Tire Pressure?

TerryD1023

TerryD1023

Filing Flight Plan
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TerryD
My 1963 172D manual says to fill the nose to 26 psi and the mains to 23 psi. (6x6 4 ply was standard for the mains).

Question: I've just bought this plane and replaced the mains with Michelin Condor 6x6 4 ply tires. The tire pressure rating is for 29 psi... Is there any reason NOT to go to 29 psi? Do I stray from the 23 originally recommended?

Any thoughts are appreciated.
 
Why would you go up? You'll get less contact and thus less traction
 
Assuming the tire is rated for it I’d go for 5 lbs over book.

Unless you are checking pressure everyday you’ll likely

find tire pressure has dropped.

Under inflated tires run hot with a short life.
 
The rated pressure on the tire is a maximum for the tire itself. The tire manufacturer has no idea of the weight of the plane they are installed on. That's why the POH has a pressure. Having said all that, 4-5 psi difference just isn't that big of a deal.
 
If you run 6 ply tires you better run 30 psi minimum...I would go 35 psi. If your main tire pressure is too low and you brake hard after landing you will spin a tire and tear the valve out of your tube...I saw this happen last weekend. Go to Desser tire and look at the recommended pressure for your tires. The pressure goes up with number of plys.
 
TerryD1023 said:
Any thoughts are appreciated.
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FYI: in a number of aircraft the tire type and pressure levels are an integral part of how the landing gear absorbes landing loads. Straying from either OEM recommendations can have other effects on the overall system.
 
I’d rather a few extra psi rather than less. I guess the ‘book answer’ is to follow the manual. With Winter temps you could air up at 50 degrees, then go flying at 20, lose a bit.

I usually go 5 high. It’s also a tad easier pushing solo back in the hanger.
 
sourdough44 said:
I’d rather a few extra psi rather than less. I guess the ‘book answer’ is to follow the manual. With Winter temps you could air up at 50 degrees, then go flying at 20, lose a bit.

I usually go 5 high. It’s also a tad easier pushing solo back in the hanger.
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I go exactly by the book. Mooneys, with the rubber biscuit gear, doesn't exactly ride luxuriously on the ground. Adding pressure above POH recommendations only makes the ride rougher.
 
Bell206 said:
FYI: in a number of aircraft the tire type and pressure levels are an integral part of how the landing gear absorbes landing loads. Straying from either OEM recommendations can have other effects on the overall system.
Click to expand...
This was a big deal in the Cessna 140 group. They highly recommended going with the published numbers to reduce the shock to the airplane.
 
I just ran the pressure calculator for 30 psi. If you air up at 50 degrees & fly at 20, you’re down 3 psi. I guess we have to check psi every flight.
 
sourdough44 said:
I just ran the pressure calculator for 30 psi. If you air up at 50 degrees & fly at 20, you’re down 3 psi. I guess we have to check psi every flight.
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I check and adjust the tires on the plane for every preflight. And yes, for any tire a good rule of thumb is 1psi of pressure change per 10 degrees F of temperature change.
 
Lowflynjack said:
This was a big deal in the Cessna 140 group. They highly recommended going with the published numbers to reduce the shock to the airplane.
Click to expand...

I watch my pressures pretty closely. As mentioned already, low tire pressure can cause the tire to spin on the rim and cause a failure quickly. In a tail dragger that could be a bit more interesting than landing a nose dragger ...
 
Maintenance also has an affect. Some airplanes can use 4 ply or 6 ply tires. 4 plies uses less pressure. Talk to your AI and ask.
 
I’m confused. What ply, or plies is your airplane certified for? And what ply are you actually using?
 
William Pete Hodges said:
Maintenance also has an affect. Some airplanes can use 4 ply or 6 ply tires. 4 plies uses less pressure. Talk to your AI and ask.
Click to expand...
Number of plies affects the maximum rated pressure that the tire allows, but does nothing to change the size of the contact patch, or the desired pressure for each specific application. 30 psi is 30 psi. Put 900 pounds on top of a 4 ply tire with 30 psi and you will have 30 sq in of contact. Change to a 6 ply with 30 psi and you will have the same 30 sq in of tire contacting the ground. Can’t change physics.

My POH list tire pressures.

Now go from a 4 ply tire up to a 20 ply tire and the shear amount of rubber and cord is holding up the airplane and you effectively have a run-flat tire at 0 psi, but it weighs 100 pounds. So this only applies for similar tires (4-6 ply).
 
Daleandee said:
I watch my pressures pretty closely. As mentioned already, low tire pressure can cause the tire to spin on the rim and cause a failure quickly. In a tail dragger that could be a bit more interesting than landing a nose dragger ...
Click to expand...

I lost one on mine! Turned out less eventful than I thought but In also fly an old slow gal, and had a TW instructor that taught me to be on the brakes asap and get her to taxi speed quickly instead of coasting it out. I was glad i did that day. I didnt notice till i went to turn left to exit the runway and the plane would only turn right... i had sheared the valve but must have got to taxi speed by time it was flat. I ditched the hubcaps so I can check more often more easily after that...
 
Lowflynjack said:
This was a big deal in the Cessna 140 group. They highly recommended going with the published numbers to reduce the shock to the airplane.
Click to expand...

yea we don't need to help the spring gear bounce us back up for anything less than a perfect kiss to the ground than we got already! I have 800s and run em at 20, seems to work well...
 
I think most Grumman owners run their tires a bit higher than the manufacturer's recommendations, which are low enough that tires look kinda sad. When I took trips the FBOs felt sorry for me and "filled up" my tires for me. I find the rolling resistance quite high at the recommended pressures. I like to run my tires at 30 psi, whereas the manufacturer's recommendation are 24-26 psi. In cold weather, my tires will still be at or above the recommended pressures. If you decide to do something different, it might be helpful to consult a owner's type association for recommendations. That's how I got advice for my Grumman tire pressure. FBOs don't "top up" my tires anymore now.
 
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