"Tundra Tires"?

[Paul Z]

There are several things that play into the tire diameter.
First, 21" is the tire diameter, not the "Tire Height".

I would bet if you went and measured the molds the tires are made in at room temperature they are 21". When they form the tire the mold is hot, the bias ply belts are hot, and the rubber is hot. As they cooled down there is shrinkage. I've never worked with the molding of rubber, but I have with both plastics and aluminum. The are all effected by the coefficient of thermal expansion (CTE) as thing heat up they expand, and as they cool down they contract.


Also if you measured the diameter of the tired after installing it on the rim, air them up when they are mounted to the wheels, and sitting on the flat on the floor and measure the diameter of the tire, without any weight on the tires. I would bet the tires would measure about 20 3/4" up to 20 7/8".

With the 300+ lbs on each of the tires the weight of the aircraft the aircraft it flattens the tire. Mine measure 20" with the planes weight on the tires, with 15 PSI air pressure.

With less pressure the tires get flatter, if you measure the tire with 15 PSI from the floor to the top of the tire you will get a different measurement than if you put in 18 PSI.

I would venture to say the tire diameter is measured in the Free State, with no weight on the tire, laying on its side, and aired up to a engineering specific PSI Air Pressure. I have no clue what pressure they may have specified on the engineering design specification. Also, per the ASME Dimensioning and Tolerancing Standards it states measurements apply in the Free State, unless otherwise specified on the engineering drawing, or specification.

[B767]

Good explanation Paul, thank you.
Thought as much. Still, my diameter of about 19.5 inches is off the mark more then casting or moulding errors and tolerances would allow.....you would think.
For what it's worth, my tires are mounted on the rims, OFF the airplane, pumped up to 30 psi and sitting in the hot sun......thermal surface temp of tires at 4pm was over 100 degrees..........yup still 19.5 diameter..
Again, don't get me wrong. These tires have a great rep, and I'm sure I will be satisfied. I was just looking for a min diameter of 21 inches, which would have made the difference from my old 7.00 tires to these new ones more worthwhile.
I'm sure they will be fine.

[Kurt.A]

Excellent explanation Paul. Just one thing to add is that rim width also affects tire diameter. The wider the rim the shorter the tire becomes once mounted and inflated.

[SkySteve]

Here ya go, Paul. Just for you:

[Foxfan2]

I have been running the 22" Desser smooth Tundra tires for a year now on my Kitfox 5. Over 100 landings, mostly on Willamette River gravel bars, some pavement as well. I love them. They show no wear so far. I have them on Cleveland wheels, therefore, I have tubes. I'll take some heat for this but here goes. I'm running a 6 psi. I started with 18 psi and kept reducing till I stopped at 6. I did several landings on pavement with heavy braking to see if they were going to slip on the rim and shear the stem. I couldn't detect any slippage. I'm not saying I recommend it but they sure are soft. Still easy to taxi too. It helps to have a 650 lb. airplane. Now I want the 27".

[Esser]

650lbs Model 5 with tundras? Tell us your secrets...what equipment and powerplant/prop do you have.

[Foxfan2]

Well, I bought, didn't build. No options on the airplane that I'm aware of, including a trim indicator. I took all the steam gages out and installed the small Danon EFIS. Rotax 912UL, so only 80hp with an IVO ultra light proop. It may not be the lightest one around, but it's got to be pretty close. Does a nice job off airport.

[SkyPirate]

my model 5 registered LSA weighs 750 empty 912 UL but with 3 blade tapered tip warp

[Jerrytex]

My Nancos are giving it up. I guess the pavement is too hard on them. I was running about 10 pounds, any higher and the bouncing started. Basically where the sidewall meets where the "tread" starts, they are paper soft and now the cords are starting to show. I am grounded until I get new tires. Also while inspecting them, I noticed they are only rated for 365 pounds. I think I'll look around for some different tires with a little higher weight rating and better wear on pavement. I put 75 hours on these. While cheap enough, Its a hassle to to have to change tires every 75 hours. I see the aero classics and the dressers are pretty popular. Anyone find any other tire "deals" here lately. I have the 8" Douglas wheels.

[Av8r3400]

If you are still running the 8" wheels. The new Desser 27" tires are an option for you.



The Matco "internal" brakes used on the Douglass setup may not be up to the task, unless you do something to improve them...