Big Tires!

Bob Turner

Well-known member
#1
I have posted this elsewhere. It usually gets blood boiling -

Big tires are neat. They have two very different and important functions:

1. They enable you to land on very gnarly surfaces - surfaces that few of us would ever risk an airplane on.

2. They are a huge macho boost! I personally do not need a macho boost, but I approve of such things. If you want big tires, get them!

But there are caveats. Here are some that I sent to my local Super Cub students, who use 26" and 31" tires exclusively on pavement (well, once in a while they go into a mountain strip, but I have landed there in my Decathlon, so it is not a "big tire" strip).

Big Tires?

Alaskan Bushwheel says the following:

We know that heavier tires have more inertia, and we know that more inertia in tires increases the tendency of airplanes to pitch the nose down at touchdown. We know that more inertia in tires means that it takes more force to push/pull/drag or otherwise control their travel and that of the aircraft on the ground. We know that more inertia increases the bending, twisting, shearing loads that the landing gear and fuselage must bear if these loads are effectively delivered from the tires to the airplane structure.

We know that more inertia in big tires reduces braking capacity. We know that bigger heavier tires reduce the aircraft’s carrying capacity, alter the aircraft center of gravity, and increase in-flight aerodynamic drag. We know that certain operating conditions, principally crosswind takeoffs and landings on sticky pavement, exacerbate the ground contact control of the airplane.
The FAA of course has some input – see AC 23.733-1, Appendix 1 for test results on various larger tires. A couple of excerpts:

The ground handling characteristics of airplanes equipped with tundra tires are known to be substantially poorer on pavement than on grass . . .

Tundra tires adversely affect airplane performance. For example . . .rate of climb … for the standard tire was 526 feet per minute . . .for configuration . . .e [Goodyear Blimp] 464 feet per minute . . .

For any given center of gravity/weight, the lateral and directional stability tends to deteriorate as tire size is increased.

Do not be deterred – these things are designed for off-airport operations, and if you do off-airport landings and takeoffs, big tires and safety cables are a must. But remember, off-airport means rough stuff, not graded gravel or grass. Running around San Diego with big tires is okay, so long as you remember that it is for show, and has a negative performance effect on every thing you do in a Cub.
 

aftCG

Well-known member
Location
Tacoma, WA
#2
The Desser 8.50x6 tires (and tubes) weighed the same as the thick Goodyear 7.00x6 (and tubes) they replaced. I was concerned that the larger diameter would affect braking with my single puck brakes. However, they hold for run ups and I can lock them up on dry pavement at pretty much any times so that concern is unfounded.
At the 12psi I run them at they do not corner for s***, so if you are someone who side loads gear much you'll want to bring extra shorts.
 
#3
FWIW the 26 inch ABW’s I put on weigh the same as the 8.00x6’s that came off and they didn’t have any effect on climb or cruise so in my experience they work pretty well for a Champ but yea, they are crazy expensive. Like the equivalent of five sets of regular tires and they wear out five times as fast if you’re landing on pavement so I find myself eschewing perfectly good runways and landing on the turf next to them but it’s not for show because mostly nobody is watching. I just really enjoy it. They are a lot of fun.

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