption is if your wearing big tires that your after floatation, and that comes with low pressures. You want some “belly” in the tires. That’s where the put air into the tires until the outside groove just lifts off of the ground, and yes I’m aware that Good years for example have far fewer grooves than other tires.
At least bigger and heavier aircraft an issue of running low pressure is that if you get on the Brakes hard the tires will slip on the wheels and that will pull the valve stem out of the tube and you have an instant flat of course.
Some will drill through the screw holes that hold the hub cap on and use longer sheet metal screws that will screw in into the tire carcass to keep it from slipping.

In my opinion a 140 isn’t a good bush plane, for three reasons, first and most importantly it just doesn’t have the power, but it’s also too slippery, meaning that it just glides too good and it’s flaps are ineffective. Nothing wrong with running big tires of you want to, just I see a 140 as for its class anyway a decent cross country airplane, where say a Cub isn’t so good at that.

Thayne, I have 800s on my airplane and have run anywhere from 30 to 10 psi in them depending on airstrip surface and what I am doing. Nominal pressure for me is 20 psi. I have also painted witness strips on my tires to check for slippage, particularly at the lower pressures, and have found some minor slippage now and then. The slippage is not from normal runway use but from short unimproved surface use. And by the way, the 120 even without flaps powered by a C-90 riding on 800s does actually make a good bush airplane.

I run my 800s just under 20