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View Full Version : 31 Alaska Bushwheels Tire Pressure



scottperry
03-20-2010, 01:11 PM
What tire pressure are you guys running in your 31" Alaska bushwheels?

StewartB
03-20-2010, 01:19 PM
I run them by the amount of squish, and that turned out to be 5# last time I checked.

SB

DW
03-20-2010, 01:47 PM
Gravel baring 4 1/2 lbs

Iflylower
03-21-2010, 01:37 AM
No DW, we were looking for Squish pressure, not pounds.

At those low psi, I'll bet squish is more accurate on level ground. :D

arcticflyr
03-21-2010, 03:11 AM
bias or radials?

aktango58
03-21-2010, 11:36 AM
type of terrain you are landing?

Tim
03-21-2010, 01:00 PM
8 or 9 pounds for pulling the plane in your hangar over a 3 inch lip, 5 or 6 for everything else

Tim

Widebody
03-21-2010, 01:16 PM
Normal use 15 psi. Tire will wear longer.
Rough terrain 5 psi.

Brad

5191H
03-21-2010, 01:24 PM
Has anyone marked the difference in take off roll with everything being equal with 5# vs 15# in 31s?

StewartB
03-21-2010, 01:35 PM
I'd say that depends on whether your tires leave tracks or not (soft versus hard surfaces). The best demonstration I can offer for differential tire pressures is the effort required to push your plane around. Overinflated Bushwheels are harder to push through soft ground than Bushwheels at lower inflation pressures. Bias ply tires like 26" Goodyears are the opposite. They need more air because the tire itself is too stiff to push with the sidewalls bulging. My bushwheel inflations are the result of compromising to what works best all-around. I never change my tire inflation so it needs to work throughout the weight range of the airplane on surfaces where I normally operate. Like I said earlier that's judged by contact patch. The only reason I measured was because somebody asked the inflation question last summer. 5# in the 31s on the -12 and 10# in the 29s on the 180 is what I've settled on.


SB

5191H
03-21-2010, 01:44 PM
SB,

That's a very intersting observation, I have 31 radials and ass-umed that a higher tire pressure would reduce ground roll in most situations.

David

scottperry
03-22-2010, 11:39 AM
Thanks for the responses gentleman. I noticed when I got the airplane back from annual the tire pressure was much higher than I usually keep and my landings were much bouncier :oops: Definately easier to push in and out of the hangar though. I just couldn't remember what Alaska bushwheels recommends and was too lazy to look it up.

Gary Fields
03-22-2010, 12:10 PM
My 31's have 8 PSIG stamped on the sidewall as the minimum. Interesting to see what some of you had to say.

StewartB
03-22-2010, 12:36 PM
I disregarded the recommended inflation pressure early on. My best guide for inflation is the tracks I leave. Here's an example. Look at this photo. I linked it to the actual gallery photo so you can blow it up. Except where I stood on the left brake to swing the tail there's no trace of tracks from the mains. The standard 8" tailwheel is leaving a trench. If you look on the right side you can see my footprints. This sand wasn't exceptionally soft, but it illustrates the point. If I pumped up the tires you'd clearly see tracks from the mains. I guess a guy needs to decide why he has big tires and what he wants them to do for him. No single answer is correct for everyone. BTW, the tailwheel was replaced with a Baby soon after this photo. The easier my tires roll the less damage I do to my prop.

http://www.supercub.org/photopost/showphoto.php?photo=28877&ppuser=14

SB

spinner2
03-22-2010, 01:41 PM
An interesting picture Stewart. It reminded me of one I took recently. I took the skis off and put the 31's back on. Last year I ran 8 pounds of air. Checking the pressure after reinstalling this year they were 7.5 pounds each and I left them at that.

The tailwheel is a Baby Bushwheel.
http://www.supercub.org/photopost/data//762/medium/2_april_10_040.jpg

StewartB
03-22-2010, 03:27 PM
Scott's comments reminded me of the day of the -12's first flight. Marty reduced the pressure in my 31s to about 4# and said that would prevent me from bouncing my landings. I don't think I've ever had more than 5# in these tires except during construction. For what it's worth, bouncing has never been a problem. My conclusion to reduce pressures to reduce the track depth came from my experience with the 29s on the Cessna. With that airplane not only is the weight distribution better but the braking power I can develop with lower tire pressures is significant.

Nice picture, Dan. I like winter but I'm really looking forward to this one ending. You're ahead of us.

Stewart